Over a Barrel (BGM187)
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Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1216
Location: UK (South East)
Fri Oct 11, 2019 11:55 am quote
+1

Looking forward to the power delivery and spread and how it differs from my relatively stock BGM setups. You'll really appreciate having a reliable and skilled machinist that you can take bits and bobs to on a whim
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Fri Oct 11, 2019 7:26 pm quote
Looks fast now doesn't it? All looking as it should be. little more practice at BDC then into the abyss. Will be no harder than the BDC, its just at the top.

This now being a 190cc, with this kind of port timing and a 26/26, is going to go at least as well as a decent bolt on 210.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sat Oct 12, 2019 1:04 am quote
I have several jobs in mind for my new best friend, but lets not count the goose that laid the golden horse in the hand before the stable door was belt and braces; if I get my flywheel done I'll be happy for now - then I've got loads of old bits he might be able to fiddle with.

As two rugby games are cancelled due to typhoon Hagibis, and as this morning's ride has confirmed hub is sorted, (only a short ride worst time of year with wet leaves and mud filling the potholes in the lanes), I find myself with a spare hour, so thought I'd expand on the 26/26 question as it's cropped up on a few threads. I started posting this on your thread last night, Hibbert, but got tangled with links to Youtube showing loads of adverts, then was worried they were contradicting others' advice***, so trashed it until I had more time, and you'll read it here if it's still relevant, anyway.

For the engine I'm running now, the spritely DR with an Si26, I drilled my float chamber to 1.8mm. I opened up fuel flow through banjo, filter and needle valve (inlet and outlet). I haven't used the larger needle. I've got a Polini vortex, but not their filter; have tried RamAir filters (clogs quickly and works out expensive to change), Patrick's internal filter medium (unsure, but may have been too restrictive), keeping the bellows didn't work well with my low TSR seat but I have a louvred sidepanel, so now I have just a gravel mesh (off an old computer fan intake) over the carb box inlet. Other than giving Patrick's 3D printed Vortex a go for this one, I don't really intend to do much different (may drill 2mm, but 1.8mm first). I've never had fuel flow problems.

I'll try these links again, but it's easy enough to find them on Youtube anyway (FMP Si carb mods), ***not saying I agree with it all; just take what you want from it:

.
"https://www.youtube.com/watch?v=YxDK1-Kl2Pk&list=PLri8t7DWSkg2lpj30ypqMnU_14JbB0itU"

.
"https://www.youtube.com/watch?v=opZXBGud3vw&list=PLri8t7DWSkg2lpj30ypqMnU_14JbB0itU&index=3"

.
"https://www.youtube.com/watch?v=K7TJXHEAfaA&t=53s"
(not so sure about the 2.5mm; 1.8 or 2mm maybe)

This is what I did, and what I intend to do again:

1.jpg
Not even a new carb - cheap and cheerful then as now

2.jpg
Cleaned up inlet through filter to float bowl

3.jpg
Not sure if 1.8 or 2mm, drilled from top - careful not to damage valve seat

4.jpg
Only 1.8mm to start with, don't use cheap drills, they'll snap off and then you're buggered

5.jpg
Luvly Jubbly

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Sat Oct 12, 2019 8:04 am quote
Sime - remarkable work/ workmanship.
Good read over coffee this morning.
You've really opened up the ports nicely.
Curious about how you determined the depth of the grinding you did to the skirt (see below for reference 8mm).

The base and head gaskets are very nicely executed as well.
Suspect everyone reading was impressed with the fit and finish - know I was.
Any tricks you would like to share on crafting those - the outcome was remarkable for fit.

Also noticed you seem to have stacked head gaskets - with some form of material between them. I am curious about material choice (copper/paper?) and if you plan to keep two head gaskets or if that was only for fitting?

Great read as I head in to my (somewhat less sophisticated) build.
Thanks!
- CM

Screen Shot 2019-10-12 at 8.47.42 AM.png
Double head gaskets with paper of some kind between? Can you expand on this?

3_barrel_cuts_12405.jpeg
Blue arrow points to area I was curious about. - how did you determine this max?

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sat Oct 12, 2019 10:24 am quote
Thanks CM; so far so good, but trickiest bit is next I've just finished off bottom of exhaust BDC and masked it off for cutting top of exhaust, tomorrow probably.

To your questions then (don't quote me; I'll say what I did, which is not the same as saying what you should do):

1) Down to the divider was the intended depth. The 8mm was a rough, non-critical, measure from existing skirt opening to divider inside transfers in barrel, not a max, and not exact because divider is slanted, in fact, with Jack's dissatisfaction with my first feeble attempts (to the high point), I went to 13mm in the end before my hesitant scrapings were approved; so now the window meets the divider horizontally at its low point, which really opens it up as you can see. I have updated my drawing, but not reposted it yet; there's a few tweaks to my drawings like that, but I'm so near to finishing this part of the job, I've delayed reposting; I'll take stock when the barrel is done and make sure all my calcs and drawings are up to date and agree it's a reference point for later if any tweaking is needed.

