Oil leak, suspect gearbox

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Oil leak, suspect gearbox

Postby Griffy » Tue Jun 04, 2019 9:05 am

I recently acquired a G5 from a friend, and since it had not been serviced for a while renewed the oil in the engine and topped up the gearbox according to the manual.. just below the inspection cap. Since doing so the bike has leaked fresh oil (which is why I suspect the gearbox) when left for a while. Any ideas on what may be causing the leak?

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Re: Oil leak, suspect gearbox

Postby Ozmadman » Tue Jun 04, 2019 9:22 am

Has the level dropped in the box? normal places for the box would be the kick start or gear change shafts and the rear main seal at the other end (possibly oil running down the centre stand)
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Oil leak, suspect gearbox

Postby clanger9 » Tue Jun 04, 2019 2:04 pm

"They all do that, sir" :roll:

Seriously, leaks from the kickstart or gearchange shaft are common. If there's nothing visible from the kickstart end, then it's probably leaking from the rear seal (as Paul says).

Despite what the owners manual says, there's a service bulletin that says correct oil level is 1/2" below the oil filler hole:
http://archives.jampot.dk/technical/Ser ... cation.pdf

That could well be correct. Mine leaks noticeably more if I fill it right up to the top, so I leave it between 1/4"-1/2" below and it barely leaks at all...
1966 AJS Model 14 250 CSR cafe racer
1989 Moto Morini Dart 350
1993 Ducati 750SS

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