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Cams ????

redbloke1956

Well Known and Active Forum Website User
Non-VOC Member
Hi all, As I mentioned in a previous post I have just received my newMk 3 cams....OR HAVE I ? I went for the Mk111 to minimise modification to the bike, while fitting the cams I noticed that when the cam was rotated, the exhaust cam lobe made contact with the Exhaust valve lifter arm ET69FAS, yet the original cam (even though worn) did not, I then took measurement from bottom of base circle to top of lobe on the cam and it is .050" (50 thou) larger than the original. (in my very humble opinion I don't think a worn cam could be missing 50 thou off the lobe...assuming base circle has little wear)
I contacted the Gent I purchased them from (New, from a reputable seller/manufacturer, marked as a Mk3) and asked if they may have been a Mk2 and incorrectly marked, the response was that I should file/grind a little off the ET69FAS to give clearance, he also first told me to adjust the Valve lifter and give it a little more slack, again in my opinion I would think that it shouldn't matter the position of the lifter, it should never be possible for it to make contact with the cam?:confused:
Am I missing something here? Is this a common occurrence?

Kevin
 

timetraveller

Well Known and Active Forum Website User
VOC Member
Kevin, you need to measure the diameter of the base circle as well. The lift on the valve is a combination of the diameter of the base circle, the height of the lobe and where on the cam follower the cam is touching. I suspect that you will find that the base circle on the new cam is larger than on the old cam and hence the height of the nose of the cam has to be higher to give the correct lift. Sadly, 50 thou of wear off the nose of a cam would not be too unusual. It is also quite common to have to grind a little off the valve lifter if cams with higher noses are fitted. The best way to find out if you have a mark three is to fit it and then do the lift profiles as discussed in these pages a few days ago.
 
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