2) I'll stick some work-in-progress photos of making the gaskets below. I started with a plastic template from a previous build; if I didn't have that, I'd make one, starting with a paper rubbing of what's there, sticking that to card or plastic to cut out, and then deciding what needs opening (what I want to do with the barrel and what I can do with the casings). Then make rough blanks with a scribe on the correct thickness sheets aluminum or copper, and get them close with old scissors, tin-snips, files, drills, a scalpel anything that works really (on the thin copper, some old curved nail scissors worked lovely in the transfers). The base gasket becomes the template for cutting the barrel and the casings, and gets tweaked at the same time, and if it gets too tatty then I have to make another (better to bugger that up than the mating surface on the barrel).
The trickiest bit is getting the hole in the middle of the gasket, which I do by a string of small drills, which I join with a fret-saw. I stick them together for drilling the stud holes, so the centres are identical, there's nothing in between, I think you can see a burr in my photo from a rough scissor cut, I put the thicker one on top because it stops the thinner one deforming whilst drilling. When cutting the barrel I used the thicker base gasket as my template, and when I was done I used M7 bolts to fix it to the casings to tweak them, so they matched the barrel and base gasket. When they were done I sandwiched the thinner one between the thick one and the casings and used files and Dremel to finish it off. Then it's just a case of getting it all matching putting barrel and gaskets on half a casing helps to see bits that need a tweak; it all needs several tweaks to get tidy. When done I rubbed down any scratches by sandwiching them between two sheets of wet-and-dry and some oil, and giving them a gentle swirl about.

3) I might be wrong with this, but I like to have a thick and a thin gasket because I can just fine-tweak the thickness of the thinner one to get the PBT and squish right. Example here is that my head gaskets are 0.5 & 0.3mm, but I might end up using a 0.2mm instead to narrow my squish. Previously on the engine I'm running around on now, I had 2.0 & 0.2mm base gaskets; when that proved a little too frisky, as part of the detuning I took out the 0.2mm copper gasket and just left the 2mm aluminum one there, lowering my timings a tad.
Maybe the comment about a single head gasket being a better seal is valid; I don't know, but I'll soon find out, it's the first time I've used any head gaskets! I've used copper for the head and the thin base gasket, and aluminum for the thicker base gasket. Copper is good for conducting heat at head, and softer for a good seal between casings and barrel, aluminum is light and cheap for thicker base gaskets. Base gaskets are bespoke, so for me from scratch is best, I could have bought an 0.8mm copper head gasket for about 10, but if I then decided a fine-tweak to 0.7mm would be better, it's a waste of money; better to just get on and make them from 10s worth of various thickness sheets that'll last me forever; sheet is cheap enough, and I quite like fiddling with the little jobs, particularly this one when time is not an issue at all (this build was intended to be my winter job, and winter hasn't even started yet).

That's about it really; the best way to work out how to do it was to have a go. I know the rich kids with the big-boys tools do it in five minutes with plasma/laser cutters, but I'm working on a work bench in a cupboard, and an extension lead for my Dremel.

Some previous work-in-progress photos of gaskets; hope some of it was useful:

1 Thickness for correct PBT and Squish.jpg
Correct thicknesses for PBT and Squish

2 Stud Pilot Drills Before any cutting to keep aligned.jpg
All together to keep stud centres aligned

3 String of drill holes for inner removed with fretsaw.jpg
Drilling thicker ones to remove Centres...

4 Trim outer with whatever works.jpg
...and trim outer with whatever works

5 rough cuts before first fitting.jpg
Still don't fit until tweaked more to go over head and barrel

6 still taped from drilling first fit on barrel.jpg
Taped together for drilling, and fitting to barrel, then ready to start with the Dremel with just the thicker one.

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sat Oct 12, 2019 10:46 am quote
Just to get it back on track after that brief diversion:

BDC Exhaust done Masked up for Top of Port.jpg

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Sat Oct 12, 2019 11:04 am quote
Thanks.
This was the pic I was looking for - wondered your approach while trying to avoid a lot of distortion at edge when you cut out the internal shape. Explanation of custom gasket process was clear and also helpful.
Much appreciated.

Ex. port looking good!
-CM

Screen Shot 2019-10-12 at 11.58.22 AM.png

Hooked
1984 PX(177)EFL
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Location: Cornwall UK
Sun Oct 13, 2019 5:04 am quote
Happy with that:

Exhaust Raised 1.6mm for Ed-181 and Lowered 1.55mm  for BDC.jpg

Dimensions Compared with Original.jpg

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Sun Oct 13, 2019 7:29 am quote
wow sime66 impressive! Thank you for detailing the carb mods. Watching the FMP video of drilling the jet supply duct reminded me of a dentist visit and a simple cavity filling turning into a root canal and crown. I think I can do that but need to figure out tooling or maybe have it done. Not sure I picked up the boring of the needle duct but from your photo's it looks like that is bored same as jet duct?
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sun Oct 13, 2019 8:44 am quote
That FMP video of the float bowl-main jet drilling is far more aggressive than I did it (his method and hole size); mine was very gently with a modelling/jewellers pin-vice and turning with just three fingers until it worked through. Gently does it!

Pin vice example:
https://www.amazon.com/Hexagonal-Double-Twisting-Jewelry-Design/dp/B01N9ZWD5Q/

The main thing to take from the valve needle channel mod is to do it downwards (same direction as fuel flow), so you're not going near the valve seat with anything sharp if you scratch the soft brass valve seat you're buggered. I don't remember the size of that one, logic says not less than float bowl-main jet drill, otherwise it'll empty the bowl, but make sure you still have plenty to seat the rubber valve on. What I will do when I get as far as doing mine is to see (for both holes) what drill already fits through, then decide, and probably do both to 1.8mm first. Don't make any big changes, and remember if you're sticking to using an Si24 your sizes might be different anyway.
I'm trying to impress on you guys that I'm happy to tell you what I'm doing or have done before, but, unlike Jack, I don't have the experience or confidence to tell you what you should do he's still telling me what I should do, as you can see from my build.

