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March 3, 2014

Valve Train

The 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.


I'm 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.

Also, 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.  

There 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 way (Link).  

In 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 anything.

Going 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 adjusters.

I 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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