G11 top end off for the first time

Information relating to the Matchless G11 or AJS Model 30 600cc twin
Various
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G11 top end off for the first time

Post by Various »

I'm just stripping the top end off my G11 for the first time (had the bike 2 years) because of an oil leak which seems to come from the left-hand base gasket (oil streaming down the back of the crank case). I expect to be putting new valve seals in as well while I'm in there.

I expect the job to be simple enough, but in your experience is there anything I should pay special attention to?

Thanks

Matthew
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Les Howard
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Re: G11 top end off for the first time

Post by Les Howard »

could this be a high pressure leak from the top of the crankcase centre line joint between the cylinders where the cam shaft feed runs? If it is, a full engine strip down is required!
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robcurrie
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Re: G11 top end off for the first time

Post by robcurrie »

...and there are no valve seals!
Best to read up about engine stripdown before putting spanner to metal, look in Christian's archive.

Rob C
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dave16mct
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Re: G11 top end off for the first time

Post by dave16mct »

Lets hope its just the barrell base gaskets. I'd recommend using Wellseal as well as the gaskets. Also you can get solid copper head gaskets with Viton o rings which I'd also recommend using. Carefull torqing of the head is needed to 22 lbs ft. Retorque next day. On the rocker boxes Wellseal to the cap and grease the other side.
Dave.
Various
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Re: G11 top end off for the first time

Post by Various »

Thanks for the feedback, taking the comments in order...

1. Crankcase centre joint seems pretty dry, fingers crossed!
2. No valve seals! Can you point me towards Christian's archive please. Is there a link somerwhere?
3. Can you tell me where I can get copper head gaskets from? Kettering?

Matthew
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Samuel
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Re: G11 top end off for the first time

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Sam
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robcurrie
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Re: G11 top end off for the first time

Post by robcurrie »

Matthew, you can get parts from the club spares: www.amoc-parts.com

Rob C
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dave16mct
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Re: G11 top end off for the first time

Post by dave16mct »

You can get the copper head gaskets from AMC Classic Spares . spares@amcclassicspares.com
You can also get thicker barrell base gaskets which may help you with this problem. :D
Dave.
Various
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Re: G11 top end off for the first time

Post by Various »

Thanks for the replies, I'll be ordering bits tomorrow.

I'm still puzzled though, I'm sure I can feel something in the exhaust port on the valve stem which is loose and rotates, it's also a bit oily. I assumed this was a valve seal, but evidently not!

I suppose this is why we work on bikes, there's the challenge and learning associated with doing it and the the pleasure (surprise) when it works out!
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robcurrie
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Re: G11 top end off for the first time

Post by robcurrie »

Sounds like a loose valve guide that is turning and leaking oil from the rocker box.

Regarding your oil leak at the back of the crankcase, first thing to check that it isn't oil from the primary chaincase. It is possible that the engine is wet sumping. When this happens, excess oil in the crankcase overflows into the primary. When the level in the primary is above the primary chain, it gets flung about and can find it's way out the breather hole (or other openings in the case) and end up running down the back of the engine.

Oil leaks can be difficult to pinpoint, I had a persistant leak that I couldn't trace, so I attended to all the likely places, but still would find oil on the bottom of the frame after a ride. Finally the culprit emerged - it was a hairline crack on the bottom seam of the oil tank and it would only leak when the oil was hot and thin!

Just another thought, there are two bolts holding the crankcase together just below the barrel on the left hand side. The forward bolt hole is an oil channel as well and there should be a copper washer under this bolt head, otherwise it will leak oil.

Rob C
Last edited by robcurrie on Fri Feb 06, 2015 6:54 pm, edited 2 times in total.
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