Main Motorcycle: Triumph TR7
Join Date: Feb 2012
Location: Norwich, England
Other Motorcycle: T140
Extra Motorcycle: Most of another T140
The 'R' followers have a larger radius (1 1/8") than the standard followers (3/4"). This affects the rate of lift. The inlet followers have hole, to reduce weight. The exhaust followers couldn't have holes due to the oilway that goes down to the small hole in the face of the stellite tip - so the exhaust follwers were lightened by means of the pair of semicircular cutouts on thier side faces. The shafts of genuine followers also had reduced diameter sections, partly to reduce weight and also to improve lubrication: some modern pattern followers don't have this feature and are probably best avoided.
The reason for there being 3 keyways is to enable fine tuning of the valve timing. This is only possible on engines with seperate inlet and exhaust cams (unlike Norton & BSA twins etc, on which the inlet & exhaust timing was unadjustable due to all being governed by a single camshaft). Each of the 3 keyways is 120 degrees apart, but the number of teeth on the camshaft pinion is not divisible by 120 (or 3), meaning that, in relation to the teeth, each keyway will give a small degree of difference in terms of where the cams are in relation to the crank. It is hard to explain without diagrams but I'm not aware of any on the forum I can point you to (Mr Pete knows far more about this subject, and has a different method too - maybe you can search his posts?)
Basically, to move a cam's timing (ie: position in relation to the crank) by a whole tooth would equate to about 15 degrees - ie: a lot. But if you use the keyways, that approx 15 degrees is split into approx 5 degrees per keyway. To set the cams absolutley by the book timing-wise, you need a degree disc on the end of the crank and a dial gauge in contact with either a cam follower or a rocker or a valve spring collar - plus, of course, all the correct setting figures. It takes quite a bit of time to set them as near to spot-on as possible, and therefore this was not done at the factory on normal production bikes - hence one reason for the variation in performance of these bikes.
It can make a very noticeable difference. I did this on my T160 years ago. It took hours (6 cam lobes to deal with instead of 4!) but I got it within a degree or two over each camshaft and it ran like a Swiss watch. I didn't bother when rebuilding my TR7 this year, partly due to the fact that I no longer have a dial gauge and I wasn't 100% confident in the relaibility of the setting info I could find, and also due to impatience to get it back together! I took my chances and used the same keyway the old cam was on, and the standard timing marks, and it is fine. I hope you marked the keyway your old cam was on? If not, you may have no choice but to use the degree disc/dial gauge method.
Like I say, there's a one in 9 chance of ending up with it best or worst, and much more chance of something in between. Bear in mind that even worst isn't 'wrong', its just as far from ideal as you can get before it becomes wrong, if you see what I mean!
Hope this is of some help.
Last edited by JohnA; 10-27-2012 at 06:13 AM.
Reason: Add info re. follower shafts.