Modern Vespa

No, you're just calculating how long the ports are open & closed. That's determined by the relationship between the stroke and how the piston moves in the cylinder.

You still have a bit of a challenge with the squish, though. That's another reason I like the BGM--it has no such problems.

Is the VMC intended for a 60mm crank? Normally, you have both head and base spacers because the cylinders are designed for a 57mm stroke.

All,

So what are the ranges one shoots for in Timings? Exhaust?, Transfer? and blowdown?

Hec

Thanks Chandlerman!

From my research I have found out that for a touring set up the following Cylinder Port Timings are optimal. Do you concur?

* Transfer Duration (126 +/- 2 Degrees)
* Exhaust Duration (170-190 Degrees)
* Blow Down (25-30 Degrees)

Your results are very close to what I got using the Lambretta Port Timing Calculator which yielded : 124.85 TD/187.45 ED/31.30 Blowdown

I think I'm starting to get this now! I have already added the 1.25 mm additional thickness to the base. I had the right combo of paper and aluminum base gaskets for the additional 1.25 mm exactly! My new PBT is 2.61mm.
Tomorrow I will torque it all down and do a proper squish test with solder. That result should tell me how much material to remove from the cylinder deck. I'm guessing around 1.5mm needs to be removed.

Stay tuned.

Hec

I wouldn't modify it until it's run in. Duration isn't the only factor and stelvio is already a touring cylinder. And you're running it rotary, which is higher crankcase pressure. Ports are clipped for higher pressure already.
Run it with just the 1.5mm base spacer. And see how it pulls the transmission. Going higher on the exhaust duration is the issue. 180 on a box is a good target.
With the 1.5 packer and some sealer. I guess it will be about 182.
Transfers are low and blowdown high; see what rpm it hits the torque wall.

Edit: The points. These will only take you so far. Work fine at stock and lower power. Less so with higher rpm and richer mixture. Ok for now if we set the timing higher.

Jack,

Here are the numbers based on only using the 1.50mm spacer and a couple of 0.20mm aluminum gaskets. Using the Lambretta Port Timing Calculator yielded : 117.94 TD/182.73 ED/32.39 Blowdown. The TD is lower and now comparable to a stock engine. Correct?

Stay tuned for squish results.

Hec

Measure squish without the 2 gaskets and just the 1.5mm packer. I have a feeling VMC have angled the transfers to compensate for the low duration.
Although stock 125cc TD is more like 108 degrees.

Ok will do!

Today I found the instruction sheet that came with the VMC STELVIO kit. It states squish is 1.40mm +/- 0.1mm. I assumed it was 1.0mm based on SIPs listing of the kit. Sorry everyone I should have read the actual directions! My bad!
I performed a squish test using solder. I had the 1.50mm spacer and two 0.20mm gaskets. I also measured 1.28mm PBT.
I torqued everything to spec. I did the squish test 10 times which averaged out to a squish measurement of 1.85mm. So I'm 0.35mm off from spec.

Here are some pics of the cylinder.

Stay tuned and please bear with me!

Hec

New squish measurements

Per Jacks request I performed the squish measurement using only the 1.50mm spacer.
The PBT=0.90mm
The squish=1.47mm (within spec now)

Mail man dropped off my clutch nut today!

Hec

Perfect. Bolt it up.

Next order for parts, need a new clutch. Cosa ultrastrong. That 6 spring will get destroyed. Change it before it explodes. It will be ok for a few hundred miles.

Bolt it up with no gaskets on either side of the spacer?
As for the clutch, I have the Malossi up gear kit installed. The clutch and Cush drive drive gears were replaced with straight cut gears. The Malossi up gear kit will not fit Cosa clutches. If I use a Cosa clutch I would need to change the drive gear on my Cush drive which would mean opening everything up. So fingers crossed with 6 spring clutch.

Hec

You should be making considerable power and Jack is right, your stock 6 spring clutch will suffer. Have you considered sourcing a 7 spring clutch? You can also do this mod and get even better results. There's a small case modification to go 7 spring but it's easy. Look here: Honda CR80 clutch disk page, what have you got?

Yes, no gaskets, just spacer.

If buying a whole ultrastrong it can come with a 23 tooth(or 22 tooth) to fit your ring gear. The 24 will probably be too much for the VMC. But worth a try.

Jack,

My gears on the clutch and Cush drive are now straight cut. Not Helical.

Should I apply the Erling Dirko HT to both sides of the spacer then?

Hec

Sealant on the spacer works good. No need for paper gaskets top and bottom.

Your malossi is 63/24?

You can just buy the 23 primary gear (but you can just get the super strong clutch that comes with straight teeth)

I ran with a straight teeth primary for the longest time. Swapped it out because I didn't really like the noise.

Granted I'll be splitting the cases more often with helical.

