Timing cover leak

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Timing cover leak

Postby Oggers » Fri Apr 19, 2019 2:04 pm

Curses. It all was going so well on the test ride post rebuilding the speedo and sorting out the wet sumping, until after about 5 miles when it started leaking oil - quite alot - from the offside timing cover join - again! Same place - at the top edge about an inch forward of the barrel. I took it off previously, emery paper/wet/dry as much as I saw fit, and then applied two layers of Wellseal and another on the crankcase side. Obviously no joy, so rode home after right boot and the rear of the bike became covered in a film of hot oil.

Some Qs

Is this normal? I find it surprising that it should leak at the top edge - rather than the bottom. Is it pressurized in any way inside?
How tight should the cover screws be? I didn't want to damge the cover by over-tightening any...
Not entirely convinced by Wellseal. Would the blue Hylomar or similar be an improvement?

Many thanks again

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Re: Timing cover leak

Postby ajscomboman » Fri Apr 19, 2019 2:18 pm

It's not common but I have seen it on a few twins and 1 of mine suffer from the same issue. Wellseal and the like I don't bother with now. I simply clean the faces off with thinners and then smear a very fine bead of clear silicone on the cover and then assemble. Provided it's only a bead thick enough to seal and without excess there is little to no risk of any going into the motor. 30 odd years of using this method have proved the case.

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Re: Timing cover leak

Postby Mick D » Fri Apr 19, 2019 2:27 pm

Hi Oggers

The timing cover should not be pressurised in any manner, if the joint is faulty it will leak from that point, Hylomar won't be any improvement on Wellseal in my experience.

If you don't have the means to flatten the faces I'd make a gasket to suit, gasket paper is available on line but it may be worth proving the concept with clean card.

Great weather eh, had the G3 out :D

Regards Mick

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Re: Timing cover leak

Postby Oggers » Fri Apr 19, 2019 4:20 pm

Chaps

Thanks for that - all good stuff. Tempted by the silicone. Its still on Castrol 20/50 for engine oil, ordered GP50 so maybe that will help.

I noted the pressure relief valve is near the leak....any link here?



Mick - yes, fantastic weather. The idea today was a run out to Ballater planned for my day off - foiled again :headbang:

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Re: Timing cover leak

Postby Oggers » Sat Apr 20, 2019 2:52 pm

Thinking about, I think a more accepatable engineered solution would be the gasket paper! Advice on what thickness appreciated. Since last, filed and sanded down the mating facte on the cover - seems beetter. If anything the leaking edge is now very slighly raised - it leaves oil on the mirror....most of the rest does not.

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Re: Timing cover leak

Postby Mick D » Sat Apr 20, 2019 3:53 pm

Hi

To be honest, I'd use whatever I had available - think cornflake box thickness.

I'm pretty sure the rocker cover gaskets on my FH were 'Frosties' packets.

Regards Mick

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Re: Timing cover leak

Postby Oggers » Sat Apr 20, 2019 6:29 pm

Mick

I assume it has a cereal number then? Thanks for the info....1 mm thk seems cheap enough on fleabay....

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Re: Timing cover leak

Postby 1608 » Sat Apr 20, 2019 11:03 pm

The most important thing is to make sure Both mating faces are flat. If the screws have been over tightened then the mating faces will have a raised portion at those points. Also the screw holes on the crank case face will be slightly raised too. Then only a relatively thin gasket will suffice. Using a too thicker gasket can lead to distortion.And yes the close proximity of the prv will have an effect in that area.

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Re: Timing cover leak

Postby Groily » Sun Apr 21, 2019 5:52 am

I've always made gaskets and I've usually used Flexoid paper, about 12-15 thou thick from memory. Never gone as fat as 40 thou / 1mm.
Can't say I've never had leaks and weeps, but most often in my life it's been the dynamo joint that has caused the most hassle. Now and then over the years a barrel base gasket has weeped too.

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Re: Timing cover leak

Postby Oggers » Sun Apr 21, 2019 10:42 am

Well, 1mm thk Flexoid ordered. I'll give it a try c/w some Wellseal. I am still unsure why it leaks where it does. I can understand it leaking at the bottom near the pump unions, but not at the top if it is not pressurized within.....I do hope the crankcase breather is OK.

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