Rm250

muddy226

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#1
Does anyone know what things can cause a seize of the bottom end ( left side I think ), which caused the flywheel to get too hot to touch, and now the bearing rattles. I haven't got further than taking the engine out and the cylinder off yet, but on doing so there was a little water ( beads only ) inside the cylinder. I'm pretty sure its not head gasket. The engine has just been rebuilt due to gearbox problems, and had new main bearings, cylinder re-plate, piston etc. On first re-assembly and for running in I put a used piston in, and on taking this out to put the new one in there were chips off the top of one side, and it appeared that the re-platers had left a small ridge at the top which the piston struck. I filed this off ( mostly ) with a diamond file, and now there appears to be a small gap about a millimeter down from the top. However I didn't get all of it, and the new piston has a little chip as well. Where could the water come from ? any help much appreciated.
 

muddy226

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#3
I don't know about C3 bearings. The main bearing were the only thing I had done by a dealer because I thought I might need a press. I will investigate, thanks for idea.
 

muddy226

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#5
I've finished taking it to bits, they are C3, the one with the problem was difficult to remove, stuck to c/shaft. I spoke to shop, the suggestion is that I didn't seat the bearings properly ( by striking each end of c/shaft after assembly ) and so I've just ordered a copper faced hammer ! The shop also said not to worry about water, probably from power washing. All sounds reasonable to me, so here's hoping
 

muddy226

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#6
The oil seals had been put in the wrong way round, perhaps this might explain it. I'm doing it all myself this time !
 

muddy226

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#7
Nothing works. Stripped down again, new seals, new bearing, run-in by three five minute warm-ups with cool down between, then gently run for 15 minute session, and cooled again. Then on track again using properly and started to get tight after 10 minutes, and on looking again the flywheel was too hot to touch, so end of play again. I have a flywheel weight fitted, and because its a thread on type it doesn't appear to run true, although upon removing the weight the actual flywheel and end of c/shaft appear true. If the bearing housing in the crankcase was out of true could this be the problem ? Any ideas or suggestions most gratefully received, as I'm almost at the stage of ordering new left crankcase and crank, and I really can't afford it. Thanks in advance for any ideas
 
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#8
I feel for you. My gut instinct says the crank is out of line or the bearings are being pressed against the crank. I had a Honda engine that was welded & the cases were trued after that but it needed a thicker centre gasket (this engine used a gasket) or the crank would be tight. Also I relieved the crankcase bearing seats so the bearings would press right the way in.

Obviously you are pressing the bearings in by the outer part not the inner. Just checking.

In the old days crankcases were usually matched pairs. With more accurate machining I don’t know if this philosophy has changed but it seems unlikely that your cases are dud, I mean presumably the bike has been fine in the past.

For the sake of prudence I’d find a decent tuner (not just the local bike shop) & send him the bottom end for evaluation c/w flywheel weight (which doesn’t sound healthy but I would have though unlikely to destroy the plot in such quick order).

Was vibration noticeably bad?
 

muddy226

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#9
Thank you for your suggestions. I think the one concerning having an expert look at it is probably favourite. As far as I can tell the bearings are completely home, although I must admit that I don't have a press, but I put the bearings in the freezer for 3-4 hours and heat the crankcase with a blowtorch and they seem to go in just fine with a bit of persuasion. There is a centre gasket which I renew every time, and the crankcases seem to go together with no problem. Perhaps when first splitting the the cases it might have pulled one housing out of true ? The baffling thing is that when assembled the crank seems to spin perfectly freely. Anyway, I'll just have to bite the bullet and send the bottom end away to a proper engineer to be looked at, and just hope it doesn' t take too long, and that I choose the right engineer! Once again, thank you for help.