speedwayaus Posted May 20, 2014 Report Share Posted May 20, 2014 Hi all. My kids ride trials and other motorcycles. Been really good for them so far. The mystery I have now is my sons 2013 Sherco 125 has blown the left side main bearing. The mystery part is the main bearings have only got seals on one side. (the wrong side, as it happens) The main bearings only have seals on the side that faces the crank fly wheel. The other side that points away from crank wheels don't have any seals. My understanding is these bikes run fully sealed main bearings. Has anyone seen this before from the factory? Another question regarding these sealed bearings, is why do they still run crankcase crank seals? I cant see why you would need them. Quote Link to comment Share on other sites More sharing options...
zerorev3rev4 Posted May 20, 2014 Report Share Posted May 20, 2014 sounds like the seals gone missing ,you need the main seals to seal crankcase from the outside ,ie to stop dirt getting in and to make it air tight or it would suck air from here and not the carb , i see what your saying though if the bearings sealed you shouldnt need them ,but i dont think they would be good enough to make air tight for long ,, personally i would prefer unsealed bearings lubed from the fuel mixture 1 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 21, 2014 Report Share Posted May 21, 2014 My memory of the reason for the bearing seals in Sherco motors is that when that motor design went into public use in the late 1990s, they had open (seal-less) main bearings, and also suffered premature main bearing failures. It was found that running sealed bearings extended the life of the bearings, so now they come new with sealed main bearings and recommend that sealed main bearings be used when the main bearings are replaced. I don't want to go into the theory for why the seals help with bearing life because it is a subject like "how much oil should I use in my premix" or "what brand premix oil is best" Quote Link to comment Share on other sites More sharing options...
speedwayaus Posted May 24, 2014 Author Report Share Posted May 24, 2014 Has anyone tried using two base gaskets to make 125's a bit easier to start for 11 year olds? Do you need to change the jetting? Anyone with a 2013 125 needs to be aware of the possibility of their bike also having no seal on the wrong side of the main bearings. Can't imagine that ours is the only one they built that day. You can see the bearing if you remove the left hand crank seal.. Quote Link to comment Share on other sites More sharing options...
tony27 Posted May 25, 2014 Report Share Posted May 25, 2014 I don't really think that only having the seal in the bearing closest to the crankshaft will be a problem, from memory the holes in the cases from the transfer ports is still there & will allow oil in, sealed bearings aren't sealed that well & even if both seals are still fitted you'll still be getting oil through them but the seals should keep out most foreign matter. The sealed bearings do last a lot longer than the older non sealed type, I'm picking the cause of the short lifespan of the older bearing is related to airbox placement/design as the basic internal design of the engine is no different than a beta & they aren't known for having the same problem I've heard of people fitting 2 base gaskets to 250s & 270/280/290s to make them easier to start, should work the same for a 125. Haven't heard of jetting changes needed Quote Link to comment Share on other sites More sharing options...
copemech Posted May 25, 2014 Report Share Posted May 25, 2014 All this stuff is a bit of a mystery to me , but the bearings have come sealed for a number of years now and with good results it seems. If they opened the outside of the ones on 125 or others I am not sure. The 125 does use smaller bearings and seals that the others of larger displacement. Seals on the bearings themselves are not designed to withstand the pressure changes of the outer seals, but just keep the pre-packed grease in the bearing. And keep crap out, much like a wheel bearing. I know this is all contrary to a conventionally lubed open bearing using pre-mix oil, yet it seems to work. I believe the biggest problem with any of them would be the demise of the outer seals due to the alcohol induced fuels for which they were not designed, then washing out the seals on the bearings and the lube! Thus you would be well advised to go back with the Viton replacements from Splatshop, or change then every couple years or so. I have sealed bearings running over 20K hours in electric motors at similar temps, so cannot be all bad! Who knows? Quote Link to comment Share on other sites More sharing options...
speedwayaus Posted May 25, 2014 Author Report Share Posted May 25, 2014 I don't really think that only having the seal in the bearing closest to the crankshaft will be a problem, from memory the holes in the cases from the transfer ports is still there & will allow oil in Wrong, wrong wrong... Best to keep the info on this thread correct, as there would most likely be other bikes out there like ours. With incorrect bearings fitted, that will blow up eventually.. There's no way for oil to get to the outside of the bearing if there's an inside seal fitted. I don't doubt the fully sealed bearing theory, much to the dismay of my engine building mates Love how mechanics get set in their ways. I fitted 2 standard .5mm base gaskets and the squish is now 1mm. this means it was running with .5mm squish.. Does that seem correct? Quote Link to comment Share on other sites More sharing options...
speedwayaus Posted June 20, 2014 Author Report Share Posted June 20, 2014 To update this 2013 125 rebuild project. The bike runs and starts perfect now. The question about not having seals on the outside of the bearings still remains a mystery. The only theory I can come up with is that the same company most likely supplies cranks to both Gas Gas and Sherco. As Gassers don't have the seal in the outside of the bearings.(lubed by gearbox oil) It's my guess that somebody fitted the Gas Gas bearings to the Sherco crank that day. Quote Link to comment Share on other sites More sharing options...
copemech Posted June 20, 2014 Report Share Posted June 20, 2014 So your new replacement bearings were sealed on both sides then? Seems correct to me. Quote Link to comment Share on other sites More sharing options...
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