Andy,
In reply, perhaps the best thing I can do is quote from the Late Great Bob Stafford's "Ab Initio". It covers the cams, the pinion and the cam bushes - your early meteor bushes might be different to later ones (ie without the 3/16 dia peg??):
Three patterns of cam pinion were used, the standard plain gear, the lightened, recessed and polished
one on the specials and T.T.Rs. and the recessed and slotted type on the front camshaft of the Twins. The
interference fit of the shaft in the pinion is 0.001” to 0.0015” and theoretically any of the cams can be fitted
into any of the pinions and the same timing marks (if any) can be used. It should be mentioned that originally
no timing marks were used on the T.T.Rs, and where replacement gears have been fitted it is likely that they
too will be unmarked.
The camshaft bearings are merely iron or bronze rings, 1.126” OD with a 3⁄4” bore. Originally these
bearings were just trapped in a housing when the cambox cover was clamped down, later a 3⁄16” diameter
peg projecting 1⁄8” was fitted into the OD of the bearing, this peg being threaded either 2 BA or 3⁄16” BSF,
and it is to ensure that should the bearing ever come loose it will not rotate in the housing. Nevertheless,
if a seizure does occur the bearing does sometimes move and on rare occasions has been known to cause a
fair amount of damage. The inner bearings (ie. next to the barrel) are always iron as oil only reaches them
through a catchment on the cambox wall. The outer bearings can be iron or bronze as the oil supply to the
rockers runs by these bearings and some is diverted to the camshaft under pressure. It should be noted that
the outer bearing of the front camshaft of the Twins is always of bronze as this has also to withstand the
drive to the mag-dyno. The inner bearings have an oil hole in the top to line up with the catchment hole, the
outer bearings have a 1⁄8” wide 5 1⁄16” deep groove around the OD to pass oil to the rocker feed pipes and a
1⁄16” diameter hole drilled into the bearing to feed the camshaft.
The Series ‘A’ cams were known as 2X, 4X and 5X; timing figures approximate closely to Mk. I and Mk.
II post-war cams although the actual form is different, 2X were original equipment in Meteors, 4X in Comets
and 5X in Specials and T.T.Rs. Rapides were fitted with either 2X or 4X. The cam form is identical for all, that is the same shape on the rise and fall but the actual theoretical lift varies as follows: 2X — 0.320” lift inlet and
exhaust, 4X — 0.331 lift inlet and 0.333 lift exhaust, 5X — 0.333” lift inlet and exhaust: these differences in
lift are negligible but because of the variations in radii used on the various cams the valve timing is altered
appreciably, incidentally the radial relationship between inlet and exhaust cams is 172degrees (or 188degrees, depends which way round you go); on the Series ‘A’ models the cam nearest to the cylinder operates the exhaust valve.
Now to the theoretical timing of the cams which is as follows:
I.O. I.C. E.O. E.C.
2X: 40 BTDC 52 ABDC 65 BBDC 33 ATDC
4X: 44 BTDC 56 ABDC 68 BBDC 38 ATDC
5X: 48 BTDC 60 ABDC 71 BBDC 42 ATDC
Obviously it will be almost impossible to obtain these settings on worn components so my own method
is to use a degree plate and to set the inlet valve opening at its correct position then take a note of the actual
opening and closing points as they occur, the engine then has to be run to observe the performance.....
Peter B