lot of smoke after rebuild, Help Please

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Groily
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Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: lot of smoke after rebuild, Help Please

Post by Groily »

"With only mounted cylinders and without the heads you can notice that the movement of the piston trough the kick starter pulls upward oil and the oil is going up past the pistons."

In the very first post in the thread Clive - but maybe I misunderstood what Maurizio was saying. Is why I didn't think it was (primarily anyway) a metering jet or top end over-supply problem.
Cheers,
Bill
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clive
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Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: lot of smoke after rebuild, Help Please

Post by clive »

Groily wrote:"With only mounted cylinders and without the heads you can notice that the movement of the piston trough the kick starter pulls upward oil and the oil is going up past the pistons."

In the very first post in the thread Clive - but maybe I misunderstood what Maurizio was saying. Is why I didn't think it was (primarily anyway) a metering jet or top end over-supply problem.
Cheers,
Bill
you did a better job that me in interpreting that Bill. I think you are right if the oil was being pulled up past the pistons with only the kickstart then the rings are the place to start.
clive
if it ain't broke don't fix
Mick D
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Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: lot of smoke after rebuild, Help Please

Post by Mick D »

Hi Maurizio

Have you raised your concerns with the manufacturer of the pistons? - would you care to share their response?

Regards Mick
maurizio66
Posts: 20
Joined: Sat Mar 26, 2016 7:34 pm
Location: italy

Re: lot of smoke after rebuild, Help Please

Post by maurizio66 »

I sent a few email to AMOC and raised the issue and kindly he told me that I could send pistons and rings back and he could sent to the JP and see what they said, but at this point I prefer to wait for the BMW rings that seem to be good quality 1 compression cromed and oil scraper 3 pieces, and try to adapt if needed. When I am ready I will keep you informed,

thank you all, Maurizio
g5wqian
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Location: wiltshire
Location: near swindon wilts

Re: lot of smoke after rebuild, Help Please

Post by g5wqian »

hi maurizio ;
i was wondering if you have JP or GPM pistons and rings .
i am presuming you are using JP and not GPM .

i have an AJS model 30 i have recently fitted new rings to , but i had also fitted new pistons and rings one year ago as well , i got them from the club spares but they are GPM made in italy .

mine are +040" oversize .

i had to remove the cyl heads and barrels again recently due to an oil leak at the top end caused by using some solid copper head gaskets which i bought from the club but they were too thin, ie 0.93mm instead of the 1.5mm they should have been , so i changed them for the standard composite head gaskets from the club and at the same time i honed the bores and replaced the rings again .

because i had to hone the bores out by +.006" for piston running clearance i found that the 040 rings were gapped wide at .028" , so i put a set of .060" compression rings in and filed the gap to .012" .
the oil rings are from an .040" set and have the wider gap .

i noted that the oil ring had a bevel on one edge only this year when i bought them but last year the oil rings had a sharp edge both sides .
there should be a photo attached of the way in which the rings came in the packet from GPM so i am presuming they are fitted in this way, and i have them fitted like this in my bike at present .

i have my bike running and have ridden it 130 miles in the last 2 weeks and it runs fine and very little smoke on startup .

on the 2 times i have rebuilt the upper engine and then started it for the first time i did get a fair amount of smoke for the first amount of time running the engine up but it cleared after a few minutes , and also after riding it for a few sessions on 50-70 mile trips i find only small amounts of smoke appear just at times when i either start the engine or when i leave it idling and then rev it up and pull away, but this is only a puff or two of smoke and nothing else .

i started the engine today after not using it for 3 days and it only smoke for the first minute or so of running and to be honest most of that was probably moisture and not smoke .

if you are using GPM pistons or want to use them then i dont see you having any problem when running .005" clearance even if you are using the same size overbore rings as opposed to doing what i have done here with the compression rings .

my engine actually runs much nicer now with the thicker composite head gaskets back on as opposed to the thin copper ones and it doesnt leak oil from the mating surface between cyl head and barrels , it revs much more crisply on the throttle and doesnt pink going uphill [ and i dont have octane booster in now but i did before] on 97 octane unleaded fuel .

my compression test from when engine was first assembled was 135 psi each cylinder [10 kicks on kickstart] , that was before i ever started the engine up

my engine was previously running very rich so i have set the needle on the top position so it is at its lowest , and then re adjusted the idle mixture to suit , but also i am now using champion N5C spark plugs because the N4C were staying black , and i will keep using the N5C until i have run the engine in and then maybe play around with others in the summer if i find they get too hot .

with the n4c i was getting a lot of carbon built up , so running a hotter plug i am thinking might reduce this [along with lower needle position also] .

i hope you get the problem sorted soon but maybe if you have the time try running the engine for a while and see if the smoke goes away after a while of running it .

i didnt really see any oil coming up the bores when i assembled the engine and turned it over , but there obviously was a fair amount of oil used for installing the pistons and rings which needed burning off at first startup .

on my bike i only had to tickle the carb and it went on the first kick over , but i know thats not allways the case with every bike .

regards
ian
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