Modern Vespa

Hi,

My crankshaft is old (Px200e - 1988 - 45000 km), I want to replace it.

For about the same amount I can purchase a classic one (112/6) or an advanced one (138/6), 57mm stroke.

Is there any interest to take the advanced one ? I'm running stock cylinder for now. (I may upgrade to 210 Polini but not shure I don't feel like port matching the casing), I want reliability.

Thanks

Why not put in a 60mm stroke crank?

I'm thinking your advanced crankshaft is what we call a race cut crank? If so, they are great in stock/basic applications. Should be very reliable as long as you buy it from a reputable brand.

I could, but on stock cylinder I would have to put a spacer under the cylinder, would that be an upgrade on stock cylinder ?

The timing is different I think… It may require some timing adjustment

Actually, stock cylinders were initially designed for a 60 stroke but they decided to go for a 57. A 60 crank on a stock cylinder will bring the piston flush to the top. I had an O-Tuned 200 motor with a Pinasco 60 crank and used no spacers. Also machined the head to a 'normal' squish…

I understand, but then that requires a modified head.
I have no problem using a 60mm cranck with a spacer as long as it brings something on a stock engine ! I think it will be interesting if I decide to go for a kit later, but without porting the case I'm not sure that will be efficient.
Port matching the case to the cylinder is risky as there is not much material left after that on the casing…
Don't get me wrong I can to that myself, but that is a non ending story, upgrade the carb, clutch, gears… possible failures … I want something reliable, a bit more powerful than 200 stock if possible for cheap and keeping reliability !
I may be a dreamer…

I am doing a mild O-Tune on a stock P200. I'll have it on the road tomorrow for break in. The link is here: https://modernvespa.com/forum/post2629778#2629778

Nice job !! Quite a lot of work, well done ! Good luck for the 1st start tomorrow !

I still don't know if I'd better take an advanced 57 crank or stock... No one seems to know if it will be beneficial on stock engine !

It would be a 208cc with a stock cylinder, these videos do a good job of explaining a 208 benefits and some setup for timings.

P208 dyno video

Have you used a timing calculator to map cylinder timings and see what you have?

I have more of a KISS approach. . . and you may as well.

57mm crankshaft, just decent quality. Tamini, Jasil, SIP come to mind. BOX exhaust and upjet. I would at the very least make sure you cylinder, piston, and rings are healthy. Remove you exhaust port and get that cleaned up as well.

I think I might have this approach.

Here you can see the condition of the piston :
Is this piston ok ?

And the head
Normal head surface from Piaggio ?

With an open engine, I would consider a 60mm crank, just to future proof the build. SIP sells a lovely 60mm crank with either stock inlet timings or with a sportier cut. A later addition might be a GS piston and a tickle of the exhaust port with a Dremel. Just my 2 cents FWIW.

Will this requires a spacer under the cylinder ? Or a custom head as the squish will be different if no spacer ?

Good question. One for the experts. Is there sufficient 'excess' in the stock P200 head to absorb the extra compression of the 60mm crank or will it need milling?