Yz 125 bottom end rebuild noise

New main bearings and new transmission bearings, etc. cases were put together with heat, all the bearings were put in with heat, and now when you turn the crank by hand it makes a thud noise. Will this be a problem?

Yes. You need to find out what is making the noise.

That's not a sound you want to hear. Check it out before you proceed.

Turns out it's the main bearing.

It was fine before it went in. Froze the bearing heated the cases up to drop it in. The heated the inner race of the bearing to drop the crank in. Anything wrong with doing that?

Why is the main making a thud sound? It should roll smoooooooooooth.

It was fine before it went in. Froze the bearing heated the cases up to drop it in. The heated the inner race of the bearing to drop the crank in. Anything wrong with doing that?

Some do it that way. Not recommended to use a torch to heat race. I usually just pull the crank in with tool. You can freeze the crank and drop it in a heated bearing but usually done with even heat like oven or hot plate. Usually the cold crank will drop right in and no crank pull tool is required. Make sure you didn't over heat the inner race.

Drop some two stroke oil in on the bearings and see if that clears it up.

I put tons of oil on it. The bearing has a flat spot some how. Like I said everything was done with heat. Not sure how it got the flat spot

I put tons of oil on it. The bearing has a flat spot some how. Like I said everything was done with heat. Not sure how it got the flat spot

 

 

Time to crack the case and replace the bearings. This time use oven on cases, freezer on bearings and crank. Once the bearing are in let them cool, then drop the frozen crank in after the cases and bearings cool down a little, that way you can drop the crank in one side, clean case mating surface, yamalube the other and pull together with proper tool.

New main bearings and new transmission bearings, etc. cases were put together with heat, all the bearings were put in with heat, and now when you turn the crank by hand it makes a thud noise. Will this be a problem?

Were they O.E.M. or after market bearings ?

It's all balls, which uses koyo whitch is oem

Unless you buy OEM bearings thru a Yamaha dealership or vendor,

 

don't expect any aftermarket part to be 'just like OEM' in quality even if it does come from the same manufacturer.

 

AllBalls stuff regularly gets a bad rep in less critical applications,

if going thru the trouble of rebuilding an engine I wouldn't gamble on them being 'just as good'.

Edited by mlatour

Considering one is already bad I would not consider them just like OEM

Counterfit KOYO bearing are out there and they "look" OEM. If you look close you can see the the stamping of JAPAN (size) and KOYO, looks a little fuzzy. If it is not well pronounced in the steel, it is most likely not OEM. Or like!!

FAG and BOSCH have NOT been as counterfeited as KOYO.

Edited by PALMER84ONE

Okay thanks guys! I will stop buying the all balls. Not the first time Iv had problems with them.

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