CB750 engine rebuild

for the last year, I have been picking away at my own person CB750 project. this frankenbike is a build up mostly from accumulated parts I had lying around, along with a few purchases I have made. I decided a few days back to do a full engine rebuild. the engine's primary chains were pretty sloppy, the top end was quite weepy and since I am doing a ground up bike build, I wanted peace of mind that the engine is solid.

after quickly cleaning up the head, I refaced the valves and cut new valves seats.

Once the valves were refaced, I back cut the valves with a 30 degree angle above the contact area to remove the lip and allow better flow.

100% seal on the vacuum test.

I finished the head off with a quick resurface to get a great seal with the head gasket. 

I am considering cleaning up the combustion chamber and ports a wee bit, but for now, it's onwards to the bottom end...

new work rolls in

last week, M. dropped off his '72 CB750 with a small list of troublesome gremlins: a leaky shifter side cover, an exhausted charging system, and an antiquated ignition system.

the pamco ignition rotor proved to be a little troublesome on installation. this was due to too loose of a tolerance where the rotor installs on the stock advance mechanism. with some manual machining, the two parts mated up perfectly. 

( the rotor on my personal CB750. Notch is 0.160" wide)

(M.'s rotor is 0.008" narrower. too narrow for the advance weights to fit in)

also on installation, I did notice that M.'s ignition advance springs were not fully working. as they do not make the springs anymore, I'll be heading to the salvage yard this weekend to dig up a pair in better condition.