Primary drive
One of the weak points of the CB 750 SOHC/4 engine is the primary drive, namely the two primary drive chains.
Stock primary drive
There are a few things that can be done to extend the stock primary drive live span. First is to check the chains on a regular basis - take off the oil pan and check the tensioner. Then you can use a stronger spring for the tensioner or shim the stock spring.
When assembling the engine, make sure the chains are not worn and have equal length. Place them on the sprockets so that the outer chain links of the two chains are offset by one tooth:
 |
 |
Good |
Bad |
Heavy Duty primary chains
Eventually, heavy duty primary chains are available. These are today's technology, with seamless bushes, larger bolts and larger bearing area. These chains are available in the U.S. from Classic Cycle City.
Hy-Vo primary drive
The other known cure for the primary drive blues is using a CB 750 A crank (the 'Automatic') which has a Hy-Vo primary chain. The GL 1000 Gold Wing sprocket can be riveted to the 750 clutch, but you still have to make up your own tensioner, unless you decide to go without one - which again calls for regular checks and timely replacement of the chain.
The bad news is that no 750 Automatic cranks are available from Honda anymore, and cannibalizing an Automatic just for the crank doesn't sound reasonable.
The chain can be made out of two primary chains off a CB 750/900/1100 DOHC or a Yamaha XS 750 triple.
Chains with correct length are available from Michael Niemann at EGLI-Racing.