1988 rm 125 crank problems

[IZ 250]

My 1988 rm 125 has a very hard turning crank after I relaced the main bearings and seals and had the crank rebuilt. Is this normal. Also when im turning it I hear no grinding and it turns smoothly but hard. I have torn the bottom end apart 5 times to see if I could get the crank to loosen up but its not. Also I have a super thick gasket in it to and have all the screws in it and tightened. But when there not tightened the crank turns alot better. What should I do?

 

[shane.ballard.nf]

sounds complicated, maybe you should seek help from someone with alot of 2stroke experience or someone who does this kinda stuff for a living

 

[steve650]

did you make the rebuilt by yourself?, if so did you take the special crank puller to do it? If not you have probably bent the crank or the case and this will result to the problem you are describe above!!!

 

[IZ 250]

Yes im rebuilding the bike my self but I got a small engine mechanic to rebuild my crank. My crank is not bent because when I turn it with my drill both sides of the crank dont wobble.

 

[steve650]

so if you are sure the crank is not bent, think you have bent the case when putting it back together! did you take a special tool to reassemble the engine... Explain how you does it! think the prob is the case!

 

[QKENUF4U]

do you still have the motor apart/out of bike other than the case halves being bolted together w/ crank in them ?
if you can put the bottom end w/ crank on a table, then take a soft blow and hit the crank shaft one way or another (on the ends sticking out of the cases/bearings). if you hit the right end it will prob. loosen up a bit and will turn a bit easier. if you hit the wrong end it will get tighter. had to do this at a shop that did ALOT of banshee motors. just a small trick the mech. there taught me.

 

[IZ 250]

Because of my crank being tight i have chewed up two sets of main bearings. I have tooken the crank to a dealer in town and they put it on Vblocks and it is dead straight. The dealer mechanic said the crank has to turn freely. How loose is freely I have it loosened up so that i can turn it barely with one hand. I have tapped on the right side of the crank with no result. I have tapped on the cases with a dead blow hammer. What else shold I do?

 

[QKENUF4U]

im not talking a TAP, you have to give it a nice hard smack (with a soft blow hammer not a steel/brass hammer) you may need to hit one way or the other a couple times to move it

 

[steve650]

if it did not work, just make a puller yourself. With the puller you will be able to pull the crank in the case.

 

[jason33]

well check the crank!! mine came with a set of thrust washers that didnt go to it!! i used the stock ones-- i figured this out after assembling it and it wouldnt turn the same way!!,and i new they didnt go to it but i used them any way,since it was a hot rod kit,i figured they did there home work--no, well i had to rebuild the crank ,now no problems
it was my first crank rebuild so i dont feel too bad :bang:
what happened was the crank was binding up when i tightned the cases,because the thrust washers i was useing
you shouldnt need a thick gasket!!! it is a precise machene
--tollerances-with the gearbox ect... let us know what was wrong

 

[IZ 250]

It probly might be that the thrust washers are wrong. I put 2 of the athena gaskets to gether in the cases, that loosened it up alot. But the damn things blown the right side main bearing again. But i think i have found my problem. I went to clean the air filter and the tube that connects the carb to the air box was full of a black oily substance and pebbles. I have since made the airbox spotless and the tube spotless. Do u think that could have been part of my problem? But damn that little bugger has top end it kills a 1990 rm 250 in a drag.