C25 Inner camshaft bush

[Andy Edwards]

Does anyone know what the flange thickness of the inner camshaft bush of my early C25 should be? the part number is 40-0955.

The recess in the crankcase into which the flange fits seems to be 0.0625" deep. I have 2 new bushes from different suppliers, one has a flange thickness of 0.072" and the other 0.0675".  If I fit either of these, I am then unable to fit the inner cam follower as it fouls on the protruding flange.  I have lost the original bush that I removed when I stripped the engine 17 years ago!

[Spaceman]

Although it is tempting just to replace the bush, you ideally need to measure the free play for the camshaft afterwards. In this case, because the inner follower is interfering with the LH bush, I would also measure the available clearance between the follower and the crankcase with the bush removed. Armed with all this information, you can then work out how much the inner bush flange needs to be reduced not only to allow clearance with the follower but also to give the correct free play for the camshaft. The measurements are straightforward but you do need the use of a depth gauge (digital vernier calliper fitted with a depth gauge foot).

[Andy Edwards]

Thanks Spaceman. This is a shame as the camshaft end float had been set to 0.004".  I'll do as you suggest and measure the clearance between follower and crankcase. After machining the flange I'll have to readjust end float at the inner timing cover bush.

[Spaceman]

Unless the outer bush has also been changed, I would have thought machining the inner one to provide clearance for the follower should get you back to the correct end float again?

[Andy Edwards]

With the bush removed, there is 0.004" clearance between the the follower and crankcase. 

I was just wondering if the flange should actually be machined down to the same level as the crankcase face to prevent the follower from contacting the lip of the flange on it's downward travel. I see that the inner camshaft lobe is machined such that if the bush and crankcase were at the same level, the camshaft would still run against the bush and not the crankcase. I'm probably over thinking this!

[Spaceman]

That clearance would seem to imply the bush should be flush with the crankcase - one of your bushes will only protrude 5 thou and so not much needs to be machined off. I assume with that bush fitted, the camshaft end float is then -1 thou, ie 1 thou of interference? If you fit the bush and the camshaft and inner timing cover (followers not required), that amount of interference should stop the camshaft turning freely and mean it would be then safe to machine off the 5 thou from the bush.

[Andy Edwards]

Thanks again Spaceman, I'll get back onto the job tomorrow.