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March 3, 2014
valve train in this project was fairly involved. There was a lot
of wear, especially on the rockers and rocker shaft. I bushed and refurbished the rockers, and bought a new shaft.
always a little hesitant about aftermarket parts, and this shaft
reinforced my feelings. Even though the shaft measured within
spec for OD, the rockers didn't slide on easily. The reason was
tiny burs left on the machined areas on the shaft. A light touch
with a wire wheel on these features fixed that problem. Seems
like the manufacturer should be doing that.
on the suggestion from a few people on TR6 forums, I decided to check
the bore of the shaft for foreign material. Though many of these
shafts have plugs pressed in both ends of the shaft, I lucked out, and
mine had simple set screws threaded in each end. I pulled them
out and ran a brush down the bore and probed the oil holes. This
produced a worrying amound of metal machining swarf, some pieces big
enough to plug a rocker oil passage. In sighting down the bore,
there also appeared to be a partial blockage on one side. I
finally decided this was a step left where the holes drilled from both
ends didn't meet perfectly. This probably doesn't materially
affect the function of the shaft, but it doesn't leave me with a warm
feeling of confidence, either.
I now had everything I needed to build the rocker shaft assembly. The shaft pedestals clean up nicely.
With the shaft assembly built, and the new valves and springs
installed in the head, the only remaining piece of the chain was the
pushrods. Since I had shaved 0.130" off the face of the head, the
rocker shaft and rockers, plus the valves and springs had all been
lowered relative to the cam shaft. This made the stock pushrods
too long. They would bearly fit, but left no allowance for lash
or adjustment. I assumed that there would be some Triumph
part--possibly from earlier, higher compression versions of these
engines--that would fit, but I wasn't successful in finding them.
is a school of thought that says that the rocker shaft pedestals can
simply be shimmed to account for the compressed distance between the
lifters and rockers. I looked into this, but it appeared to me
that this would change the valve-side rocker geometry in an undesirable
the end, I ordered a set of custom pushrods 0.130" shorter than stock.
This should restore factory geometry both for the pushrod and
the valve sides of the rockers. The new rods are a little larger
in diameter than the stock ones, and are tubular. They also are
about 15% lighter than the stock ones, not that I'm counting grams or
on the premise that it would be good to have all the metal-to metal
wear surfaces new to start with, I also ordered a new set of stock
assembled everything with a daub of ZDDP grease on the wear surfaces,
torqued down the pedestals, and set rough clearances onthe rockers.
Topped it off with my new trick valve cover, and this engine is getting pretty close to finished.
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