Timing cover/dynamo leak 55 G9

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Timing cover/dynamo leak 55 G9

Postby Oggers » Wed May 06, 2020 7:21 pm

Once again I dive into that awful abyss that is my rubbish joint twixt dynamo and timing cover. You may recall several moons ago me going through several of the cork gaskets, plus silicone, plus tightening of the dynamo, plus many more tweaks etc ad infinitum to get the blessed thing oil tight. It worked - for about 200 miles or so - but sadly has reverted to type, and now beginning to deposit that familiar unseemly oil drip onto the pristine surface below. Not at all good when it is fresh white concrete on someone else's driveway let me tell you!

Pretty sure it is not the crankcase joint. I cannot see much there - so back to the dynamo. Frankly, I think the cork seal is utter pants. The inner is an especially poor fit round the dynamo boss, and the stuff is pretty incompressible - meaning little sealing abilty when the dynamo is pushed home. Therefore options as below

O- ring - I like O rings! Pliant, compressible (is that a word?), seal well, good chemical resistance etc. Present cork gasket inner is @38mm by 4mm thick. So, O ring of inner diameter 38, perhaps 37? and 4 or perhaps 5mm thick would appear to suit? Thoughts very welcome. Has anyone tried an O-ring here?

Thick gasket material - I have some about 8mm thick. It is akin to high density foam, compresses down to 3 or 4mm, but hard to cut to an exact circle as per the cork gasket. Due to its high pliability I guess it does not need to be exact as I suspect it will deform quite well when the dynamo is pressed home.

More cork gaskets - I may have been unlucky in my supplier, but I feel as if I am not getting very far here.

Thoughts much appreciated as ever

Kind regards

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Re: Timing cover/dynamo leak 55 G9

Postby Groily » Thu May 07, 2020 6:46 am

O ring is a quite common option and works for many people. Like you, I have been plagued by leaks in this department on my 500, for most of a lifetime! Sometimes I have made a 'laminated' gasket of two bits of klingerite-type material, sometimes used the standard part, sometimes O rings, always silicon sealant. At the moment all has been oil tight for a while using an O ring, but I can't remember any fix lasting more than about a year or several thousand miles on that one.
Assemble not tight initially, with silicon goo, let goo go off, tighten draw stud and then the strap, and it might behave . . .
By contrast, my 650 doesn't suffer from it to any serious degree. (Swapping dynamos between the 2 doesn't improve things, either, on the leak-prone one.)
It is a poor design - even pristine machines often show traces of oil mist down there - with far too small a contact area, especially where the draw stud comes through. Dynamo-equipped Trihards and Notruns with the same general arrangement aren't nearly as bad from my own experience - and Beesa twins have a dry compartment for the dyn drive in the timing chest and are fault-free. (Well, as long as the chain doesn't eat the insides of the thing!)
But I convince myself it's a small price to pay for the other pleasures of owning these things! It goes along with the use of too-fine 2BA screws for the timing cover, an inaccessible arrangement that needs double-jointedness and little-girl hands for getting the seats on and off, inability to get a rocker shaft or pushrod out without removing at least one cylinder head, horror show of getting the tank-mounting bolts in (assuming there's any thread for them to enter), terrible tin primary cases . . . etc. But for all that, we still love 'em 'cos they are such great machines to ride and the really important bits are so reliable!

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Re: Timing cover/dynamo leak 55 G9

Postby Oggers » Thu May 07, 2020 9:28 am

Groily

Yes all agreed. I have subsequently ordered a suitably sized silicone rubber O-ring. Usually these things compress really well and deform to seal on compression. Hopefully when I push the dynamo home, then the ring will compress far better than the cork to improve the sealing capability. I'll also order up some nitrile O-rings if these fail. I'll also smear some silicone sealant around the O-ring as I did on the cork gasket, plus all other tips as per previous posts with regard to holding the dynamo in place.

The bike is indeed a rather fine machine otherwise - which makes the oil leak all the more annoying.

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Re: Timing cover/dynamo leak 55 G9

Postby Oggers » Thu May 07, 2020 8:54 pm

Another thing I noticed, and possibly mentioned in previous posts, is that under the dynamo boss - the seal cover I think - the thing that actually mates with the timing cover over which the gasket goes - is a film of oil. I wonder if it is leeching behind the pinion somehow and behind this cover, There is nothing to suggest it is getting into the dynamo. Bit of silicone here I feel........

