I'm currently re shimming my 71 sc and all was going well until I got to number 4 inlet, I shall explain my problem. With a .417 shim I have .003 clearance, so I fitted a .412 to bring me to .008 but ended up with .020 I have repeated this operation 3 times with the same shims and got the exact same results each time. Has anyone got any idea why this is happening?
Valve clearances
- Thread starter restojon
- Start date
JVY
Active Member
Did you mic the old .417 shim to see if it was .417? From what you have said, you fitted a .412 shim that increased clearance by .017 (rather than expected .005). So, this would have meant the orginal shim was .434. This seems unlikely as a shim may be have been ground down to less than the "stamped" thickness but I would not have thought it had increased in thickness??
Have you put the old .417 shim back in and double-checked you still have only .003 clearance?
Are you sure no.4 inlet is definitely closing OK (it was maybe OK when you took initial .003 reading but now has some crud stuck between valve and valve seat??)?
Are old and new shims of uniform thickness?
Was there maybe initially an additional .017 shim on no. 4 inlet as well as the orginal .417 and this has fallen off unnoticed (knowing my luck this is what would have happened to me
)?
Have you put the old .417 shim back in and double-checked you still have only .003 clearance?
Are you sure no.4 inlet is definitely closing OK (it was maybe OK when you took initial .003 reading but now has some crud stuck between valve and valve seat??)?
Are old and new shims of uniform thickness?
Was there maybe initially an additional .017 shim on no. 4 inlet as well as the orginal .417 and this has fallen off unnoticed (knowing my luck this is what would have happened to me
)?I think somewhere along the line you've taken measurements with the tappet resting on the valve spring retainer rather than on the shim, because that particular shim that's in there at the time is too short.
I'd remove the shim and check the clearance without any in there (the tappet resting on the spring retainer) see what you've got then, and then work upwards (as the clearance should be large) rather than downwards as you are at the moment.
All of the shims have been measured at least 3 times by two different people.
I'd remove the shim and check the clearance without any in there (the tappet resting on the spring retainer) see what you've got then, and then work upwards (as the clearance should be large) rather than downwards as you are at the moment.
All of the shims have been measured at least 3 times by two different people.
It's all I can think of, it's not a problem I've ever encountered. I could see how if the valve was cut too far into the head you could possibly end up in a position where the maximim clearance you could get would be with the tappet resting on the valve retainer. (The same thing happens on V8's if you cut the valves too far into the head, it messes up the lifter preload.)
Keith Coman
New Member
restojon said:
The most plausible suggestion is that the nominal .412 shim is not. Given that many of these items have been around in service for a long time, the best idea is to individually measure them using an electronic vernier caliper.
I found and cured the problem, the shim I was using was .025" wider O.D than the rest and was resting on the chamfered part of the spring retainer rather than the valve itself. I went back to no shim and measured the height from the top of the bucket to a fixed point on the cam carrier and inserted shims of a known size measuring this height and recording the results, then using those results and a shim that brought the bucket up to the correct height from the cam carrier I refitted the cam and it was sorted. More than one way to skin a cat an all that
That's not something I've ever experienced, and I doubt I ever will, but it had to be something along those lines, so well done for working it all out and sorting it.
PS Don't send that oversize shim back to me, keep it for posterity. It's the last thing I need having an oddball thing like that mixed up with mine.
PS Don't send that oversize shim back to me, keep it for posterity. It's the last thing I need having an oddball thing like that mixed up with mine.