[Mgs] setting valves after head machining / 1500 MGA

[Barney Gaylord]

At 11:03 AM 7/13/2009 -0400, Tom Gunderson (thgun at comporium.net) wrote:
>.... I purchased a redone head. Now a few of the valves are too 
>tight to adjust. Can I use shims all the way across to raise the 
>rocker assembly? If so where can I get them? Any other tips.
>....

The condition is not normal, so something is wrong there.  Assuming 
you have the right pushrods, either the head has been milled 
substantially or the valve seats have been cut too deep into the head 
so the valves are riding too high.  It would be more convenient for 
measurement and inspection if the head was off, but maybe some 
investigation can be done without removing it.

Original head thickness was 3.187".  How creative are you at 
measuring the vertical distance from top to bottom of head in 
situ?  That dimension would tell you if the head was milled too much.

Next is to measure the height of the valve stems from top of head.  I 
just measured on my spare engine and found 1.600" plus or minus a 
smidge from valve to valve.  This one had new hard seats and new 
valves installed not too many miles earlier, meaning the valves 
should be very close to as-new height.  There is plenty of rocker 
adjustment from there, so I could believe that stem height of 1.625" 
should be an easy accommodation for the adjusters.  If your head has 
the valve seats cut abnormally deep for clean up the stems would sit higher.

If head thickness and valve stem height are in the ballpark, then 
maybe the pushrods are too long.  If you re-used original pushrods 
that should not be a problem.  I suppose it would be very unusual for 
anyone to ever mill the rocker pedestals to make the rocker shaft lower.

Moss Motors does sell the rocker pedestal shims, but they are not 
originally intended for that purpose.  Later engines had 0.010" shims 
under #2 & #3 pedestals only to put a small bending preload on the 
rocker shaft to keep the shaft from wiggling about in the pedestal 
bores.  None of my engines for decades have ever had these shims, and 
I have never seen any detrimental effect from their absence.  You can 
could install some of these shims under the pedestals to open up the 
rocker clearance, but it seems like treating the symptom rather than 
curing the disease.

Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com