You'll need to modify the case (knock off a tab and dremel some of the inside of the clutch cover) to fit a Cosa clutch. Andre mentions this in the video.

If not for this I'd say ride a bit with your current gearing and see how it feels to you. You can up or down gearing by switching the cog on any Cosa2 clutch.
But it will more difficult to break the oil-feed tab in-frame, and you'll risk a bit of aluminum falling into the gearbox if not careful. Pre-break the tab?

Cosa shifting is a huge improvement over what you have now.

I've got a 23/64 combination (DRT cog) on my BGM clutch/BGM 177 and your gearing. Very happy with this gearing combination -- the BGM clutch not so much

Apply the Dirko as a narrow bead in the following manner. A "smear" will add a little to squish, since it begins to solidify rather quickly when exposed to air.

https://www.sip-scootershop.com/en/product/clutch-gear-cog-23-teeth-drt-clutch-cosa-2-primary-64-teeth_87477000?q=Clutch%20Gear%20Cog%2023%20teeth%20DRT%20for%20clutch%20%22COSA%202%22%20for%20primary%2064%20teeth

Ray,

Thanks a million! I like your plan of action! I was concerned that the Malossi gears were proprietary to Malossi and wouldn't work or mesh properly with other manufactures gears. If the straight cut gear profiles have all been standardized, then I have a viable option!
I also like the idea of removing the case rib now incase I need the bigger clutch. The time to remove the rib is now while the engine is on the bench. I can position the engine as shown in the picture which cause the filings to fall to the bottom.
I also like the idea of riding the scoot with the current set up and see if a clutch cog change may be needed!
That Dirko video is great! That stuff really flows well! A little goes a long way.

How much Horse Power do you estimate the engine will make? Keep in mind no case machining is being done.

Hec

You will need a new clutch. The 6 spring will explode at some point. Far away from home and probably raining.

Careful removing the tab. This is the oil way to the clutch outside. Remove as much as is necessary and no more.

Estimating horsepower is really hard without some serious software. That being said, I'm going to do it anyway and guess you'll get 13 HP, a little more than a stock P200. The difference is that you don't have the low end power band that the P200 does, which is why I'm worried about your gearing.

Since you're going to be upgrading the clutch sooner than later anyway, I agree that you should get it running, see what you think of the current gearing with the six spring, and then make a decision.

And, yes, that's the correct tab. I did my in the bike and used a pair of vice grips. I put the 7-spring on and marked where to break it off. scored it, and it snapped off cleanly on my SprintV motor and the vice grips caught the piece. All good

Update

The VMC Stelvio 177 is on! Installed piston rings and ensured the ring gaps stayed on their pins. I applied a light coat of Elring Dirko HT to both sides of the 1.50mm spacer. I applied a light coat of 2-stroke oil to the cylinder walls, rings, wrist pin bearing and con-rod bearing too. Then I slid it all together carefully and torqued everything to spec. I did add an M7 flat washer and lock washer to the head bolts. The kit only supplied the long M7x35mm nuts. I watched FMP's Stelvio video and he added the hardware on his. So Monkey see Monkey do.
I rechecked the squish measurement and it's 1.48mm. Within Spec!

Exhaust Spigot installed too!

Hec

count your lucky stars, this wasn't always the case and up until a few years ago getting the gearing you wanted was some real black arts level of chicanery involving questionable methods and compromises along the way. it's like the mfgrs looked at small frames and thought- duh! we can do that to large frames too and people will buy the gears durrr! I'd say 13~14 would be a win considering the collection of parts. there's definitely more power there with a carb, exhaust and some porting.

smart on doing the clearance for the clutch now. like others have said, you're going to need the upgraded clutch in the future.

Thanks for that Greasy!

So what gives out on the Six spring clutches? The basket, or bushing wears downs then it wobbles? Or the clutch linings come apart? All the above?

Hec

E- all of the above.

usually the basket flowers out. you can combat this with a banded clutch (like we did back in the day) but today's cosa variants or even a stock 7 spring will be more than enough to quell the beast.

don't get me wrong, you *can* build a 6 spring to take an astonishing amount of abuse. but it'll kill your clutch hand riding it and they shift like crap when set up that way.

more than likely you're going to smoke your plates straight away as you learn how to ride it with the new gearing/kit trying to find where the power is as you break in and jet everything. so I'd definitely put a set of plates on order.

That's a peculiar place to measure your squish test solder. Is your cylinder head's combustion chamber as well as the top of the piston completely flat? I'm not familiar with the VMC cylinder, so i have no idea what they look like. Normally a piston has a crown, and a cylinder head has a dome. When you take a measurement of your solder, you just measure the very outer edge of it.

https://www.rb-designs.com/rb_designs_llc_017.htm

I can't tell for sure, but it looks like you have a random nut and washer that are threaded onto the end of your input shaft. If that's the case, i'd be inclined to swap out the nut, tab washer, and that round flat washer for the real parts.

