SPLITTING THE CASE

[RodneyCB750K1979]

I'm getting mentally prepared to split the case in order to replace the shaft seals on a 1979 CB750 L.  I read the shop manual and another repair manual. Are there any helpful hints before I begin? Does the case joint require a gasket or will HondaBond be ok?  

[seestheday]

I've never split the case, but one thing I read over and over is to not use silicone sealer.  Use case sealer (Hondabond, Yamabond, ThreeBond 1104).  If you use silicone your engine may only run a very short time after you put it back together before you throw a rod due to lack of oil.

[Lucky 1]

Which engine ,what year are we talking about.No gasket on the cases.
Hondabond is the just fine. Unless you have Gaskacinch.

You do not have to spit cases for shaft seals. Which shaft?
 They come out from the outside in most cases.
Have you checked on that?

[Lucky 1]

Absolutely right.

When I see blue or orange RTV or Silicone on a motorcycle
engine, I know there was a amateur working on it or a car person.

[RodneyCB750K1979]

Yes. For sure the case has to come apart to change the chain sprocket shaft oil seal - aka primary shaft oil seal.  The oil seal has an external lip that fits in a groove in the case housing.  This is also a 2-piece oil seal. Any shock or driving of the seal in will cause the inner seal to separate.  Apparently this oil seal "enhancement" started with 1979 models.

[RodneyCB750K1979]

After removing the generator rotor, the case halves came apart.  I installed new shaft oil seals and cleaned the mating surfaces.  I also cleaned material from the gear case bottoms. I applied a very thin coating of Hondabond to the mating surfaces.  The main bearing caps appeared to have sealant at one time applied to their mating surfaces.  I applied a very thin coating there also except near the inserts per the manual.  I tried installing the lower half case but the shift forks wouldn't line up.  After finding the problem, I tried installing again.  The case at the back end lacked about 3/16 inch from full closure. I removed the case and checked all the shaft bearing seats and set rings. I tried again several more times and the back end of the case would not seat properly. During one try, a main bearing insert dropped out and became wedged nicking the surface. I was able to lightly scrape the nick smooth using a razor. After several more unsuccessful attempts installing the gear case half, I located the problem. The countershaft bearing has a hole that must fit over a small dowel pin in the bearing seat.  After doing this, the case halves went together with no problem.  I installed a few bolts finger tight and checked that all 5 gear positions worked. I then oiled all bolts and installed them and torqued per the sequence.





Replacing one oil seal required removal of a bearing.

[Lucky 1]

Rodney it looks like you did a good job, but you need to build yourself a
work bench so you do not have to work down on the floor.

Thanks for the photos!

[RodneyCB750K1979]

Thanks for the advice.  I put it on the floor because I was going to have to wrestle that joker up-side-down and right-side-up.  It's back on the bench now where I installed the generator, clutch cover, and oil pump.  Now I'm trying to adjust the valves.