Author Topic: Idler pinion oil seal  (Read 333 times)

Offline Rudgeman

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Idler pinion oil seal
« on: 18.06. 2019 10:59 »
Hi again. My conversion to a tacho drive setup on my '61 SR continues.

I've refurbished the pump, replaced the cork on the breather (the rotating valve only just engages with the peg on the gear), and now I'm repainting the dynamo (keeping 2 bands unpainted for earthing), fitting a new dynamo strap etc.

Btw - isn't getting the old strap pins out a nightmare ? The slots were chewed and I had to cut the strap and drill holes through the pins to gain any purchase.

I tried to buy everything I thought I'd need ahead of time so bought an 'idler pinion oil seal', 67-708 which turns out to be a cork washer. I can't see an obvious home for this. Should I have fitted it on the shaft before fitting the inner timing cover ? I can't see it going behind the sprocket on the other side - it'd be chewed up in no time. There was no sign of anything like this when dismantling - but there again there was one other important part missing too (washer twixt crank pinion and oil pump worm).

So, do I need to take the inner timing cover off again, or us this seal typically not fitted ?

Thanks for your help as always,


Online berger

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Re: Idler pinion oil seal
« Reply #1 on: 18.06. 2019 13:32 »
yes it goes behind the dynamo drive sprocket

Offline Swarfcut

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Re: Idler pinion oil seal
« Reply #2 on: 18.06. 2019 13:44 »
BSA use cork because it is relatively easy to compress. The cork washer goes under the big dynamo drive sprocket, sandwiched between the raised boss on the inner cover and the underside of the sprocket. It is not really an oil seal, it's more of a thrust washer, and when assembled will remove any end float on the idler pinion shaft. Treat it to a smear of grease before assembly, to prevent friction burning on first start up before the grease in the dynamo cavity works its way down.

 There are various thicknesses of cork washer available to go between  the camshaft drive gear and the breather sleeve, the drive peg should be well located into the breather sleeve. Choose a thickness which ensures a reasonable seal without any camshaft end float, but not too thick to load the sleeve against the inner cover and put strain (and friction) on the inner cover as it is tightened down. You can rub a thick washer down on a sheet of abrasive paper to get a nice comfortable fit. This washer pushes the back of the cam gear against the  cam bush, and controls the cam end float, which should be zilch.

 If the cover has been worn, likewise the breather sleeve, this could be the reason for the poor engagement. Have a look for evidence of a wear ring on the face of the sleeve, caused by too much load in a previous life. Quick fix is new parts or just a new longer drive peg....messing with the outer cam bush alters the lateral position of the cam, so is a no-no.