|The MGA With An Attitude
SUBSTITUTE CLUTCH PARTS - TC-306A
and MGB Clutch in the Twin Cam
As noted in the prior article, purpose of the "spacer" (labeled in the diagram) is to allow use of a thicker clutch disc for the Twin Cam. The Twin Cam clutch pressure plate assembly is also different design than the standard MGA clutch, but aside from the thicker friction disc and spacers the flywheels and clutches are physically interchangeable. This makes it easy for people to find some advantages to substituting non-original parts for the Twin Cam clutch.
The first substitute clutch part that comes to mind is the friction disc, as it is an easy swap any time the clutch is separated from the flywheel. Most MGA (including Twin Cam) originally use a 10-spline clutch disc. MGA 1600-MK-II used a 23-spline clutch disc beginning with engine 16GC-3929 in October 1961. All MGB also used a 23-spline clutch disc, but slightly larger diameter at 8-1/4 inches (or sometimes 8-1/2 inches). I have used MGB clutch discs with a standard MGA clutch. Occasionally an MGB disc on the larger end of the range, or a generic 8-1-10 disc that is a little oversize, may interfere with the standard MGA clutch cover shell. On one occasion I ground down the OD of a substitute clutch disc slightly to fit without dragging on the edge.
Splines on the gearbox input shaft of course must match splines in the clutch disc when it comes to mixing and matching parts. In addition to matching splines, keep in mind that the original Twin Cam clutch disc was thicker, so when substituting a standard MGA or MGB clutch disc you need to delete the six spacers originally found between the flywheel and clutch cover.
It is generally understood that you can substitute an MGB clutch in place of an MGA clutch, while changing the number of alignment pins from two (original for MGA) to three (standard for MGB). The MGB diaphragm type clutch is thinner than the MGA clutch, so this requires use of the MGB release bearing, release arm and front cover from an MGB 3-synchronizer gearbox (pre-1968). There are also some caveats about recent replacement part MGB clutch covers not fitting well inside the MGA gearbox bellhousing (see article CT-102A). A number of people have installed MGB clutch in the Twin Cam, but you should couple gearbox to engine to be sure there is no rotational interference before installing it in the car.