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MG MGA - Pilot Bush Snug Fit

After replacing the pilot bush the alignment tool is a very tight fit. It will turn in the bush but feels very snug ...but it’s not a burr .........how tight is right..? I soaked in oil over night and then put it in the freeze for an hour then tapped it in with drift. Any thoughts......Tom
Thomas Koch

Actually, it doesn't matter how tight the tool is, but it matters how tight the input shaft is in the bush (they may be identical but I have seen some with variation).

If you have a spare input shaft you can use it to double check fit. What can happen is the the drift you use can slightly mushroom the hole in the bush and that may need to be eased before you install the clutch.
Bill Spohn

Thomas. Often, the plastic tools for use in aligning the clutch are slightly oversize to give a better, closer fit when installing the driven plate and the pressure plate. As Bill notes, the important thing is the fit of the input shaft of the transmission to the pilot (spigot) bushing. This can be checked by using a dial caliper to measure the outer diameter of the input shaft and the inner diameter of the pilot bushing. There is not specification, that I can find, as to the required clearance between the OD of the input shaft and the ID of the bushing. Somewhere in the neighborhood of a .005" difference would be a good place to start. I would note that the clearances have to be checked after the pilot bushing is installed because, since it is a drive in fit, the inside diameter of the bushing closes up (becomes smaller) when installed.

Les
Les Bengtson

Most such bushings have a nominal size bore so they can be finished with a standard reamer, and the shaft will be 0.002-inch smaller to allow for oil film clearance.

For instance, the MGA spigot bushing in the crankshaft is 0.625 bore, while the gearbox input shaft spigot nose is 0.623 diameter. Rocker shaft bushings also 0.625" bore, while the rocker shaft itself is 0.623 diameter. For reference you can use an old rocker shaft as a gauging tool to assure that a new spigot bushing has enough clearance (not mushroomed over).

Front suspension trunnion bushings are 0.750" bore, while the mating steel bearing tubes are 0.748" diameter. Get the idea? Hope this helps.
Barney Gaylord

This thread was discussed between 28/05/2021 and 15/06/2021

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