Dynamo seal leak 55 G9

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Re: Dynamo seal leak 55 G9

Postby Mick D » Sat Jul 20, 2019 4:50 pm

Hi Oggers

To me it seems like you're chasing a solution rather than the problem.

The extra washer will reduce the pressure at which the filter by passes, (I think), and blocking the prv could result in over stressing the pressure pump. I'd look for a reason yours is leaking whilst many others don't rather than dicker with the lube system.

Regards Mick

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Re: Dynamo seal leak 55 G9

Postby Oggers » Sat Jul 20, 2019 5:09 pm

Hi Mick

Bypass pressure should remain the same. I haven't tinkered about with the PRV spring. What will change is the pressure at which oil enters the engine at start up - lower hopefully - and will thus reduce the chance of pressure build up in the filter tunnel, hopefully reducing the chance/duration of the PRV relieving. Besides I prefer oil in the engine rather than in the timing case....

I know its a bit of a bodge, but dynamo seal has been apart 3 times now! Still think the jets of oil possibly directed towards it from the PRV holes are one possible root cause. We shall see.......

Cheers...

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Re: Dynamo seal leak 55 G9

Postby Groily » Sun Jul 21, 2019 5:45 am

It's hard to know with this particular problem. But I don't think tinkering with the valves in the system will solve it, unless there is something very wrong.
On one of mine, the dynamo joint has been a pain in the proverbial on and off for over 40 years.
To eliminate the possibility of the prob being at the crankcase joint on the filter tunnel, I made an alloy plate to blank off the timing cover, so I could run the engine for a good bit with the dynamo off. That proved that the cases were tight.
But the leaks at the seal could be awful as soon as the dyn went back on.
Tried O rings, + or - cork, paper, you name it. Followed all suggestions from all and sundry in quest for oil tight. Replaced dyn oil seal, replaced dyn bearing retainer plate in search of better fit, tried dynamo off my other twin (which is much better in this department), tried all potions and lotions from jointing compound people various. Also looked at pressure relief valve (early type that isn't captive on this engine). And the filter end cap bits, same as you are. But nothing to see there sir, and all correct.

The thing can be oil tight - but it takes in this case a very substantial gasket on the dynamo, with some goo. I make a 'laminated' gasket out of one of the heavy duty materials like Klingerite, several layers of, gooed together. This usually works for a few thousand miles, sometimes longer, before there's any tell-tale weep. The timing cover joint to crankcase doesn't leak, there's no evidence of excessive oiling in the timing case itself, . . . it has just been, always, THAT joint on THIS engine. Ever since 1976!

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Re: Dynamo seal leak 55 G9

Postby Oggers » Sun Jul 21, 2019 1:09 pm

Tinkering with the valves may relieve the amount of oil horsing through the PRV plunger and subsequently directed to the (IMHO) weak dynamo seal - which I cannot believe was designed to withstand any amount of hot oil pressure very well. As Groily states, I do think it is a hopeless design, so anything I can do to reduce the loading on this seal may help. Post this morning's ride, still one or two drips - but definitely reduced. Whether this is due to a better dyanmo seal or my valve modifiations I don't know.

I do agree with Mick that all my slight modifications are not the cutting edge of advanced root cause analysis, and some folks may have no issues at all - for some reason. As I don't know what those reasons are, then I am forced into plan B.

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Re: Dynamo seal leak 55 G9

Postby Groily » Sun Jul 21, 2019 3:49 pm

It might, yup. Be interested to hear more in due course after more running time, esp with some rpm, hot.

Other makes with forward-mounted dynamos with the gear running in oil seem to be less troubled, and they, such as Triumph, don't have their prv adjacent like ours. . . .
But in my own case, even suppressing the prv completely so it couldn't operate didn't stop mine leaking at this pesky joint.

I even thought of modding the dynamo's drive endplate to use a second stud as near as poss opposite the single draw stud provided, with a nut in the timing case. But a PITA to do, and means the dyn wouldn't come off without removing said case and probably the dyn drive pinion 'n all. . . which isn't so very clever.

At the moment I am oil tight here on my '54, but know it won't last for ever. The '61 650 is just starting to weep if the motor is given a lot of beans, after a long period of continence. I don't regard her as a 'problem' in this area, or at least, not like the 500! It seems to me that it's the beans that do it, unfortunately. I can run all day at 50mph on the 500 or at 60 on the 650 and nothing to see; up it to 60 and 70 maybe on the bigger one, and things can start to happen if they're going to. First indication being when boot slips off gearchange rubber owing to slime being present! Once it's started, the problem doesn't go away again, and I end up with oil under the length of the dynamo, then sucked into brush end, then notice reluctance of filthy dynamo to cut in on starting her up. A well-worn path I fear, hereabouts. And well up there on my list of the things that I wish were a bit different.

Nevertheless, I really like the pernickety beasts, as we owners will insist on doing!

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Re: Dynamo seal leak 55 G9

Postby Mick D » Sun Jul 21, 2019 5:18 pm

Hi

Being more problematic when giving it the beans could suggest a breathing issue to me.

Is there a good illustration of the twin oil system anywhere? I'm struggling with AMC's terminology.

Regards Mick

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Re: Dynamo seal leak 55 G9

Postby MalcW » Mon Jul 22, 2019 7:55 am

A friend of mine has recently acquired a Model 20 that a PO has fitted a timing cover breather to, at the top rear of the cover. Perhaps this is the reason? It should be on the road very soon, so we'll find out the leak situation.

Malc

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Re: Dynamo seal leak 55 G9

Postby SPRIDDLER » Mon Jul 22, 2019 8:03 am

Twin oiling (640x311).jpg


I'm twin-ignorant but is the above relevant?
You do not have the required permissions to view the files attached to this post.
I poke badgers with spoons.

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Re: Dynamo seal leak 55 G9

Postby Oggers » Mon Jul 22, 2019 9:03 am

A friend of mine has recently acquired a Model 20 that a PO has fitted a timing cover breather to, at the top rear of the cover. Perhaps this is the reason? It should be on the road very soon, so we'll find out the leak situation


Yes - I thought of that too, but surely the crankcase breather "should" take care of any pressure build up problems within the timing case? Again though, I fear it comes under the heading of bodges to be considered, rather than root cause and fixing properly.

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Re: Dynamo seal leak 55 G9

Postby Groily » Mon Jul 22, 2019 9:34 am

Probably not an issue on a '55, I think? Hole will be there?
I'm not sure the crankcase flapper breather is that effective tbh, esp at revs (as Mick hints). I have a big bore one on my 650 straight off the timing cover near the mag, and I do think it helps, whether it ought to or not! But could just be just imagination of course. That engine gets serious beans, and is reasonably continent at the dynamo usually. The 500 gets fewer beans, but leaks more often.
Any excess pressure sure won't help, but not that easy to tell if there is or isn't. When I've been at the far end of piston and ring life (which I have been a few times over 100s of 1000s of miles) I haven't thought 'oh heck, the dyn leak's getting worse'. So . . . just dunno!
I've just got used to redoing the joints now and then, when they start to make enough mess to annoy. While being a teenzy bit jealous of other people's that don't do it!

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