Motorcycle Repair: Noisy Engine - 1985 Honda VF500F Interceptor, honda vf500f, piston rings

Question
Chris,
I have a 1985 Honda VF500F Interceptor that is making a noise that sounds like a lawnmower engine on top of the normal engine noise.  It increases with engine speed.  I expected it to be a problem with the valves, piston rings, or something else that might cause a compression leak but found the compression in the 4 cylinders to be 150,150,150, and 165 psi (indicating that there is no problem with compression...right?) The engine also overheats after about 10 minutes of riding.  The engine had never overheated before the noise began.  I got new plugs, changed the oil, replaced the coolant, and cleaned the air filter.  What could be causing this noise and overheating that wouldn't have shown up in a compression check?  Is there more that I can do before taking the engine apart?  The bike has 27K miles on it and is very clean...appearing well-kept.

Thank you.

Chris

Answer
Hi Chris.
 You may want to check the valves and valve springs.

 The fact that you have 3 cylinders giving you a lower pressure than the other could indicate a problem with adjustment rather than a more troublesome failure.

 All 3 cylinders should have near to the same (ideally, the same) pressures.

Check those and let me know what you find.
Good luck.
FALCON