Crankshaft axial play and transmission problem

[gouvis]

I am new to your forum but i'm building engines about 6 years now. My problem is that on my 139qmb, i installed a naraku hd crank about 2 years ago and 25.000 km. I was ready to install a new 50mm bbk to replace my old one but i found out that when i pull and push my crank from the variator's side i get a little axial play. There is no up and down play and my engine doesn't make any bad bearing noise. Is this normall? Also a second problem is that one week ago my scooter started making a very strong noise from the transmission. I remove the belt, the clutch and i found out that when i turn the wheel it is making a rattling noise. But when i turn the clutch bell no rattling noise. Also i noticed that when i accelerate the noise almost stops but when i leave the throttle the noise is starting again. I replace all the bearings and the problem still exists. Any opinion or experiences from similar problems would really help.
Thank you

[90GTVert]

The crank shouldn't be moving around, and with 25,000km on it it very well may be time for a new crank or bearings. Most replace the whole crank because of the effort involved in removing and replacing the gears on it properly vs the cost of bearings vs a crank. It would be advisable to look at the bearing seats while the cases are apart to be sure they aren't worn.

[GrumpyUnk]

Axial play in the shaft & bearings should have a specification somewhere. In this case, it would indicate some 'side play' in the crankshaft ball bearings. In a 'plain bearing' engine, the play would be controlled by thrust faces built into one of the bearing inserts.
Given that the inner race of the ball bearing is pressed onto the crankshaft, any measurable play beyond some number would indicate I think to side play in the ball bearings & races. To my knowledge there's nothing else to control end play.
End play should not hurt anything, within reason. The variator can move a bit and the belt & clutch will accept that, and as long as the flywheel doesn't run into the stator, or the blower wheel into the shroud, things should be fine there also. Within limits, of course.
Have you removed the clutch bell and inspected the shoes? If they break, you can get some pretty clunky sounds. If the bell rotates smoothly, then spin it over until you have seen the rear wheel rotate one full turn. ( a video to figure internal final drive ratio by 90GTvert is available) You have to rotate that many times to have all the teeth of the final drive shaft(output) go through one complete rotation. If there is tooth damage, you should feel it. If there is bearing damage, rotation would likely feel 'rough' at some point in the procession of the gears. Is the gear oil level correct?
tom

[gouvis]

Thanks for your answers guys. A very little crankshaft play i think is normal for this engine. I found videos that show gy6 crankshaft have axial play more than mine and work perfectly. I think that this play maybe there for clearence when the engine gets hot. If there wasn't this play, bearings would get side forces from the expansion of the crankshaft. That's the way i think it works. As for the transmission the problem was a slightly damaged tooth on the input shaft (clutch shaft). Replaced it but i didn't manage to find the same at any store that sells parts for 139qmb here in Greece. Mine was 155mm and the one i got is 149mm. It fits but the problem is that the naraku crankshaft is made to work with an 155mm, so there is no perfect alignment between my clutch plate and variator. I will buy one new from china but i have to wait about 40 days to receive it. I need my scooter so i will go with this one for now. Sure when i receive the new one, the belt will be replaced too.