flogged bearings

[vandy010]

i'm kicking this one off for everyone i guess, so feel free to add your story as it goes along.
so here's my dilema,
left side main bearing has "spun" in the case, bearing was about 5hrs old with fresh seal and rebuilt crank and the motor felt tight and strong.
so i've heard the bearing can be "plated" out to a suitable oversize.
has anyone done it? had any luck with it? recommend it?
or should/could i source an oversize bearing and get the case machined out to suit the larger bearing?
my other option would be to source another set of cases but lets explore our options first hey.
c'mon fella's, your help will be greatly appreciated.

[brent j]

Here's some ideas, keep in mind that most of my bike engine experience is with XT/TT500's but as a fitter & turner I do a lot of bearing work.

Is the bearing in a steel sleeve in the cases or straight in the alloy? What abaout having a sleeve put into the case? If this was done you would need to find the original specified size to bore it to. I'd be boring it in place too.

To plate the bearing I suspect you'd be looking at dismantling it, getting it plated then putting it back together.

If the bearing has spun I'd say it's from lack of either lube or lack of clearence. Was it a genuine bearing or aftermarket. Crank bearings are usually listed as a certain clearence (C!, C2, C3, C4, etc) this is to give a specified clearence when fitted.

If the bearings are fitted and removed cold you can find that over time the bearing seat can be eroded and this will reduce the fit. And we are taiking a 30-35 year old engine?

hth

Brent

[firko]

This was a fairly common fault with RT1s back in the days of poor standard oil. For some reason it didn't occur on DT1s nearly as often. I replaced the case back then but they're getting harder to find these days so a sleeve the hot ticket. I had a sleeve in an RT1 engine that somebody had made. I sold that engine to a mate and it's still going fine. Unfortunately I haven't got any dimensions or material ideas. Perhaps Lozza is over his sulk and might like to contribute an idea?

[vandy010]

i'm yet to fully dismantle the motor but do recall "chattering" marks in the bearing seat when i rebuilt the motor. i guess i can chalk this one down to my own ignorance.
i like the idea of a seat over the plating as anytime down the track the std bearing can be used without any fuss.
yes Brent, the std bearing came from Yamaha and the motor is definately 30yr old being the RT1 as Firko mentioned.
it'll be afew weeks off a solution but when i get a plan of action together i'll give an update to it all then.
cheers

[evo550]

Vandy,
If the bearing still feels good in the housing and just spins under pressure you could try some high temp loctite, I had the same problem on a hydrolic motor once, loctited it never had a problem since.