TOP crank = total crap?

So at the ride last night I broke my Grande. Hard. I thought it had seized, but it didnt. Got home and took it apart, and turns out my TOP crank has sheared itself in half right were the shaft meets the crank half. It also seems that the flywheel side bearing has way too much play. So the question is: did the bearing go first, or did the crank damage the bearing when it sheared? What can cause a sheared crankshaft besides crappy metallurgy? I dont want to order a new one just to do it again.

Re: TOP crank = total crap?

A few questions:

did you rebuild the motor yourself? if so did u replace the bearings with new ones?,

if you did not then they will easily cause a crank to shear when they go bad, in exactly that manner.

how long did you ride till this happened? if not long on that crank then one might suspect it was installed incorrectly.

Re: TOP crank = total crap?

probably wasnt shimmed correctly.

Re: TOP crank = total crap?

I rebuilt the motor myself. I installed new bearings, one 6202 and one 6202/C3 (flywheel side) from Zippys. This was around 450 miles post-installation.

I have rebuilt this motor once before using the stock crank and did not have a problem.

Re: TOP crank = total crap?

Re: TOP crank = total crap?

HOLY FUCK!

wow.

Re: TOP crank = total crap?

i know matt got some ceramic bearings made up for his gila kit. I'm probably going to try the same all around on my engine rebuild.

the ceramic would promote longer bearing life right?

Re: TOP crank = total crap?

Save your money.... ceramics have their place but for the most part wont help in our application.

I have been down the ceramic path in RC and some other applications.

Ceramics are a must in a nitro RC car clutch for example because they can withstand greater heat than a steel bearing with little lubrication. They also excel as a front bearing in a RC nitro engine because not much fuel air mixture gets to the front bearing.

They dont seem to hold up as good as wheel bearings and dont seem as good in a semi dirty application or one that has shock loads. While the balls are very hard they also break or chip easily.

The cheaper grades (yes there are many grades of ceramic bearings) are really just a ceramic coat over some substance that turns to a powder when hit with a hammer...lol

I also tested... the best I could.... the common belief that the ceramic bearing has less resistance... spin better... but I couldnt find any proof.

If you must go ceraminc stay away from the cheap chinese imports and work with a reputable company... I have used BOCA Bearing in the past with success.

I believe they have some good reading on ceramics on their website

Re: TOP crank = total crap?

yeah, I dont think ceramics are the answer. Presently my thoughts are it was either a poorly made crank, or possibly the subframe isnt straight, leading to the shaft spinning at an angle relative to the rear clutch assembly, which would load the bearing axially instead of just radially. I will have to measure the subframe to see if it is straight, and if it isnt Ill have to get my friend to weld up some reinforcements. We'll see.

Vindicated

Alright, I ran this by one of the guys at work who used to race moto x, motogp, superbike, and everything else except enduro and supermoto, and ran a dealership for a while. Between looking at the picture of my two-piece adjustable crank and handling the drive-side bearing I brought in, he is completely sure that this was simply a poor-quality crank, probly a void or inclusion in the forging process.

Re: Vindicated

i was actually eyeing a TOP crank for my grande...i like the idea of forged steel over cast iron.

is it possible that the grinding could have weakened the crank in any way?

Re: Vindicated

why two different bearings???? i have both 6202s and they work great. i'm running the stock crank though. how did you rebuild your engine??? vespa cases have much tighter tolerences than any eninge i have put together before. if it doesn't slip together easily, then something was wrong. did you rember to put the shims in properly???

Re: Vindicated

Yeah, the shims were both one good. The two different bearings are specified in the Vespa manual, the C3 is a slightly higher clearance than the CN, for some reason it is indicated for the flywheel side. Really the difference between a 6202 and 6202/C3 is not much, the clearance scale runs from C1 to like C5, and a CN is right about 2.5, so not much off a C3. I just used it cause thats what came with the rebuild kit and thats what Vespa calls for.

I rebuild mine the no pounding or hammering way, like you, I guess. Freeze the crank, heat the bearing just a bit on the stove and it just drops onto the crank. Heat the large case half, drop the crank in, heat the small one and put it on, let it cool and put the case bolts back in.

Re: Vindicated

Got my replacement today. What Zippy Moped is selling as a stock 10mm crank to be a DMP race crank. No, I'm not complaining.

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