Vintage vespa with sidecar
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Addicted
Joined: 26 Jan 2019
Posts: 689
Location: california
Tue Oct 01, 2019 10:19 am quote
Gents - one more hot one.
The is the shaft that goes inside the xmas tree gear cogs.
What ever that is called.

One thing I can't quite fathom.
Why is there a key slot at near the threaded end?
I am fairly sure there was no key that goes here - so is this shaft from a different motor? Is there supposed to be a key slot on this?

Thanks!
-CM

IMG_2023.jpeg

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Tue Oct 01, 2019 10:35 am quote
Hi CM, I haven't really kept up with this one, so not familiar with your numbers, but it looks to me like you have your transfer and exhaust measurements in the wrong boxes in your calc on previous page, giving you BD=-24.59; swap them round and it all looks a lot more sensible with (118.8/180.9/24.6) BD=24.6. Maybe, it will help to confirm your measurements:

PBT (say which crank when measured) = ???
Deck to Top of Transfer port = ???
Deck to top of Exhaust port = ???
Squish (say which crank when measured) = ???

Also, to be clear, the head gasket does not change the timing because it isn't moving the ports relative to piston; changing the base gasket or stroke, or moving the ports changes the timing.

Your more recent question is simpler; those (the ones I'm more familiar with) have a special locking washer on the outside with a 'key' to hold it relative to shaft and tabs to hold the nut, like this:

https://www.sip-scootershop.com/en/products/securing+plate+input+shaft+_58560000

or, depending on your engine, this:

https://www.sip-scootershop.com/en/products/securing+plate+input+shaft+_16305000
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Joined: 26 Jan 2019
Posts: 689
Location: california
Tue Oct 01, 2019 12:17 pm quote
Sime66.
Thanks for weighing in.
Much appreciated.
Have been following your dissertation - apparently not very well...
Ok - let's keep it simple.
Here are my numbers:

For the 57MM Crank - and current set up
PBT (say which crank when measured) = .20
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish (say which crank when measured) = .95
1.70mm base packer in place to lift the cylinder for the above #s
All above = 57mm crank.
And its a torquey fun set up as you note.

Those were measured before I left (brought my notes with me - now on the continent).
Looks like I swapped exhaust and transfer - was wondering why that weird negative... Thanks.
If I plug those in to the calc - I get: 118.82/173.07/27.12

Not sure how you are getting 180.9. where I get 173.07.
Am I plugging something in wrong? See below.

If correct - the question I am struggling to decipher is: What is the 60mm crank gasket/packer plan - and how do I calculate with web site so I can purchase a range of gaskets that would likely suite (I will of course install and do actual measures to ensure I have it right once back).

Thanks for taking a minute to have a stab at this - can you clarify how you got to 180.9 vs my 173.07? that one has me miffed.

Edit: thanks for links! makes sense. the slot was where my locking washer went in - just forgot and couldn't figure out why it was there...

Screen Shot 2019-10-01 at 10.13.53 PM.png
This is the calc using my current 57mm crank.

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Tue Oct 01, 2019 1:13 pm quote
The sheet you just posted is for 57 crank, the one where I spotted the error was for a 60 crank; I just swapped those Transfer and Exhaust dimensions round and kept everything else the same; I should have left the correct blowdown 24.6 as the point I was making, but I then hurriedly added the full timing figures in brackets as an edit afterwards, and it looks like I part-copied some of your figures instead of mine - the 180.87 is from your sheet). I can't do it as quickly as Jack, and I saw you were still online when you posted the second question, and was trying to catch you whilst you were still there.

I agree with your new sheet for 57 crank.

It's late here, and I don't want to make mistakes tonight, and don't know, without reading the full thread, what casings, kit, crank etc. you have, or have bought, are are buying, or what timings you had or are aiming at. I'll spend an hour on this in the morning, while I'm having a break from cutting mine up, and see if I can catch up. If I've got anything helpful to add I'll post again.

Just for clarification, and to help me catch up, what port timings are you aiming for, and is it that you're considering a 60 crank to achieve it? I don't follow what you're trying to change and how or why.
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 4887
Location: So Cal
Tue Oct 01, 2019 2:27 pm quote
Guten tag bruder.
Try running the calcs again with the 60mm crank. Note that PBT needs to be changed to account for the longer stroke (itll be a negative number). Also run calcs without the .2mm base gasket and see what you get.

Gasket at base = revs
Gasket at head = torque
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Tue Oct 01, 2019 7:18 pm quote
charlieman22 wrote:
For the 57MM Crank - and current set up
PBT (say which crank when measured) = .20
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish (say which crank when measured) = .95
1.70mm base packer in place to lift the cylinder for the above #s
All above = 57mm crank.
And its a torquey fun set up as you note.
Maybe I have not understood fully but what you have written sounds like your 57 Polini cylinder is running with a 1.7mm packer now and a PBT of 0.2mm. This would mean your original crank is already 60mm? Confused.
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Location: california
Tue Oct 01, 2019 8:29 pm quote
All - for those of you that find calc's mind numbingly boring - I promise to be back to pictures of fresh beer and scantily clad tail ends (talking about my scooter of course) shortly. But first...