(He'll probably tell me my exhaust work is rubbish tomorrow it took three goes to pass muster with the base transfers).
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Sun Oct 13, 2019 7:41 pm quote
You shouldn't be so hard on yourself. Port looks just right. Can't see that you have chamfered it, so chamfer is not quite big enough.

Once they see this engine go, I think you'll be getting a few BGM barrels in the post
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Mon Oct 14, 2019 2:45 am quote
I'm actually pretty happy with the way it's going so far, but always expect to need a tweak before approval. I'll chamfer more and generally polish and tidy now I know we're there with size and shape.

Anyway, I'm just back from New Best Friend, who has done a spiffing job on my flywheel, which is now precisely 1900g and shiny-like-new; I'm very pleased with it, and together with the exhaust port, this leaves me at a place to enjoy progress, before going on to crank-inlet-carb box-carb next....

take a look at this dazzling beauty

1900g profile.jpg

1900g beauty.jpg

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Mon Oct 14, 2019 10:21 pm quote
sime66 wrote:
I'm actually pretty happy with the way it's going so far, but always expect to need a tweak before approval. I'll chamfer more and generally polish and tidy now I know we're there with size and shape.

Anyway, I'm just back from New Best Friend, who has done a spiffing job on my flywheel, which is now precisely 1900g and shiny-like-new; I'm very pleased with it, and together with the exhaust port, this leaves me at a place to enjoy progress, before going on to crank-inlet-carb box-carb next....

take a look at this dazzling beauty
Looking good. And done quickly. Be sure to grind the taper. It's not a race but looking like CM has nearly caught you up .
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Mon Oct 14, 2019 11:32 pm quote
It was a team effort, he had the lathe and I had the scales and SaFiS's example for reference. We used the puller to hold it as suggested, and cut and weighed about five times to get it spot on, then gave it a polish with media/water washer. About 2 hours in total with all the re-aligning on the lathe to keep it square after each weigh.
What is this 'grind the taper' malarkey? Do you just mean make sure it's free of rust; it is very clean, and I made sure we didn't go near it or the puller threads with the washer, but I'll give it a rub with fine wet & dry to be sure it's pristine, or is there something else?
There's quite a gap between casings and flywheel now; I have a bit of a notion to fix a strip of thin aluminum inside the scroll from about 9 o'clock to 1 o'clock, to keep Cornwall out and all the lovely cooling air in.

(CM can be the hare; I'll be the knackered old tortoise with a gammy leg).

Strip.jpg

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Wed Oct 16, 2019 11:47 am quote
(Not asking for any input from you on this bit Jack; I know you're busy, this is mainly to demonstrate to CM how to measure the crank and pad, and work out cuts for inlet timing, without confusing the issue more by posting on his thread).

I've marked up my inlet opening on my pad, just quickly to get it posted; I'll do it more precisely with a new Sharpie before cutting, which won't be until I've marked up the carb outlet above it for blending them together.....

To recap my numbers, check myself before cutting (and maybe help CM along a bit):

My pad opening is 39.1 ending at 72.3BTDC (72).
The available pad to cut on the Io end will allow me another 10, so that's 49.
My crank opening is 139.3 (139) opening at 3.3BTDC (4)

This gives me 117/71 (with the 10 Io pad cut).

Because of the timing on the 'Race' crank, I can do nothing with the 71ATDC; it's what I get with the opening on crank and opening on pad, so I'm going to leave both Ics as they are, and we've agreed 71ATDC is OK anyway.

I want 125BTDC (125/71), so I still need another 8 on the Io. I've already taken as much as I can out of the pad, so this has to come off the crank. So my 4BTDC on the crank becomes -4 (the other side of the bearing).

So my two cuts are 10 on the pad Io, and 8 on the crank Io.

This can be shown by the sketch and calc sheet, reposted below, and a photo of a quick mark-up, which is below that:

Inlet timing Crank and Pad mods.jpg
Measured with an old-fashioned pencil, paper and $1 Protractor - keep your bleedin' Buzzwangle

Crank Timing calculator for 125-71 with ls Crank.jpg
Crank cut, after pad cut

Pad Cut.jpg
Rather rushed Pad Cut mark-up (crank to follow after casings are done)

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Wed Oct 16, 2019 10:21 pm quote
Sime - that is a fancy curved abacus you have there.
I get that the combo of crank opening and inlet opening creates a set of timings.
I suspect one of us is miscalculating something - and I think its safe to assume it's me.

Here's what I understand on yours:
- The inlet pad has only so much area to open - giving an over all physical limitation both on the closing side to "the right" looking from flywheel, and the opening side on "the left"
- However - the Inlet Close side can't be widened on the pad - there is physical pad to cut into, but the crank has been cut back already so it would be too much.
Question: is this because opening up that side would allow the inlet to be open when the transfer ports are also open? If not - what is the limiting factor of opening up the Ic side of the pad?


The reason this raises an eyebrow for me on calculations:
While I did not use your glorified Fibonacci gauge, I put my cylinder on and set with the proper base gaskets and rotated the crank. Here is what I found.

Starting at TDC ( making it the zero point) and rotating, my transfer ports close at 118 BTDC. my Inlet then opens about 5 later at 113 BTDC. My understanding is - that is nearing a bare minimum relationship between the inlet and transfer ports being opened at the same time.

There are roughly 20 degrees of pad available on the Io (left) side - but if I use them by either grinding my crank, or opening the pad on that side - it would mean my inlet would be open when my transfers were open.

Traveling for a couple days. Will go back and more closely examine - suspect I have something incorrect.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Wed Oct 16, 2019 11:05 pm quote
"I get that the combo of crank opening and inlet opening creates a set of timings"

Then surely a good place to start would be to measure them individually and accurately; wouldn't you agree?