Hi
Just to give you a point of reference which may or may not be helpful.
I fitted a vmc super g ( just bolt on) along with a bgm fast flow 24/24 carb and a polini box exhaust and with standard px125 gearing I get 68mph ( gps verified) with plenty of bottom and midrange.

Whodatschrome,

The piston is crowned and head isn't flat. Trust me, I inserted that length of solder through the spark plug hole, while holding the head on my lap, to ensure it was reaching the outer edge of the cylinder. Every squish measurement was 10mm wide at the end of the solder. This jives with the head contour. I made sure the solder was at 3-O'Clock or 9-O'clock to line up with the wrist pins.
As for the primary nut you referenced? I didn't post pics of the clutch side in my last post, so you must have mistaken it for case stud hardware. It happens! I have the proper hardware for the primary shaft.


Hec

Andy,

Your info is very helpful. Its always good to hear back from VMC users with similar setups. Do have the 23/64 up gear kit too?

Hec

If you still have the solder. Measure just the tip. It's not parallel.

The input shaft hardware you have is not for this model. Sounds pedantic but with higher power, even slight issues can crack the engine case at this point.

+1

That funky-shaped washer on the input shaft is there to protect the cases from cracking under load or a sudden shock (e.g. a missed shift).

When it's properly installed, it will transfer any stress on the shaft to the clutch cover (large, round, strong thing. Also, relatively sacrificial) or the output shaft section of the case, which is one of the thicker, stronger parts--and also round.

Definitely don't ride it until that's replaced.

Are we all looking at the same thing? Am I missing something? What is installed is the hardware that came off the engine when I disassembled it. I did receive a different one from Scooter West with the case stud kit I didn't use. It's shaped different. In addition, the washer that sits on the locking tab is thicker and therefore the nut doesn't thread on as far. So I decided to reuse the hardware that came with it. Funny thing I actually ordered a new replacement from Scooter Mercato because their picture looked identical to mine. The one I received looks like the one from Scooter West. Are these not to be reused?

Hec

We are. It's the circled washer and it goes under the locking tab. Two port motors didn't put out enough power that the inherent weakness of the case in that area was an issue, but it became an issue with three port motors, and tuned motors are obviously a whole 'nother topic...welding additional reinforcing plates into the cases.

chandlerman,

The assembled order of the hardware installed is exactly as it was when I removed it. I took pictures of everything and I checked. This agrees with the parts diagram. Installing the washer first then the locking tab would reduce the amount of engagement between the locking tab's tang and the input shaft groove by the thickness of the washer. I would think more engagement is better.
Now I'm confused. Again

Hec

Hec,
Just remove the round washer and replace it with that flat-sided securing washer in your kit. Blue loctite.

Ray,

Thank you! I will try that and see how many threads of engagement on the nut I get. I can see the advantage of that shaped washer over a round one. Lucky for me my case isn't cracked there.

All,
Here is a video from Scooter West's P125X engine rebuild. Go to time mark 57:21s. He installs the same exact locking tab as I have on that engine with the same order of assembly. BTW you can see a crack in that engine case in the video.

Hec

Nope,haven't touched any of the internals, I was lucky enough to buy a scoot that had been fully rebuilt by retrospective scooters 700 miles before I got my mucky mits on it. so 'all' I've done is literally bolt on the kit, check the squish, jet it and ride.

Put on the 3 parts from SW. These are correct.
Was good of WDC to notice.

Jack,

I will install that arrangement tonight and report back. Yes I am grateful for WDC to notice and call that to my attention! I am also grateful for all the help I receive!

Thanks

Hec

Update

I performed another squish test and measured the tip end of the solder per Jack's request. I measured 1.46mm of squish! Nice! and in Spec.

I removed the original primary shaft securing hardware and this is how it looks with Scooter West hardware and clutch cover on. It not torqued down yet.

Should I go with (original hardware), (Scooter Mercato lock tab with Scooter West washer and nut), or (Scooter West hardware). I know the original isn't anyone's fave.

Thanks again everyone!

Hec

Update

Today I dropped in at the paint shop to see how the paint work was coming along. It's all primed up in epoxy primer and getting ready for a guide coat and light body work. I also picked out my colors, so that's out of the way.

Slowly but surely!

Hec

I haven't read thru your whole build here but from what I read in the beginning your setup shouldn't be all that dumifferent then mine and 8ve got about 1500 miles on my 6 spring clutch! 8m running a P125x with Malossi 166 kit, everything matched , a Mazz race cut Crank , si 24/24 and a road plus or something pipe, can't even remember. Wheelies no problem in first and second, clutch going strong!

Exact same experience exact same setup here a few years ago.

Unbanded clutch.
Blew up in a week after installing a Vape ignition. Clutch basket opened up enough for the ring to release and pow.