Wednesday, October 15, 2008

Camshaft end float(2)

Assembled casings with bushes in place and had 1 thou endfloat which was OK. Had time on my hands so decided to strip and re-assemble with cam followers in place to check. Cleaned up the feet of the followers with an oilstone and then assembled them in place, with the oil holes facing backwards, and replaced the camshaft and the outer cover. Using a screw in the end of the camshaft and an electric drill I then ran the camshaft at low revs holding the followers down with light finger pressure to see how it all ran together. Seemed fine. That is until I took another look. When disassembled the top lip of the inner timing bush had been lightly tapped by the cam follower foot leaving a mark. This showed that they floated slightly and also that the 1-2 thou clearance I had given the bush when fitting was going to cause problems as it provided a snag. I had a think about this and it answered a question I had. The bruising of the bush seen from the inner crankcase had, I thought, been caused by the bush wandering out and meeting the flywheel. It was the other way it went out into the path of the cam follower foot, which explains my bent pushrod and marked piston. When the foot was caught on the top of the lip it could not fall with the cam and therefore the valve was held open as the piston rose to meet it. The bush needed no attention on the inner crankcase as not necessary, but what I did do was scrape the bush on the follower side, with the flat edge of a stanley blade, to remove all of the excess. The bush and the surrounding casing are now level and there is nowhere for the foot to snag agian. I reassemble all and tried again with the drill and light pressure on the followers and all is fine. There is 2 to 3 thou end float on the shaft but not enough to worry about pushing the outer bush inwards to take up, as it was already loctited in postion. I would think a 50W oil would soften any gaps in this area.
I have ordered the remainder of the gearbox bushes and that will be my next area of attention while I wait for the maching on the timing bush. Will post soon.

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