Feature Bike - Part 2
With the barrels removed, close inspection revealed that one stripped thread had previously been helicoiled. The other was original alloy which came out wrapped around the pillar stud. This meant that one drilling was already somewhat larger than the original size. This would require a smart solution.
The good news was that one existed - in fact several. One was called a 'Timesert' - a thin sleeve with internal and external threads, that could be locked in the alloy, and take the internal thread back to its original size. Problem was - it used much the same size thread as a helicoil - and that was already destroyed. It was also a lot shallower than the original thread, and as the original had already given up the ghost, a shorter one looked a little unsubstantial.
Another solution was a stepped pillar stud - with a larger thread into the barrel. This required drilling out the stud hole and tapping a new thread - hopefully strong enough to hang on to things for a year or three.
broken helicoil, timesert and stepped stud..
The stepped stud certainly looked like the sturdiest answer, so the work of removing the remains of the helicoil, and drilling and tapping was farmed out to an engineering company, in order that a high degree of accuracy would be obtained. The cylinder head is a very neat fit over the studs, so any movement from perpendicular would cause problems
the result..
Unfortunately, the finished job presented a few problems. The two new studs fitted securely in their oversize threads, but one was not perpendicular to the barrel surface, which prevented the head fitting. Not pleasing considering the "experts" had been invoked. After much fitting and refitting to obtain the best compromise, a small amount was ground off the top edge of the stud, as can be seen here, and then the head reluctantly fitted.
The modern approach..
These days there are some options available to triple owners that were not around in the 70's. Although copper head gaskets became a standard fitment on the later models, the rockerbox gaskets remained in normal gasket material. This was not ideal when you consider that the head bolts passed through both - so the rockerbox gaskets compressed and prevented a good seal at the head gasket. Eventually some useful folk began to make copper and aluminium rockerbox gaskets, so these will be used.
Coming together..
Now the cylinder head is fitted and another new feature. In the past, the pushrod tube seals were simply square section white neoprene, which did not respond very well to either over or under compression. Now there are proper formed seals with lipped concave edges that do a better job of keeping the oil on the inside. Still important to check the amount of compression before final assembly though, as the thickness of the rockerbox gaskets plays a part. Checking in progress..
Go back, Jack, do it again..
Once the exhaust rockerbox is fitted, the same process is repeated on the inlet. Check and check again. Seal compression,
surfaces for flatness, all present and correct. It is possible to get the pushrods in a position whereby there is virtually
no compression of any valves during the fitting. The head tensioned with no problems - so a big sigh of relief in the knowledge
that the problem we are in here for has been rectified.
All set for a feel..
Valve clearances come next. This bike has had adjusters fitted that feature an allen key method - makes adjustment an absolute pleasure. Something else worth noting for any triple owners. The factory valve clearances were 006" in and 008" out. There is a current school of thought which advocates setting the clearances to 008" in and 010" out. This creates a smidgen of extra clearance which assists the oil film on the cam lobes and followers. By effectively retarding the cam timing, this also provides a little more low end torque. Sounds plausible. It was done.