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Valve v valve seat

Oliver Boy

CB750 Enthusiast
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Oliver BC
AMC forgive me for I have sinned.
I am into the second rebuild of my ‘82, in my first rebuild I swapped out used exhaust valves for other used exhaust valves from a spare engine.
I lapped them in etc, but I now see from some of your other threads that this was not my smartest move.
I got a solid 6 thousand kilometres out of the rebuild; I failed to cure the original smoking issue ( I didnt replace the piston rings, please forgive this rookie :) but the bike ran and started 100% better and returned a steady 57 mpg.
So ; now I am into the second rebuild, with considerably higher expectations :)
Trouble is, some of the exhaust valves will only give me minimal clearance with 235 shims- the thinnest I can source.
I am now anticipating replacement of all 16 valves; ( plus springs and seals etc ) I dont want to give up on my CB as a daily commuter but also I dont want to rebuild it every 18 months.
Is replacing the valve seats a necessity?
If so, is it remotely a DIY undertaking?
I got a quote to rebuild the whole head and valves professionally, its would be $4K Canadian.
 
Valve seats are not do it yourself. After install they need to be recut concentric with the guide. If the guide is worn it has to be replaced prior to cutting the seat. If minimum shim isnt small enough then seats are worn and valve is sunk too far into the head. If you arent going to do the bottom end to fix the oil burn issue I would just look for another used head that is better then yours, otherwise its a waste putting a new head on a worn out bottom end, it will more then likely use even more oil with the new head as it will be nice and tight with no compression leaks. I dont know how canadian $ converts to us but if your going to go for a rebuilt head I would contact APE or Cycle X.
 
Aw man, sorry to hear this Oliver. So how is the bike behaving after 6Km? I would imagine low compression and oil out the exhaust? Ugh. I also lightly lapped my valves and had the seats ground. AMC said it wouldn't run long but my machine shop assured me that I would get a few seasons out of the machine work of less that $75 and it would be plenty of time for me to source a new head etc. From the sounds of it, I better start looking too....
 
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