Sime - No trouble, and big thanks for taking a minute after hours to double check. Looks like we are all on same page now on EXISTING set up's calcs so all good on that front. I've made the error of adding head gasket to my measures before - thinking it increased the distance to top of cylinder. Good catch.
Quote:
Just for clarification, and to help me catch up, what port timings are you aiming for, and is it that you're considering a 60 crank to achieve it? I don't follow what you're trying to change and how or why.
1. Why the 60MM crank: More CC's, More low end grunt. More horsepower.
2. What timing targets: Great question. I am trying to figure that out myself - the performance I want is a touring like for someone who rides two up all the time - or in my case, has a mostly empty side car. Wide power band with good torque, and as much HP as I can squeeze out reliably.
3. Why I tore down in first place: My drive shaft is toast, and my crank rod has play, and I some people think I can't leave well enough alone.
Quote:
Guten tag bruder.
Try running the calcs again with the 60mm crank. Note that PBT needs to be changed to account for the longer stroke (itll be a negative number). Also run calcs without the .2mm base gasket and see what you get.
Guten tag. chuckle. Ok - interesting and instructive. Here are the calcs.
Assumption made.
- Crank numbers change from 57 to 60.
- This alters PBT
- Other measures stay constant

If my target was 118-120/174-175/28 ish
Doing this - I can now see the solution.
1. Adjust base gasket thickness to optimize transfer port timing: e.g. 119
2. This leaves exhaust port timing a little high (I think) so if I want to lower it a bit, I can grind the top edge of exhaust port.
3. Add head gasket to bring squish to ~1mm target

Third image below shows this.
Think I have a handle on how to make adjustments to reach targets.
Which leave's only one question.
What should my targets be?

Screen Shot 2019-10-02 at 5.45.23 AM.png
Keeping my existing 1.7mm base gasket, PBT goes from .2 to negative 1.3 due to additional 1.5mm of crank reach

Screen Shot 2019-10-02 at 5.46.41 AM.png
This shows what happens with no base gasket. So PBT jumps an additional 1.7mm to a full -3 from -1.3

Screen Shot 2019-10-02 at 6.03.59 AM.png
Taking 1.1mm out of my existing packer stack leaves me at .6 base gasket thickness and -2.4 PBT. Then a grind of 1mm of exhaust port gets me to ~175 exhaust duration target

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Tue Oct 01, 2019 11:28 pm quote
I'm trying to wade through the confusion and just get back to a few straight forward numbers to do some timing calcs with; I'm taking this as fact, if it isn't then what I calculate below here is also incorrect:

For the 57MM Crank
PBT = 0.20
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish = 0.95


But then you say:
1.70mm base packer in place to lift the cylinder for the above #s
Your Deck to Top of Port dimensions are physical measurements on the barrel from Deck to Port; they do not change unless you grind; it is the PBT (and Squish) that changes with the base packer. Having made that point, and cleared the confusion, I see you've used the same dimensions, so think you have that.

But then, more as an aside really, but important to me:
And its a torquey fun set up as you note.
No, I didn't; I have made no recommendations or comments about your timings, I did give you my targets on my build, but not as recommendations for yours, and have made it clear that I don't know enough to be able to advise your timings; that is very definitely for others to help you with.

Going back to basic lumps of metal, forgetting the base gasket (for now), the piston will travel 1.7mm higher, so PBT and Squish will decrease by 1.7mm without it, so these are fact for 57mm crank (stop me if I'm wrong):
PBT = -1.5
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish = -0.75

And for a 60mm Crank (still with no base gasket) the piston will travel 1.5mm higher still, so the PBT and Squish will reduce by 1.5mm:
PBT = -3.0
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish = -2.25

I'm already thinking something is wrong, or your barrel is already skimmed, but lets see if it's me; putting your 1.7mm base gasket with a 60mm crank will increase PBT and squish by 1.7mm:
PBT = -1.3
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish = -0.55

Checking your last sheet (ignoring the exhaust grind still just trying to get basic figures to work with), reducing base gasket by 1.1mm to 0.6mm will decrease PBT and squish by 1.1mm:
PBT = -2.4
Deck to Top of Transfer port = 46.11
Deck to top of Exhaust port = 34.45
Squish = -1.65

So you'd need a 2.5mm head gasket to give 0.85mm squish (not a recommendation, just an observation). You'd get the following:

118.73/170.42/25.84

Then raising the Exhaust 1.0mm (still just checking, not agreeing you should do so, without target timings), you'd get:

118.73/174.33/27.8

(The discrepancy is because I've used 34.45-1=33.45, and you've used 33.35). It looks like we agree the basic numbers we're using, and now just need target timings. I'm out of time this morning, so will post this, which shows the numbers. It would seem to me that you can increase the base gasket to increase Transfer timing, reduce head gasket for Squish, and tweak Exhaust.

