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MG MGA - TACH DRIVE GEAR

I'M REBUILDING MY 61 COUPE MOTOR AND AS I REMOVED THE TACH DRIVE GEAR FROM THE CAM SHAFT I FOUND NEITHER A KEYED CAM SHAFT NOR A GROOVED CAM SHAFT FOR A CIRCLIP. THE GEAR WAS JUST PRESSED ON THE CAM SHAFT. WAS THIS ANOTHER METHOD FOR INSTALLING
PETE CERKA

Pete, all of the ones I have seen, and this includes the 3 main MGB, are keyed. It is possible to cut a key way in the shaft and reinstall. In fact the only difference I can see in the camshaft from an MGB 3 main engine and a early 5 main engine is the lack of the key way in the 5 main. Alternatively, you could just leave it the way it is--there is very little load on this gear as it only drives the tach and no indexing is required.
James Johanski

james
the after market cam that is being installed in the motor has a key way and the gear slides on with no resistance and free wheels.
PETE CERKA

Pete, Without a key the gear will free wheel. I thought you said that on the cam you had, the gear wheel was pressed on? If it was pressed on it shouldn't freewheel. I have never seen one pressed on as all that are designed for the 3 main engine with a tach drive have a key way in the cam shaft end and on the gear. If you you do not have a key slot on the shaft, it is possible to cut one at a machine shop.
James Johanski

It depends

The originals were keyed, but when rebuilding engines I have found that the gear is a tight fit on the camshaft (so tight in some cases that it's very hard to remove the gear without breaking things. If it's tight, a key is unnecessary, whether it has a keyway or not, but if it's loose it's not going to drive the tacho, so a key or something else is going to be required.
dominic clancy

Current Moss price for the correct (keyed) gear is $58.95.
Del Rawlins

YES JAMES THE AFTER MARKET CAM HAS A KEY WAY AND THE GEAR FREE WHEELS ON TH SHAFT AND IT WAS A BEAR TO GET OFF
PETE CERKA

Pete, All you have to do then is install a key.
James Johanski

This thread was discussed between 04/12/2009 and 05/12/2009

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This thread is from the archive. The Live MG MGA BBS is active now.