Hi guys
I need some help. I am having trouble with my engine rebuild. I can't get my cases to close up front. I did a bottom end rebuild, the crank is within the specified width (59.95mm), I installed the main bearings by heating up the cases, but the only thing left to check is that they are seated all the way. How "flush" should the outer race be against the inner face of the crankcase? Because they protrude a little. I already installed the main seals, how much temperature can they withstand? Or should I simply take them off before placing the crankcase in the oven again? I ask because I'm pretty certain that you cannot reuse them. Aditional info, the gap is less than 1mm, probably less than 0.5mm. I have rebuilt this engine in the past, and everything was straight forward, so I don't really know what's going on.
Appreciate any help.
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Do the cases go together good without the crank installed? Dowl pins seated? You can set a impact socket on inner bearing race and then heat the socket with a map gas torch, this will on,y heat the inner bearing race, so you can drop frozen crank in again without worrying about seal damages. I usually place a socket that fits over outer main bearing cage & give a few taps to make sure bearings are seated within the case.
Well I am pretty sure that the crankshaft is completely seating on the bearing race. I suspect that I didn't seat the bearing fully in the crankcase. The dowel pins don't seem to be a problem. I am thinking about using dry ice on the main bearing instead of dropping the case in the oven (and hopefully saving the main bearings this way). Thanks for the extra tips.
Try “dry fitting” the cases together with just dowels and transmission parts installed (no crank or sealant. This will let you know where it issue is and you can avoid damage. If the cases go together nicely with out the crank, you can narrow it down to a main bearing not being seated fully.
if it still hangs up, you can remove dowels and trans parts and further narrow it down. I had an issue on a ‘13 YZ250 engine where the cases wouldn’t quite close fully. I used this method and found one the shift fork case bosses had a burr in it and prevented the cases from fully closing. Luckily I did this as I could have damaged the cases permanently. Good luck and let us know what you find.
^ yes and I personally found the yz transmission setup to be more annoying than others to get in properly so at that point I'd try without the transmission and see if you get any different results.
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Thanks guys, I will report back for sure. Regarding the transmission not fully seating, it is weird because at the pivot bolt hole it pretty much fully closes (I am using the Tusk crank puller/installer BTW, so it is indeed pulling from the front side of the engine, where the gap is found)
In addition to above info, It'll often come together easier on one side (the front) so be sure to go slowly and possibly tap the rear/transmission area to get the shafts to slide into the necessary holes. If the front gap is really small and the rear is still large, open up the front again and retry so the gap decreases evenly around the entire case halves.
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