OK; I'm running late, and hurrying makes errors, but what about if you did try to get my figures on the engine I'm running now? (123/171/24):

Exhaust is too high ( using PBT -1.6 = 122.84/173.55/25.36), you'd have to raise the Transfers not the barrel.

The next job would be to see if you're better off sticking with the 57, but I really am out of time, so maybe you can do that, and I'll look again tonight, or in the morning. Hopefully before then you might have better target timings.

I know that was long-winded, but I had to make sure the basic numbers were right first; I still haven't read back through the history of the build so far.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Wed Oct 02, 2019 2:48 am quote
I thought a good way to proceed might be to see what sort of timings you can achieve with either crank, just by changing base gasket (not considering squish or head gasket for now)....

57mm crank (actual PBT = -1.5mm)
Ex from Deck = 34.45mm
Tr from Deck = 46.11mm

New PBT (-1.5mm + Base Gasket) Timing:
0.2mm 118.82/172.66/26.92 Already agreed, and re-checked (except it's 34.45, not 34.35 as I pointed out in my post this morning)
0.5mm 120.44/173.89/26.72
0.9mm 122.58/175.52/26.47
1.0mm 123.11/175.93/26.41


60mm crank (actual PBT = -3.0mm)
Ex from Deck = 34.45mm
Tr from Deck = 46.11mm

New PBT (-0.3mm + Base Gasket) Timing:
-2.4mm 118.73/170.42/25.84 Already agreed, and re-checked.
-2.0mm 120.8/171.99/25.6
-1.8mm 121.82/172.77/25.48
-1.6mm 122.84/173.55/25.36

With both cranks, and subject to checking myself, and hopefully confirmation by someone clever, it looks to me like the Transfers are too low relative to the Exhaust to get the right Blowdown for any given Transfer duration. This would mean setting the base gasket for the Exhaust duration and raising the Transfers to get them right to give the correct Blowdown.

To proceed beyond here (except checking myself when I have a quiet hour or you checking now you have the hang of it), you need those target timings for your engine and your 3-wheeled vehicle; I honestly don't know the answer to that.

I'm using this below as my crib sheet for target Blowdown for a given Transfer timing, but am unsure of the source now, and ready to be corrected (sorry if it comes out huge or tiny; posting images direct is still a bit of trail and error for me):

PORT TIMINGS vs Transfer Duration.jpg

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Wed Oct 02, 2019 11:37 am quote
Moving on from my two previous posts, and still with no target timings, this evening I had a look at what PBTs with each crank would give Ed 171, and then what would need to be done to Transfers to achieve Td123 and thus Bd24.
I think the work involved with the Transfers would mean that the following are not a viable option; I'm wondering now if some compromise can be agreed with Bd, but once again we're coming back to not having a target. Anyway, here's my numbers for the exercise I just did:

60mm crank with PBT = -2.25 gives Ed171.01, but Td of only 119.51; raising the Transfers 0.7mm then gives Td123.09, so 171.01/123.09/23.96.

57mm crank with PBT = -0.20 gives Ed171.01, but Td of only 116.62; raising the Transfers 1.2mm then gives Td 123.11, so 171.01/123.11/23.95.

You reckon it was torquey fun before? 118.73/170.42/25.84? My crib sheet doesn't even go as low as 118, but Bd26 is more like Td124/Ed176. There must be some compromise between where you are now, quite happily apparently, and what you can achieve without raising the Transfers in the barrel; it's the physical spacing of your Exhaust and Transfer ports relative to each other that gives you too much Blowdown at whatever height you set your barrel.

Guess what; you need someone clever to give you some achievable target timings............

(I'm going back to working out how to cut my Nikasil; all of a sudden it seems easier).

Screenshot of my four timing calc sheets; hope you can read them, but the main points are written above, and I don't think it is a good idea anyway:

CMs Build Achieving 123-171-24 with either Crank.jpg

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Wed Oct 02, 2019 2:22 pm quote
Sime
All input appreciated.
Good of you to put so much time in to crunching around the numbers.
Thanks!

My approach will be to avoid grinding transfers - too touchy for me.
The Polini cyl seems to have pretty good grunt - so I think the blow down realized from the transferport/exhaust port differential can be solid.
I will have a careful measure when I am back in the states and ensure I have it right.

Have enough in the mean time to get the crank and some base/cyl gaskets so all set for time being.

