Advice Bearing to CB Shaft gap is .102mm

[stormchaser]

Hey, about a month ago had the rattling sound in the engine commuting home from work. Cracked the case and found the cb shaft was rattling around in the crankcase on the right side.  Got a cheap cb shaft for $20 from a fellow gstwiner and bought four new green bearings according to the crankcase. Just got done measuring the gaps with plastigage. The crankshaft looks all about .051mm. Left cb shaft gap is about .076mm and the right is .102mm. Crankcase on the right got a little gouched. I thought about buying yellow bearings for the cb shaft to bring it close to service limit of .08mm. Bikes got 40K want to squeeze some more life out of it compression is good at 150 psi on both. Advice appreciated. Don't know if there is oversize bearings I can get somewhere.

P.S. The book shows the bearings range from 1.486 - 1.502 mm.  Do I double this amount for two bearings to find out how much I can adjust by or is this measurment for both bearings as a pair.

Double P.S. Anyone needs two pairs of unused green bearings left me know.

[GeeP]

Hi Stormchaser,

You can double the mileage on that engine once you get 'er back together. 

The bearing selection is based on both the journal diameter and the case bore diameter.  To pick the correct bearings, you need to reference both the letter stamped in each end of your new balance shaft near the journals as well as the letter stamped in the case to obtain the correct bearings.

Did you do that, precisely as outlined in the service manual?

Let's say you did. 

You used a Green bearing, with a thickness of 1.486mm to 1.490mm and got a clearance of .102mm total.  The service limit is .080mm, but the maximum new clearance is .044mm  therefore, the bearing thickness needs to increase an absolute minimum of:

(.102mm - .080mm)/2 = .011mm

That means the minimum bearing thickness must lie between:
1.486mm + .011mm = 1.497mm
1.490mm + .011mm = 1.501mm

You probably require a Yellow bearing.

The figures cover two bearing ranges and still don't get inside the new tolerance.  You need to re-do my calculations with the actual thickness of the Green bearing you used, to get inside the center of the service range.

Before you go out and buy/trade the bearings, check the following:

1)  Re-check your bearing tables and new balance shaft to make sure you didn't accidentally order the wrong bearings.  It happens!

2)  Plastigauge it again, just for shits.  Make sure everything is absolutely sterile.  You're measuring distances thinner than the hair on your head.  Any dirt or nicks under the bearings or on the case halves or difference in torque will destroy your reading.

3)  Measure the thickness of the current new Green bearing you took the measurement with.  Re-check the above calculations using the ACTUAL THICKNESS of your bearing to make sure you hit the center of the service range.  Remember, each .01mm of bearing thickness decreases the Plastigauge reading by .02mm!

4)  If in doubt, measure the crankcase bore diameter and the balance shaft journal diameter.  Choose your bearing that way.

[stormchaser]

Thanks for that. My right crankcase CB shaft holder is gouched don't know if the yellow bearings will work. Is there oversize bearings that are avaiable?

[GeeP]

Is the case is damaged, or the CB shaft journal?

There are no oversize bearings available that I'm aware of.

[stormchaser]

The case on the rightside is gouched a little where the cb shaft sits. Both upper and lower. Journal looks good got it used from someone on the site. Could order a new journal, I know they're not that much.