Camshaft wear

[Keith Clements]

From the recent OCR whilst I was searching for things on 'Camshafts' I found this from 2000-06. OCR is now a lot better but still has problems with the dimensions.. This is where the Legacy team can start work extracting all the technical articles.

T.l.O.'s REPORT
This is the balance of Bill Lock's report held over from last month.
A recent common problem I have had with the engines for my Javelin and Jupiters has been to do with camshafts.
I have found that most crank cases, but not all, have a worn centre bearing housing for the centre bearing on the camshaft, or it is found that the centre bearing housing is out of alignment with the others. The solution is to line bore the housings to the minimum oversize required to correct the fault, and fit a camshaft with oversize bearings. This can be achieved by either metal spraying the camshaft journal and regrinding, or by fitting a new oversize camshaft.
Also, I have found that although the camshaft housing is still within tolerance(i.e. diameter = 1.5-1.501in.), the centre bearing on the shaft is worn more than 0.001in., giving a total clearance of 0.0015in. or more. This lowers the oil pressure and increases noise to unacceptable levels, and deprives the nearside rocker shaft of oil. If the camshaft lobes are still sound - and most are not – the bearings can be metal sprayed and ground back to the appropriate size (0.0005in clearance), or another good second-hand or new camshaft fitted. So before fitting the camshaft to your engine, check:
* cam lobes for loss of surface and wear,
* camshaft journals dimensions (should be 1.500in. , +/- 0.00005in.),
* diameter of camshaft housings in crankcase (within O.OO1in. of camshaft journal size),
* wear on chain wheels, as even fitting a new chain will not correct your valve and ignition timing and will soon allow noise and wear levels to increase.
-WL

[Keith Clements]

I dug out some of the camshafts from the cellar and the ones waiting to be put into the 4 engines awaiting rebuild.
I measured the journals and the maximum diameter of the lobes.

camshafts.jpg

I have two oversize journal cams (1 and 5) of which one is destined for the original Javelin engine block from Amy's car. I have yet to check the blocks of engines awaiting rebuild to see if they need one.

Cam 2 is for the new engine for the SA with cam 15. This is the one that featured in the Practical Classics exploded view.

Cam 14 is for the a spare engine for the SC.

As for the worn ones I think it is fair to say that the centre journal wears more than the other two. There does not seem to be much correlation between the valve and wear although No2 inlet has four wearing more than 30 thou. I suspect that wear is usually caused by a non-rotating follower or possibly a wide tappet clearance for many miles, unless as in the case of cam 12 it was consistent over all the lobes. The debate on non-rotation has been aired elsewhere on this forum.

I wonder if it is worth putting some Stellite weld on those single lobes on an otherwise good cam. e.g. Cam 13 or cam 7. Anyone any experience of doing this?

[BobCulver]

I have about six reasonable camshfts after sorting through stacks, but only about two good.
I suspect cam journal wear accounts for the characteristic Javelin clatter, worn valve seats, broken valves, and contributes to low oil pressure. Worn lobes were often a legacy of the early mutigrades which rapidly were not. Avoid the sport rated valve springs. To try and prolong valve seats, an endless problem with my car (run weak), I ran for years with just the outers, but could not greatly exceed 60 mph, my self imposed cruise speed anyway. Much to be said for oils with a good base viscosity. 20w50
With any journal build up or regrind process it is easy to lose the critical exact centre.
The new camshafts are/were a great innovation, assuming they wear OK. If say just .005 oversize could possibly scrape journals to fit, or ream or hone the end ones and use a bar to correct the centre, then hone that.
I bought steel back bearings with a view to fitting but never completed.
Also resorted to lapping halves together etc but do not try. Apart from much else the dowels for flywheel become misplaced.
Modern cars with modern oils run cams direct in alloy heads.
Some cams have been reground. Confusion exits about follower radii and cam slope, neither of which Javelins had.