Thanks!
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 03, 2019 1:15 am quote
Raising Transfers, with the roof angles and whatever scavenging design is there, is a tricky job, I shied away from it in a previous incarnation of the engine I'm doing now with a different kit, and I wasn't suggesting it for you; it's just where your numbers took me, but does seem to be something unhelpful there if your dimensions are correct.
Definitely have a very careful measure when you get home with your new bits of kit; make sure your 46.11, 34.45 & PBT numbers are right to start with. In my opinion, which is what I was trying to stress with Hibbert before on his build, it's not the flash parts that make the engine perform well, it's getting this boring, tricky stuff right. Or, in your case, if you do have to reach a compromise, then at least one reached understanding the implications of it, and not just accepted because it was too hard. Tiny dimensions do make a big difference and Blowdown is important. Have a read of this for a simple explanation of 'Port Timing Basics':

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

You can do the calcs yourself now anyway, and an accurate re-measure might make it look better (you have to doubt Polini were too far off), or someone who knows better might say it's gonna be fine anyway**, and you also know how it performed before; hope it turns out well, sure it will.

**I read back a bit this morning, and I saw that on August 22nd Jack had also said PBT 0.5mm, 120/174/27 will do for now - is going to go OK. Those are the same numbers I got yesterday with the 57 crank, so perhaps you can find similar with the 60; I also did some numbers for that yesterday, but wise to re-measure before you do more calcs I think...


A quick digression:
I was in Germany, when it was still East and West; 30 years ago; October 1989 I was in West Berlin when the wall was coming down Checkpoint Charlie and all that, went to East Berlin, which was so different. I still have some of die mauer and a bit of rebar I grabbed one dark night after a session in a bar with West German friends. I love Germany, but then, although I'm (English/Welsh) British, I'm a European at heart. Back then it was Eine Deutschland, now effing Brexit progress!?

Nicht auf deine nelly!!
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Fri Oct 04, 2019 8:01 pm quote
You may have noticed that I forgot you shortened the cylinder. The day job is so busy at the moment I am actually having to think to do it.

As said before the transfer timing is the first thing to get right. For 26/26 carb on rotary and your sidecar, 123 would be appropriate. Next importance is blowdown. 27 degrees is nominally where this should be for the power you need. Exhaust affects this heavily but 27 is a fair compromise to start with. Port width should be 70% chord. Any less is just wasted torque. Port shape we'll do in pictures later.

This means on a 60mm crank, 1.4mm of piston out the top of the cylinder and 1.00mm up on the exhaust port. With the piston poking out you will be able to set the squish anywhere you want it. I would go 0.8mm on this.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Fri Oct 04, 2019 10:59 pm quote
Jack, when you have a moment, I'm curious why 27 blowdown is better for this engine.
For PBT -1.4mm I get 123.85/174.33/25.24, which I thought was already a bit high, but with the 1mm exhaust mod, it's 123.85/178.19/27.17.
Is the clue in the 70% chord-width, or something specific to the sidecar-pulling power requirements, or was I just barking up the wrong tree?
The latter would not surprise me, which is why I'm glad you're steering it back on track.
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Sat Oct 05, 2019 2:46 am quote
Quote:
I love Germany, but then, although I'm (English/Welsh) British, I'm a European at heart. Back then it was Eine Deutschland, now effing Brexit progress!?
Don't mention the war. Basil Faulty
Quote:
The day job is so busy at the moment I am actually having to think to do it.
Been suffering the same. Highly inconsiderate behavior by those that pay my living - really.

Thanks for weighing in with targets.
Quote:
transfer timing is the first thing to get right... ...Next importance is blowdown
Very helpful.
Am on board with shaping/sizing exhaust port.
Have spare set of rings to thrash.

Couple questions:
1. If owner of sidecar was talked out of 26mm carb and into DRT 24MM version by SIP technicians while visiting, would targets remain same or adjust for 24/24?
2. What is ideal exhaust target with the 123/?/27 you suggest?

Side note: Got a few minutes in at SC, and a half day in at SIP. Tech sat with me and we sorted out all bearings/shafts needed to convert gear box too Lusso. I will make a full posting on the conversion with part numbers so anyone finding later/ wanting to follow has a cheat sheet. Couple good finds of specialty parts to help solve. More to come...

IMG_2016.jpeg
Time was cut short - only a short visit - knowledgeable expert group - but a bit less retail friendly then SIP crowd in my experience

IMG_2053.jpeg
Competition of the gray buildings. They all know ea. other - tho pretty far apart geographically (SIP just outside Munich - SC just outside Dusseldorf)

Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sat Oct 05, 2019 7:09 am quote
Q2: You already know it. Blowdown is the period, in degrees, after exhaust opening before transfer opening. So the 27 is the result of 123 transfer and 177 exhaust; It's the difference divided by 2. (Simplified numbers): 177-123 = 54 /2 = 27; what I'm hoping to learn is why 27 is good for your engine. Anyway, a little rough sketch, excuse shaky quality been grinding all day:

blowdown.jpg

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Location: california
Wed Oct 09, 2019 8:01 am quote
Back from travel.
Sime - thanks for the drawing/explanation.
Seems obvious now...

