Modern Vespa

has anyone cut their smallframe crank according to the malossi top end kit instructions? results, opinions?

I've done it on large frames but it's a lot of work. Given the fact that you'll be cutting an old crank in questionable condition I'd just go with getting a "race crank" that comes cut and polished with a better bigend bearing.

I've got a small taper one I'll sell you if you need it.

i would have preferred bone stock, but this bike came with a malossi top end like my last one. it put me right on the brink of the slippery slope. i'm gonna go ahead and portmatch it like that 100 sport i had, but i was surprised to see that the malossi instructions actually suggest cutting the crank, as well....and 21mm, at that. seems like a lot of extra duration to me. this bike is gonna be my daily rider though, so i don't want to give up much, if anything, in daily drivability. i'll keep weighing it all before my cases arrive next week, and await additional responses here.

you can always open up the inlet port on the casings by the same amount.It gives the same duration as recomended but stops the imbalance of the crank and so cuts down vibration.Better for a commuter.

The ET3 cranks already have a longer intake duration on the crank. Those and 100 sports have the longest. The 2 port cranks had shorter intake durations and benefitted more from modification. You shouldn't really need to cut an ET3 crank any more than it already is, unless Malossi has some spec specifically for the ET3. On the other hand, port matching will yield lots more power.

yeah, after weighing it all, i decided against crank modification. my last malossified and portmatched smallie was plenty powerful. and with this bike i have electronic ignition and four gears...and going at the porting a little more aggressively than last time.

That looks good. Just remember, smooth flow is as important as overall volume. Make sure there are no overhanging lips, sharp corners, etc.
And be careful on the flyside, it gets a little thin in one spot there. Have fun!

is nearly perfect. have about a half a millimeter of material in one corner to take back this evening, but otherwise i'm very satisfied. clutch side of course won't be nearly as volumous or squared out...i don't wanna buy myself any welding work as a result of overambition with the dremel.

btw, this is a VERY interesting idea. i don't plan to do it with this bike, but i'm going to ponder the solution at some length and catalog it mentally for future reference.

edit: just thinking about it really quickly, i guess the first thought is: once you do it, you just bought the cow forever. you just commited every engine you build with that set of cases to +X duration.

I recommend you put a NOS system on it and turbocharge it too! And for truly mind blowing power, I recommend you swap out that engine for a 500 cc or larger. Of course you'll have to stretch the frame and spend A BILLION DOLLARS on R & D and custom development. But hey, it's your daily driver, and you simply CAN'T HAVE ENOUGH POWER!