When I did the head on the L-1 Salonette, I was fortunate enough to have a
friend nearby with a South Bend Lathe and a post grinder who has owned a PB
since the 60's. He showed me how to set up his lathe and post grinder to
machine the valve stems to the exact dimension required to give the proper
clearance when the eccentric bushes for each rocker are set at the optimum
rotation for proper valve timing.
First assemble the rockers, spacers, thrust washers and supports onto the
head, and then finally install the camshaft. The gear mesh of the vertical
drive is critical and my friend set that up himself. We used all modern
bearings and seals and had shims of various thicknesses made up to position
both the camshaft and vertical drive gear at the optimum setting. Once this
was done we moved on to the valves.
First set the eccentric bushes in each of the rockers according to the
diagram in Philip H. Smith's "Tuning and Maintenance of M.G. Cars," which
also has a good description of this process. Then insert all the exhaust
valves and check for clearance. you may have to switch some around if there
are any "short" ones or particularly "long" ones! Next, using a valve
grinder and fine grinding paste, mate the final selection of valves to their
respective seats and number the valves with an indelible marker so they
don't get mixed up. After cleaning everything up really well, recheck the
clearances. Now the fun part begins! The idea is to take off only the
absolute minimum from the tip of each valve stem so that the clearance is
spot on when the eccentric bush is exactly at the proper rotation for
optimum valve timing. In other words, adjust the valve to the rocker, NOT
the rocker to the valve! Repeat the process for the intake valves, taking
care to note that the clearance is slightly different for intakes and
exhausts!
Take your time, and remember the old carpenter's adage: "Measure twice, cut
once!"
- Mike Hughes -t?t-
> Have finished rebuilding the block, any tips and advice on assembling the
> head and camshaft etc.
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