Parts start rolling in today.
Pretty pictures to follow.
Still collecting some small bits and bobs.

First - a practical question based on the numbers so I can get what I need.
To hit the targets Jack proposed, I will use ~1.5 base gasket.
This will put my piston at 1.5mm above cylinder deck (1.5pbt)
(I shaved the deck of my cyl down already on prior build).

My options for head gaskets are only in .5 increments off the shelf.
If I use a 2.0 head gasket - that would give me ~ .75 squish.

All:
Question - Does one stack multiple head gaskets - cut em from scratch from some mysterious material - other?
Will the .75 be too tight?

Getting psyched to start this build.

Thanks!
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
Joined: 26 Sep 2013
Posts: 4887
Location: So Cal
Wed Oct 09, 2019 9:27 am quote
Ive cut my own gaskets from aluminum sheet. Kind of fiddly, but not as hard as it sounds.

image.jpg

Molto Verboso
Joined: 26 Oct 2015
Posts: 1825

Wed Oct 09, 2019 10:30 am quote
Id still get both sizes of those head gaskets just in case. You never know exactly what your final squish will be until you get everything torqued down. If they dont work out for you, then youre only out $10-$20. If they do work out for you, then youre golden. Plus you can double stack them if needed to get a very accurate measurement of your squish when you mock it up. Of course its always better to have just a single gasket for the final go. I dont have enough experience to say if two head gaskets are a bad (or real bad) thing or not. FYI, my generation of KTM 2 stoke dirtbikes came from the factory with double stacked base gaskets in order to get the correct squish (wich it about 1.2mm for that bike). I also have about a 1.2mm squish in my T5 172, and my Lammy 225.
Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2256
Location: Chicago. Well, Evanston, but that's almost Chicago
Wed Oct 09, 2019 1:04 pm quote
SoCalGuy wrote:
Ive cut my own gaskets from aluminum sheet. Kind of fiddly, but not as hard as it sounds.
Yeah, I've done my own, too. Feels like hackery compared to nice laser-cut ones, but the quick turnround and port matching makes up for that sometimes.

I've also double-stacked gaskets before. I just put a really thin smear of head sealer between them before I torque it all down and never had an issue with leaks. Mostly, it just makes matching the gaskets to the ports a little bit more irritating, IMO.
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Location: california
Wed Oct 09, 2019 1:53 pm quote
Hey - thanks you guys.

Mine is really just a head gasket issue.
Will go with the single base gasket this time (have stacked 1.5 & .2 currently).

Socal - damn - that looks like a lot of work. Impressive - but difficult to do nicely. I'd have to find a 2.1 or 2.2 thick piece of metal to do the job for me - but I might have to go there if the 2mm wont work.

Same guy that talked me out of the 26/26 carb at SIP was adamant I wouldn't need a 2mm+ head gasket. I mighta forgotten to tell him I had already shaved down the cylinder deck... That one's on me.

Quick look online - appears no one carries the polini 2mm gasket here in the States.
WhoDat - I like the stack for dry build approach.
Leaves me in shape for working this weekend on it.
New crank.
Dummy bearings.
Clean cases.
Engine stand (to replace the tire I was using...)
Buzzwangle.
So much for getting anything done on the house.

Chandlerman - did you mean the base or the head gasket you've stacked and coated?
(Obviously more pressure to deal with at the head).

Think I will dry build with stacked 2mm, check actual timings and squish, and determine if a stock 2mm head will work or if I am gonna have to fabricate.

Thanks all!

-CM
Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2256
Location: Chicago. Well, Evanston, but that's almost Chicago
Wed Oct 09, 2019 5:04 pm quote
charlieman22 wrote:
Chandlerman - did you mean the base or the head gasket you've stacked and coated?
(Obviously more pressure to deal with at the head).
Base gaskets. Should've been clearer there
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Location: california
Wed Oct 09, 2019 7:51 pm quote
Quote:
Base gaskets. Should've been clearer there
No trouble. Thanks for weighing in.

The missing voice here is Jack.
This may be due to one of three reasons.
1. Work is inconveniently actually demanding his time
2. My mutiny on the 26/26 carb
3. He is trapped under a heavy object and is struggling to reach the computer.

In any event - here is my query.
Sime - you asked why a blow down of 27 - and posted a cheat sheet of sorts that would have suggested something considerably lower.

But if you look at what FMP touts, he is inline with Jack.
In fact, FMP's target for "optimal" with the Polini 177 is:
118/174/28 for the 57mm crank.
And
120/176/28 for the 60mm crank.
Blow down is pretty close to what Jack is proposing.

Now - those that have followed this thread even tangentially know - I have no f*king clue why those are or are not the magic numbers - I'm just the labor - but my prior setup was 118/174/28 (give or take) with 57mm crank - and it was a fun ride. There was torque throughout, and it revved happily under load to ~8K+ with my 'granddaddy Polini" grunting away - to borrow Ginch's term.

