Last week I posted about compatibility problems I was having with
reproduction rocker arms, push rods, and a rebuild head on my 66 TR4A. I
was unable to use the new push rods as the cups were to small, and they
were a bit longer. Though the rocker arms looked like the original,
careful measurement showed them to have about .10ths more "angle" when
mounted on a shaft. Randall Young put me onto the right track by
providing the head thickness measurement (3.325-3.330). Mine measured
3.295, or about .45ths removed during resurfacing. Assuming the
machinist removed about .05ths during valve grind, and that the engine
had been decked another .05 or .10ths, there was about .60ths
difference. I removed a rocker arm assembly from a TR4A engine that
never been rebuilt and installed it on the head using the original push
rods, and was able to adjust the valves. I then removed the reproduction
rockers from the new shaft, used the original ones with the original
push rods and a new stock head gasket. I was able to adjust the valves,
and now have the engine running. So, essentially, I choose not to use
the reproduction arms and push rods, and go back to the old ones. Seems
the problem was combination of material removed from the head, undressed
valve stems, and variance in the reproduction push rods and rockers.
Another solution would have been to use shorten push rods and or dress
the ends of the valves. After getting the engine running, I did a
compression test, to see if any damage was done by over heating when the
head gasket blew. Cylinders 1, 2 and 3 were right around 173 lbs., and 4
was a 160 lbs. The variance in number 4 is a a bit worrisome, but I feel
lucky not having knocking rods or some other dire result of the engine
getting very hot. A test drive around the block, and she seems to run
smooth. I'm going to live with the push rods and rockers for now, but on
the next rebuild I'm going to search out some high quality parts to
replace the ones I used. Thanks a lot to all who
responded. Jerry
Oliver, Olympia WA. 66 TR4A
CTC66838L 66 TR4A
CTC70200L 61 MGA
Roadster 58
Jaguar
Roadster
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