I now know for definite it's a valve timing problem!

Big step forward tonight! I actually know that the reason the engine won't start is because the valve timing is way out, 90 degrees on the crankshaft, that's 45 degrees on the camshaft sprocket.

I was hoping to be able to use a special dial gauge holding spark plug adaptor that I used to use to time Japanese 2 stroke bikes in the 70s to check TDC with my dial gauge, however as the plug holes are recessed on the triumph there wasn't room for the gauge. I used the adaptor though as a reference point face and then measured the piston distance down the plug hole at TDC on the pulley timing marks and just a tad before and after the TDC marks using a digital vernier. This confirmed to me that the pulley timing mark for TDC was spot on ruling out any slippage of the timing mark band on the rubber damped pulley assembly which had been suggestted as a possible reason for the timing constantly drifting.

Taking digital caliper measurements to verify TDC marks on the Cranshaft are correct using a dial gauge spark plug adaptor as a reference face.

I then followed the Triumph Workshop manual, setting the valve clearances on valve 12 and 11 to 40 thou and then rotated the engine until valve number 1 and 2 were at the rocking point, ie one valve just opening and the other just closing. This should correspond with TDC for cylinder No 1 if the valve timing is correct. However I found it is actually set at about 90 degrees After top dead centre. That'll be why she wont start then!

Valve number 1 and number 2 at the rocking point, verified by feeler gauges as both have the same valve clearance.



Pulley Wheel position with valves number 1 and 2 at rocking point. This should be at TDC but TDC mark (the groove on the pulley)  is about 90 degrees ATDC!

I now have to strip down the front of the Engine to the timing chain to find out why. This means draining the new coolant I put in last month as the radiator has to come out to gain access. I did also note that the chain sounded rather noisey while I rotated the engine to check the valve timing so I reckon it's certainly faulty.

One good thing that will come out of this is that I've had a leaking timing cover oil seal for years so the oil leak will end up getting fixed by default.