Assembly lube / Valve Clearances

Hi everyone,

I have a 1978 Kz650 SR that I recently got my head back after having a valve job done. I bench shimmed it and it is now assembled with the cams in, but when I retook the measurements it looks like a lot of my clearances are too tight. I used a 50/50 mix of STP and engine oil as an assembly lube. Would the thickness of this mixture effect my readings drastically and cause them to appear tighter than they are? Or was the error in my calculations when I purchased the shims?

thanks!

Bench shimming the head is ok to get in the ball park but once fully assembled and everything is bolted down and settled they nearly always need further adjustment.

When a valve job is done the valves sink deeper into the head and the clearance closes up. Hopefully your machinist tipped a few thousands off the valve ends to compensate or you will find there is a large shift in the shim range toward the low side.

I'll go ahead and double check my measurements and order the appropriate shims tonight.

The valve job was done well and all the stems were tipped in addition to having new springs and retainers in as well as guides. My number 3 valve could only be tipped so much and is still not within spec, and many of the valves are still low in the shim range despite being tipped. Will I eventually need to replace the seats to restore the valves to a healthy shim range?

cg94 wrote: The valve job was done well and all the stems were tipped in addition to having new springs and retainers in as well as guides. My number 3 valve could only be tipped so much and is still not within spec, and many of the valves are still low in the shim range despite being tipped. Will I eventually need to replace the seats to restore the valves to a healthy shim range?

Going by the book you should try a new stock valve first to see if that gets you back in the range with plenty of shim.
If not then fitting bigger valves (1mm os etc ) will put the valve seating area further out on the unworn part of the seats and should solve the problem ( this is the most common reason these engines get bigger valves and not for performance gains ).
Only after all that fails would you replace the seats.

thanks for the info! Does adding larger valves require any other steps? Wouldn't they sit further out and risk hitting the pistons?

Surprised things changed so much after bench shimming...... mine stayed almost exactly maybe only a couple a half a thousands diff...... did em all on the loose side.....did have the head skimmed 4 or 5 thousands though so maybe that helped. Ape did a good job on tipping the valves too as they are all very near the center.

cg94 wrote: thanks for the info! Does adding larger valves require any other steps? Wouldn't they sit further out and risk hitting the pistons?

Larger valves will sit at the same height as stock, they just use the wider lesser worn part of the seat .
The valves seats still need cutting and the stem height setting.
The larger heads will mask the ports slightly and the throats are usually enlarged to compensate but you probably wouldn't notice in a stock motor.