Interestingly - 118/174/28 were both Jack and FMP's targets on that 57mm crank.
But as I move to the 60mm crank - there is a difference of opinion.
Jack's thrown out 123/177/27 which has the transfer ports significantly higher than FMP's 120/176/28 optimal target for same.

So some pretty experienced voices with the 27 or 28 target blow down, but I am left curious about the higher over all timing that Jack proposed vs FMP.
What's it going to mean for overall power.
What's it gonna mean for drivability.
Any and all wanna pontificate on likely performance differences - I'd welcome your view point.

In the mean time - I will be warming up my grinder in the garage.
Weekend is almost upon us.
Time to make some choices.

Thanks!

-CM
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Thu Oct 10, 2019 2:43 am quote
That's FMP's default timings - he feels they work well on pretty much all Vespa cylinders for a balance of tourque vs power.

And just for you...

Clipboard01.jpg

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Thu Oct 10, 2019 7:57 am quote
Ginch - Thanks. Got it.
I love your grandaddy too! (Strictly in a platonic manner of course.)
He's tough and not too thin skinned like the others.


Ok - keeping it simple then:
Internets basically say - higher port timing narrows band of exhaust resonance.
Means higher I go - narrower the power band - but more the power. (read in Finish accent).

Tho previously discussed here - I am wrestling with the exhaust width percentage. Not if it should be 65% or 70% or cord vs radius. I can determine those risks myself. Instead I am just stuck in 1st gear trying calculate the percentage...

Baffled.

FMP shows a Polini 177 cyl (how convenient!) and his calculations.
But it is some kinda Aromatherapy-Alchemy best I can tell.

Below is an example.
This is for a 177 cyl - thus 63mm Dia.
He shows 44.6mm = 65%
and 42.5mm = 62.5%
But 42.5mm = 62.5% of 68, not 63.

Then he shows a random piece of paper with what appears to be 1mm taken off the number - thus 42.5 goes to 41.5.
Ahh - maybe you have to take a MM off your measure.
Great:
42.5 - 1mm = 41.5
Then he shows 41.5 = 62.5%
Problem is, 41.5 is 62.5% of 66.4, not 63.
Hmmm.

Bracing for the obviousness of the answer.
Someone wanna dope slap some enlightenment into me?

So fun learning in front of a crowd...

Screen Shot 2019-10-10 at 7.08.29 AM.png
Numbers on the right are his port width measures (I think). He clearly wants to grind 2 mm extra width to get to 65%. But 65% of what Im not sure.

Screen Shot 2019-10-10 at 7.07.55 AM.png
45.4 - 1mm then some hyroglipgics = 44.4 mm = 65%. (that's 68.3mm. ??)

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Thu Oct 10, 2019 8:49 am quote
Quote:
But it is some kinda Aromatherapy-Alchemy best I can tell.
Yes, trying to follow Mr.FMPs math can be a challenge. Love the guy, but sometimes hes like a hyperactive child who just gulped down a Mountain Dew.

Stick with Jennings.

The width of the exhaust port is a percentage of bore diameter.

The safe and sensible approach is to begin at 62-percent, with a shape that is as nearly an ellipse as is possible.

... the radii at the port window's corners should be about 15- or 20-percent of the port width.

Jennings draws a simple picture on p.111 of his Handbook how its measured. Ill see if I can copy and paste it when I get to a computer.
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Thu Oct 10, 2019 10:34 am quote
SoCal - thanks.
Was preparing myself for a math lesson on basic percentage calculations. went full Jethro adding knots plus knots but to no avail.

Welcome the info from JENNINGS. Searched for just solid example online of someone doing the Percentage calcs with chord and arc but found neither.

With that said. Curious.
Anyone understand what exactly FMP might be calculating and why he subtracted 1 mm on the second example?

Mountain due - perhaps - but there is method to the mans madness and a certain irreverence to his style. Suspect someone can decipher?

(FMP. If you are reading this - enlighten us?! Always interested to know!)
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Thu Oct 10, 2019 11:52 am quote
FMP can explain (if hes reading this). I think he might be working with a different size barrel.

Heres what I understand:

65% of a 63mm diameter bore = 41mm. Unless you plan on racing your hack, thats your MAXIMUM exhaust port width.

I think 62% is more realistic, but its your call.
62% of a 63mm bore = 39mm.

Measure twice, draw or tape lines, fire up dremel, grind. Done.
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05 Stella, '62 VBB, 76 Sprint V, 63 GL
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Thu Oct 10, 2019 2:34 pm quote
Ima gonna get nerdy here, but you asked

If you read your Jennings, he explains it pretty well, and definitely better than I can, albeit at a level of detail most folks won't want to get to.

