Modern Vespa

I'm starting to build a P200 type engine with a set of Malossi VR-One crankcases


Since i'm building a fresh engine, I'm starting off with a 60 stroke crank. Since the cases have reed valve intake, I have a bit of a challenge on choosing a crank. Possibilities are full circle, bell-type or just regular disc valve models. I'm looking for information on what would be a good one or are there some cranks to avoid?

Malossi's own crankshaft - I'm a bit put off by the price of 588eur
https://www.sip-scootershop.com/en/product/full-circle-crankshaft-malossi_53161760


Mazzucchelli full circle - much more affordable at 265eur
https://www.sip-scootershop.com/en/product/full-circle-crankshaft-mazzucchelli_45040000


Mazzucchelli bell - is this weaker than the full circle one?
https://www.sip-scootershop.com/en/product/bell-shaped-crankshaft-mazzucchelli_45041000


Sip Premium rotary - any downsides on running a rotary crank?
https://www.sip-scootershop.com/en/product/long-stroke-crankshaft-sip-premium_45021510


DRT rotary - DRT products have been always nice in my experience
https://www.sip-scootershop.com/en/product/long-stroke-crankshaft-drt-sip-vnox-gt_45047000


Or should I go straight with 62 stroke Uncle Tom bell? I've read that the cases have to be machined to remove rotary pad, but Malossi cases do not have this to begin with. Could this be a straight fit without machining the cases?
https://www.sip-scootershop.com/en/product/bell-shaped-crankshaft-sip-premium-uncle-tom_45022500

Good work getting hold of VR one cases. Crank choice depends on which cylinder. Then how the cylinder will be adjusted and set up. And all this depends on how you wish the scooter to ride.
So, how you want the scooter to ride?

I seem to recall Rob Hodge having a brand new 62mm Uncle Tom crank that he's trying to sell.

The Uncle Tom 62mm needs the fly side of the crankcase itself machined out 1mm to fit on a regular P200 cases. I have no idea if the Malossi's come pre-sized for it, but I'd be interested to know.

The bell is going to give you the best performance, especially on the lower end, because it allows more crank case volume. The full-circle or flowed are allegedly smoother, but I have that P200 bell crank in my LML 150 and it's much smoother than any of my other motors, especially at high RPM's.

Also affecting this decision is what your other design/performance goals are. Tell what kind of motor you're looking to build, and we can suggest a parts manifest that will give you the best odds of success. What cylinder, carb, pipe, gearing, etc. and and any specific performance thresholds are you looking for?

In the absence of those, any advice that turns out to be accurate will be pure luck.

I always have an idea of "I'll just spice it up a little" but last time it (again) turned into a 153cc 20.3hp smallframe. Since this will be having more displacement, I'll propably be shooting for something over 25hp. I will not be going to the deep end of BFA's or Quattrini so no excessively long conrod will be needed (yet). I might go with a box exhaust first but am prepared to switch to expansion chamber type too with the short(ish) gearing.

The setup I have been planning:
Gearbox from BGM, maybe with short fourth
PX150 xmas tree z68 with SIP Ultrastrong z22 clutch
Stock PX200 Ducati ignition
Cylinder Malossi Sport or VMC if they get their cylinder out in time

I measured out the diameter of the case halves and it would be superb if someone here would have the dimensions for the Uncle Tom crank or the dimensions from the original cases. The only ones I could find with quick googling were for the Kingwelle cranks which require both sides be machined to 100mm. The dimensions were taken from the case and caliper laid on the cases for taking the photos.

Flywheel side 97,03


Clutch side 99,94

Anyone have stock 200 cases in hand to compare the measurements ?

I need to split my 200 cases, but that's a few days out.

https://www.sip-scootershop.com/en/product/long-stroke-crankshaft-sip-performance_45021630

Scroll down to the bit that says 62mm crankshaft.

Just in case someone is looking later.

Mounting information: Do not forget to modify the smaller half of the engine casings, this requires machining to a internal diameter of 99.5mm.

The 62mm stroke is not suited to the original crankcase. To be more specific, not into the smaller flywheel side of the casings. This requires machining to a internal diameter of 99.5mm.

So, in summary...VR-One cases...still need to be machined for a 62mm crankshaft. OG P200 cases also need to be machined.

Also worth noting, I build a jig that fits in the bearing seat that I used to machine out a test case half and it worked great. Maybe not quite as pretty as CNC'ed, but for $5 of hardware store parts and a little bit of my time, I'll take it.

Last edited by chandlerman on Tue Jun 28, 2022 8:08 am; edited 1 time in total

Better than I was thinking, free hand with one of these.

https://www.northerntool.com/shop/tools/product_200901506_200901506?cm_mmc=Google-LIA&utm_source=Google_LIA&utm_medium=Power%20Tools%20%3E%20Grinders%20%2B%20Accessories%20%3E%20Flap%20Discs&utm_campaign=Klutch&utm_content=3348053&gclid=CjwKCAjwzeqVBhAoEiwAOrEmzaCNHDORlmIss9ycvx4LC4-7eKU06PEgWJmaHs0lYO-VurXyT7GI2hoCxUkQAvD_BwE&gclsrc=aw.ds

Oh HELL NO!

That'd take days and still be lumpy as all hell by the time you got done. I'd probably use something like that to polish it after I finished, though.

It's a couple minutes setup and a couple minutes worth of work. Problem solved

Thanks for pointing to the right info! That crank is also a pretty good option. Good idea to collect all info in the same thread because links eventually break. Seems like this is the case.

Good job on the jig! Pretty neat idea and looks like it works well!

Last edited by FINYoshi on Tue Jun 28, 2022 8:09 am; edited 1 time in total

Doh...I missed the 97mm measurement. I'm going to edit my original post so the search engines don't mislead people. Thanks!

Yes, the jig works well. I did bases for both the two-part and one-piece crank bearings, so I can do any largeframe motor I wanted to with them. I took a deeper cut than I should have for that test, which let to the one spot where it dug in a little too far, but other than that, it's good.

Actually I messed up and edited my answer. I looked at the image of clutch side case and was wondering how can the rotary valve work if the pad is machined away on a standard case.

It's a reed valve case, so the answer is that there's no rotary pad to deal with. Just a big ol' reed block opening

Yep! The SIP Premium 62mm crankshaft Jack linked to was listed as Disc valve-type crank and due to this I didn't pick it up when looking for cranks.

The product info does not say anything about having to machine the clutch side of the cases so it should fit in with regular P200 clutch side with rotary pad if the flywheel side case is machined.

Kingwelle cranks on the other hand are full circle type and need machining of both cases.