Clutch cover oil leak

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Clutch cover oil leak

Postby BrumLoz » Tue Dec 31, 2019 12:41 pm

Can anyone help please. just recommissioning a 1959 Model 31 and investigating a rather large oil leak, and on removal of the clutch cover I see there is a hole below the alternator cable outlet which goes to fresh air (as in image). I this must be the reason for the oil leak. There must be something missing to blank of this hole off I presume. Can anyone shed some light on this.
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Re: Clutch cover oil leak

Postby dave16mct » Tue Dec 31, 2019 1:53 pm

I don't know if you're familiar with these twins but here's a few tips to keep the chaincase reasonably dry. When first starting up don't top up the oiltank until you have run the engine for a good few minutes. Then check the oil and top up if necessary. Never leave the bike on it's sidestand for long periods.The level of oil in the chaincase only needs to just touch the very bottom of the primary chain. You can block that hole up with a rubber bung but only a small drip should come from there.
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Re: Clutch cover oil leak

Postby 1608 » Wed Jan 01, 2020 7:18 pm

The hole is for the wiring from a crankshaft mounted alternator, when fitted. And, I may be wrong but the primary chain looks a bit tight, may be wrong though.

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Re: Clutch cover oil leak

Postby McBob » Thu Jan 02, 2020 3:27 am

I also run the alt wiring out through the lower hole, sealed with a grommet. The upper hole is shrouded and with the correct oil quantity hopefully only the slightest mist will escape.

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Re: Clutch cover oil leak

Postby Mick D » Thu Jan 02, 2020 7:30 am

Hi

I'm with McBob here - the top hole is the breather and the bottom the access for the alternator wiring via the dedicated grommet:

Alt Grommet.png


Regards Mick
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Re: Clutch cover oil leak

Postby BrumLoz » Thu Jan 02, 2020 8:06 am

Many thanks for the help, I understand now the wiring was put in the vent hole. Will check the chain tension as well. Will rebuild and see how it goes. :D

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Re: Clutch cover oil leak

Postby electrajohnt » Fri Jan 03, 2020 2:46 pm

Mick D wrote:Hi

I'm with McBob here - the top hole is the breather and the bottom the access for the alternator wiring via the dedicated grommet:

Alt Grommet.png


Regards Mick


On mine someone in the past has sealed the top hole with some kind of soft silicon type material. From what is said here seems like I need to remove that sealer, is the hole just left open or is there a breather pipe to somewhere? (or do need to put a breather pipe to somewhere as a modification).
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Re: Clutch cover oil leak

Postby Mick D » Fri Jan 03, 2020 4:16 pm

electrajohnt wrote:On mine someone in the past has sealed the top hole with some kind of soft silicon type material. From what is said here seems like I need to remove that sealer, is the hole just left open or is there a breather pipe to somewhere? (or do need to put a breather pipe to somewhere as a modification).


Hi

As far as I am aware there never was a breather pipe attached, the shielding boss and casting were designed to prevent oil escape.

You can leave the orifice blocked with silicon if you want to, the case will still vent via the main shaft access.

Me? - I'd unblock it as per design.

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Re: Clutch cover oil leak

Postby robcurrie » Sun Jan 05, 2020 1:29 pm

It's not a good idea to block the breather hole, the engine breathes into this cover and if blocked, it will pressurize the cover and possibly cause the oil to leak out the joint and clutch opening.
When I first got my CSR, a previous owner had blocked it with a bolt and nut and the cover visibly bulged when revving the engine.

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Re: Clutch cover oil leak

Postby electrajohnt » Sun Jan 05, 2020 6:01 pm

Given the advice above I shall remove the silicon plug. Thanks'
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