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 bjorn » Tue Nov 15, 2016 10:26 pm

Clanger,

"Yes, you can run an 'open' breather (into a catch tank).

This isn't as elegant as the negative-pressure arrangement (you get more pumping losses and oil leaks), but at least it works. It will also keep working when the engine is thrashed hard and/or has more blow-by from a racing piston, hence this arrangement is more common on track bikes..."

I agree, you can run an open breather but as you say it gives you more oil leaks. I would use the standard breather with the thin disc any time. I do this on my road bike (no leaks) and also on my Seeley G80CS road race bike which spends most of its running hours at 5000 to 7000rpm with no oil leaks.

Marty, from pictures you posted earlier of your 1955 G80CS it appears you have a breather pipe from the rocker box cover. This is not necessarily a good idea. The oil that drains from the cylinder head through the push rod tunnels has to pass through the "slots" in the cam follower guides. Air flow upwards can lead to excessive build up of oil in the push rod tunnels and also the head.

regards
Bjørn

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Wed Nov 16, 2016 8:02 pm

bjorn wrote:Clanger,

"Yes, you can run an 'open' breather (into a catch tank).

This isn't as elegant as the negative-pressure arrangement (you get more pumping losses and oil leaks), but at least it works. It will also keep working when the engine is thrashed hard and/or has more blow-by from a racing piston, hence this arrangement is more common on track bikes..."

I agree, you can run an open breather but as you say it gives you more oil leaks. I would use the standard breather with the thin disc any time. I do this on my road bike (no leaks) and also on my Seeley G80CS road race bike which spends most of its running hours at 5000 to 7000rpm with no oil leaks.

Marty, from pictures you posted earlier of your 1955 G80CS it appears you have a breather pipe from the rocker box cover. This is not necessarily a good idea. The oil that drains from the cylinder head through the push rod tunnels has to pass through the "slots" in the cam follower guides. Air flow upwards can lead to excessive build up of oil in the push rod tunnels and also the head.

regards
Bjørn



Interesting theory Bjorn. I've ordered correct crankcase relief valve discs, and may well shorten the pipe to dump swiftly after the exit point from the case in lieu of the existing setup with about 40cm of pipe.

As for the rocker cover breather, well, the bike came like that, and apparently a thing the USA guys used to do a lot. Perhaps I'll plug the breather, or find another standard cover and see how that affects things. I see your theory there, however, one would think, the rocker breather would not cause 'much' difference in air pressure in the crankcase, but amazing what happens I guess, and, the breather was NOT a standard matchless idea. I'll give it a go.

I checked valve guides last night, and wouldnt' call them worn. That said, there is a bit of give in them, so will have an Engineer check them. The valves and seats are quite pitted, particularly the exhaust valve, so will need dressing and seating.

It is my understanding though, that the only way excess oil can enter the combustion chamber is via the intake valve guide between the valve stem and guide?

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Thu Nov 17, 2016 8:46 pm

Further update.

Seems I now need a new piston for the '55 G80CS. I took the piston and bore to engineer to hone and gap the rings. (different engineer to the one that put a new sleeve in the barrel, bored and set the ring gaps.) He took one look at the bore, and said "ring gaps were too tight, bore is glazed, and piston has come close to seizing. Next item, I showed him the flowering of the wrist pin circlip recess, and asked why it was like that. He replied "the pin has been hammering back and forth... so it's too short! Not to mention the rings are made out of rubbish.

Too short? yep. 1/4" too short. So, JP supplied the +0.020" piston with a pin that was MUCH too short, and the rings are junk. So now, I have a worthless paper weight in the shape of a JP piston, that's done 3000 miles.

Now I'm up for a +0.030" bore and new piston, rings and pin. Joy.

Word from the wise... the 0.006" ring gap in the Matchy books, DOES NOT WORK in AUSTRALIA with JP Pistons!

As for the head? Seems the guides and stems have worn a fair bit, so looks like new guides and a grind and lap job.

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Re: Blue Smoke on decel and accel

Postby bjorn » Thu Nov 17, 2016 10:19 pm

Marty,

Sorry to read all the trouble you are going through with the bike(s).

