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Oil pump to timing case seal

Submitted by chris_brewer on Monday, 18 August, 2025 - 09:59
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I have just become the new owner of an es2 1953 on starting and running the engine there seemed to be excessive amounts of oil coming from the the timing case breather, I removed the cover to se if there were any obvious problems and thought that the fibre washer that provides a seal between the pump and the casing seems rather hard, when looking through some parts lists I noticed that one shows a domed rubber seal, is that correct for this model year? This is my first British bike and I would welcome any advice from you experienced guys.  

Submitted by ian_soady on Monday, 18 August, 2025 - 10:01

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... is standard but I always used the rubber one on my ES2 as I felt it made a batter seal as modern fibre washers tend to be pretty incompressible.

I'm with Ian. S on this one.
after much measuring, testing and checking I found that the rubber seal designed for the twins goes straight in. No modifications needed. 

Also as per Ian McD's photo I fitted a 3/8 " non return valve to the engine breather. It created such a vacuum that no oil was making its way to the timing chain.  I have to lubricate it manually before a big ride. ( very easy to do).
Don Anson 
Melbourne  1956 ES2

Submitted by peter_shand on Tuesday, 19 August, 2025 - 11:37

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If your engine was designed to use the fibre washer the clearance will be incorrect for the conical rubber seal. I know Mike Pemberton modified the timing cover to accept the rubber seal (or an O ring) and i have done the same when rebuilding client engines.
The timing case breather is actually the magneto chain casing breather. If you are getting loads of oil there it could be an indication the cam bushes are worn
I don't know about using batter as a seal, Good on my fish & chips though 

Submitted by ian_macdougall on Thursday, 21 August, 2025 - 17:21

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I now punch the pump washer out of Viton sheet. More compressible than fibre, oil & heat resistant, and available in a range of thicknesses.
My 1956 19S also leaked copiously from the timing case breather. Eventually sorted by attending to all of the following areas:
Oil pump seal, as above.
Cam shaft bushes, as mentioned by Peter.
Timing case pressure relief valve. Make sure that the ball seats correctly and that there is sufficient pre-load on the spring (maybe replace it). If the valve opens at too low a pressure it will flood the timing chest.
Engine breathing. I have replaced the ball valve on the crank case drive side with a compression fitting, drilled out match the pipe bore (more air flow on piston down stroke, less pressure build-up). At the end of the short tube pointing towards the gearbox sprocket I have fitted an in-line reed valve.
Breather

Thanks Peter,Ian for your responses, can the wear in the bushes be gauged by measurement and if so what should the clearance be.

A new bush would be reamed to fit the shaft, just so the shaft can rotate freely, approx 0.001"
max. What clearance can you measure there? If your getting .005 to .010" clear they are worn and so passing excess oil into the mag chain case  

Following the advice from everyone I have replaced all of the items in the timing case including the bushes, I have reset the ignition timing using a timing light from the magneto guys. I now have another problem, whilst I was waiting for parts to complete the timing case issue I replaced the kick start return spring which seemed a little weak and would not return the kick start to its fully upright position, this seemed to go without issue until I tried to start the bike after completing the timing case work, the kickstart became very stiff and would not return, as suspected on examination the spring had come out of the locating hole in the inner casing. I have refitted it and it seems to be working ok without the outer case fitted, it is an AMC box No N5156 Im not sure whether there is something I am missing as it,s difficult to see from the parts list, is there a dedicated parts list for a 1953 AMC gearbox.
Many thanks for all your help so far.

Submitted by chris_brewer on Saturday, 30 August, 2025 - 12:52

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Replaced Kick start return spring, started the bike second kick no oil leaks and it ran nicely however return spring has again removed itself from the hole in the inner case. I'm thinking of adding a bit of an angle on the tang of the spring to make it a tighter fit and to give it a bit more purchase.

Submitted by peter_shand on Saturday, 30 August, 2025 - 20:13

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1953 bike, should have a laydown box. Are you sure its an AMC box? Has the box been fitted with a kickshart shaft that has two holes in it. The new shafts have two holes to cover the different model boxes. An AMC box has a peg that the spring anchors to, and a hole in the shaft that the other end fits in.
Photo please of what the box innner cover looks like. 

 



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