I had a similar relentless ticking on the M. I pulled the rocker assembly
after multiple attempts to adjust out the ticking, and found my problem lay
in the wear pattern of two rockers. I found that what read as 0.12"-0.13" on
the feeler guage was really the proper gap plus the height of the indentions
on the rocker arms' cam surfaces where valve stem heads had worn in.
Naturally the shape and stiffness of the feeler gauge is such that these
depressions are ignored. In some cases I found additional slack of up to
0.05" or so.
The cure is simple. You can have the cams reground, or can if careful do it
yourself by hand. I used Emory cloth and a block of wood in which I chiseled
out a channel. Tearing the cloth into 3/4" stips, two sheets sufficed to
resurface all 8 rocker arms. You simpl hold the arm in the 'socket' in the
block of wood and drag the cloth strips grit side up against the rocker
surfaces, taking care not to lose the horizontal alignment. I went with each
one until the depressions were removed, checking each each rocker with a
square. I used an agressive grit on the worst ones, and 220 to finish them
off. Polishing was achieved by running the worn out strips of 220 between
the rockers and my thumb.
One of the hidden advantages of hand finishing the rockers is that you only
end up with a round contact patch, rather than a horizontal band that runs
across when a machinist does it. This gives a better chance of centering the
contact between the valve stem head and the rocker. I found that whoever
professionally ground the rockers in the 70's did not get perfect alignment,
and most of the rockers had assymetrical wear patterns. I checked my
handwork with carbon paper and a block of wood after the rockers were
reassembled on the shaft and posts. All 8 marked paper righ in the center of
the cam when pressed through the carbon paper against the block.
Total time: 2-3 hrs.
Allen Miller Bn2M
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