I made two attempts at translating your numbers into a set of cuts that I could suggest, and although I did reach a result and composed posts I trashed them; I just didn't have faith in your measurements to post it and have them adopted for use, so decided it was safer to post a worked example on my thread with numbers I know I can trust. I am not suggesting my result will be the same as your result; I'm giving an example of the working.

My numbers are correct for my crank, pad and intended timing.

You're both away on business now so there is no urgency to stop you buggering it up, and I can leave it alone now. My only suggestion to you would be to do some simple measurements in a simple way, with pencil, paper and a $1 protractor (if you think that's a glorified Fibonacci gauge, then get a schoolchild to show you how to use it); something along these lines below and post the results and any further questions on your thread for easy reference to your engine history - or don't, entirely up to you:

(Didn't I read Jack's post yesterday tell you that the Inlet / Transfer overlap would be OK?! You said that at present Tc is 5 before Io; my understanding of the overlap is that up to 10 overlap is OK, so you have 15 before any concern. I have a 7.5 overlap on mine, which is shown on my timing diagram on the previous page. I made it that you need less than 15 on your Io - if your numbers are right; about 11.5-12, which you will be able to check, if you decide it's worth it, and confirm on your thread in a few days).

measuring angles without a Buzzwanker.jpg

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 17, 2019 11:56 am quote
Moving on with my own build....

Having marked-up the pad I couldn't leave it alone, so set about it with needle files this evening, initially just to get up to the edge of the pad opening on all four sides, which I nearly am. This is only first-cut 'til I was bored with it and paused to take stock of progress. Clearly when I've done the carb outlet there are a couple of areas which will be much less bumpy when removed (two main areas can be seen marked as blue triangles within the inlet), and I can make more of an angle to the new Io edge, but have to be careful of the carb stud there.
Earlier this afternoon I also did rubbings of carb, carb box, and crank case, and have started to sort out the gaskets (red), and the cuts (dark blue); that will all get tweaked and tidied as I cut, but gives me an idea of what needs doing. I won't make the gaskets yet anyway; I'd only lose them and have to do it again, but I have templates for matching the three parts together.
I will also re-measure the angle of the opening in the pad when I'm done (should end up 49 opening ending 72 BTDC), as another check, before cutting the crank; you can't have too many measures before cutting.

I may get some time tomorrow to tidy this up more, but after that I don't expect any progress this weekend; I just wanted to get the thread back on track before I leave it and the build for a few days.

Inlet First Cut 2.jpg

Inlet First Cut 3.jpg

gaskets and tweaks.jpg

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Thu Oct 17, 2019 10:05 pm quote
Looking great. Can tell this isn't your first rodeo

That pad is really nice condition. Unusual. Going to really help with the torque.

A few thoughts on duration of the inlet. Why does increasing the inlet duration make such a big difference? Easy answer, the engine has more time to draw on the carb. But how much more? Well, as you ask. A stock 200 has ~160 degrees of total inlet duration. At wot it takes about 40 degrees to open equivalent to the area of the carb and the same 40 degrees to close. This means that the vacuum has 80 degrees of full area to pull fuel through the carb. This is not so much time considering there is 180 degrees of vacuum, so the velocity has to increase. Physics being what it is it has to balance. Carbs have a velocity window where they work. How big you think this is on a 26/26?..........The more time, the more torque. This is an equation I like.
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Thu Oct 17, 2019 11:23 pm quote
*Moved this discussion to my thread to clean up.
http://modernvespa.com/forum/topic163570.20

Last edited by charlieman22 on Fri Oct 18, 2019 3:58 pm; edited 1 time in total
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Fri Oct 18, 2019 1:37 am quote
sime66 wrote:
Because of the timing on the 'Race' crank, I can do nothing with the 71ATDC; it's what I get with the opening on crank and opening on pad, so I'm going to leave both Ics as they are, and we've agreed 71ATDC is OK anyway.
CM: Your question about my Ic on the pad and crank: A high ATDC is not what I want for my type of engine, my last build was 55, I was aiming for 65 (as you are), 71 for this build is agreed as OK, but no higher, as previously explained.

made me question how I was measuring

Me too!

For example, see if you can get Io = 113.5BTDC, which you stated previously, from those numbers 'A'-'F' above.

Let me also repeat this request and make this plea can you post questions specific to your build on your thread please, because:
1) When I reference back to my own data, when I'm checking myself for my own build, I don't want to wade through a load of your data, which is irrelevant to mine, bloats the thread, and makes my own checking more confusing, prone to mistakes, and laborious.
2) When I'm trying to reference your previous data and cross-check it against new, to try to help you make progress, like now, I have to have both threads open. If I'm meticulous it's because I still find all this stuff quite challenging, and have to double-check myself often, and that's easier if it's all in one place.

I hope you move your post above to your thread, and before reposting it, check why your 'B' (43.4) is not near to being the same as your previously posted 61.2 (113.5BTDC 307.7ATDC (52.3). I suspect you're getting your Buzzwankered (combined) timings muddled up with your actual (physically, simply measured) degrees. You've stated 52.3 as BOTH the Ic ATDC AND dimension 'A'.

My way was not just "one of the ways", as you say; it was a cross-check as a means of making sure your numbers are correct, because I previously found them doubtful, which your new numbers above now seem to confirm as they appear to me not to agree.

Remember to reply, after checking, on your thread please.
(I'm not back at it tomorrow; a weekend off it for me, but looks like the guvnor's back anyway).

