Modern Vespa

It's just come out. Nice.

What does your piston, cylinder head and barrel look like? Post pictures for all to see. If you were having damage from super lean it will be visible on those parts.

If this is the issue then you need to sand the cylinder gasket mating surface down on the engine case so it's all flush. If this isn't something you feel comfortable doing, then I suggest you bring it to someone professional as the cylinder mating surface is critical to safe operation of the engine. Otherwise you will never get it to be air tight.

But you need to be sure that is the issue. Did you bolt the cylinder down before shining light down to see?

Recently just did this myself. Posted here:
https://modernvespa.com/forum/post2545343#2545343

The lines on the barrel I cannot feel so they appear ok. Lot of carbon build up after only a short time.

What's the head look like by itself without the cylinder over it? If you had an air leak at the head you can see oil marks dripping out past the cylinder mating surface.

That is a very strange looking piston top and commoner head oil/carbon pattern. One of the experts in here will probably be able to point you in the right direction with these images.

Last edited by swiss1939 on Sun Jun 05, 2022 4:27 am; edited 1 time in total

No I just quicky threw it on. Sorry, not the best way to show you. Shame you live in the states as you could have done mine.

The head is fine. No sign of leaks. Its definitely at the base. There was a huge air leak flywheel side which I thought I solved by adding more sealant. This obvisously did not last as I needed to upjet to a 145 and it still was not bogging completely.

Well if you just place the cylinder down without bolting it down then you aren't getting a true picture of whether there is a sealing issue at the base of the cylinder due to the mating surface. You need the cylinder torqued down to spec to see if there is proper surface levelness when installed to spec.

Edit: I guess if you know it's a huge air leak then it would be visible regardless. But best way to check is to get everything tight as is when installed and running to check.

What is that lump of metal near where the cylinder sits? It's raised beyond the sealing surface and could stop the cylinder sitting flat?

Put a nut on it. Whack it with a mallet. Hold the crank as it will fly out.

There is a lump that flywheel could hit, file it off. Swiss can give you direction on surface sanding cylinder sealing surface by hand.

I would try a piece of plate glass with rounded edges, a suction cup to hold it, and something like a 600 grit wet dry sandpaper to polish surface and look for high spots.

So just to update you all. I have stripped the engine and now in the process of cleaning it all, including all mating surfaces. I have replaced both flyhweel and clutch side oil seals. I now intend to purchase 26/26 carb and start a slow rebuild with pictures on the way as to gain advice from you all. I am having a few weeks break.

I will be back soon and provide some pictures of my progress.

Thanks again for your help in this very long post. I never meant it to take so long.

I may sand the cases where the cylinder sits but will post a photo to see what you think of them. They do not appear to be that bad.

I don't think I can run this with a normal air filter. Can someone recommend a filter setup to run on this thing as I may as well buy that along with the carb and save waiting for stuff to arrive.

I would recommend having someone with a mill set it up, zero it out, then take .001 off the gasket surface. This stuff, doing it by hand, is not recommend. might be something i would do if i was in the middle of nowhere, broken down, and this was the only option to get home. Spend the $30-40 and have it done with accuracy.

Before I buy all of this new stuff, here is a picture of my rotary valve pad. The clearances with the engine built up was nearly 0.15mm, well above the recommended 0.05mm. No point buying all this stuff if the valve pad is fucked.

General question for anyone reading this who may know, I've been curious. What would happen with a 62mm P200 rotary crankshaft in this case? If cases need to be machined larger to fit crankshaft could that be used as a fix for a worn rotary valve? Thinking that option wouldn't be any more expensive than cost to fix valve by adding metal.

I agree, I would be doing it as a quick, lets see what I have. I have all the stuff at home to do it.

Agreed. I did it cause my cases were already somewhat messed up from welding and it was a shot at doing it on the quick since I don't have anyone with your skill within driving distance. But I am sending those cases to gick in a week or two for welding repairs anyways and I'm sure he'll go over that surface on a mill since the repair he's doing is along the edge of that surface anyways.

Roody, best option is always to have a machinist do repairs correctly if you have one locally. My cases are suffering from using a local welder with no experience with working on vespa engine cases. As a result, I'll be paying twice for repairs and shipping halfway across country to get it done correctly.

