Modern Vespa

SWA - thanks for weighing in.
Good for me to bench race this a little before I cut steel and aluminum chips.

I'm going to do the opposite.
Because I have a tool grinder that can hold close tolerances on things like automobile crankshaft journal re-sizing.

My plan is to cut the P200 crank journals to match exactly the VBB.
This allows me to fit the crank into my VBB cases as if it were a VBB crank.
The only remaining issue is then the groove - which the cases will need to have added - or I would have to mill off the lip from the P200 style crank.

VBB cases have the same circlip - but they have the bearing and seal reversed from PX cases - the bearing being close to the crank and the seal outboard of that up against the circlip. I could possibly leave the crank alone on the clutch side and use PX order of assembly - but I am more comfortable keeping it all VBB.

I loved the thumpiness of my move from 57 - 60mm crank.
Going to 62 is a risk - but im interested to make it work.

You're a wild man - I love it!

qas - always good to have you along!

All, riddle me this:
SIP shows duration timings for crankshafts.
My current one is "123/6"
The one I'm considering buying at is "141/0"
(the Maz in pics below is likely 138/6)

SIP explains the numbers here: Sounds simple - but when I take a crank and put it in a case half - its instantly clear that the inlet is neither opening or closing anywhere near 6° after TDC. How could it? At TDC, the crank pin is near the middle of the cases where the piston skirt will go. It is no where near the inlet open or close.

Can anyone help untangle this for me/ show me what I'm missing?
Interested t better understand.

The problem is the translation SIP doesn't mean actual TDC they just mean the big end pin. Opens 138 degrees before the big end pin and closes 6 degrees after the big end pin. The numbers in relation to TDC depend on your casings and length of inlet.

Yes. Took me a while to figure this out.

Thanks gents.
Ok - so if the pin is the mark that they are referencing - let's compare two theoretical crank numbers - for a friend.

Crank 1: 123/6
Crank 2: 141/0

Crank 2 will have both longer duration - AND - later closing time.
There are two effects according to Bell.
1. Later closing = more at the top
2. Later closing also = more blow back and reduced mid range.

So in other words - my crank choice is not necessarily aligned with my desired curve.
Hmmm - may have to keep my port timings lower.

What is your intake opening on your case in degrees? Mine is 43°, and then add that to the duration of 123° (crank 1 = 123/6). Only gives you a 166° ID. So you would have to start hacking on the crank (assuming you are maxed out on case intake) by 14° to get Intake Duration (ID) to 180°. Grinding on the crank on the closing side, those 14° would effectively make the crank a 137/6.

xxx/6 vs xxx/0
This number is kind of worthless when looking at the crank alone. It is a good for comparing 2 cranks though, because we know that xxx/0 will open the intake 6 degrees sooner than a xxx/6 regardless of cases. Via the discussion in this thread and in my long stroke thread, I wish I got a xxx/0 or better (xxx/-5) instead of the 138/6 I got. Why? Because it is going to be very difficult to cut the intake side of the crank back with the big end right there. It can be done, but I would rather have had the factory do it.

Math is hard, cheat
If you have a good set digital calipers, you can measure the chord length and use this website to cheat back to degrees. On website, set your units to mm, radius is 49, and then plug in your chord length measurement you got from your calipers and boom it pops out degrees.

Total Package
Going back to the example timing from the long stroke thread, you want A as close to D (and maybe even some overlap), and B falls where ever based on what you want your total intake duration to be. Jack mentioned 90° ATDC is the limit for where the intake closes for Vespa engines. For me, I don't have any more rotary pad left to cut on the opening side so thus this leaves me to start cutting on the crank opening near the big end if I want A and D to be best friends.

Captcha - good stuff. That is a definite keeper! Thanks.

Couple things:
- My rotary pad has been opened already.
- It is remarkably long - there is still room if I wanted it.
- I have a 123/6 crank in there. My measured timings are ~180 if memory serves. That means I have 180-129 = ~51° of inlet opening currently.
- Using that with the 141/0 crank = 192°. That's lower than Jack would like - but about 7° more than I would like - cause I am still focused on minimal blow back and wider/flatter power band.
- I want to get my volume through width - with SOME additional timing

In my mind, the long stroke will suck hard - so width is going to be my friend on this inlet. The expansion pipe will also suck - so having a little overlap on transfer openings and should be okay (thanks for the note SoCal).