- - - - -

Thanks Jack, I see what you're saying; my Si26's velocity window is not for the full inlet duration (I don't know the actual answer in numbers***), and that is when the open area is equal to or greater than the carb area. So the bigger the opening on the pad the longer the velocity window, the greater the torque, which is why we like a big opening. My opening here is restricted by the race crank giving me 71ATDC already, without which I could have had a bigger opening and a longer carb velocity window. I'm going as early and wide as the pad permits to make it as big as I can as quick as I can, but the ATDC is my limit, so a shorter ATDC on the crank (like a standard crank) allows more degrees of opening on the pad, and longer carb velocity window, and more torque.
That doesn't explain, though, why an even longer ATDC now, with this crank, wouldn't improve my torque by increasing my velocity window length; clearly other factors, which currently don't spring to mind.

This next bit is a later edit (Friday evening); I've been pondering your paragraph on velocity windows, and wasn't sure if you'd asked a question I was intended to try to answer, but I've been wondering if this was one of your old-time clues to a gem, so tried to put some ***numbers specific to my build into it anyway:
Lets try this for my Si26 velocity window.
My Inlet duration is 125/71 196.
My pad opening cross-sectional area (subject to finalsing and checking) is 543mm
An Si26 carb cross-sectional area is 490mm.
So I need (490/543) 90% of my pad inlet open to be within the velocity window of my carb.
My pad is 49; 90% of 49 = 44.1.
So for the first 44, and the last 44 of my Inlet duration I'm outside of the velocity window because my pad opening is partly covered.
That might be drivel, but maybe it suggests that of my 125/71 (196) of Inlet duration, My carb is only within its velocity window for 81/27 (108).
But then there's velocity; is it passing the same volume quicker during those 44? Or is it passing less volume? I imagine that depends on what's happening up the hot end.....? Is it also a bit of a clue why 10 overlap isn't a problem, and using it allows the carb velocity window to begin earlier?

Also, because I like to have my thread being vaguely relevant to my build, and it's something going on in the background; those casings were only 50, and the only real issue is the stuck long bolt (which I'm working on), and the slight damage to the mating surface (aesthetic, not functional) resulting from previous owner's difficulty separating them due to the bolt. I'm going to let New Best Friend have a look at it, I have been regularly soaking it in WD40 and some other stuff he gave me ('Corrosion Block' similar, marine version I think), and I've mined through solid concrete inside the swing arm to expose the inside of it to attack it from there too. The dilemma is that I've cleaned the threads up and it is perfectly useable, so I don't want anyone to try anything that will bugger the threads, which would leave me with no choice other than to remove, or risk getting too medieval and damaging the casings, which now have quite a lot of my time invested in them. It's a work-in-progress, and I don't yet know if I'll get it out; just wanted to finish the post on something to do with my build.

https://www.nocorrosion.com/collections/corrosion-block-anti-rust-spray/products/corrosion-block-1oz-sample

engine Bolt 1.jpg
You can't hide in there....

2nd pad cut 1.jpg
A little progress today, with the top of the crank case...

2nd pad cut.jpg
...and blended in better now. I've marked '*' the worst of the pre-existing scratches in the pad; I might be able to lose most of this with the opening width - gotta get my crank out and check the web width first, but I'm done now for a few days.

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Posts: 630
Location: California
Sat Oct 19, 2019 12:20 pm quote
Wow finger filing looks great! Just a little snag at the end maybe not hurt?
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sat Oct 19, 2019 12:33 pm quote
Thanks Hibbert, I think the needle files are a safer option for this job.
That's not my slip; I was highlighting a pre-existing scratch right along the edge of my new pad opening where I'm contemplating going a little wider. I need to check how my new crank sits over the pad first to see how tight I can go; 1.5-2mm. I'll get rid of most of it, but it will still leave that last little bit where the '*' is, but I don't think it will matter; the pad is in very good condition for 1982 casings. I'll rub that last little bit down very gently so it doesn't mark my new crank.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sun Oct 20, 2019 9:51 am quote
Squeaky-bum time!

I just thought I'd have a casual Sunday night check with crank in to make sure I could lose that score in the pad along the bottom of my opening that I highlighted on Friday, whilst I still had about 2.5mm of pad-width left, but I'm already right on the limit; lucky I checked before tidying.

I marked my crank through the inlet and was surprised it was so off-centre, and so close to the edge on the clutch-side, so I had a much closer look and precise measure before I was happy that it was just about still OK (I hope).

Best way to show it is with a picture or two, which I'll add at the bottom, but a description might help too:
The mark is about 1.5mm from the edge of the crank web. (You can just see it in the photo; I had to swap the relatively fat Sharpie for a fine pencil when I saw it was tight).
I stuffed feeler gauges under the web and measured 1.1mm.
I knew I had about 2.5mm left in the pad to the edge of the opening, which I had thought was plenty.
But that means I only have 1.4mm overlap coulda been nasty!
I measured the width of the opening; 11.85mm, which made me realise my target 14.1mm wasn't achievable either, which reduces my cross-sectional area of the opening too.
The actual web width is 15.3mm, but there's a chamfer of approx 0.2mm, so an actual width of 14.9mm, which also takes 0.2mm off my overlap, which is now down to 1.2mm.
Allowing 1.5mm on the other side (1.3mm overlap), the maximum width of opening I'll get away with is 12.4mm, and that's pushing it, and it now gives me a cross-sectional area of 495mm, which is just about the same as an Si26.

