Author Topic: Score! A few head rebuild questions  (Read 923 times)

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Offline Silverback

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Score! A few head rebuild questions
« on: October 24, 2009, 01:19:59 PM »
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.
« Last Edit: October 24, 2009, 01:26:06 PM by Silverback »
Chris
"It's hard to define soul. You get it in art. You get it in music, and occasionally you get it in machinery."
78 CB750F racer
78 CB750F stock
75 CB750K Baby Blue Sold (She was a great bike!)
71 CB750K (rusty rod)
77 cb550F Sold :(  Bought it Back :)
Basket case 73 CB750, 77 CB750F (Building now)
01 Aprilia Falco
76 kz400
96 BMW K1100LT

Offline Silverback

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Re: Score! A few head rebuild questions
« Reply #1 on: October 24, 2009, 07:23:28 PM »
Well, I was able to answer my own questions.;D The springs will work and are considered a good upgrade for higher lift cams. However, the K retainers and keepers must be used.  .............and the valves will go right in. Thanks!
Chris
"It's hard to define soul. You get it in art. You get it in music, and occasionally you get it in machinery."
78 CB750F racer
78 CB750F stock
75 CB750K Baby Blue Sold (She was a great bike!)
71 CB750K (rusty rod)
77 cb550F Sold :(  Bought it Back :)
Basket case 73 CB750, 77 CB750F (Building now)
01 Aprilia Falco
76 kz400
96 BMW K1100LT

Offline Hush

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Re: Score! A few head rebuild questions
« Reply #2 on: October 24, 2009, 08:30:56 PM »
Nice find, lucky you. :)
I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!