spun crank bearing?

[redrooster310r]

opened cases for machining to fit 350 pv and the crank bearings stayed on the crank and the clutch bearing popped right out with my finger . all the bearings look like the races were spun in their bores.....and suggestions besides new cases?

[GOTFEAR]

i mot sure you can spun a crank baring but normal to come out with the crank thogh but wher the barings ride usaly looks discolard

[C-LEIGH RACING]

Normally when you split a TRX250R case, the crank & bearing stays in the flywheel side & the crank will be free to come out of the bearing on the clutch side, that normally, but nowdays sence we have all the aftermarket cranks & bearings, bearing kits thats not the case anymore.
With a stock Honda crank, the clutch side of the crank is machined just enough for a slide in fit into the bearing, Hot Rods cranks are not machined like this.
Both bearings in the cases should be a tight press in fit into the cases.
If the bearings will pull out of your cases freely on both sides it probably means someone has resized the area where the bearing fits.
If someone maybe cleaned up the surface area where the bearings go that could be why.
It dont take very much cleaning of the surface to open them up enough for a slip fit.
If it had been a bearing spun in place while the engine was running the bearing wouldnt come out so easy like yours are doing because there would be a slite lip still left at the very edge of the bearing hole keeping them from comming out easy.

You could as a fix in a pinch, ding up the surface area with a center punch where the bearings will sit, but that just a temp fix.

I did a test quite a few years back where both main bearings were free in the cases & the crank was also free in the bearings, that engine ran races for 3 years with no problems that I could see.
Only reason the engine was pulled down then was because I realy didnt know how long it would run & didnt want to take a chance of something comming apart & destoring the whole engine.
Neil

[atvmxr]

hmmm interesting. on the forum for the LT500s its made out that spinning bearings in the case is a bad thing will lead to crank failure and that steel or brass inserts should be used to stop the bearings from spinning in the case... :confused:

[86 Quad R]

Originally posted by redrooster310r
opened cases for machining to fit 350 pv and the crank bearings stayed on the crank and the clutch bearing popped right out with my finger . all the bearings look like the races were spun in their bores.....and suggestions besides new cases?

have any pics of the areas in question?

[zedicus00]

generally a trully 'spun' brearing is one that has locked up and spun badly in the bearing race, this leaves a nice groove and usually causes a grenading of the bottom end. starting with the bearing and metal particles into everything

a bearing that is slightly loose and could spin some is not a bad thing. over time if its loose enough it could cause excessive play and waller out the bearing race, with enough play bad things start top happen. but odds of it getting that bad quickly are pretty slim.

now, how big of a gap between the race and the bearing will it take to cause a problem? i dont know, neil said he ran one for quite a while that was a drop in fit. i would think a drop in fit would be o.k. but if there was a measurable gap around it i would be looking into shiming it. maybe have a a beed welded and machined back out or something, i dont know that i would want a piece oof brass banding in there.

[redrooster310r]

ok .... sorry no pics....having probs d loading.... the crank bearing seem ok ...i mean they came out of the bores with the crank and the new ones dont exactly drop in so i think im ok there,,,,thanks the clutch bearing had to be sleeved with a press in shim..... there was no gap and there was an edge on the bore so it was def movin around...there were score marks on the outside of the race.......closest to the bore. thanks guys