Tuesday, October 7, 2008

Cam shaft bush fitment and end float

While trying to replace the inner camshaft bush it came to light that the engine had been altered by the fitting of a later type camshaft. I have not seen any difference from the normal C15 Star cam profile so I do not think it was to facilitate a different cam profile. The problem is, is that neither of the stock bushes available do the job any more due to a difference in cam shaft diameter and size of the hole in the crank. A one off bespoke bush has to be turned in a suitable material. I had a good look at the one I removed on dismantling and found that although not the prettiest bush in the world, it was within acceptable tolerance. This bush had drifted in service as was evident by bruising where the crank had hit the edge of the bush as it drifted into its path. This was all cleaned up with a smooth file and the bush and case were cleaned thoroughly with acetone before using an old camshaft to tap it back into place. Loctite was applied liberally before this, that was the reason for cleaning with acetone, so it could get a purchase. I made sure that the outer side of the bush sat proud of the aluminium case by 2thou (approx) and that the oilway lined up.

top right picture
Looking at the camshaft there was no bad wear on the profiles or the shafts so could be re-used. Light dressing with an oilstone took a small wear burr off of the end of the smaller inner shaft and avoided the shaft dragging through the bush on re-assembly.
I wanted to set the end float of the shaft before the loctite had a chance to start setting so the next step was the outer camshaft bush. I had already measured this and found it also to be within acceptable tolerance. The guide I used for this was, with one end of the shaft in its bush ( secure the bush first lightly in a vice) there was only 1/32in play up and own when measured with a steel rule. Any more and I would have scrapped them both. Remember though that there has to be some clearance as a bush works by it's component parts being separated by a film of oil.

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