Previous postings (and a very recent one) have discussed the cam spindles and why they are marked 'IN' and 'EX' to indicate correct fitment. I hate not knowing the answers to these things but by a sheer stroke of luck I came across the vital information while browsing some old magazines last night.....
On the rear of the spindle is a 'stub' which fits into the crankcases. The spindles are pushed in until they come up against a shoulder machined onto the spindle.
This shoulder is cut away to provide clearance for the foot of the tappet when it is in its lowest position on the base of the cam..so the spindle is always fitted in the same position radially, to position the flat in the correct place.
On some examples the stub that fits into the cases has a flat machined on it, the purpose of which I was never able to deduce.
Apparently, due to the proximity of the cam spindle holes to the timing side main bearing housing it was found that when the cam spindles were pressed in they could distort the bore of the main bearing housing, affecting bearing installation. Machining a flat on the stub relieved the pressure at this point, solving the problem.
As the flat on each stub had to face towards the main bearing housing they necessarily had to face each other (when fitted) and were therefore 'handed' and thus marked accordingly for correct fitment.
Earlier spindles do not have the flats machined on them and from memory, some of the ones with the flats on were not marked..I'll have to check that...but it appears there may be four types in total..
1)An early 'drilled through' pattern with the drilling filled with lead at the back to blank it off and a round stub.
2)A second pattern, not drilled through but with a round 'stub'
3)A third pattern, not drilled through, with the flats machined on, but not marked for fitment.
4) A fourth pattern with the same features as (3) but marked 'IN' and 'EX'.....
Another mystery solved!....Ian
email (option): ian@wright52.plus.com
hi ian ,just a thought,have you ever checked if there is any eccentricity between the two diameters,ie the cam bearing diameter and the one that inserts into the crankcase,this would allow for adjustment in the backlash in the timing gears,cheers rick
email (option): richardholt@rocketmail.com
Hi Rick...There is no eccentricity between the diameters as standard, though that would be a nice feature...Unfortunately the outer end of the cam spindle has to be a snug fit in the outrigger plate to support the spindle effectively and the flat machined on the shoulder, where it rests against the crankcase currently, has to be in the correct position to clear the foot of the cam follower. Also there is the question of the correct location and function of the flat area detailed in my posting to consider...and of course the spindle is an interference fit in the crakcases. So, a considerable rethink of the layout and some involved re engineering would be required to build in that feature. Possibly, retaining a smaller diameter fixed spindle with an outer eccentric sleeve would be the basis of such an alteration..adjustment method and locking details would have to be worked out..Ian
email (option): ian@wright52.plus.com
Hi John..as well as the flat on the stub that relieves pressure on the main bearing housing each spindle also has a flat machined on the shoulder to clear the tappet foot...this must be positioned under the tappet foot, so the spindle cannot be rotated through 180 degrees.
Viewed from the front both spindles have a flat on the top to clear the tappet foot...the 'stub' of the exhaust one also has the flat on the left hand side, adjacent to the main bearing housing. The inlet one, however, has the flat on the stub to the right hand side, also next to the housing...That is the reason for them being 'handed'...I can only guess as to why it took so long for the problem to be identified!.Ian
email (option): ian@wright52.plus.com