I believe the 0.006" to 0.008" referred to in the period AJS/Matchless shop manuals applies to the rings used in the early fifties which had gaps at 45 degrees. This would mean that a measured gap of 0.006" on the 45 degree rings corresponds to a horizontal "gap" (allowable movement) of 0.0085". If you look at data for late fifties models, which use rings with vertical gaps, the recommended ring gap is 0.010" to 0.015" for the long stroke 500 and also the competition models. I believe these figures are more in line with what you should be using.

A quote from Phil Irvings classic "Tuning for Speed", albeit for race engines: "The correct amount for engines which are given time to warm up is 0.005 in. per inch of diameter, but wider gaps are advisable for engines subjected to rapid cold starts, 0.010 in. per inch is a good figure to work to."

regards
Bjørn

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Re: Blue Smoke on decel and accel

Postby robcurrie » Fri Nov 18, 2016 2:00 am

Gudgeon pin hammering the circlip is usually caused by a bent conrod. It may be worthwhile checking before assembling your engine.

Rob C

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Re: Blue Smoke on decel and accel

Postby bjorn » Sat Nov 19, 2016 11:46 am

Marty,

The 1/4" end float on the gudgeon pin is of course far outside what it should be. A well-engineered piston/pin combination will typically have minimal end float, in the order of 0.010” – 0.04”.

That said, it is not necessarily the end float alone that is causing the “flowering” of the circlip recess, although it is probably contributing.

As Rob says:
“Gudgeon pin hammering the circlip is usually caused by a bent conrod. It may be worthwhile checking before assembling your engine.”

I would agree with that, but there can also be other causes which are worth checking:

-The cylinder bore can be out of alignment with the “vertical” centreline due to sloppy work from the guy doing a rebore or installing a new liner. If part of the original liner is in place (it should be), the liner thickness should be equal all the way round the bore, both at cylinder top and cylinder bottom.
-A small end bush with a bore that is not in alignment with the rod eye centerline will have the same effect as a bent rod.
-Crankshaft not built up properly/ out of alignment.
-Too much side clearance on the big-end, allowing the rod to “wander”.
-Crankshaft axial movement. (This should not be possible, assuming you are using the crankshaft shock absorber and spring. A broken or “slack” spring would however allow the crankshaft to wander.)

Regards
Bjørn

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Sun Nov 20, 2016 9:02 pm

Thanks all :) Most informative :)

The previous Wellworthy piston had a 'fitting' gudgeon pin, and although the piston (+0.020") was WAY too small for the bore it was in, was not marked or bruised from the pin hammering. That said, the bike has now done 3000 miles since the JP piston and new cylinder sleeve. I checked the flywheels in the lathe and seemed to be within 0.002", but could only check one side as my dial gauge setup leaves a bit to be desired.

Side float in the big end is minimal. Thinking the big end is pretty new. End float on the crankshaft is 0.040" which will be rectified at re-assembly. I wasn't going to split the fly wheels, so checking the con rod may be hard. How does one check it? (It should be mentioned that my Father in law flogged the crap out of the bike for a 2 hour ride on day some time ago, and I think that has a lot to do with a few problems I'm having... At first, he rode it that hard, the timing chest came loose, and it was spewing oil out everywhere and he didn't even notice and just kept riding. I had a hell of a time catching him up to stop him. Could he have bent the con rod then? Possibly. Ugh. :(

As for the cylinder bore and small end, the both seem fine. I can see left over original bore at the bottom of the barrel and seems to be even thickness.

The plot thickens....

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Re: Blue Smoke on decel and accel

Postby bjorn » Tue Nov 22, 2016 7:12 pm

Marty,
It is unlikely that the thrashing your father-in-law has given the bike has bent the con rod. If it is bent it will likely have been damaged by ham fisted previous owners.

“I can see left over original bore at the bottom of the barrel and seems to be even thickness.”…check top of bore also.

You can check if the rod is bent or twisted without dismantling the crankshaft. You will need to make a mandrel to go through the small end. This must be straight and a tight (sliding) fit in the small end bush. Make one in a lathe, or use an 8” length of cold drawn bar or seamless pipe to the closest size smaller than the piston pin diameter, roll it on a flat surface to make sure it is straight and wrap tightly with paper in the middle to fit in the bush.

