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Bottom end rebuild - what to replace

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I've split my cases to replace a couple of gears in my tranny. Is there anything else I should replace at any place inside the engine while it's in pieces on my bench?

Apart from new gaskets, I'm not sure what else I should replace.

 

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You've got it open. Maybe replace all bearings? It's all staring you in the face...

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You've got it open. Maybe replace all bearings? It's all staring you in the face...


All of them? Is that worth it? If it's something I really should do I will, but I'm a student so don't have the biggest budget.

Did a quick Google search for bottom end rebuild kit, lots of results for crankshafts and a couple of bearings. Are crankshafts a high wear item I should also do?

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Yes crankshaft is most definitely a wear item. You should at least check the big end bearing for play but depending on how many hours are on the bike, it may be best just to replace it while you are in that deep. As far as bearings, you probably don't need to replace the ones that don't see a lot of action like on the shifter, etc but again, you are in there already and that is the hard part.

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Yes crankshaft is most definitely a wear item. You should at least check the big end bearing for play but depending on how many hours are on the bike, it may be best just to replace it while you are in that deep. As far as bearings, you probably don't need to replace the ones that don't see a lot of action like on the shifter, etc but again, you are in there already and that is the hard part.

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So should I be replacing the crankshaft? I'll check the big end bearing tomorrow for any play. If there is some play in it, should I just replace the bearing, or do the whole crankshaft as a system?


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So should I be replacing the crankshaft? I'll check the big end bearing tomorrow for any play. If there is some play in it, should I just replace the bearing, or do the whole crankshaft as a system?


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If you want to rebuild the crankshaft, that involves splitting it and replacing the rod and bearing. For me, that means having someone else do it so I prefer to buy and replace the whole crankshaft assembly rather than undergo the time and cost even though it would probably be a little cheaper to have someone rebuild it.

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12 hours ago, thredbo said:

 


So should I be replacing the crankshaft? I'll check the big end bearing tomorrow for any play. If there is some play in it, should I just replace the bearing, or do the whole crankshaft as a system?


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There are specs in the workshop manual for width of the crankshaft ( basic runout measurement) and a clearance for side to side for the rod.   Do you have a workshop manual?   It tells you what to check.   Bearings are pretty easy,  smooth running,  no notchiness and no apparent visual defects.   If you find parts right at the limits laid out in the workshop manual it's probably time to referb or replace.

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I would replace the main bearings at least, those things take a beating! If the crank specs out according to the service manual it might be ok. A good test for measuring big end play is to hold up the crank by the conrod in your fist, then strike the top of the conrod straight down with the palm of your other hand. If there's a noticeable "tink" or "clunk", it means there's some play in the big end and you should either get the crank rebuilt, or buy a new one. 

My 2c

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I would replace main bearing (Crank shaft bearing) and top end bearing depending what your doing to top end.

I got set of main bearings for $34 of internt for WR400 few years ago so shouldn't be too expensive. 

Edited by FOXCHARLIE

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