There is a second option for a crank.
SIP makes one - It's not like the cut crank web of the Pinasco.
There are some tradeoffs:
- Pinasco insta just going to send it to me for the cost of shipping...
- It has 130° of duration vs the Pinasco 141°, but it closes 16° earlier - which is better for mid flat power band.
- It uses a full size web on the fly side - so I would now have to machine my cases on the fly side to let it fit! good grief.
- It's not cut like the Pinasco pork chop as noted. Did some digging. The cut crank is sportier - will rev faster. BUT - it creates more crank case turbulence - for what thats worth.
- The snow mobilers like the pork chop cut for the woods - revy and quick. The drag guys like the full circle style crank - think fly wheel inertia.

Both would work for me - but perhaps ride a bit differently.

Unable to leave well enough alone (if you're a critic that is), I came across someone building with the SIP full circle style crank in a P200.
They are using the 60mm so no fly side issues of fit.
This is a picture they shared. The crank has been "flowed" significantly it appears. Not bad.

Still posting - y'all just go about your business.

Ran some carful measures of a VNB set of cases (Allstate).
Believe they are same as my VBB.
Compared these to P200.

Purpose - looking at wall thickness in area I will need to cut a groove.
Good news - castings are identical.
Now all I have to do is figure out HOW to cut a groove...

Also: since I got that image off the internet of the SIP "full circle" style flowed crank - I compared it to the Maz P200 crank I have.
For fun - set it up and shot identical picture.
Comparison below.
Remarkable how much flow space has been created in the SIP in comparison.

Loving the direction this is going in, not much to add as I've not worked on a vbb...

That SIP crank is a bit good looking... wonder how it goes??

Love the persistency with keeping the rotary... inspired to go back on another engine case...!

It is ironic that reed induction would actually suit the unicorn better. More torque and more mid range. Can go a long way with the rotary though. If you can get the BTDC to 127 and ATDC to 63 you can achieve the 200 without moving the powerband very much. Add that to the P200 width and it might be the ultimate rotary.
Surprising the casings care no thicker. I know they are thin right where the groove is from cutting in reed blocks. Easy to go through.

What happens if you concentrate purely on opening up the BTDC opening and not touch the ATDC part of the opening? Would that improve the low and midrange without moving the peak power up the power band?

Presumably you will add to the size of your charge, and it will be felt mostly in middle.

I don't know if any of us know empirically.

Doubling down on that, I would say the same about a cut off line on total duration of open time for your inlet. At what number do low/mid revs start experiencing greater blowback? Hard to know!

Expansion pipe ca. Hell with the sucking - which can help control/limit.

My current set up - may it rest in piece - had precious little blow back. There will be a tilting point on inlet duration that will worsen that. I believe this is also true of reeds.

I am going to disassemble and see where my numbers truly sit.
Trying to re-learn how to measure inlet/crank durations from my old posts!!

Where is SIME?

I like this video kind of short but informative.

This tutorial also.

https://blog.scooter-center.com/en/tutorial-measuring-the-inlet-timing-vespa-px/


I think I can measure and get BTDC and ATDC with these when needed. Doesn't seem bad to do actually. Doing it this way gives actual numbers from measuring degrees, should help reduce measurement error.

https://youtu.be/j3R1veLlGcY

Thanks Christopher!
Appreciate that.

I'll brush up on it all before I dive back in.
In the mean time - I am watching guys weld cast aluminum - cause I am developing my plan...

Then - on a whim - with the wife out of town and a quite night on my hands - I decided to reassemble my motor - to see if I can get a few more weeks out of it/ have something to ride in this gorgeous weather.

I see you decided the same as me. The risk of more nicssil coming off outweighs the not riding it. We both have a missing patch above the exhaust port now.

How did you snap a stud? They only need to be 15 ft/lbs. Good work getting it out though.

Stud snap was BIZZARE!.
Took everything to 13lbs.
Then when I went to 15 (that was my actual setting) it seemed to strip - before making that PING! snap sound steel does when letting go in tension.
Since I had already had the cylinder on and off once (air leak) it meant a third time.
I was imagining all sorts of trouble removing it and had no intention - but wanted to wipe off the Hondabond before it set, and see what was up - so I begrudgingly pulled the cylinder for the second time in 45 min.

Was kinda stunned to find the stud just snapped off like that.
Then - in a decision that usually leads to more repairs - I decided to just try and pull it.
Got it out so quickly with the slot that I ended up having time to re-assemble.

Less worried about nikasil than the rod big end bearing - but given time it takes to get parts right now - figured this was best plan for pub commute.

Next up - some practice welding on aluminum cases...

https://youtu.be/aBrFpUORnvc

Wooohooo! That's awesome! Happy Easter!

Impressive work as usual!!

I just had 5 holes to drill in the floorboard of the SS, (did one) and worked on trying to bang some more dents out. Not quite as productive.

Yes it is!
Off to the pub in an hour. Ha!
Wife is out of town - means legit to spend sat evening with tunes playing/cold beer flowing/ wrenches turning. Was kinda a pleasure.