Summary:
I think I just got away with it.
The pre-existing score on the pad will have to remain, which makes the tight web overlap even more critical.
The pad width can only go about another 0.5mm wider, on the fly-side, and it will only be 12.4mm wide, not 14.1mm wide.
The area of my pad opening is now only about the same as the area of my carb.
Best to leave it all alone until I have my final bearing fitted (though I could measure its width as a check). I think I'm just OK, and should leave well alone.

Photos and sketches:

Web - Pad Opening Measure.jpg
Wasn't expecting that!

Pad and Crank Measure.jpg
Better have a careful measure...

new pad dims and areas.jpg
Checked in revised drawing and got new opening area

Crank Bearing Height.jpg
Not sure if this makes it better or worse; I have 0.5mm under the circlip, so bearing could go in further and reduce my 1.1mm on other side (and increase my overlap), but bearing is actually already proud of casting; you can see on left why that's possibl

Addicted
Joined: 26 Jan 2019
Posts: 689
Location: california
Sun Oct 20, 2019 9:17 pm quote
Sime,
If helpful - here is a pic of my casings (Piagio Italy).
That gap doesn't exist in mine - the slot will set the circlip so that the bearing can not go past flush.

The slot was likely cut after casting.
It appears there is a bit more meat above my circlip slot than yours.
Perhaps they cut your slot to accommodate a readily available bearing that was a touch taller than what the casting had been designed for originally - and simply moved the circlip up.

If it were me - I would determine the height I wanted the bearing to sit (within reason) and if that meant leaving a gap - perhaps shim it.
I suppose it is also possible that there is a bearing with a slightly taller wall available?

Cheers.
-CM

IMG_2025.JPG

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Sun Oct 20, 2019 10:18 pm quote
That was close. Definately an issue with rotary, they are not all the same and some come out bigger. Easy to see why with each new casing through the years the pad inlet area gets bigger with every new engine design (P200, T5, LML).

A shim on that bearing might be a good idea. Don't want it moving around when it gets hot.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sun Oct 20, 2019 10:58 pm quote
I'm going to take that bearing out and have a really careful measure of the whole area later today, and check the new bearing is precisely 12mm too.
It might be a shim to take up the gap, or it could be better to go in a little deeper up to the circlip and give me more of a crank/pad overlap. I've been looking at lots of photos this morning (including my build of current engine), and it does seem that the bearing normally sits proud of the casings (up to the circlip), in which case that helps me. It sounds bad but it's only another 0.5mm, and that 0.5mm really helps me on the other side.
In any case the critical point is that, the edge of the pad opening is already there, so I must have my bearing located spot on to give me enough crank/pad overlap when I do final build, which can be checked by making sure the final gap from crank web to casings is no more than 1mm (my 1.1mm with feelers last night).
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Mon Oct 21, 2019 2:46 am quote
First point is that both old and new bearings are identical width, which is a tad under 12mm (11.98mm), so, with the gap under the circlip as well, it won't be any worse than I measured last night (1.2mm crank/pad overlap), but I might be able to nick a little for comfort, so a precise measure of that bearing surface area with the circlip grooves is still useful, but I can relax about it.

I've had a good measure, again it's easier to show with pictures, but some words might help:
Given the width of the circlip grooves and the width of the circlips (both 2mm), there can be as much as 12.45mm between them, as it was (flush with inner circlip), or taking up the gap, (flush with the outer circlip); whether shimmed or not, there will be a gap, and I can take advantage of it.
Either way my 1.2mm overlap will be the minimum (if I set my bearing such that the web is 1.1mm from casings). But I can give myself a bit of tolerance by going further towards clutch with bearing (up to 0.45mm more).
Sitting proud of the casings, as I suspected, is not an issue; there was never enough bearing surface there (9.95mm) anyway; it will be about 2mm proud however I locate the bearing.

For my own peace of mind, when I have a quiet moment, I'll measure the crank precisely; that's located flush to the inner bearing face, and I'll sketch it in CAD to show the exact crank/pad overlap, but not necessary for now because I'm satisfied that the 0.45mm I measured today is the same as the 0.5mm I measured last night, and it means that my 1.2mm overlap was the worst it will be, and can be made a little more comfortable (or pad opening wider if I'm feeling confident I'm not; this will make me even more cautious before cutting in future).

A 12.5mm wide opening with 1.2mm overlap both sides, seems ideal, but would need some very precise cutting, and setting of the bearing.

The exercise also gives me a better idea of exactly where the seal will sit, which is another question for later; I have three seals and a choice to make.

Photo of area in question and dimensioned sketch:

Precise Casings Measure for Main Crank Bearing Area in Question.jpg
Area under scrutiny

Precise Casings Measure for Main Crank Bearing.jpg
A careful measure

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Wed Oct 23, 2019 2:04 am quote
This part is done, as far as I want to for now, but it might get a tweak, just to get bearing spot-on and optimum opening width, when I fit the final bearing. Points to make first:
Moving the bearing within the tolerances between the circlips lets me centre the crank web and pad opening as previously measured, which means I can stay safe or optimise the opening width (up to 12.5mm +1.2 +1.2 = 14.9mm web-width).
Because of the Mazz crank timing, and the narrower pad opening than expected, my Inlet opening area is less than I expected; I don't know whether that's important enough to try to gain an extra fraction of a mm and risk overlap being too small.
I don't need a shim; I can't quite identify why, but I can't get a feeler between bearing and circlip when both circlips are fitted though I can tap it over to centre the web/pad, which is the main thing, so I'm not worrying why, but I'll confirm it when I fit the final bearing. I've checked again and my 12.45mm is correct.
There has to be some tolerance in my measurements; the image below shows area of wear within the crankcase, Either the crank or bearing must have been slightly out of true. It means that my dimensions can vary depending on where I measure them (along the length of the opening). It's crucial to ensure crank is true and the bearing is parallel with the casings, which it looks like it wasn't, The crank is new and I can check it, though without being able to check the back of the web with feelers, I'm not sure how to be certain about the bearing.
Because of the need for a tolerance, I think it's safer to keep the pad opening width as it is; since taking the photo below showing the overlap in blue marker, I've had a tiny tidy of each side of opening, not to make it deliberately wider, but to just straighten them up, so the width is constant.
As part of the final tidy of Inlet I've matched carb box to carb and mating surface on casings, then blended into my Inlet down to pad opening. There's one area I could go thinner, and wonder if anyone can say a width beyond which they wouldn't go, to keep carb box sealed on casings; I have 4.3mm, and would like to go to 3mm to remove a ridge, but I imagine a decent seal is more important than a bump in the flow. The carb box is already narrower, but I don't want to cut the casings any more before checking.

