Changing crank bearing?

Joined
Apr 28, 2000
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#1
My friend has a 1980 yz125 that needs the crank bearing changed. He asked if I knew who split the cranks and I didn't know what to say because I don't know how it is done or if somebody at work can do it (I work in the parts dept at a GM dealer, used to sell and fix Polaris quads but everything is in our other store in a different city now). So, how is this done?
 
Joined
Jun 30, 2002
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#2
I'm restoring that same bike right now. It's pretty easy. Get yourself the Clymer manual which is titled "YZ100-490 Monoshock, 1976-1984. You have to completely disassemble the motor and transmission. Basically you pull the motor out of the frame, pull the top end, pull the flywheel (you need a special tool), then turn it over and pull the clutch, shifter, primary drive gear etc. The case halves come apart without any special tools. Then knock out the old bearings and seals with a bearing driver (cheap at Harbor Freight) and replace. You might as well change all of the bearings and do the crank/connecting rod while youre in there. You will need the manual and a good torque wrench to get it back together.
 
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Jun 30, 2002
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#3
I read your post wrong. You were talking about the connecting rod bearing, not the main bearings. It's all the same, but take your crank assembly to a machine shop. They have to use a very large and expensive press to disassemble the crank and replace the bearing. Or you can just order a whole new crank assembly from Speed and Sport for about $250. And you should still replace all the bearings as long as you've gone to the effort to split the cases!
 

zoommx

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Apr 23, 2001
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#4
If you replace the rod bearing, when the crank is reassembled, it will need to be re-aligned using dial indicators. this part especially is better left to someone with experience as one just thrown together could make the bike vibrate itself to death
 
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Nov 18, 2003
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#5
Bman, cut and thread a 3" piece of plumbing pipe to fit the flywheel's outside threads. Buy a hard-grade bolt that matches the inside threads, along with 3 thick, stout washers. Therad the pipe inot your flywheel. Put the bolt thru the washers and pipe, into your flywheel. Tighten bolt slowly. Your flywheel will be drawn off. This type tool works for bearings, seals, stuck axles, etc.

**Word of caution on the Yammie; I have often spent more $$ in the long run fixing up a
bargain" bike than I have on other newer, cleaner bikes, b/c parts go up CONSIDERABLY as a bike ages; this is due to re-tooling/demand costs...so figure out absolutely every single thing you would want to replace, then compare the bottom line. 8>]