I recently picked up a couple of CB750s (78K and 73K) for $350 in hopes of rebuilding them after I finish my 78F. While the motor for my 78F was in the shop getting all the go fast parts installed, I was going to throw one of the other motors in the frame so I can ride. So, I pulled the 73 motor, but it had a stripped spark plug thread. I pulled the head to repair it and what did I find; a 64mm piston kit (812 I believe) and a Kenny Harmond D grind cam. The cam chain is stock so I am assuming there has been no bottom end work done to it. The head has been ported somewhat, although rough and unfinished and the there was a mild attempt a de-shrouding the valves. the compression is good on all cylinders.
Well, I have a number of engine parts from the F motor since I am upgrading the valve springs and whatnot. I have read that the F springs are stiffer. Can I exchange these springs for the K springs in the 73 motor to aid in valve return for the higher lift cam?
In addition, I have a set of superflow valves just sitting around. Do I need to do re-cut the seats to accommodate these valves, or can I just lap them and install them? The valve seat angle looks to be the same.
While I have the head off I am going to polish the exhaust ports and smooth out the port job a bit. I will also finish de-shrowding the valves. I would love to port it a bit more, but I really don't have the knowledge to do so and I don't want to throw any cash at this motor, yet. Both of the new project bikes will be completed eventually.
Oh, I have a set of 29mmCR carbs that will be installed on this motor. If it runs as a good as I hope, I might just save the "hot rod" F motor for the 73K project.
Any assistance would be appreciated.
