Moss Motors, Ltd

I have recently completed the restoration of a MG TD (I do all of the work myself) but was never able to get the engine performing to my standards. After reading the article in your Fall 1991 issue, I decided to check the camshaft based on your article on T-Series camshaft identification. I have a machinist background, and the precision measuring tools, so I was able to do a thorough job. I mounted a dial indicator on a rocker cover stud, and using vernier calipers, I was able to verify the valve position with a high degree of accuracy. By measuring the opening of the intake valve and the closing of the exhaust valve individually, the method you described will even determine the installation of racing cams, which you cannot measure as a total distance on the crankshaft pulley. However, one caution must be observed, and that is that the measurements must be made at the closing or opening of the corresponding valve, and not when the lobe on the camshaft reaches bottom.
The real issue I have is that there is an arithmetic error in the article. The diagram states that a crankshaft rotation of 10 degrees equals 1/4" of displacement on the crankshaft pulley. It also states that a rotation of 35 degrees equals 11/2" of displacement on the pulley. Since 35 is 3.5 times the 10 degrees, if the 1/4" is correct (sorry, we goofed, it is not. See revised figures above-Ed.), the displacement for 35 degrees would only be 3.5 times 1/4", or 7/8". This is critical for the correct identification of the shaft. The actual displacements are 0.360" (about 11/32") for the 11 degrees BTDC for the intake valve opening and 0.785" (about 25/32") for the 24 degrees ATDC to the exhaust valve closure. This is a total distance of 1.145" (about 15/32") between intake valve opening and exhaust valve closing which results in a total crankshaft rotation of 35 degrees.
Keep up the good work with your articles and tech tips. They are of tremendous value to those of us who love these cars, and want to keep them in first class operating condition.
H. Mahaffey III, Lincoln University, PA