Blue Smoke on decel and accel

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Re: Blue Smoke on decel and accel

Postby Matchymarty » Fri May 13, 2016 3:22 am

UPDATE: Piston bought @ +20, rebore in process, and hopefully re-assemble next week before the weekend.
Fingers crossed it holds together then. :)
Thanks all for help.

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Thu Jun 23, 2016 2:34 am

UPDATE #2:
All rebuilt, and run in complete. Loads more power and no smoke. Success!
Loving my '55, except for all the liquid coming out of her! ahahahaha.
Thanks for all your help.

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Sat Nov 12, 2016 11:52 pm

#Update 3.
3000 miles, copious amounts of blue smoke, on decel, accel, and idle.
1. No decernable smoke when started from cold. While engine is warming up and I'm riding along, doesn't appear to smoke much if at all.
2. Once warm, smoke whilst going along, pipe is soaked and wet, plug is wet and oily, smokes big on decel & accel and smokes a bit all time.
3. After idling at traffic lights, then heading off again, huge plume of smoke engulfs entire town.

Just pulled top off, rings appear fine. Definitely signs of piston against bore rubbing on RH side, front and back of bore and piston. Minor only and can't 'feel' anything in the bore. Honing marks still visible.

Oil comes out of bottome end of this engine everywhere. Between the cases, out of sump plug, and Including engine bolt holes. I'm beginning to think Oil pressure problem, as it consumes around 1L per 100 miles.

In process of removing chain case to inspect Crank Case relief valve.

How do I know if the crank case relief valve is working? I just removed it and it seems fine, not overly dirty or anything.. and the diaphram, is not the usual disc one, it seems to have petal shapes cut out of it.
Starting to look like the rest of the engine needs to come out... and check all the oil passages.... ??

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Re: Blue Smoke on decel and accel

Postby petert120r » Sun Nov 13, 2016 10:31 am

I'm not that knowledgeable on singles but the symptoms sound very similar to a problem with a G11 rebuild I recently completed. Fired up fine when cold then smoked more and more as it warmed up, eventually oiling up a plug. I'd fitted new pistons to rebored barrels and checked the valves and guides which were fine. Oil pouring out everywhere - dynamo to crankcase joint, drain plug, even the timing cover.

Eventually turned out to be the flap valve on the end of the crank. Instead of the original someone had fitted one with a ball and spring which didn't allow the engine to breathe into the primary case, instead forcing the oil up past the pistons and anywhere else it could escape to. Replaced it with the correct one and all problems solved.

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Re: Blue Smoke on decel and accel

Postby SPRIDDLER » Sun Nov 13, 2016 11:42 am

Matchymarty wrote:.
copious amounts of blue smoke, ...... pipe is soaked and wet, plug is wet and oily, smokes big ....huge plume of smoke engulfs entire town.

Oil comes out of bottome end .... Between the cases, out of sump plug....
Starting to look like the rest of the engine needs to come out


Probably.
I poke badgers with spoons.

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Sun Nov 13, 2016 9:45 pm

petert120r wrote:I'm not that knowledgeable on singles but the symptoms sound very similar to a problem with a G11 rebuild I recently completed. Fired up fine when cold then smoked more and more as it warmed up, eventually oiling up a plug. I'd fitted new pistons to rebored barrels and checked the valves and guides which were fine. Oil pouring out everywhere - dynamo to crankcase joint, drain plug, even the timing cover.

Eventually turned out to be the flap valve on the end of the crank. Instead of the original someone had fitted one with a ball and spring which didn't allow the engine to breathe into the primary case, instead forcing the oil up past the pistons and anywhere else it could escape to. Replaced it with the correct one and all problems solved.


Thanks Peter,
I've checked my crankcase relief valve and it seems fine, however, I'm not sure if singles have a 'flap valve' as I can't seem to find reference to one in the parts lists. ??
Marty

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Re: Blue Smoke on decel and accel

Postby bjorn » Sun Nov 13, 2016 9:55 pm

Marty,

You wrote
"How do I know if the crank case relief valve is working? I just removed it and it seems fine, not overly dirty or anything.. and the diaphram, is not the usual disc one, it seems to have petal shapes cut out of it.
Starting to look like the rest of the engine needs to come out... and check all the oil passages.... ??"

I would guess your crank case relief valve is not working. The petal shaped disc you have appears to be much thicker than the very thin disc that should be there. The normal disc does not have much (axial) space for movement. Probably the thicker petal shaped disc is actually jammed against the outlet hole in the crankcase. Result: no breathing, but a gradual build-up of pressure in the crankcase due to piston blow-by resulting in a pressurised crankcase which will leak at any and every joint.

Measure the thickness of the petal disc and see if it has free axial movement.

regards
Bjørn

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Re: Blue Smoke on decel and accel

Postby bjorn » Sun Nov 13, 2016 11:21 pm

Marty,

Here is a picture of a G80CS breather valve. The disc is only 0.25mm thick. I believe the ones now supplied by the club are slightly thicker, 0.4mm?
Notice the "witness ring" where the disc has impacted the breather hole in the crankcase. Also the disc has a slightly smaller diameter than the aperture it fits in, it is meant to be a sloppy fit so it can move back and forth even if there is some oil present.

Bjørn
G80CS breather valve.JPG
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Re: Blue Smoke on decel and accel

Postby Matchymarty » Mon Nov 14, 2016 1:16 am

bjorn wrote:Marty,

Here is a picture of a G80CS breather valve. The disc is only 0.25mm thick. I believe the ones now supplied by the club are slightly thicker, 0.4mm?
Notice the "witness ring" where the disc has impacted the breather hole in the crankcase. Also the disc has a slightly smaller diameter than the aperture it fits in, it is meant to be a sloppy fit so it can move back and forth even if there is some oil present.

Bjørn
G80CS breather valve.JPG


Thanks Bjorn, strange that mine is 'petal shaped'. The one in my '56 is similar to the photo you posted.
In any event, I guess if mine is clear, it should be working, unless there is an oil gallery or hole somewhere else blocked. Oil return to my tank works fine, so I'll strip the cases this afternoon and see if the relief hole in the case is blocked or not.

Any other ideas where to look for blockages that cause crank case pressure build up?

Cheers.

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Re: Blue Smoke on decel and accel

Postby robcurrie » Mon Nov 14, 2016 3:39 am

The oil return to the tank might be better than usual if it is helped by crankcase compression.
Rob C

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