YZF426 2002 Main Bearing to Shaft Clearance Question

[bradon]

While investigating a knocking sound on the ride side of my engine, I found the clutch basket was hitting the idler gear for the oil pump and the crankshaft primary gear nut was loose.
I replaced the clutch basket for thinking the bearing was wore out. Do not know how the primary gear nut would have come loose. It has never been off. (Thinking it came from the factory that way)
My question is: should the main bearing be able to spin around the crankshaft with little effort? I can spin the race at the mainshaft with very little effort. I found the same thing on the transmission shaft. I thought the bearing and main shaft should have a little interference fit! Not enough clearance to allow the bearing to slip on the shaft! Is this something I should replace?
Thanks for your help.

 

[nickyd]

Not sure if I understand correctly - are you saying cases are split, the bearing is out and you are trying to slide the main crank bearing onto the crank?

same thing with the output shaft bearing? the tranny I'm sure of will slide right in - it doesn't have to bear a load the way the crank does....

From my experience, there has always been some kind of interference fit when putting the crank back into the case half - I don't think I've ever seen it specified in a manual thought with a measurement.....guess you could mic the crank and take a bore gauge to the inner race of the bearing and see what the difference is.....interference is usually is thousandths - you can't rock the bearing can you? heck if you've got the motor all the way apart - spend the $25 and get a new bearing right?

 

[bradon]

Have not split the cases yet!. Just have the right side cover off and found the main bearing nut was loose and the I could spin the main bearing race around the crankshaft with out any difficultly. This does not look right to me. I have replaced bearings in numberous 2 strokes and have never seen the main shaft slip through the bearing without interference. I will go ahead and rebuild the lower end to ensure everything is good and will check the shaft and bearing measurements when apart.

Thanks

 

[SFO]

I think your use of the term primary nut is not the clutch hub nut which I think you are reffering to.
Clutch hub nuts usualy will be loose if they are not included in your service inspections, ie, if it is as it was after it left the yamaha mothership.