Scooterotica

If only the inner is showing signs of damage, then I would conclude a failure with that component alone, principally with it's heat treatment. Possibly that could have happened during fitting, but you'd have to have subjected it to a lot of heat & would surely notice....

If both raceway & the rollers are damaged, then any number of factors could come into play. The wrong inner (quite often left on a crankshaft in my experience) which could contribute to too loose or too tight. (Too loose causes the rollers to skid which in turn causes heat build-up) Lubrication could have been absent due to inadequate amount, getting leached out via a failing oil seal or simply a poor quality grease. You didn't have loads of KY Jelly left over & took a chance, did you?

Lastly, as Adam said it could be misalignment.

I have my doubts though about that (which is a good thing!), & this is not meant to sound like I'm a complete Tw@t, but if that came out of one of my own engines that I knew the complete history of, I'd suspect the quality of the bearing itself, especially if the rollers haven't deteriorated to the same extent.

I hope that ramble makes some sense? Gasp!


(From my understanding, CN is 'normal' & therefore usually supplied & what I have used in over 40 years of tinkering. I've always been aware of the classes available but figure that the alloy magneto housing heats up & expands @ a greater rate than the steel crankshaft to obviate the need for additional clearance. That doesn't mean I'm right & I stand to be corrected if CN is somehow inappropriate. C2 is tighter & C3 is looser etc)

RManson wrote: ↑Wed Jan 03, 2018 11:31 pm
Looking at a NU2205-E-TVP2-C3. Anybody use one?

is what I use

looks like a twisted crank to me. Weather it was caused by the welding or not is hard to say but the a-symmetrical damage on the race tells me that the 2 sides are not in line with each other.

True the crank, replace the main 2 bearings and call it done.

Pulled the engine apart and trammed the cases/bearing surfaces. Turns out there was +/- 0.015 difference side to side on the drive side bearing surface, even more on the mag flange. Ended up machining both the drive side bearing surface a touch as well as the mag flange mounting surface of the case to ensure things are at least on the same plane. I'm sure things moved during welding even though I jigged things up and tried to keep it as solid as possible. Feel good about the results, now just waiting on a couple crankshaft bearing shims to space the crank off the drive side bearing slightly as you know it now rubs on the oil seal plate! If it's not one thing it's another, but all's well. The mag flange requires shimming as well, but that was to be expected and needed to be done from day one anyhow.

IMG_6292 by PotvinV8, on Flickr

Had a look at the crank as well and it was out a few thou more than I would prefer, so I trued it up to less than a thou runout and welded the pin just a touch in the hope that it will hold together. Finger's crossed!

IMG_6273 by PotvinV8, on Flickr

I think at the end of the day, both of these issues played into the bearing race damage, so I've replaced it with a NU2205-E-TVP2-C3. Hopefully that sorts it!