DETERMINING CAMSHAFT TYPE

by Dave DuBois

[Or, as Dave puts it, stolen from an undetermined newsletter many years ago and provided by Dave DuBois]

DETERMINING CAMSHAFT TYPE

Two different camshafts were supplied as original equipment for the XPAG and XPEG engines. The earliest type, part number AAA5776 (earlier numbers MG862/171 or X24084), was used in all TB and TC engines, and in TD engines up to engine number XPAG/TD2/24l15. This early cam requires a valve clearance of 0.019 in. The later type, part number AAA3096 (earlier number 168553) was used in all later TD and TF engines and requires a valve clearance of 0.012 in.

Unfortunately, now that even the newest TF is almost 40 years old, the engine numbers quoted above are not necessarily a valid guide for purpose of camshaft identification. Engines originally equipped with AAA5776 may have been fitted with AAA3096 in the course of an overhaul.

 With the engine cold, remove the rocker cover and turn the engine over with the crank until #1 intake valve (2nd valve from front of engine) is wide open. At this point, #4 intake valve (7th from front) will be fully closed and on the exact center of the heel of the cam lobe. Set #4 intake to 0.021 in. clearance. This is the correct checking clearance for both cams, regardless of whether you use the degree wheel and dial indicator method or the simplified method which follows.

Now, wipe all the accumulated gook off the crankshaft pulley, and get out your measuring tape and a piece of chalk. Measuring around the rim of the pulley. make one chalk mark between 5/32 in. and 11/64 in. to the right (as seen from the front) of the top dead centre mark on the pulley. This corresponds to 5° BTDC, which is when the intake opens on the later cam (AAA3096). Make a second chalk mark 23/64 in. to the right of the TDC mark. This corresponds to 11° BTDC, which is when the intake opens on the earlier cam (AAA5776).

 Next, turn the engine over with the crank (it's easier with the spark plugs out) until the pushrod for #4 intake valve just barely locks up enough so that you can’t spin the push rod between your fingers. At this point, the timing pointer on the timing chain cover should be more or less aligned with one or the other of the chalk marks.

 If the pointer aligns with the 11° mark, then you have the early cam (AAA5776) and you should set the valve clearance to 0.019 in. with the engine hot. If the pointer aligns with the 5° mark then you have the later cam (AAA3096) and you should set the valve clearance to 0.012 in. hot. If the pointer does not align with either mark, go back through the entire procedure again to make sure you did it right.

             What effect does the wrong valve clearance setting have on the engine? This is a bit difficult for the novice to pinpoint unless he can compare performance to a properly set up car. In general, however, an engine equipped with AAA5776, but with the valve clearance set at 0.012 in. will be very low on power. An engine equipped with AAA3096, but with the clearance set at 0.019 in. will be slightly down on power and will produce a really awful amount of valve clatter. You should also bear in mind the fact that while clearance which is too large is noisy, it doesn't necessarily produce any mechanical damage. On the other hand, burnt exhaust valves will almost surely result from unduly small valve clearance, as in the case of an AAA5776 cam set at 0.012 in.