bottom end re-build, what bearings to replace?

I just finished stripping my cases tonight. This is for a 650 motor, 1977 style. Before I tape it up for sandblasting, I am wondering what bearings and seals should be replaced?


I plan on new main bearings, and new rod bearings (is rod bearing size determined by measurements with a micrometer or plasti-gauge?)

As for seals, I will replace all seals in the countershaft cover and both crank seals.

Should I change the Secondary shaft bearings (if so all or just the outer roller bearings or inner needle bearing as well?) Should the bearing in the transmission be changed, again just outer bearings or inner needle bearings as well? Shift drum bearings?

I know all these parts are 30 years old, and I will undoubtedly flog this motor daily.... so it seems like a good call; but I do not want to be taking time and money away from other parts of the motor for a fools errand.

Thanks in advance for your input.

main/rod bearing size will be determined by what work is done to crank and finished dimensions.the rest of your bearings should be roller bearings,as long as they dont have any flat spots i wouldnt worry about them.id definately replace all seals

There is defiantly 4 or 5 small roller bearings in the tranny and starter clutch shaft.

The shift drum also rides on roller bearings (and that set feels sticky...)

I am inclined to re-use the bearings like you say, as I can still see tool marks on many of the contacting surfaces in the tranny... I think this was a young motor.



O.T. Plummen should I send the crank to APE or Falicon.... price dictates one reputation dictates the other. What would your .02 buy?

falicon did the crank for my turbo motor,depends on what youre having done and what you can afford.just dont let anybody get the hook set in your mouth,kind of hard to get it back out sometimes.

Send us the crank. You will get top reputation and best price.

aperaceparts.com/mailers/crankmail.html

hey Jay, while I have your attention; could you tell me the valve stem length of the stainless valves you carry for the 900/1000's through 1980?

Ex: 12005-1006 30.00 X 7.00 X 92.60mm
In: 12004-1007 34.00 X 7.00 X 93.00mm

Those are the numbers I have for stock gpz750 valves, and you list an exhaust in 30.00mm X 7.00 X ????? and an intake in 36.00mm X 7.00 X ??????

Do you know off the top of your head if the intake valve seats can handle +2mm?

Thanks!

The 36 intake is 92mm long. The 30 exhaust is 90 mm.

We can make you the valves you need from blanks.

I have some old data that shows a 36 will fit the 750 seat.

Probably best to send us the head so we can see before we make them. Then it would come back with the valves installed.


Jay