Modern Vespa

I've got a newly built P200 engine (I built it, first time I've done that from the ground up) that immediately showed signs of a leaking clutch-side main seal. Massive amounts of gasoline in the gear oil. I finally got the chance to take it fully apart. The seal (the brown metal one) seemed to be installed correctly, but the interior rubber/spring portion looked to be a *very* loose fit on the crank. It was admittedly cold in my garage (45 degrees f) but the inner lip of the seal made no contact with the crank (a Maz cut rotary-pad crank). I've attached a photo of the seal installed, you can see how much daylight there is between the seal inner and the bearing. I also have a blue corteco seal that is also loose on the crank.


Any ideas?

It's probably the crank if both seals are loose. Maz crank quality has been constantly declining. Have you tried the seal on your old stock crank??

This.

Have you measured the diameter of the crank shoulder of both the old and new cranks? What's the size of the seal?

Obviously, only one of them can be correct, and I'm kind've leaning toward the seal being correct and the crank off.

Grab your calipers and get some measurements. They'll end any speculation pretty much right away.

Do you have seal seat on the cases with or without a groove? Grooved one takes rubber-body seal and metal body goes to cases without groove.

Also note that one possible spot for leaks is between metal body seal and the seat on the case. I caught this on one engine with pressure test.


Long story short: Do a pressure test

CM, nice deep cut

That seal looks odd.

Depends the year. Later P/PX cases came with a metal seal like in OP's pic…

Right, it's just the way I looked at it in the photo. Depends on whether the case has the groove for the rubber seal. My Malossi case takes the metal one.