Scooterotica

Most Vespa cranks 'converted' for crankcase reed valve induction are just chamfered,or bell shaped but ours is a bit more extreme.

The outside diameter of the inlet side web is firstly reduced by approx 10mm BEFORE then also being chamfered. therefore greatly increasing flow over this side of the crank This allows maximum flow from the reeds into the motor unhindered,especially in conjunction with the larger and better reed blocks available now .

There are also benefits via weight reduction and LPC.

This current crank is part of a Malossi MHR 221cc build......60mm crank 110 rod ,crank weight 370 grams lighter than a std ..port timings approx 186/128 giving 29 degrees of blow down .piston windows enlarged as per the piccys .


















Dyno graphs to follow......

Nice work. Im planning on doing a reed Polini so be interested to see if ur pleased with the new crank mods.

we actually have used one of these cranks on a reed valved std polini with an old pm pipe ,it still made 22bhp and 19ft/lbs at only 6,500 revs over a 3500 usable rpm range. A better and more suitable pipe would give even better results .

proper tuning, taking a piece of kit then taking it to another dimension well done.

Seen this crank in the flesh last week whilst visiting the garage & it's a piece of art!

Lovely work Sean...

Engine finished.......

Out of interest.. what's the advantage to a lighter crank?

Muttley McLadd wrote:Out of interest.. what's the advantage to a lighter crank?

It weighs less. Heavier ones weigh more. I can carry at least 3 light ones, but only 2 heavy ones.

That's the main advantage.

Everybody is making bigger cranks and bigger casings to house the bigger cranks like Jap style cranks with fat webs with more surface area on the pinsto stop twisting..........................
So good luck Dan if you can make them smaller and work all the same CERTAINLY REVOLUTIONARY.

shamrockexpress wrote:Everybody is making bigger cranks and bigger casings to house the bigger cranks like Jap style cranks with fat webs with more surface area on the pinsto stop twisting..........................
So good luck Dan if you can make them smaller and work all the same CERTAINLY REVOLUTIONARY.

What you are talking about is an entire new design of high-end and very expensive casing, to house bigger cranks. Like the BSG 305cc engines etc. These are usually small production run or bespoke billet casings. This is incomparable to what we are doing......? We are simply reworking existing cranks, on factory casings, as it suits the budget of 99% of our customers. In addition.......of all the metal removed, nothing we do reduces the amount of metal around the interference fit of the pin. So twisting isn't a problem. And in any case....we rarely see Vespa cranks twist, unlike Lambretta. You have to compare like for like when talking about cranks and casings, and unlike Lambretta, the PX reedvalve blows directly onto one main web......which Sean has therefore flowed heavily. We have very good results with these cranks.

I can however see the benefit of thicker webs and bigger crank casings on Lambretta.....but that's a different story.