The centerline of the mandrel and the centerline of the crankshaft should be parallel and in the same plane regardless of which position the big end/con rod are in. If they are not parallel the rod is bent. If they are out of plane the rod is twisted. Lay the crank out on a perfectly flat surface (not your workbench – the wife’s indoor kitchen workbench top is usually better). To check for twist: ensure the crank centerline(crankshaft axles) is parallel to the table, make up two supports, identical in length (short bolts with tight fitting nuts will do) and place under the mandrel ends. Any clearance will indicate a twisted rod. To check for bend: Measure any difference in center to center distance between mandrel ends and crankshaft axles, or make up distance pieces for comparative measuring – compensating for different diameters on drive side and timing side axles. The actual measurements are not of interest, only any difference from one side to the other.

Regards
Bjørn

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Thu Nov 24, 2016 8:20 pm

bjorn wrote:Marty,
It is unlikely that the thrashing your father-in-law has given the bike has bent the con rod. If it is bent it will likely have been damaged by ham fisted previous owners.

“I can see left over original bore at the bottom of the barrel and seems to be even thickness.”…check top of bore also.

You can check if the rod is bent or twisted without dismantling the crankshaft. You will need to make a mandrel to go through the small end. This must be straight and a tight (sliding) fit in the small end bush. Make one in a lathe, or use an 8” length of cold drawn bar or seamless pipe to the closest size smaller than the piston pin diameter, roll it on a flat surface to make sure it is straight and wrap tightly with paper in the middle to fit in the bush.

The centerline of the mandrel and the centerline of the crankshaft should be parallel and in the same plane regardless of which position the big end/con rod are in. If they are not parallel the rod is bent. If they are out of plane the rod is twisted. Lay the crank out on a perfectly flat surface (not your workbench – the wife’s indoor kitchen workbench top is usually better). To check for twist: ensure the crank centerline(crankshaft axles) is parallel to the table, make up two supports, identical in length (short bolts with tight fitting nuts will do) and place under the mandrel ends. Any clearance will indicate a twisted rod. To check for bend: Measure any difference in center to center distance between mandrel ends and crankshaft axles, or make up distance pieces for comparative measuring – compensating for different diameters on drive side and timing side axles. The actual measurements are not of interest, only any difference from one side to the other.

Regards
Bjørn


WOW! Thank you so much Bjorn! You're a life saver! I will indeed check this before assembly this weekend. Thank you! Much to learn my end!

UPDATE:
Took barrel to new Engineer, a friend of my neighbour's. He took one look at the bore and said 'it's glazed, the ring gap is too tight and it's almost seized a number of times." Looked at the piston with the flogged out wrist pin circlip recess, and said "the pin's been hammering, either it's too short or the conrod's bent". Confidence in my new found Engineer on a high. :) So He's since used my second hand Wellworthy piston +0.020", cleaned it up, put new rings on it, gapped to 12 thou, and the piston now has 7 thou clearance to the bore, and it has a 'fitting' wrist pin. The JP piston was set up with 5 thou clearance, and 6 thou ring end gap. According to my new Engineer, that ring gap and piston clearance will never work in Australia, particularly NOT in the northern states where I live. I guess pommy tolerances will never work here. Things that I'm learning.... :)

Fingers crossed now for the assembly. I'm going to replace the main crank bearing and maybe the timing side bush, then try and get the crank end float down, as it is running at 0.040" at the moment, then reassemble with my freshened bore and piston, and head that just came back from the head job... :).

Busy week coming up! Thank you again for all your help!
marty

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Re: Blue Smoke on decel and accel

Postby Matchymarty » Mon May 01, 2017 9:35 pm

Update #2.
This is driving me batty. After above replacement of piston, rebore and new rings, I also got head checked (the cylinder head that is - not mine... although I probably should!) and the engineer did a valve grind and seat and said valve to guide clearances were ok.

What are the clearances supposed to be ? 2-3 thou? Less?
My bike was ok for a bit of the run in, but then started blowing smoke on accell and decel all over again, and I suspect it's back to its old tricks of coming down the intake valve. When I pulled it apart last time, there was a black burnt round spot on top of the valve, and the seat was all gummed up - indicating excess oil coming down the stem?

This is driving me bonkas... I'm having to put over half an oil tank of oil in it every 80 miles. Not to mention I feel terrible covering everyone in stinky smoke at rallies etc. (yes, it just stinks and although not big plumes of smoke while going along, it's definitely is burning it.

Also , if idling for 30 secs to a minute - like at a traffic light, when I take off again, I leave a cloud of smoke akin to an old diesel tractor.

Help!!! so Assuming valve guides are at fault... what is the Guide to Valve stem clearance?
Cheers

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