The key to understanding port timing, IMO, is getting back to the fundamental reason that ports exist: namely, to allow the flow of gases into (transfers) and out of (exhaust) the cylinder. The port timing is therefore a function of the displacement of the cylinder (how much gas needs to be moved), the area of the port (how much gas can move through it at any given time, which is itself a sinusoidal expression of area over time) and the ports' duration (which varies by RPM's). I'm going to ignore other factors like the roof angle, because if you're learning anything from this post, your best bet for controlling those is to find a jug that implements your desired shape to start.

Anyways...What that means is that port timing is effectively an expression of the RPM's at which the motor will produce peak power, combined with an expression of how broad the power band will be. If put the power band too high, you wind up with a "flat spot" where the motor isn't producing enough power for the gearing, typically just before the power curve.

So if want to adjust the power curve of the motor, you have two options: Change the size and shape of the ports, or change the amount of time they spend open by adjusting the port heights.

So while that value will vary depending on the cylinder, the optimal values for different tuning objectives are either published (e.g. my beloved BGM 177) or known through Tribal Knowledge of forums like this.

I hope that helped
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Thu Oct 10, 2019 2:35 pm quote
SoCalGuy wrote:
...

65% of a 63mm diameter bore = 41mm.

thats your MAXIMUM exhaust port width.

I think 62% is more realistic, but its your call.
62% of a 63mm bore = 39mm.

Measure twice, draw or tape lines, fire up dremel, grind. Done.
Imma try that soon! You make it simple, thanks Mike.

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Thu Oct 10, 2019 6:38 pm quote
Another trick which seemed super-obvious in hindsight once Jack suggested it to me, is that if you're drawing lines across the barrel, use the piston as a ruler and they'll come out dead straight and perpendicular.

Also, use a sanding wheel, not a grinding wheel for better fine control if you're grinding cast iron.
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Thu Oct 10, 2019 9:22 pm quote
Quote:
I hope that helped
Yes - it did!
Thanks.

Voodoo - small shards in eyes - not good. Safety goggles in the plan. Tks.

Just read Chandlerman's 1976 Sprint V mechanical rebuild
Swa's VBC1M (190 Super) engine build

Plenty of good learning there for me.
Thanks gents for posting.

Raised a couple observations/question.
- Swa made a point of mounting the bearings to the crank prior to assembly of the cases. Can anyone comment on that related to my older VBB build?
- Is there any magic to placement of the same bearings? Do they get gapped or are they pushed up flush against the crank webs?
(note - my current bearings stayed with the case - crank just slid out of them).
- Chandlerman - believe yours ended up about 124/176/26. - would you target same if you were doing again?

Like the piston trick for marking. Don't know if you guys have seen this guy - but he's fun to watch. Uses piston rings for marking - I've tried - works really nicely - put in cyl, then use piston to push it in place - dead straight and doesn't move.
FMP likes 200 inlet timing.
Other's commented about getting too racy above 180 on two noted thread's above. Hmmm.
Little concerned my crank timings may be a bit aggressive out of the box - but not really certain how that will affect overall.
Will put in and do some measurement's to see where our tru starting points are upon arrival (which UPS tells me is "slightly" delayed).
Annoying - but perhaps I will try this in the mean time:

Screen Shot 2019-10-10 at 10.01.16 PM.png
Chandlerman's innovation

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Posts: 1825

Thu Oct 10, 2019 9:51 pm quote
Engine parts in a dishwasher? Must be a single guy...or soon to be. My momma chewed me out big time for doing that once.

200 is quite a bit for a non race bike! I really have no need to set any of my road going junk over 180. Youd probably have to go after a proper expansion chamber exhaust if you went to a 200 degrees.
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Fri Oct 11, 2019 3:52 am quote
Lot going on here. Not quite sure what the question was but still like 123/177/27. Will suit your needs better. As would a 26/26 carb. I wonder why the SIP guy talked you out of it. Maybe he thought you couldn't handle it?
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Fri Oct 11, 2019 4:03 am quote
whodatschrome wrote:
Engine parts in a dishwasher? Must be a single guy...or soon to be. My momma chewed me out big time for doing that once.
I waited until my wife wasn't going to home long enough for the cycle to run. She still figured it out when she came in and said, "Why does the whole house smell like a garage?" with shiny engine cases sitting on the counter.

Later innovations in scooter cuisine included baking my exhaust when I re-painted it (smelled up the whole house. Do this when you're being left without adult supervision for at least the weekend); heating the cases in the oven to see if that made bearing installation significantly easier (it did compared to using a torch, not so much compared to a heat gun); and putting a gas tank in the clothes dryer to scrub rust out of the tank ("Does is smell like gas down here to you?").

As to the port timings, they were fantastic. My re-measure with the new piston had them down to 123/175, so we'll see how it does. It won't really be an apples-to-apples comparison, though, because of the air leak. Still, I think it'll be solid.
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Fri Oct 11, 2019 5:31 am quote
Oh, hai! I found another picture! Cookin' up a fresh Sip Road. Yummy!