I'm sure there are many in England given the wider popularity of these scooters and the thriving tuning scene over there. It's really rare to find someone with gicks ability and experience with Vespas over here in the USA, so we have limited options for this type of repair. You should be able to find a pro close to you.

Will a 24/24 carb suffice or do I need a 26/26? Will both carbs bolt-on without issue or will I have to widen the intake oval hole on the casing? I don't want to start messing around with cases as I am bound to fuck it up.

I don't mind paying a little extra and ordering one of those BMG Pro fast flow carbs with the holes already drilled out.

Thanks.

Get a 26/26 being smooth is less important than being big.

Your inlet pad is in good condition. Could really do with opening up. plenty of info on here about how to do it.

This is a 24G carb? Are they not a bit different than the others? I work near where this is being sold and was going to buy it.

Yes, different but for under 20 quid it will be better than the small carb. You'll still need to get a 26/26 later.

Will all my jets fit it OK?

AC and pilot won't fit if using a filter but as you are not using a filter your jets will work as temporary.

I spoke with a guy who has vespas. He said its not worth getting the 26/26 carb over the 24/24. He reckons they are infact only 25mm and no real difference over the 24/24. He also said the 24 would fit easier and not require engine cases to be machined at the intake, unlike the 26/26. Thoughts? Ideas? Thanks as usual.

I have also just relaised that when I fit the new clutch side oil seal, the bearing does not rotate freely. I need to shave some off the seal rim. About 0.7mm apparently. I have ordered another seal.

Everyone has their own opinion. Garbage, spoken like someone who couldn't set up a 26/26. Yes, carb is 25.5 not 26 yes but bigger is better until its too big (about 40mm). They are difficult to jet but you came to the right place.

More importantly those seals that rub (metal brown cheap) are not really for performance builds, they are ok when modified for stock rpm. Malossi or BGM seals for the best outcome at higher rpm and the pressure that goes with that.

I had best order some BGM seals then. Why don't they make the seals to fit properly?

I ran a 30mm carburetor on a rotary motor, that's about the limit. I would measure and adjust rotary intake opening for at least 180° since you have it cracked open are staring at it. Some here will say 200° if your after a higher performance motor, I wanted lower rpm power.

Usually something like 120° before top dead center 60° after TDC is a safe conservative starting point. People go out to 130° BTDC 70° ATDC as a little higher rpm more aggressive setup. My Pinasco crankshaft and case combination gave my about 180° and I left mine alone until I put in reeds.

Last edited by Christopher_55934 on Tue Jun 07, 2022 4:04 pm; edited 1 time in total

I have no idea how to do that adjustment. I did not know it could be done. How is it done?

Here is a search with several videos on the topic, they'll explain it better than I can.

https://www.google.com/search?q=vespa+measuring+rotary+intake+opening&oq=vespa+measuring+rotary+intake+opening&aqs=chrome..69i57j0i546.20455j0j4&sourceid=silk&ie=UTF-8

intake area of 24 mm carburetor = 452.4 mm
Intake area of 25.5 mm carburetor = 510 mm

That 12% more area, nice bump in my opinion.

Lol super good question.

And careful with tapping it in… depending on your cases, can go wonky and the gap between the bearing can be uneven

There should be a cheaper crank pulling tool. One thats around 40quid

I got my crank out and have ordered an install tool from ebay. I have seen on Youtube that you can install it by using the clutch and a few washers.

Yeah tried that too… it works, but the pulling pressure doesn't seem too even probably because it spins around, and even with a tight grip.

Pulling tool with 2 wrenches seems to work best… I end up using the same tool to pull the output shaft as well (changing the threaded adaptor)

Engine dismantled and cleaned. Awaiting a few parts before rebuilding.

Looking spiffy

I am going to clean the mating surfaces a bit more before putting it all back together. Hopefully get a good seal on the cylinder base without a gasket to bring the squish down a bit. With the gasket I measure 1.5mm.

My bits have arrived. Should I grind some off the rim of the new clutch side oil seal before fitting it? I don't want to leave that other one on in case it wears out quickly as it touching the bearing.

Have you brought another cheap oil seal? The ones that stay in don't need modifying. The seal coming out when running can really make amess of the cases.

BGM or Malossi seal and Loctite 603 is the best chance.

Your rotary pad looks perfect. I'm not sure why you're getting such a large clearance.

BGM but it's exactly the same measurement as another cheaper on that I have.