crank bearings

[gsustaitav19822]

Ok while doing routine maintenance on my blaster doing leak test I found out it have a leak on the stator side seal but when I took it out I noticed that there is some play on the shaft once I hold it and shack it side to side there some play on it, yu can nearly feel it but it's there.
Should there be any play in there ????
And what's the best way to go cuz I will have to have to split the case and I'm tented to install a stroker crank in there intend of having some one rebuild the stock one sence I all ready have a ported cylinder and head mod do I have to do any thing else to install the stroker crank in there im.leaning on the +3 from vittos. Will there be a notice gain compared to the stock one

 

[deeeebeeeeee]

The +3 stroker crank requires a spacer ( 1mm ) and an additional base gasket .020" (.5mm), this raises the cylinder the same distance that the longer stroke raises the piston.

Not sure how much play you can get away with on the main bearings but the stator side bearing doesn't see near the pressure that the output side bearing sees, a little slack in the stator side means should definitely check the right side.

Main bearings can be replaced without having the crank sent off and serviced, the condition of the big end rod bearing and the crank itself will be the deciding factor as to whether the crank needs serviced if so then the stroker crank is not much more.

Of course if you want to build a stroker now is the time.

 

[jimmu]

I too am replacing my seals and noticed a slight amount of slack when handling the flywheel shaft. I don't really want to split the cases if I don't have to so I'd like to know if this is normal.

 

[gsustaitav19822]

Well I did split the cases and I found two difrent part numbers on the crank bearings
6305r1
83a915 both are koyo bearings is this normal

 

[deeeebeeeeee]

Yes this is normal, the bearing on the output shaft side is larger because is sees more force (the output gear powerin the transmission obviously puts more force both from the transmission holding against the torque of the motor, and the force of holding the gear mesh together) there is a name for it?, the stator side only sees the force of turning in a balanced flywheel.

I looked through the service manual,and was not able to find specs for the main bearings, the specs for crankshaft runout (how straight) is something like 12 ten thousandths. I guess Yamaha figures that the main bearings, although prone to damage and catastrophic failure, simply won't wear out,
Actually the .0012" spec is listed twice once for runout when checking the crank while out of the motor, and again for the installed crank. I am not exactly sure how to take the second mention and if it is referring to main beating play.


The way I see it if you are splitting the cases and then replace them while your at it. If there is any noticable play or if they aren't butterery smooth then it is probably a good idea to replace them anyhow. I really don't have much experience with this sort of thing and would prefer to error on the side of caution. Its around 50 or $60 for Koyo (Wiseco, and one or two others carry Koyo bearings) main bearings and seals, it's much cheaper than redoing an engine job as soon as a fresh top end is broken in.

I am sure there are others on here that could give you a better idea of how much main bearing play you can get by with.