motobarnvc
CB750 New member
Hello all,
I am new here - I have come across a problem in the rebuilding process of a DOHC CB750 and I don't know where else to go!
A little background about the bike: 1979 CB750K DOHC engine fit into a SOHC frame, mileage is unknown, started to make cam noises (spinning noises) so removed cam cover and cylinder head to inspect..
A few of the intake valves were "mushroomed" at their tips and would not slide out of their guides. I didn't want to damage the guides by just hammering the valves out, so I made a grinding tool out of a small socket and some high grit sandpaper rolled inside of the socket, stuck it to the end of a drill, and very carefully removed just enough material from the tip of the valves to where they could slide out of their guides. It worked very well, despite being a very slow and tedious process..
I was able to remove all of the valves with this process and moved on to cleaning the cylinder head. After removing all of the carbon, I noticed that 2 intake valve seats have serious pitting and only have 2 angles! Ouch.
If I took this cylinder head to a machine shop to get those 2 seats cut to remove pitting and recreate 3rd angle, the 2 intake valves that correspond to those seats would then sit further "into" the head, thus making their tips even closer to the cam... they already have "mushroomed" tips, so I could only assume this would get worse if they were making even more contact with the cam.
This is a very confusing concept, and even harder to explain, so please let me know if I am not making much sense....
My question is: Should I start looking into replacing both the head and valves, or is there a way to salvage this head?
Thank you all!
I am new here - I have come across a problem in the rebuilding process of a DOHC CB750 and I don't know where else to go!
A little background about the bike: 1979 CB750K DOHC engine fit into a SOHC frame, mileage is unknown, started to make cam noises (spinning noises) so removed cam cover and cylinder head to inspect..
A few of the intake valves were "mushroomed" at their tips and would not slide out of their guides. I didn't want to damage the guides by just hammering the valves out, so I made a grinding tool out of a small socket and some high grit sandpaper rolled inside of the socket, stuck it to the end of a drill, and very carefully removed just enough material from the tip of the valves to where they could slide out of their guides. It worked very well, despite being a very slow and tedious process..
I was able to remove all of the valves with this process and moved on to cleaning the cylinder head. After removing all of the carbon, I noticed that 2 intake valve seats have serious pitting and only have 2 angles! Ouch.
If I took this cylinder head to a machine shop to get those 2 seats cut to remove pitting and recreate 3rd angle, the 2 intake valves that correspond to those seats would then sit further "into" the head, thus making their tips even closer to the cam... they already have "mushroomed" tips, so I could only assume this would get worse if they were making even more contact with the cam.
This is a very confusing concept, and even harder to explain, so please let me know if I am not making much sense....
My question is: Should I start looking into replacing both the head and valves, or is there a way to salvage this head?
Thank you all!