Motorcycle Repair: 1979 Honda CB750K, 1979 honda cb750k, combustion chambers

Question
Hey man at start up it it knocks a little on the #3 and #4 cylinder side but when it warms up no more knocking bearing may be oil pump or somthing else? It has 30,000 + miles. thanks man

Answer
Hi Joe,

It could be normal engine wear causing the noises. For example, worn parts have excessive clearances when cold. Thermal expansion causes clearances to tighten up a bit.

If it were more serious, the problem would be present all the time.

The noise may be combustion detonation, though I suspect it's just normal wear.

Check cylinder compression to determine the sealing properties of the combustion chambers (condition of the engine). Follow with a leak-down test if compression readings are not within service limits.

Check and adjust valve clearances. Synchronize the carburetors.

Respectfully,
Mark Shively