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Re: Timing cover/dynamo leak 55 G9

Postby Oggers » Mon May 11, 2020 9:14 pm

Right - some confirmation required please from folks who know better than me. Silicone/rubber O -ring went in twixt dynamo and timing case. Bit of slicone sealant, usual tighenting up and pressing home of dynamo- seemingly a good snug fit obtained. Ran the bike for 8 or 9 minutes. Still leaks! However, what I did not notice in the past is that on pulling of the (nearside) black cap of the dynamo, I now find about a teaspoon of oil within - which subsequently leaks out of the cap at the join with the dynamo body.

Therefore

Can I reasonably assume that it is not the joint between dynamo and timing case cover that is at fault here?
Can I reasonably assume that somehow oil is getting into the dynamo - presumably along the dymano shaft, into the cap.
I think there is a seal at the pinion end - so again, I assume that may be a first port of call.
I seem to remember that pinion is a swine to remove - hints welcome - and I have no puller!

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Re: Timing cover/dynamo leak 55 G9

Postby Mick D » Tue May 12, 2020 5:49 am

Oggers wrote:Can I reasonably assume that it is not the joint between dynamo and timing case cover that is at fault here?

Can I reasonably assume that somehow oil is getting into the dynamo - presumably along the dymano shaft, into the cap.

I think there is a seal at the pinion end - so again, I assume that may be a first port of call.

I seem to remember that pinion is a swine to remove - hints welcome - and I have no puller!


1. Yes

2. Yes

3. Not all dynamos have a seal at the drive end, check the Lucas documentation in the archive for the exact configuration of yours, however, the original drive end bearing was an unshielded one, now you can get a double shielded replacement which would prevent the passage of engine oil through the bearing.

4. If it doesn't move easily source a suitable puller - you know it makes sense.

Regards Mick

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Re: Timing cover/dynamo leak 55 G9

Postby Groily » Tue May 12, 2020 6:27 am

Should be a collar on the armature spindle, drive end, with oil seal sitting on it, in the bearing cover plate on the end of the dyn. If the collar is mullered after being grabbed in a vice etc, then can leak; also seal can wear out of course.
Wouldn't say necessarily that oil at commutator end means the problem is the crankcase joint or 'something else'. Oil from a leak at the joint on the timing cover can quite often work its way across the motor and into the brush end, making you think the worst (I've got the T shirt for opening a crankcase when the joint there wasn't the problem - ouch ouch!). But there IS a lot of pressure on the oil filter chamber joint when the oil is cold, it can't be gainsaid, so it might be worth looking at the pressure relief valve of whatever sort you've got? (Not sure if yours is the non-captive one with the spring that falls on the shed floor and gets lost, or a captive one.)
The pinion is a parallel fit, keyed, and can be tight. Not a perfect solution, but I have in emergencies grabbed the pinion in soft jaws (as in thick ali) to protect the teeth, and put a bolt (- not the big-headed special screw) to full depth down the thread, and tapped the shaft out that way. Otherwise, really needs a knife puller to do it easily.

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Re: Timing cover/dynamo leak 55 G9

Postby Oggers » Tue May 12, 2020 8:48 am

Mick/Groily

Once again many thanks for the replies. All useful stuff. I think I am persuaded that the leak is coming through the dynamo rather than at the timing case interface so that at least is helpful. As regards sorting that, if there is a seal then happy days and I can get a new one and/or the shielded bearing as Mick says. Incidentally - where from! Are there dynamo guys you can recommend here? I also noted in a previous post that a smear of RVT silicone on the shaft may also help, which seems to make sense.

Sp;ring loaded PRV is on the timing case side, and if I recall, failrly close to the dynamo pinion. Been down this route before and I seem to recollect all was working as it should.

...and yes, I will get hold of a puller!

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Re: Timing cover/dynamo leak 55 G9

Postby Mick D » Tue May 12, 2020 9:53 am

Hi

If you refer to the attached, (page E12):

http://archives.jampot.dk/technical/Ele ... 6-1957.pdf

You will see the dynamo which was originally fitted would have been pn 20035, an E3L - go back to page E7 for a breakdown of installed parts, (bearing dimensions are on pg E2)

Regards Mick

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Re: Timing cover/dynamo leak 55 G9

Postby Oggers » Tue May 12, 2020 1:44 pm

Mick

Stunningly good info - many thanks. Mine appears to be a E3L-LI-C or so its is stamped on the body. Sheilded bearing seems a very good idea. Still not sure if it has a seal as Groily describes - but I guess I'll find out when I take it apart!

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