We still cant be sure that the tiny piece of metal didnt come from somewhere inside the motor - though I simply cant imagine where - and the rod big end bearing is not long for this world - but I have AAA and its sunny out!

Love the 4x4 wood side stand!

Amazing this thing still kicks after the amount of abuse! Bravo.

runs so well - I had to clean it!

It is risen!

Me, I just stuffed my P200 motor in the sprint today, since it's going to be a while before I need it for anything else. All hooked up except for the throttle and choke, so no test ride yet.

Also, found more cracks in the Stella cases, so they're defiinitely toast. They will not be risen.

Who would know anything was wrong with it. Sounds nice. Jetting been upped? Want to be running as cool as possible with that nicasil chip. I'm doing the same.

Love it... great to see it started again so fast

Good to be back on the road!
Motor runs remarkably really - but all is not well - and I may not be able to fix that.

The head is full of hot spots from the divots - and the rod has enough play that the piston must be able to contact the head it at higher revs due to this ( IK, IK, but I just cant help it!)
Have a couple marks on the piston that are mirror images of the head...

I took some timing out of it and richened it up meaningfully.
I can see some tiny balls on the spark plug after riding tho - so I am getting some detonation.
I suspect it's related to the condition of the head creating hot spots.

Here are a few pics - one of which is using my new favorite toy.

I can't follow all of the technical aspects of your posts, but I can sure appreciate Sunday's GlamourShot! Wow!!! Fabulous pic!

(and even the car wash stations are glam in your 'hood, lovely red tile roofs and all.... I'm jelly)

K - I'm not sure my glamour shots compete - but know that it was shot with pure euphoria on a sunny day.

that Euphoria - perhaps short lived...

Sooo - pulled head to get a look - thought the piston must be striking the head right?
Uh, not exactly...

Turns out a second piece of shrapnel - a whole lot like the first piece - was responsible.
Something is disintegrating inside the motor.
Taking bets here on what we will find.
Is it:
A. Bits of metal from a seal base on crank or fly side
B. Bits of the big end rod connection that is vibrating
C. Bits of a main bearing cage
D. Someone is putting little bits of metal in my motor while I sleep

Here are your clues for solving:

crank more loose now? Probably a piece of something in the crank that is the reason it's tolerances are getting worse. just split the cases and check over everything cause eventually the damage will be to something you aren't hoping to replace soon anyways.

This is all very interesting to watch though! At least we know the limits of usable damage is way more than what one might expect...

btw, was getting glossy eyed with all the 200 crank in 150 case talk as it was a bit over my head.. but FMP just did a video on the differences, and I think you were talking about getting your cases machined to allow for the 200 crank lip. FMP is suggesting just having the lip removed from the 200 crank to work in the 150 cases:

https://www.youtube.com/watch?v=HMbKspRCyb0&ab_channel=mistaFreakMoPed

Doubt it's part of a seal.

Ditto big end or main bearing... never heard of one coming apart like that. And I think there would be other symptoms.

My guess is that little fella is probably more of the same meteorite ... it's magnetic right? Probably was stuck to a bearing or the crank and came dislodged.

The question is how many more little bits are there like that inside. Time to split.

I vote for D - it's gotta be D. Maybe the guy down the street that tells the kids to get off his lawn, and tells you to slow down! Ha!

Snort laugh.
Perhaps!

The color of the metal has either some brass inside - or some gold zink coating outside - or both.
The only thing I can think of inside my engine with zink coating on it in gold is the fly side Corteco seal.

But its on the other side of the main bearing - so not so sure how it could be leaving parts in the motor.

Gotta be the Get Off My Grass! guy.
I agree!

E. All of the above...has been my go to answer for all test questions since the 3rd grade. It's help me pass quite a few tests over the years. Hopefully it fails me this time though.

I'm going with big end rod connecting bearing...

Other things would've been easier to spot... looks like it wasn't through the carb...

Oh I forgot to take a video, but the play on the mazzu crankshaft is pretty minimal... talking less than 1mm deflection at the small bearing end...

Wasn't expecting that. To catch two in the head, there must be more.

If it was pieces of seal the pressure test might be less good. Although not ruling anything out.
Either way it's got to be split. If you have any old good crank, could do a dirty split and just fix it. Few hours and done.

Quick and dirty, just the way I like it.

I vote B.

And swiss makes an interesting point...
I remember some folks making Rally 180 cranks by grinding the lip off of P200 cranks back in the day. Seems easier and safer than grinding cases? (No idea if reducing the surface area of the crank outer muddles all your HP ciphering though?)

Key feature of grinding lip off crank is your cases are left stock if you ever want to go back.