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I have a 95 gas gas 239. There seems to be a problem with the main bearings pounding the caseings out of round. It happened once and I had the holes machined and sleeves put in but, it has happened again. What can you tell me about this problem? Is something out of ballence? Is there a problem with the cases? ( I have heard of this problem on 95's and 96"s) And what is the fix? new caseings or more machining? Please help me fix this problem so I don't pass the legacy onto the next owner. Steve Steve, I'm not aware of an ongoing problem with mains with the 95 & 96's, at least not here in the U.S. I have a 96' JTR 370 and have had no problems. As far as the sleeve fix is concerned, if it was done correctly, it should have held up just fine, however, putting sleeves in main bearing bores is a very tricky process and requires exacting tolerances due to the different expansion rates of the materials. I can only guess at the cause of the problem, with the possibility that the bearing bores were not perpendicular to the sealing surfaces or the tolerance was too loose on the sleeves. It would appear that new cases would be the permanent fix. Jon Jon, Thanks for getting back to me, the info you gave me helps. I have a couple of Questions though. you say the machining process is a tricky business. What tolerances would you recommend on the sleeve to case fit and the sleeve to bearing fit ,and can you tell me about lining up the bearing bores? (don't worry I won"t be doing the work myself but would show the recommendations to a machinist.) Also if it doesn't look like machining will work, the new cases I sourced locally cost $400.00 US per side! seems like alot of money to me, is that price out of line? The tolerances would depend on the type of material used and the thickness. You would want a slight interference fit due to the different expansion rates between aluminum and steel and you would want to install the sleeves with a stud/bearing mount type sealant. I would want to go with the new cases for a long term fix. A good machinist will be able to align bore the cases with good accuracy. Either way, I would have a good crankshaft tech person check the trueness of the crank before installation as this may have possibly contributed to the problem. If you are using the old cases, have the machinist check the installed tolerances if possible to make sure everything is square. $400 per case side doesn't sound out of line to me, some of the MX bikes run a lot more. The casting size and machine work of centercases makes then one of the most complicated engine parts used. Let me know how you're doing. Jon |
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