AJS Model 30 Oil Leak Cured

Information relating to the Matchless G11 or AJS Model 30 600cc twin
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Dale
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AJS Model 30 Oil Leak Cured

Post by Dale »

I thought that other members might be interested in how I cured the oil leak on my 1956 Model 30. I bought the bike twelve months ago with a terrible leak from the oil filter chamber. Having only owned AJS/Matchless singles, I wasn't familiar with the twin engine. After doing some research I discovered that the usual problem was the omission of the small gasket between the filter chamber. After removing the engine, I found that the gasket was indeed missing, so I carefully fitted one and re-assembled the engine. After a test run, the filter chamber leak was a lot better, but the rest of the crackcase joint was leaking. I said to myself that this can never work because the gasket effectively acts as a wedge at the front of the joint. So, I removed the engine again and made a complete gasket from 0.4mm oil paper (1/64 inch),using the RH side half of the crankcase as the template. This proved to be a straightforward job provided you have patience and use a new blade in a scalpel.
Use a jointing compound such as Permatex or Wellseal. Coat the LH crankcase, leave to go off for about ten minutes and apply the gasket. Then coat the other half of the crankcase, leave to go off and carefully offer it up and assemble. This has now completely cured the oil leak and I have a nice, dry engine ( on the outside,of course!).
Groily
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Re: AJS Model 30 Oil Leak Cured

Post by Groily »

The late, great and superbly well-informed 'Biscuit' - see loads of posts - would have agreed with you. He suggested using a material called Hallite (I think) to make just what you describe. I and probably many others have used thin gasket paper + Wellseal, with excellent results too.
To be fair, the thin gasket round the filter chamber joint IS thin, and with a bit of Wellseal or Hylomar all round, can often work just fine. I think the condition of those mating surfaces is the critical factor - any dings or nasties or distortion and there's going to be trouble; and it's a big pain to fix after the engine has been completed. Probably one of the many reasons a lot of people prefer the singles! (And are happy to wrestle with dynamo chain perils, worn oil pump plunger bores and a few other of THEIR little foibles - dig, dig, ha!). Cheers, Bill
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Dale
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Re: AJS Model 30 Oil Leak Cured

Post by Dale »

Many thanks for your comments, Bill. You might like to know that I have also sealed the dynamo flange as well, by using the correct graphited gasket in addition to the cork ring plus a smearing of Permatex or Wellseal. Even the primary chaincase is sealed by using the new type of band available from the club!
Happy Riding,
Dale
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dave16mct
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Re: AJS Model 30 Oil Leak Cured

Post by dave16mct »

The downside is....you're going to have to oil your rear chain now! :lol:
Dave.
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Samuel
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Re: AJS Model 30 Oil Leak Cured

Post by Samuel »

Dale wrote:You might like to know that I have also sealed the dynamo flange as well, by using the correct graphited gasket in addition to the cork ring plus a smearing of Permatex or Wellseal
I am aware of the cork ring.
What is this graphited gasket to which you refer?
I do not recall seeing this on any parts explosions or lists.
Sam
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bjork
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Re: AJS Model 30 Oil Leak Cured

Post by bjork »

Groily wrote: and it's a big pain to fix after the engine has been completed. Cheers, Bill
And don't I know this! Having recently overhauled the bottom end of my 650 twin, and taken the trouble to get a groove machined for an 'O' ring round the filter chamber, mine still leaks! Thought it was the filter tunnel at first (very angry at this point!) but can now see it comes from just below. Strange thing is, it seems fine when running and even for a while after stopping the engine. Overnight a little puddle appears on the floor then it stops again. So it must be something like the 'dry' sump contents or the camshaft lube well relieving itself. :evil:

I will fix it, but it's running so nicely it seems a shame to disturb it again, and there are other jobs more pressing :roll:
Using yesterdays technology to create tomorrows problems today
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Dale
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Re: AJS Model 30 Oil Leak Cured

Post by Dale »

I have looked for the dynamo gasket, but can't find one anywhere. The one I used came from an assortment of old gaskets that I had and it was the only one. You can easily make one from 0.8mm (1/32 inch) thick graphited SLS and I have attached a photo of one I made out of ordinary paper as a copy, before fitting the correct one.
P1010637.JPG
AJS/Matchless never listed this gasket, but it was common to all makes of bike that used a Lucas Dynamo.
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Groily
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Re: AJS Model 30 Oil Leak Cured

Post by Groily »

The thing I find about the dynamo joint is that we need a gasket that does its business and gets squished before the rebate on the timing side case is up tight against the register on the dynamo drive end piece (of cheese). If the cheese bottoms out before the squish happens, then there's going to be a leak. (Similar to the problem with too-thin head gaskets and spigotted barrels on twins, but less cheese there). So I make up 'laminated' gaskets from gasket paper with wellseal or whatever between the layers, until I know the gasket is categorically going to be squished without having to overtighten and strip the drawbolt thread at the dynamo. Which is more cheese-metal trouble and a pita to sort out. Graphited materials are very good for this - Klingerite etc in the old days, maybe still.
Sometimes, the dynamo is pulled very very slightly off line by the strap, which causes the joint face to go wedge-shaped - but a decent thickness of gasket & gunge should deal with that. Hopefully the mesh of the gears is slack enough to handle it too. Miine aren't perfect, but the worst they do is ooze a sort of light mist after running at high rpm, which merges quite fetchingly with road dirt to give a patina indicative of serious use, but not of neglect. Streaks of clean oil do not appear on the lower timing side crankcase, which is the objective. (Famous last words, oil will piss out tomorrow probably!) Cheers, Bill
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