Dynamo seal leak 55 G9

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

Postby Oggers » Sun Jul 14, 2019 11:18 am

Gents

I think we are finally getting there with my troublesome steed, but one thing that is not going away is the leak between dynamo/timing case. If you recall, upon seeing evidence of a leak in this area - principally oil around the interface, under the dynamo when removing it, and oil dripping from under the bike after a run - I removed the dynamo, new cork gasket installed, plenty of silicone, and reassembled. Oil leaks still seen after a run....

So, of it comes again, another new cork gasket installed - with a slight notch made for the draw bolt, plenty of silicone on all mating faces, press the dynamo tight against the timing case - length of wood on other end of the dynamo and jack against the wall to press it up tight - tightened up the strap as much as I dare, went for a run today. Same horrible drips!

Questions.

You may recall the leak on the timing case earlier - now fixed by making a timing case gasket. All fine here now. I also later stripped the primary chain case and took a look at the breather valve whilst in there. All seemed well. Spring OK, small cross-shaped blind/plate seemed OK and free to move. Is there anything else that could feasibly increase the pressure in the timing case unduly, thus causing the dynamo seal to leak?

Is there a path from the crankcase to the timing chain case that could cause over-pressure if the crankcase itself is over-pressurized perhaps?

I guess I'll have to do the dynamo seal again - 3rd time lucky perhaps. Any further tips would be most welcome.

Otherwise all good. Fine handling bike, pulling better now it has run in a little......

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Re: Dynamo seal leak 55 G9

Postby Mick D » Sun Jul 14, 2019 11:36 am

Hi Oggers

A bit of a long shot but next time you have the dynamo in your hand check that the shaft / drive gear is running concentrically.

Regards Mick

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Re: Dynamo seal leak 55 G9

Postby ajscomboman » Sun Jul 14, 2019 1:02 pm

Are you 100% certain that it is the dynamo leaking and not the oil filter gallery missing the paper washer between the crankcases. If that's missing, cracked etc the oil will weep out of the joint under the dynamo and will be seen as a drip under the front of the motor.

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Re: Dynamo seal leak 55 G9

Postby Oggers » Sun Jul 14, 2019 5:05 pm

Are you 100% certain that it is the dynamo leaking and not the oil filter gallery missing the paper washer between the crankcases. If that's missing, cracked etc the oil will weep out of the joint under the dynamo and will be seen as a drip under the front of the motor.


In short, no! and thanks for the enlightenment. To confirm, and pardon my ignorance, This is the filter housing in front of the engine holding the foam filter with the NRV/ball valve at the drive side? If it does leak from here, then (and I dread the answer) is there a simple cure? - splitting crankcases is not my definition of simple by the by....

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Re: Dynamo seal leak 55 G9

Postby ajsph » Sun Jul 14, 2019 5:40 pm

I had the same problem with oil leaking around the dynamo, and I found that the oil was seeping between the shaft on the armature and the spacer between the gear and bearing, the spacer was a loose fit on the shaft, and I gave the shaft a little smear of RTV silicone, and it cured the problem.
Poul

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Re: Dynamo seal leak 55 G9

Postby ajscomboman » Sun Jul 14, 2019 6:34 pm

Oggers wrote:
Are you 100% certain that it is the dynamo leaking and not the oil filter gallery missing the paper washer between the crankcases. If that's missing, cracked etc the oil will weep out of the joint under the dynamo and will be seen as a drip under the front of the motor.


In short, no! and thanks for the enlightenment. To confirm, and pardon my ignorance, This is the filter housing in front of the engine holding the foam filter with the NRV/ball valve at the drive side? If it does leak from here, then (and I dread the answer) is there a simple cure? - splitting crankcases is not my definition of simple by the by....


The felt filter, yes it is and no it's not an easy fix as the motor has to come out. I'd definitely try looking at Poul's suggestion first and then if it's not that decide if it's bad enough to contemplate a strip or wait till the winter.

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Re: Dynamo seal leak 55 G9

Postby Oggers » Tue Jul 16, 2019 5:55 pm

Right - had a look at oil filter gallery - nothing obvious, similarly dynamo - nothing obvious there either. Oil present under the dynamo again. Whilst the dynamo is out, I took the opportunity to start it up and see if there was anything obvious in the crankcase under the dynamo - again nothing obvious. However, not a great deal of time to check as oil came flowing out of the timing case in what seemed to be significant amounts.

I am therefore reasonably convinced it is the dynamo timing case interface causing the problem. If I am thinking right, the pressure relief valve is nearby, and I guess there is considerable splash effect from the oil bursting forth from wherever into the timing case and then to the sump. It just seems a good deal of pressurized oil for a simple cork gasket with only modest compression to deal with.

Also, harking back to the issue with the leaking timing case on the top edge beforehand, it is suggestive that oil is gushing forth at too high a pressure from the relief valve and perhaps it is the relief valve that is the root cause.

As ever, thoughts welcome.

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Re: Dynamo seal leak 55 G9

Postby clive » Tue Jul 16, 2019 10:57 pm

Have you actually got a pressure relief valve? They seemed to come and go according to the year. If you havent and my 58 G11 came without then it is almost certainly the crankcase leaking from the filter tunnel. Resolution for me was fitting the paper gasket for the filter tunnel between the two halves of the crankcase and modifying the timing side to take the later pressure relief valve. Required fitting of the later filter too.
clive
if it ain't broke don't fix

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Re: Dynamo seal leak 55 G9

Postby Oggers » Wed Jul 17, 2019 1:41 pm

clive wrote:Have you actually got a pressure relief valve? They seemed to come and go according to the year. If you havent and my 58 G11 came without then it is almost certainly the crankcase leaking from the filter tunnel. Resolution for me was fitting the paper gasket for the filter tunnel between the two halves of the crankcase and modifying the timing side to take the later pressure relief valve. Required fitting of the later filter too.


Clive

Yes- its a 55, and I've seen it! Plunger thing with a spring. Reading a little more, oil is delivered to the tunnel with the felt filter, pressure builds, ball valve on the drive end opens, and allows oil into the engine etc. thence return to the sump. I appear to have a PRV within the timing case on the other end of the filter tunnel which POSSIBLY may be relieving prematurely - which with all the oil splashing that results, may explain the difficulty with the dyanmo seal very close by.

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Re: Dynamo seal leak 55 G9

Postby Oggers » Sat Jul 20, 2019 3:22 pm

Right - I have grasped the nettle. I've decided I don't like the PRV design! What I think is happening is that when relieving oil pressure at start - or anytime else, the plunger is pushed off its seat, oil escapes at pressure through the plunger bore, out through the two small holes in the plunger, into the timing case. The jet of oil from these two holes will be quite severe, and if directed at the dynamo gasket, I can easily see why it leaks round there. So - I have blocked one hole off, and have re-inserted the plunger so the remaining hole faces downwards away from the dynamo.

The other thing done is at the other end of the filter housing - felt filter within - I have increased the width of the fibre washer which holds the cap/plug for the spring for the ball valve. The thinking here is that this reduces the pressure on the spring, therefore on the ball slightly, reducing pressure in the filter housing and therefore reducing the propensity for the PRV to relieve. Filter is clean by the by....

Testing will commence when it stops raining!

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