Oil in cylinder

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
vigo
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Oil in cylinder

Post by vigo »

Gents,
I've opened a new post as this problem was tacked on the end of "suspect carburettor".

Yes, oil in cylinder, lots of it. Head off again and wet and dry the head with a glass pane as backing, suspecting head deformation. No difference, starts and runs rough for a few seconds until oil puts the fire out.
The copper part of the composite gasket is being distorted away from the spigot in short time, seconds. Could the presence of the oil be causing hydraulic action on the gasket? The oil is then spread across the gasket surface.
Believing now that oil is coming from below past the rings and have been advised from a chap I think knows his stuff, to hone the cylinder and fit new rings. There is no apparent wear at top of +40 cylinder but suspicion is the cylinder could be worn oval and honing would do the job.

Any of you gents any thoughts on this?
Mick D
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Re: Oil in cylinder

Post by Mick D »

Hi

The damage to the head gasket is more likely to be caused by cylinder pressure when running, for it to be the oil 'hydraulicing' the head would need to be full of it at TDC. It's more likely to be the spigot, if you have one, bottoming out on the head, or a warped head and there being reduced 'squeeze up' on the gasket.

The oil could be coming from below but that's the last place I'd investigate. I''d start by blocking the flow to the rocker box and seeing if it improves things, don't run it for too log but a minute or so will be OK. If things improve look to the inlet oil feed, the screw should have a pointed head and be backed off 1/6 of a turn from nipped up. If that's OK check the valve guides and stems for wear.

Check the crank case breather is functioning, you should feel pulses of air coming out of it as the bike is kicked over.

Does you bike have an oilway up through the cylinder? if so check it's integrity at the head joint.

Then whip the cylinder off and check the ring gaps.

Regards Mick
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clanger9
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Re: Oil in cylinder

Post by clanger9 »

Oh dear, it's STILL doing this?
What does engineer's blue tell you about the mating faces? It's as if it's not clamping the gasket properly...
1989 Moto Morini Dart 350
1993 Ducati 750SS
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spitfire
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Re: Oil in cylinder

Post by spitfire »

The first thing you need to do is chuck that composite gasket in the bin. They cause no end of problems when they don't fit properly and they come apart quite easy.
Get a solid copper gasket which the club now sells.
If this does not cure the problem then it might be the piston rings are badly worn. You should be able to feel the lack of compression when you kick it over if it is the rings.
vigo
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Re: Oil in cylinder

Post by vigo »

20210424_131226.jpg
Thanks Gents,
I've attached 2 pics. The one with more oil was after running for about 2 mins the second was only 20 secs after trueing the head. Posted earlier the gasket squeeze is about 0.7mm so the spigot isn't bottoming.
The amount of oil ingress before the pump has barely time to reach the head and oil quantity in the cylinder leads me to discount v. guides.
I could try blocking the oil feed between barrel and head to rule out ingress from above completely, even across the gasket.
There is vertical scoring in the barrel and no hone marks. Then I'll progress to the barrel and as you suggest ,measure the ring gaps.
The engineers blue didn't reveal much, but after some work with a fine grade to take out all marks and imperfections there was an even contact all round.
Copper gasket, now the embarrassing bit. I knackered the one you gave me Paul. I tried to anneal it with something akin to a flame thrower, it's all I had, exit one cu gasket. There is good compression measured with kicking over.
Ps note the cu hasket starting to "egg" away from the spigot after only 2 mins running.
The more recent file is too large to attach, but a less oil version of one shown.
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clive
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Re: Oil in cylinder

Post by clive »

i am not convinced you are right about the spigot not bottoming. If the gasket is as it was when you took the head off then oil has spread everywhere across your gasket, this suggests it is not sufficiently compressed. My guess is that the copper part of the gasket (which is thicker) is being compressed sufficiently to give you compression but it is then bottoming out on the spigot and insufficient pressure is being put on the rest of the gasket so allowing oil to escape from the internal supply to the head. I had exactly this problem on a pair of cylinder heads for a G11CS, a PO had had the heads skimmed and as a result the spigot bottomed out on both. Having a little more clearance machined into the heads sorted it all out.
clive
if it ain't broke don't fix
vigo
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Re: Oil in cylinder

Post by vigo »

That was my direction of thought Clive before I ruined my only Cu gasket.
Anyway I've been busy, head back on but as suggested, I blocked the oil feed to the head completely. Put alu foil over oil feed hole in the barrel underneath head gasket.
Started no problem and lasted for about 6 seconds. Head off, swimming! Took the barrel off and gapped the top ring, 0.029" (0.75mm) . I haven't checked yet but that seems excessive. I don't think there's any doubt now the oil is coming from below.

How can I check the crankcase breather without running the engine? I'd like to remove it and take a look. This design is reported to be adequate for the 250cc but not really up to the G5.
SPRIDDLER
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Re: Oil in cylinder

Post by SPRIDDLER »

vigo wrote: Wed Jul 14, 2021 11:26 am .....I blocked the oil feed to the head completely. Put alu foil over oil feed hole in the barrel underneath head gasket.
Just interested - I've no L/W experience but........

If the gasket wasn't squashing sufficiently to seal the oil feed I suspect that the (1/2 a thou thick?) piece of alu foil wouldn't seal the feed either. :?
'There is a tide in the affairs of men
Which taken at the flood............'
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dave16mct
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Re: Oil in cylinder

Post by dave16mct »

Once you get another solid copper gasket, have you thought about opening up the oilfeed hole (in the gasket) to fit a Viton O ring? I've done this very successfully on the twins.
Dave.
vigo
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Re: Oil in cylinder

Post by vigo »

Good tip with the viton seal and Cu gasket.
Took more measurements with ring and bore. The ring gap measured at the cylinder top where there is no travel is 0.027" and maximum gap anywhere else is 0.031" a difference of 0.004" which doesn't seem much when attributed to both cylinder and ring wear. Does mean however, that the gap when set up was very generous.
There is vertical scoring but no lip to be fealt at the top, this is looking more and more like honing and new +0.04 rings.

The Alu foil blocking the oil feed was doubled so might be a thou and was underneath the comp gasket. The gasket underside was dry, no oil.
What do you guys think?
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