New crankshaft doesn't spin freely

[rosehill_rider]

I finally got my new crankshaft installed in my rm 125. However it doesn't spin without having to use a wrench. My dad says it needs a break in period but it seems to me that there is way to much resistance. Any thoughts or ideas?

 

[IndyMX]

I'd say something is binding.. And that's just not good.

It's should move freely, or else it's going to wear something out.

 

[rosehill_rider]

It's starting to move easier now, but by no means is it moving freely. My dad is convinced that it needs a break in period and nothing can be seriously damaged. Even after showing him this thread he won't change his mind.

 

[IndyMX]

are you sure you got the crank bearings in the bore all the way?

 

[TRexRacing]

If he'll pay to cover the expense of another rebuild let it rip.Crankshafts should spin freely from the start,ball bearings need no break-in.I build 'em for a living.What's dad do?

 

[whenfoxforks-ruled]

Do you have the clutch on yet? Is the crank centered, its not tight to the case on one side? Use a feeler gauge and get it even. If all thats good, who pressed the rod? Were the main crank bearings replaced, and driven all the way in? Going ahead and running it will tell what is wrong, it will fail.

 

[Ol'89r]

It's starting to move easier now, but by no means is it moving freely. My dad is convinced that it needs a break in period and nothing can be seriously damaged. Even after showing him this thread he won't change his mind.

Like everyone has said, if properly installed, your crankshaft should move freely. Did you use heat on the cases when you installed the crank or did you just push the cases together cold? If you didn't use heat to expand the cases, chances are the crank bearings did not seat all the way down in bearing bosses.

No disrespect to your father but, your crank will not break-in if it is binding. What will happen is the main bearings will wear excessively or become damaged if they have too much side force on them.

If the crankshaft was rebuilt, there is a possibility that the crank was not pushed together far enough and the crank assembly is too wide for the cases. The only way to check this is to remove the crank and measure it. This is something that should have been done before it was installed.

If the bearings are not seated in the cases all of the way, you can try this. Remove the side cases, clutch and mag assembly and lay the engine on its side. Take a torch with a large tip on it and using a circular motion, heat the cases around the main bearing boss. Keep the torch moving at all times and heat the case until you can sizzle a drop of water on the cases. Don't heat them too much since aluminum melts at a very low temp. When the cases are hot, take a small ball pean hammer and tap the cases around the bearing boss on the case facing down. The weight of the crank and the expansion from the heat will allow the bearing to seat all the way down in the bearing boss. Then, flip the engine on the other side and do the same thing.

If the crank does not free up by doing this, you will have to split your cases and find the problem.

If you run it with a binding crankshaft, you are taking a big chance of damaging your new crankshaft.

Just my $ .02

 

[kawraper]

Ive experienced a few things during my rebuilds causing binding.....one one over torquing the case bolts, the other was I was a little sloppy with the rtv i used on the case halves and when I put it together it got all over the crank. I then had to let it dry and scrape it off the crank. Just a few duh moments for me anyhow.

 

[Jasle]

Ive experienced a few things during my rebuilds causing binding.....one one over torquing the case bolts, the other was I was a little sloppy with the rtv i used on the case halves and when I put it together it got all over the crank. I then had to let it dry and scrape it off the crank. Just a few duh moments for me anyhow.

I would NOT use RTV on case halves. Use a proper sealant. 1104 or 1121 yamabond, hondabond or threebond.

 

[txkawboy]

Ol98r/etc are correct when they say that most LIKELY that the crank was not assembled w/proper clearance between the halves and the rod/thrust washer: either too little or too much, but my $$ is on too little...
If u take off the cylinder, you will likely be able to use a feeler gauge to get a good idea of its clearance's w/o having to split cases...

 

[SBC383STROKER]

Crank doesn't spin freely

Assuming you installed the bearings correctly and the crank is not out of true then the only problem left is that the crankshaft is not centered between the two main bearings. To center crank, use a piece of wood, place it on one side (flywheel or primary gear side), give it one solid smack, and then do the same on the other side. This will center your crank and should spin freely now. Please don't use RTV.