2017-07-04 14.21.21.jpg

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Fri Oct 11, 2019 6:53 am quote
Chandlerman
Quote:
("Does is smell like gas down here to you?")
Head back laugh. Uh huh.


Jack:
Quote:
Lot going on here. Not quite sure what the question was
There are four:
- Was curious why the slightly lower ex. port and blow down suggested for Chandlerman's "touring/torquey" set?
- Crank timing - am I safe up to 200 deg? (See below notes on my old crank)
- Swa made a specific point about installing the bearings on the crank rather then into the case first. Looking for enlightenment on that related to my build.
- Do the exhaust shaping notes you gave Chandlerman apply also to mine - or would you modify in some way?
Quote:
still like 123/177/27. Will suit your needs better.
On board. Those are my targets.
To achieve with my cyl - I will have to take ~.8mm of material out from top edge of exhaust port - and add a 1.5mm base gasket. I'll fit and measure first of course.
Interestingly - FMP's targets are achieved with same grinding - but with a 2mm base gasket instead and lower over all timings.
(My ABILITY to achieve .8mm of grinding- remains to be seen - but Im up to trying.)
Quote:
As would a 26/26 carb. I wonder why the SIP guy talked you out of it. Maybe he thought you couldn't handle it?
I'd might take offense if it weren't for its likely accuracy...
Him "we can put it in your box, but you will be trying to get it properly jetted still 6 months from now and ordering this one in my hands (24/24)" (German accent).

Me "oof. ok, ok, let's just go with the drilled out 24/24".

WhoDat
Quote:
Id still get both sizes of those head gaskets just in case. You never know exactly what your final squish will be until you get everything torqued down.
Agreed - tks! Done.
Quote:
200 is quite a bit for a non race bike! I really have no need to set any of my road going junk over 180. Youd probably have to go after a proper expansion chamber exhaust if you went to a 200 degrees.
Here - I have no f*kn clue again - and have to rely on the gang for advice.
That said - when I tore my motor down, I took a quick measure of existing 57mm crank.
Quote:
Zeroing out the buzz wangle at inlet opoening
Inlet opening moment = 0 degrees.
rotating clockwise until inlet is fully closed occurs at = 199.5
continue to rotate until piston top gets to top of transfer port occurs at = 141.3

Then zeroing out at TDC
TDC = 0 degrees
Rotating crank clockwise I get the following in this order:
Intake closes at 299.5
Piston top closes transfers at 121.5
Inlet opens at 100
Inlet shuts at 300
Transfers open at 240.5
Transfers close at 121.5 and above numbers cycle through again.
If I am understanding this stuff - looks like my crank had been cut and was already at 200 degrees? Even with the 150 stock cyl lifted a bit and a fat head gasket on it - for a little 150 - it wasn't weirdly peaky - ran pretty well for a little 150

Screen Shot 2019-10-10 at 9.59.38 PM.png
From Chandlerman's build - Jack's shaping notes

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Fri Oct 11, 2019 7:19 am quote
there are more than one technique on the order of reassembly this worked great on my last one. Main bearing on fly wheel side of crank. Use a wedge in the webs or fixture properly. Main bearing installed into casing after main seal on clutch half. Use crank puller to draw in crankshaft into clutch main bearing. Use hot plate or oven to heat fly side casing and drop onto other half.

I learned that order by reading this forum so thank you whoever enlightened me my previous order did not work out as well.
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Fri Oct 11, 2019 7:48 am quote
If you have a crank puller (and you should definitely invest in one if you're planning on working on these motors with any regularity), it's all pretty straight forward. Any bearing you can get to the inner race, you can throw a little bit of heat at and then draw the shaft in with the puller.
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Posts: 1557
Location: London UK
Fri Oct 11, 2019 7:05 pm quote
charlieman22 wrote:
Jack:
Quote:
Lot going on here. Not quite sure what the question was
There are four:
- Was curious why the slightly lower ex. port and blow down suggested for Chandlerman's "touring/torquey" set?
- Crank timing - am I safe up to 200 deg? (See below notes on my old crank)
- Swa made a specific point about installing the bearings on the crank rather then into the case first. Looking for enlightenment on that related to my build.
- Do the exhaust shaping notes you gave Chandlerman apply also to mine - or would you modify in some way?
No time this morning, still way to much work to do. Short answers.

The shape of the exhaust port changes the blowdown requirement. The type of exhaust and the carb/reed/duration change it too. Numbers that work on one will be only similar on another. Yours is a long way from the limits, so don't worry about half the stuff you read.

190 degrees would have been enough but 200 will give a longer draw on the tiny G rated carb .

Crank bearings on old crates is not my specialty.

No. Your exhaust needs a different shape for a different job (sidecar).
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