Some photos below that might make the words more intelligible.

Jobs to do next, in no particular order because I haven't thought past this bit yet:
Check pad opening degrees and cut crank, maybe fit flyside inner bearing ring at same time, then crank is done.
Open up fuel passages through carb basically as photos I posted before for Hibbert.
Rebuild cush-drive with double springs and fit stepped-shaft and bearing.

1 crank bearing location check.jpg
Checking Bearing Location

2 Crank Web Centred Over Pad Opening rev 1.jpg
That's better!

3 Must have some Toerance due to Uneven wear causing irregular dims.jpg
Crankcase wear

4 carb box to carb.jpg
Carb box to carb

5 carb box to casings.jpg
Carb box to casings

6 thro carb - box - casings - pad.jpg
Thro' carb - carb box - casings

7 pad done for now.jpg
Done for now

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Wed Oct 23, 2019 5:22 am quote
Looking great. Can't be long before final assembly. The inlet gasket face is only vacuum pressure, so could be just a few mm and still seal ok. it will all help.
Addicted
Honda elite
Joined: 19 Jun 2007
Posts: 630
Location: California
Wed Oct 23, 2019 9:29 am quote
wow looking fantastic sime66 I would be tempted to blend the top carb hole casing just a smidge. The cylinder spigot face looks grand.
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1216
Location: UK (South East)
Wed Oct 23, 2019 10:07 am quote
When opening my inlet up for a reed block, I went to within 2mm of the casing edge and it's fine. You could definitely go thinner where you've placed the red rectangle. Having said that, I'm not sure the disturbance in flow caused by that little step will have much of an impact on performance.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Wed Oct 23, 2019 10:51 am quote
Thanks chaps, as it happens I did that trim down to 3mm* this afternoon; it only took a couple of minutes, Dremel, then file, then polish. I may try to do a final tidy with carb box fixed to casings, and cut as one, but it's pretty spot on now anyway. Every time I photograph it I see something else though.
Whilst I was on a roll and had time, I checked my cut pad opening angle, which is just shy of the target at the Io end, which I could already tell because it wasn't down to my 1.5mm line yet. I might give it another tweak, maybe after I've remeasured my crank after cutting, but whether anyone's ever going to notice my *Io BTDC is 124 not 125 is doubtful, so I left my Io cut on the crank as intended 8 to -4, and made a mental note that the pad Inlet isn't yet final. The crank is my next job, which is all marked and wrapped-up, ready for cutting tomorrow.
Hibbert, the cylinder face photo was to show that I was able to centre my crank web over my pad opening with a tiny tweak of bearing; it was the blue marks on the web that I was showing there, compared to the off-centre marks at my first check above, which gave me a bit of a jolt at the time.
Swa, sometimes these little considerations* don't matter too much on their own, but if I try to do each job as best I can, the overall result might be marginally better, it's when the tweaks risk something else I tend to get the willies! Hope some of the care is worth the effort.

trimmed.jpg
An extra trim - thanks Chaps

confirming crank cut after pad cut.jpg
Checking Angles

Crank Cut.jpg
Ready to cut

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 24, 2019 1:52 am quote
My crank is cut, de-swarfed and re-greased without issue. I used a magnet to catch most of it, and it was well-bound against ingress anyway. Because I knew my pad cut was tight and just slightly short on the Io end, I was generous with my cut, and, after careful measurement of cut crank and cut pad, I now have 125.6/71, which I think is close enough to be job done.
My cutting isn't as pretty as Hibbert's, I had a couple of false attempts at starting or continuing my first line with the wheel cut, but no one's going to see it after it's buried in the engine (other than you few forum chaps following my progress, who I don't mind sharing the good and less-good with), so I'm happy that its function is as intended.
Some photos etc below, but I think I'm done here, and can move on to giving the carb a gentle tickle with drills and files......

