new crankshaft problem

[elliottles1]

Good day folks,

i have just installed a refurbed crankshaft on a single cylinder tzr125 with new koyo crank bearings. all went together very well with a little heat here and a little deep freeze work there.

after assembly i can feel a VERY slight play up and down on the crank bearings, and it seems that the crankshaft is a less than tight fit on the inner bearing races. the inner races rotate with the crank when i spin it, so it is the bearing doing the work,  however if i hold the inner race with a screwdriver it is possible to rotate the crank by hand in the inner race.

the detectible up and down play wobbling the crankshaft is very slight indeed.

what is the general opinion here, start again and try to improve or leave as is, or any other suggestions?

could the crankshaft be worn and a smaller diameter than the inner bearing race??

any help really appreciated.

cheers folks
les.

[Jspooner]

Are you sure you have the right bearings? You can't leave it, you need to take apart and figure it out.

[m in sc]

^ this. start over.

somethings amiss for sure.

[elliottles1]

folks

thanks. yup, already started. think ill order some more bearings from a different supplier and try them on the crank. i dont think that the correct width of the crank bearing face is available, so its suck it and see.

any other ideas are very welcome

cheers
les.

[elliottles1]

guys,

right, upon stripping, it seems that there may be some wear on the crank bearing faces, maybe it has spun the bearings up before in the past. not too easy to detect, as the bearings have to go into the crank cases before the crank goes in, so you only find out on assembly.

what would be a plan of action if, say, this was an irreplaceable crankshaft?? slightly knurl the faces? anyone come across this problem before.

i would like to try and use the crank i have if poss, especially as i assembled it with new rod etc. and it is very difficult on my press to get it apart without grinding the pin in half, as i did with the knackered one.

probably floggin' a deadun' here but worth a small shot.

cheers
les.

[1976RD400C]

Let some green loctite "wick" in there and allow to set up for a day     

[teazer]

Have you tried bearing sleeves?  They are thin wall shims.  You may have to grind down the shaft to clean it up, and in that case things can start to get complicated, but try that.

You may be able to get a new crank from the UK, Europe or Japan.

If it were really irreplacable you could have the crank ground down and metal sprayed and finished ground to size.

Or just try Loctite bearing fit and see how you get on.

[Barrie]

The first thing to is to quantify what you have, measure all the items carefully or take all the suspect items to somebody who can .
It is almost impossible that you have picked up incorrectly sized replacement parts.

[Washerman]

I have had electric motors and other drive-type shafts with the same damage repaired at good machine shops and motor shops. You will need measurements if you find someone. The loc tite thing will never last in that situation I have done it many times for our customers on our stuff to keep people running until proper repairs can be made. In low speed situations or on idler drives it works better there's too much tourque on a crank.

[elliottles1]

folks,

thanks for all the replies, new crank on the way!

cheers
les.

[tony27]

Have you tried bearing sleeves?  They are thin wall shims.  You may have to grind down the shaft to clean it up, and in that case things can start to get complicated, but try that.

You may be able to get a new crank from the UK, Europe or Japan.

If it were really irreplacable you could have the crank ground down and metal sprayed and finished ground to size.

Or just try Loctite bearing fit and see how you get on.

I would never use a crank that has been metal sprayed, have seen the damage caused by it failing. Much better fix is hard chroming then ground to correct size, I have a crank in 1 of my vmx bikes that has been repaired this way which is the method everyone who deals with these particular bikes agrees is the best longterm solution