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 clanger9 » Mon May 01, 2017 9:55 pm

You must be getting proper frustrated with this! :headbang:

Does it smoke from cold, or just after it's been running a while? If from cold, suspect the valve guides.
If only when warmed up, then I'd be looking for signs of over-oiling to the top end. They really don't need much oil up there.

Have you tried it with the oil feed to the top end turned right down? Does this make it smoke less?
1966 AJS Model 14 250 CSR "cafe racer"
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Re: Blue Smoke on decel and accel

Postby Matchymarty » Tue May 02, 2017 4:35 am

Thanks Clanger9,
Well, really, it doesn't smoke when it's cold. Well, not that I've noticed, as I don't really accellerate hard or have the chance to see it on overrun when it's cold. That said, it doesn't smoke on start up when cold. it DOES, when it's hot, always with a nice plume of blue smoke.

I haven't tried tightening down the oil feed screw, but have been thinking I should. It's the only thing that makes sense. There's only so many places the oil can come from.
I have checked it, and it's only wound out 1/6th of a turn, but will wind it in a bit and try. If that's it, and it works, I'll feel like i've won the lotto. But I'll take the head off and get it de-coked and start fresh.
Cheers.

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Re: Blue Smoke on decel and accel

Postby bjorn » Tue May 02, 2017 9:35 pm

Marty,
Just some thoughts.

2 - 3 thou clearance inlet valve stem to guide is OK.
I set my inlet oil feed screw 1/6th turn open. F.Neils book says "screw home lightly the regulating screw, then unscrew it the smallest amount possible and retighten lock nut."
Could it be that oil is leaking past the OUTSIDE of the valve guide. This can happen if the guide is loose in the head. This is not always easily detected as the guide can sit fairly tightly in the head at room temperature, but be loose at operating temperature, due to the differential expansion between the cast iron guide and aluminium head. On earlier models the guide would drop into the inlet port, but yours has a circlip to keep it in place.

The small bolts on the rear cap of the oil pump bore can come loose. This will lead to loss of vacuum and pumping capacity for oil return to the tank. The resulting oil build-up in the crankcase will cause excessive oil consumption and smoke.

It is possible to fit the guide pin for the oil pump plunger the wrong way round in its hollow screw. If the end with the reduced diameter is against the pump, the stroke of the plunger will be reduced and thereby also the scavenging capacity.

Hope you manage to sort it out.

Bjørn

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Wed May 03, 2017 4:08 am

Thanks for the ideas Bjorn.
I've screwed in the oil feed screw all the way, and will try and test ride today. I'll also check the pump covers. Good thinking there ;)
Marty

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Mon Jan 15, 2018 9:07 pm

UPDATE: 16 Jan 18.

Last few rides prior to Xmas '17, I was getting increasingly annoyed and embarrassed by the smoke pouring out of the back of my '55 G80CS. Also, consumption of 100ml of oil per 60 miles is a little on the expensive and ridiculous side.

I pulled the engine down on the 23 Dec. Bore scored, and rings had mysteriously all aligned their gaps to the timing side and gudgeon pin. There was distinct evidence of mild seizure / over heating. I took the barrel and piston to the engineer and he took one look and said that all was no good. Piston could be cleaned up ... but the bore needed to go to next size. Luckily I took him a +.060" piston.

Decided to get the piston 'ceramic coated' to help with heat control and make it slippery - ie. Less likely to seize.

Long story short, started running in yesterday nice and gentle, all running sweet. 8 Miles. Last night, another 12 miles in the cool, and all going nicely. This morning, another 10 sweet miles, then I turned around and noticed smoke following me. 100 yards before home, Charlie the Compy snuffed it. I couldn't restart, as it seemed that the plug was most likely oiled up.

That is to say, there is oil coming from the plug hole.

Note. During run in i set the intake valve oil feed as per book.

I just don't get it. I'm becoming super upset by this bike, and this is now the 3rd rebore and piston in 5500miles. I'm guessing I'm going to have to pull the barrel off and see what's what. So demoralised right now. I was prepping to go to rallies again this year starting at end of Feb, and now this has just put me back again.

Whhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyy!

Can 'TOO MUCH' oil be in the head and get down into the combustion chamber? Can sump/crank case pressure cause this? Or, are the rings just crap, and don't seal? Or, does the 2 mins that she runs on start up with no oil pumping cause this? ( tried to prime by pouring oil down plug hole, and pushrod tubes prior to first start)

I'm at a loss. and Don't want to run it again until I see what's going on. Getting VERY Tired of this. I just want my bike to run nice and not burn a hole in the ozone layer and my missus' nostrils when she's following me.!!!