Crank Io Cutting.jpg

Crank Io Cut.jpg

Crank and Pad Angles after Cutting.jpg

Ossessionato
1980 P200E, 1974 Primavera, 04 Ninja 250
Joined: 04 Apr 2013
Posts: 3990
Location: San Diego, CA
Thu Oct 24, 2019 8:08 am quote
Did you remove material from both webs? If so, why? Just curious.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 24, 2019 8:24 am quote
No John; that's actually how rough Mazzucelli produce cranks, where my hand cutting is finer than their own product! The only bit I cut is the area not covered in tape on left hand side of first image - 8 and a tidy/blend.
Addicted
Honda elite
Joined: 19 Jun 2007
Posts: 630
Location: California
Thu Oct 24, 2019 8:34 am quote
wow looks very good thanks for showing how it's done. How do you decide what timing? How do you determine Io should be 125 and Ic 70? What type of performance do you achieve in comparison to for example 117 Io and 70 Ic? Obviously longer duration but what are the characteristics of the Io and Ic?
Ossessionato
1980 P200E, 1974 Primavera, 04 Ninja 250
Joined: 04 Apr 2013
Posts: 3990
Location: San Diego, CA
Thu Oct 24, 2019 9:09 am quote
sime66 wrote:
No John; that's actually how rough Mazzucelli produce cranks, where my hand cutting is finer than their own product! The only bit I cut is the area not covered in tape on left hand side of first image - 8 and a tidy/blend.
Then I'm sorry to insult your work which was really Mazzucelli's work .
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 24, 2019 10:10 am quote
Thanks chaps, it has come out fine; I should have made clear which bit I cut, so as to distance myself from Mazz's own standard, in fact I'm gonna post another photo to do just that. Here you go, John; I could tidy it up, and 'flow' it a bit too, but don't really want to make more swarf around the bearing than is necessary, and just don't have a good feeling about this crank that came from ScooterCentre in a beat-up box that had been previously opened, and had oily fingerprints all over it returned/rejected? I just want to fit it and hope it is up to the job despite appearances.

The quick answer to your questions Hibbert, is there is no quick answer, it's always a balance, and weighing it up comes from experience I don't have, and I rely on advice of those that do for much of that side of it, however, I'll have a stab and be prepared to be corrected, or have others expand on it:

My 125+70=195, which will produce a greater peak power than a shorter Inlet duration like 117+70 = *187, simply because more air/fuel mix is passed through per cycle, if the transfers and exhaust also allow it, but I'm sure there's other factors too. For *187, I'd have said 125/62 would be better; better torque, less 'peaky', I think, but remember it also depends where your transfers are set.
[Edit: I checked your thread this morning and saw that 117/70 is what you actually have, and were advised at the time was good for your set up, so I think you should accept the advice you were given, rather than asking me to unknowingly comment on it, so whilst I'm going to leave my reply here, I'm going to repeat that I rely on the advice of those that know, and you should do the same - and respect their advice, as I do].
125BTDC Io seems to have been a common figure for me to aim for because it falls well relative to the Transfers closing for the peak power RPMs I aim for (123-125, eg 360-125=235 / 2=117.5BTDC, so 7.5 overlap between Io and Tc). That Io, combined with the target total Inlet duration, suggests the distribution BTDC/ATDC, and also that a longer ATDC will give a longer Inlet duration, so greater power, but will also reduce torque, which again, for the type of engine I like (I'm a big chap and live in a hilly part of the country), torque is important, so don't want a long ATDC that skinny kids that want to race between traffic lights might prefer. I think the optimum ATDC is a bit more debatable, which is why I just accepted that 65 or 71 (with the l/s. Crank) was OK for this engine with a longer Inlet duration. There's far more to it than that, and I'm weak on the subject, knowing just enough to understand how to make what I like, rather than anything else.

Try reading this:

https://martysgarage.info/reference/two-stroke-port-duration/

...and download these for a little light reading if you haven't already:

http://www.amrca.com/tech/tuners.pdf

http://iheartstella.com/resources/manuals/tuning/Graham-Bell-Two-Stroke-Performance-Tuning.pdf


For clarification of what I was intending to show above; in the green box is my little cut, in the red box is what a Mazz crank looks like out the box (some of the bad-looking bits is just poor painting, but the overall roughness is pretty clear):

Crank Io Cut vs Mazz Shite Standard.jpg

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sun Oct 27, 2019 12:35 pm quote
A few weekend odds & sods jobs off the list:

- Stripped and checked carb, opened-up fuel flow passages from banjo to MJ well; 2mm+ at needle valve, 1.8mm at float bowl to jet well. Blew-out all jets and channels. Cut and slotted mix screw, (so it fits in carb box with studs, and can be adjusted with long screwdriver). It's ready to make gaskets, settle on start jetting, and fit.
- Drilled-out cush drive rivets, fitted new double-springs, de-swarfed, oiled and re-rivited, fitted the stepped shaft and new bearing; all ready to fit.
- Fitted Inner race to flyside crank bearing with the 1mm gap; now ready to fit (need to check I have correct needle bearings).
- Made a fan air deflector to compensate for the big gap around casings caused by lightening flywheel. It cost pennies to make, so if it's a bad idea or pointless I'm quite happy to forget it, but if it might make sure more air reaches my cylinder maybe it's worth a go. I can fix it with or without drilling holes in casing scroll, but in any case it would be easy to remove. I'd welcome opinions on it; good or bad.

Photos of that little lot below; nothing too exciting.

To do next (In no particular order, and in no particular hurry):
Carb gaskets.
Oil sucker pre-emptive JB Welding (like FMP's video)?
Unwanted engine stud removal? (New Best Friend; gonna let him blast my casings too).
Fit new silent blocks.
Make CHT temp sensor (I have an M10x1mm brass fitting and have re-tapped the thread in the head, which was part-stripped, but good enough now).
Bearings. (esp check crank alignment before fitting seal).
Seals and 'O' rings.
Dry build, re-measure/check/tweak
Pressure Test.

1 Cush Drive Stripped.jpg
Cush drive stripped

2 Cush Drive Rebuilt.jpg
Cush drive rebuilt with new double-springs

3 Crank Flyside Bearing Inner Race - 1mm Gap.jpg
Crank fly-side Bearing Inner Race - 1mm Gap

4 Fan Air  Deflector.jpg
Will it fly?

5 Carb Mods.jpg
Carb Mods

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