I have recently completed a full rebuild of my Comet motor. At the time it was identified that the Cam lobes were bad – having worn thru the hardening so I ordered (amongst a lot of other stuff) a new cam and cam followers. At the time the supplier did not have a Cam available so he lent me one of his that I was to return when the ordered cam arrived. So the rebuild was completed (by me) with the loaner cam and some 1,500 miles later my ordered cam arrived. After I swapped out the loaner cam for the new one I noticed that the silencer (club type with a spiral baffle) was starting to“blue” about ¼ way along its length (from the inlet side). Both cams were alleged to be Mk1’s. Today I checked the cam timing using the exhaust valve, as it’s much easier to get to. Working on 0.010” lift I measured that the exhaust is starting to open at 73 BBDC and is closing at 27 ATDC. I am using a Lucas Magneto and ATD with the timing set at 4 BTDC fully retarded and Nippondenso W22EP-U plugs gaped at 0.018” – the bike is an easy starter, though it seems to run out of puff at higher revs; maximum comfortable cruising speed is around 60 mph.
Question – what could be suddenly causing the bluing of the silencer? The Mk 1 cam timing spec for the exhaust valve is open 72-70 BBDC and close 28-33 ATDC. At 73 and 27; I am within just 1 degree of the spec – would that be a contributing factor to the bluing? Should I be stripping the timing case and retiming the cam to get that 1 degree closer so it moves to within the recommended range or is it not that important?
Question – what could be suddenly causing the bluing of the silencer? The Mk 1 cam timing spec for the exhaust valve is open 72-70 BBDC and close 28-33 ATDC. At 73 and 27; I am within just 1 degree of the spec – would that be a contributing factor to the bluing? Should I be stripping the timing case and retiming the cam to get that 1 degree closer so it moves to within the recommended range or is it not that important?