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Techniques: Matchless / AJS Chaincase Seal Mod

Even if you are a technical know-nothing, the shed need not be a scary place. Honest. PaulG80 proves this by venturing forth to cure the chaincase leak on his Matchless...

Do you own a pre-1958 AJS or Matchless? Do you have a leaky chaincase? I would suspect that if the answer to the first question is yes then the answer to the second question is also yes.

[FW concurs; 'The early 500s suffer from the unsealable AMC tin primary chaincase, and leak their oil. There are many and various cures for this, including pouring molten tallow into the chaincase, allowing it to set, then adding oil!']

As most of you probably know, I am the proud custodian of Matilda. She is a 1960 Matchless fitted with a 1953 engine. I am also proud possessor of an oil leak from the pressed steel chaincase. Due to this leak I have already lost one primary drive chain so I thought it was time do something about it. If you are a member of the AJS & Matchless Owners' club then you will be familiar with Jampot, their most excellent monthly journal. Hidden away on the services and trade page is an advert for an oil-and heat-resistant neoprene seal for the tin chaincase.

At this point I would like to point out that I have no connection with the supplier. I ordered the said item and received it two days later. Marvellous service.

'My medium is light.' Nice pictures.

Sunday morning dawned bright and dry so I took myself off to the garage as She Who Must Be Worshipped was at work. I thought I would share a technical article with you and do a product test at the same time. (Now if you are expecting Humbernut levels of skill then switch off now as I am have a large coned hat with a 'D' on it that I wear in the garage). This is Paul.

So first job (after making sure the mug is filled with tea/coffee) is to remove the centre nut. Next remove the left hand footrest. Then undo the screw that holds the clamping band together and remove the band. This will reveal your hopefully original seal. The original seal has an upside down V profile. Remove this article and place it carefully in the waste receptacle, as you won't be needing it anymore. When you inspect the new seal it has a T profile. This enables each side of the case to be sealed with rubber in between them.

Next, clean all remnants of sealant and such like that have been used in the past off the edges of the case. Now fit the seal to the inside case. You will notice that the seal stays in place! Next, remember to fit the spacer on the centre stud -- this is very important as otherwise you will find it when you have finished and have to take the case apart again.

New seal in place

Right that's in place. Now fit the outer case into the seal -- it's a little fiddly but it can be done. Fit the centre nut until it's finger tight. The outer band now needs to be reattached and fixed. Now do up the centre nut nice and tight. (You did fit the spacer, didn't you?).

Quality British engineering.The footrest needs to be refitted next and, presto, job done. The case needs to have some oil inside it. All that's needed now is quick wipe down. You may now award yourself a tea / coffee / beer after a job well done.

Just to check I left it an hour and went out to the garage and not a drip dripped.


Get your seal from:

  • GW Buckingham, 152 Blue Boar Lane, Sprowston, Norwich, NT7 8RY
    Send a cheque for 7, which includes p&p.

    And don't forget to join the AJS & Matchless Owners' Club cos they can help you out with all sorts of other tech tips for AMC bikes:


    More Tech Tips?

    Can I do my 'blown a seal' gag now?

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