Author Topic: Hello from Rob Roy and help please with a leaking Timing Cover  (Read 1730 times)


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hi Folks

My name is Rob, I have a 1961 A10 super rocket.
The engine has been modified with a twin carb head fitted.

Since I bought the bike I have had a problem with the outer timing case spewing oil - via the dynamo cork gasket.
I believe that this is due to the face of the outer timing cover not being flat, and have refaced the outer surface, and may well reface the relevant joint surface on the inner cover.

I understand that the pressure relief valve vents to the timing cover.  I am not sure quite how the oil pump picks this oil up - does it flow into the sump or does the pump pick it up directly.

Any knowledge would be gratefully received.



Offline a10gf

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Hello and welcome. I hope the forum will get you all the help you may need.

If I get it correctly, your dynamo chain 'chamber' fills up? Apart from issues with gasket\surface between outer\inner cover, have you checked the condition of the cork seal (and the condition of idler pinion's bronze bush) behind the large dynamo drive sprocket?

Oil passing trough the relief valve will flow to the sump again, taking care of supplying f.ex. the camshaft on the way (the valve is there to secure a good oil pressure trough the crankshaft > main bearing > big ends, after the crank gets what it needs, the rest is 'relieved to other parts of the engine).


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Online trevinoz

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Rob, I think the oil relief vents through a gallery and via drillings lubricates the timing gears and the camshaft lobes with the oil falling into the sump where it is picked up by the scavenge pump and returned to the oil tank.
You should not have oil in the dynamo chamber, it is sealed off from the timing chest by the timing cover gasket and a cork seal behind the drive sprocket. I have never been able to fit the supplied cork seal to any of my engines, so I leave it out. I have had no problems with oil in the dynamo chamber.
If oil is spewing out, it seems as you have crankcase pressure forcing oil into the chamber. Is your timed breather sealed to the camshaft pinion with the correct thickness cork washer and is your breather clear to the atmosphere via the hole in the crankcase at the drive side end of the camshaft tunnel?

Offline shabashow

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Hi Rob,
you might want to check whether there have been any previous modifications to the timing cover. I suffered from a terrible oil leak from the cork gasket due to holes having been drilled though the dynamo chain area into the inner timing case area by a previous owner. For what purpose, I can only guess at, and assume it was to get more lubrication to the chain. I got the holes sealed up, and the iming cover, especially the cork washer area, are completely leak free.
See my previous posting - holes in timing cover.


  • Guest
Hi Folks

Thanks for your input.  My main suspect was the joint between the two timing covers, but i think there is a chance that the the idler gear / dynamo pulley bush is worth a look.

i am intrigued about the PRV overflow.  With the inner timing case cover off, is it possible to poke a wire through the breather ways, just in case.



Online bsa-bill

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I would keep a wire well out of it but if you have an airline a blast of air will show you where it exits or even an oil can with a fine nozzle and pump some oil through.
I had this trouble once and it proved to be my fault as I had renewed the idler gear bushes and got them the mixed up, resulting in one having the scroll the wrong way so the it scrolled oil into the cavity instead of away from it.

All the best - Bill
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco