Stupidity causes oil leak, but from where?

Information relating to the Matchless G12 or AJS Model 31 650cc twin
BruceB
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Stupidity causes oil leak, but from where?

Post by BruceB »

My G12, which is really trying my patience cos after fixing yet another fault after I thought I had them all, it has developed a pretty bad oil leak.

It sat over the last couple of months while the tank was away for repair (again) and ended sitting in a pool of oil, mopped this up and refilled the oil tank. This was the stupid thing as the oil on the floor looked worse that it was and most of the oil was in the engine.

Started her and run her up a few hundred yards and back and opened the oil tank to check the level, oops, tank totally filled and pressurised. Drained the extra oil out and run it up and down with the oil at the right level. Now, obviously because something has let go, I had a constant drip of oil.
I had had a camera up in the area and cant trace it. its somewhere in the drive chain area coming down the back of the chain case and dripping off the bottom.
The oil is also very grey even though it has only done a few miles since it was changed. I drained and changed it again and within seconds it was the same grey colour, not sure why this would be but it is a horrible colour even for used oil. Bike starts and runs fine if I don't mind an oil line behind the bike ( I am not exaggerating, you can see the oil line up the driveway up to the puddle in the garage)
Anyway, the question is, where is this likely to be coming from, the chain case is empty and I cant see it without stripping either the gearbox and/or the engine out.
Any thoughts on where it is likely to be coming from, nothing higher up that the sprocket seems to be wet.
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
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1608
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Re: Stupidity causes oil leak, but from where?

Post by 1608 »

Grey colouring of the oil suggests to me that there is a chafing or contact btn alloy prts, possibly in the primary chain case. Have you tried running the bike without the chaincase.
If the bike wet sumped then the c/case could have filled up. Leaking oil from anywhere above the filter tunnel ( and they are the more common leak areas on twins ) ie. behind the dynamo cylinder base gasket etc. and would be fairly obvious.
SPRIDDLER
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Re: Stupidity causes oil leak, but from where?

Post by SPRIDDLER »

BruceB wrote: It sat over the last couple of months while the tank was away for repair (again) and ended sitting in a pool of oil,
Odd that it should start leaking so badly whilst unused. Presumably it didn't used to leak/drip/flood before it stood whilst the tank was off. I know little about twins but whilst not in use perhaps a relief valve could've become stuck open/shut.............. :?
'There is a tide in the affairs of men
Which taken at the flood............'
BruceB
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Location: INVERNESS-SHIRE UK

Re: Stupidity causes oil leak, but from where?

Post by BruceB »

Sorry, petrol tank away for repair, for the second time.
The bike runs fine with no grinding, if it was alloy being ground away then it would be holed somewhere by now. :roll:
The leak is coming down the back of the chaincase from behind the clutch and dripping off the chaincase. I remote camera inserted up inside the sprocket area has not managed to see the leak point.
It may be getting slightly less bad but will have to take the bike for another run to be sure.
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
Yves.Astein
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Re: Stupidity causes oil leak, but from where?

Post by Yves.Astein »

Sounds like the oil is coming from the Vent hose positioned behind the primary chain case. Its there for venting the chain case if it has way to much oil. Thats why its always dirty, because you are just changing the engine oil and not the oil in the chain case. But your new oil will keep adding to your chain case because the crankcase vent spits the wet sumped oil from the crankcase into the chain case.

Check out the large bottom maintanance screw ( not the small drain screw) in the primary chain Case. If oil drains out after you opened it, the you have to much oil in there. And my theorie is true. Then it's probably gray oil, and thats probably the oil that you have been seeing.

Let me know, I am curious if I am right


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JEAN-NOEL
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Re: Stupidity causes oil leak, but from where?

Post by JEAN-NOEL »

I think it is just a wet sumping.
Oil was seeping in the primary chaincase, because the level in the crankcase was higher than the centre of the crank. The pond of oïl you had Under the bike means that oïl has seeped behind the primary shaft of the gear box, between primary chaincase and the rear chain sprocket.
You have now to drain the sump, and also the primary chaincase.
When you ran the engine after refilling the oïl tank, i think that oïl was blowed by the vent, on the tank, and the oïl in the sump was blowed into the chaincase, et c.
Thousands of topics are explaining the various causes of wet sumping...Generally oïl leaks in the crankcase from the oïl pressure pump. There is no relief valve : the one in the filter cap is here only to keep oïl in the camshafts/cam followers tunnels.
On the scavenge pump, the amount of oïl is only the quantity existing in the hose. On the pressure side it is the whole oïl tank !
BruceB
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Re: Stupidity causes oil leak, but from where?

Post by BruceB »

Feedback for the leak.
I had originally looked in the central inspection cover and could see no oil with a torch looking down, even while it was still leaking. The leak definitely was getting less as the bike was run but hadn't stopped.
After removing the drain plug in the drain case and draining about 300ml of oil the leak stopped, or at leak subsided to the usual drip and oil engine bottom.
It seems that it was simply oil seeping across from the sump, even though it looked low enough when originally checked.
On taking the bike to the motorcysle club tonight I got stopped by plod on the way home, no lights! The speedo light was on but no headlight. Looks like a dicky switch so obviously the new switch I put in 30 miles ago has went.
They were fine about it, on the streetlit roads I couldn't tell the light was out, really noticed it when I turned into my back road, the last 1/2 mile is country and no lights or houses!
I am starting to think the bike is hexed, used to things going wrong on an old bike but not every single time I used it! :evil:
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
MalcW
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Re: Stupidity causes oil leak, but from where?

Post by MalcW »

BruceB wrote:I am starting to think the bike is hexed, used to things going wrong on an old bike but not every single time I used it! :evil:
It's called 'Character'! My bike has lots of character...

Malc
BruceB
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Location: INVERNESS-SHIRE UK

Re: Stupidity causes oil leak, but from where?

Post by BruceB »

Its not my only older bike, nor is it even the oldest I have ever had. It is however the most unreliable and fragile.
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
Reynard24
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Location: CAMBRIDGESHIRE UK

Re: Stupidity causes oil leak, but from where?

Post by Reynard24 »

You are correct , the bike is cursed. I'm fairly sure from one of your previous posts that it's a bike I know and during my acquaintance the clutch fell off and the PRS8 switch was always dodgy.
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