Little tuning on original cylinder

[MichaelTopic starterBerichten: 16]

Hi guys,

New problems are appearing on my Piaggio SI as I try to restore it. Firstly I saw two deep scratches on my original 39mm cylinder and I am wondering if I can hone it to 40mm. But, my biggest fear is that if I put a 40mm piston on it, that would probably destroy my crankshaft at high RPM, am I right? Btw I have a original brom crankshaft which is in really good shape and brom carter, too. A you can see the piston is really bad damaged and as I saw it’s not original, it was changed.

I just want to keep my original setup. Maybe you can give me some advice?

Mihai

[JoorDonateurBerichten: 349]

Why is your piston not original?
Your cilinder should be 38.2 mm, witch you can buy at http://www.jmpb.nl
Your crankshaft (the original) can handle 46mm cilinders with high rpm, it’s very strong.

[MichaelTopic starterBerichten: 16]

Hi Joe,

Thank you for information about the crankshaft.

I know the cylinder should have been 38,2mm but it was honed before I suppose.

Would it be a good idea to hone this cylinder to 40mm to make the deep scratches disappear?

Mihai

[WimBijdragerBerichten: 3364]

If you find a new piston with the next oversize +0,25 or second + 0,50
or someting around that size.
Buy that one.
Than bring your cilinder and piston to a company who will bore and hone your
cilinder to the exact size for the new piston.

Gr. Wim.

Een oude brommer is alleen leuk als sleutelen uw hobby is.

[WimBijdragerBerichten: 3364]

Maybe you find here a nice piston:

Vespa Ciao Zuigers, zuigerveren. Vele maten en merken leverbaar. (jmpbonderdelen.nl)

https://www.jmpbonderdelen.nl/vespa-ciao-si/motordelen/zuigers-vespa-ciao.html

Or try a whole new set….

https://www.jmpbonderdelen.nl/vespa-ciao-si/motordelen/cilinders-vespa-ciao.html

Gr. Wim.

Een oude brommer is alleen leuk als sleutelen uw hobby is.

[MichaelTopic starterBerichten: 16]

Thank you very much Gr Wim!

I will probably try first to hone my actual cylinder to 40mm, but there is a little problem:

If you look in the photo you can see one side wall is really thin (around 1mm), there would be any chance to hone it or I will definitely need a replacement?

Mihai

[MichaelTopic starterBerichten: 16]

Hi guys,
Any ideas about this problem??

Could this outer part of the cylinder be welded somehow??

I really need help because I want to finish it for the summer holiday :))

Mihai

[zevenenergieDonateurBerichten: 4167]

Looks like .. with a 40mm piston would leave you 0,5mm.  But it,s expensive; 45 euros for a new piston minimum 35 euro,s for honing.
Welding is for sure not a good option to get were you want to be. And not nessesary.

To give my opinion;
I would buy a new cylinder.
For example, you have a DR 43mm for a very reasonable price and they are very good. And also spicy. Great fun.

[MichaelTopic starterBerichten: 16]

Thank you very much!

I will probably post the result for you to see what I managed to do :))

Mihai

[MichaelTopic starterBerichten: 16]

Hi guys,
After a month with a lot of work at cleaning and painting the chassis (frame) I am back with a few experiences. I tried honing that original cylinder myself and the result was not bad but the cylinder’s surface was uneven and that produced NO COMPRESSION an I kind of expected this to happen. After that I decided the easiest way will be to buy a CHINA engine kit and go with it until it brakes. I never tried a china cylinder, it’s really cheap (about 30$) and easy to find here in the city where I live and I would have the occasion the test it’s durability.

What jet should I use for a 38,2mm engine kit and a original 12.10 carb or I should use a 12.12 carb?

Any opinions?
After I will finish it I will definitely post the results.

Thank you very much for help! this forum is really helpful and I regret that my country doesn’t have one :))

Mihai

[WimBijdragerBerichten: 3364]

12-10 and 12-12 will be oke. Doesn’t matter.
Otherwise, try both carburators.
Here in the jet-database you will find the size for the jet. After that you must do some finetuning with the color of the sparkplug, so order more jets around the given size.
So you can experiment.

https://vespa-ciao.nl/sproeier-database/

Gr. Wim.

Een oude brommer is alleen leuk als sleutelen uw hobby is.

[WimBijdragerBerichten: 3364]

You could also post some pictures of your Si, so we can take a look at it.
Otherwise, create your own topic (in projects department) with your activities on the
moped and the necessary photos of course.
We love photos. 😎

https://vespa-ciao.nl/forums/forum/mijn-brommers/projecten/

Gr. Wim.

Een oude brommer is alleen leuk als sleutelen uw hobby is.

[MichaelTopic starterBerichten: 16]

Thanks for advice!

Mihai

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