Heeeelp!
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Re: Blue Smoke on decel and accel

Postby Mick D » Tue Jan 16, 2018 10:03 am

Hi

I've just skimmed through this history - did you ever run without the crank case breather? can you confirm it breathes, (ie. can you feel pulses of air from it when the engine is running?

Sounds like a breathing issue to me.

Regards Mick

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Re: Blue Smoke on decel and accel

Postby bjorn » Tue Jan 16, 2018 11:11 am

Hi Marty,

Sorry to hear you still have problems with the bike.

I agree With Mick D that it seems like a (crankcase) breathing issue. Assuming you have now fitted the thin metal disc to the crankcase breather, you should be able to feel pulses of air coming out of the breather pipe when you start the engine. Also, an open (breather) pipe from the rocker box cover, if used, will negate the proper working of the crankcase breather and may also cause oil to build up in the cylinder head.

Another possibility is that the oil return to oil tank is not working as it should. This would lead to the accumulation of oil in the crankcase and more oil being picked up by the flywheels and flung up to the cylinder/piston, causing smoking:
--Back-pressure on the oil return pipe, could be caused by the felt filter being clogged (or incorrectly cut or fitted if new) or the oil tank breather pipe being clogged.
--Oil pump not working properly or scavenge line to crankcase sump (partially) blocked.

What oil are you using?

regards
Bjørn

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Re: Blue Smoke on decel and accel

Postby SPRIDDLER » Tue Jan 16, 2018 11:56 am

Cripes, Marty, you've been struggling with this for over 18 months!

'That is to say, there is oil coming from the plug hole'.


Clutching at straws here and I've no first hand knowledge. However, I haven't spotted any reference to the make of your piston but some piston compression rings are tapered and should be fitted the correct way up, otherwise it seems they can 'pump' oil on the cylinder wall upwards.
Do you mean that oil is coming from the plug 'ole when running or when you kick th'engine over with the plug out?
I poke badgers with spoons.

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Wed Jan 17, 2018 12:49 am

Mick D wrote:Hi

I've just skimmed through this history - did you ever run without the crank case breather? can you confirm it breathes, (ie. can you feel pulses of air from it when the engine is running?

Sounds like a breathing issue to me.

Regards Mick


Funny you mention that Mick, - I do believe it is working, as it seems to spit a bit of oil out. Also, strangely, when i had the motor apart the first time, i replaced the breather disc with an original 'round' one, in lieu of the installed one which had pac man chomps out of the disc. I Now suspect there may have been breathing issues previously....

Will confirm when I run it tonight.

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Wed Jan 17, 2018 1:06 am

Bjorn,

Yes, have thin disc. As per previous reply I will try running the bike again tonight to confirm correct operation of breather.
I DO have a Webco vented (breather) pushrod adjustment access cover. Should I block this off?

I shall also drain the sump and see how much is in there. I will check the oil tank breather, but pretty sure it's fine - well the hose is, whether or not there's any issues with blockages in the breather pipe in the tank, i'd have to check.

I use Penrite HDR50, which is an Australian straight 50 grade mineral oil which most Aussies use in their old bikes etc.

Spriddler -

My previous piston was a Wellworthy, and currently using a JP Piston (Aust) rings. Top two rings do not have an up or down, ie. no rebates or chisel shape to ring. Oil ring is 'solid' as in 1 piece ring, with slots cut in it, and also does not have an up direction to my knowledge. In anycase, my engineer gaps the rings and installs them on the piston for me, as he know's the rings and pistons well, and that way I don't stuff up which way they go on. Current 'new piston' is a JP +0.060" and has been ceramic coated.

As for the oil coming from the spark plug hole, the oil seems to seep past the plug during running. Now, the first 18-20 miles, this did not seem to happen. Only on returning after 30 miles had been done, and the bike stopped and wouldn't restart, did I notice the oil on top of the head and surrounding the plug.

Thank you all... I hope I can sort this bleedin' bike out, and hoping I haven't destroyed another rebore and piston.

As for the crank case breather, it always seemed to push oil out of the long hose I had finishing near front of back wheel. Always made a mess. Does this mean too much oil in the sump?

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