G80CS... and the saga continues

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
Member
User avatar
Posts: 2499
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: G80CS... and the saga continues

Postby ajscomboman » Sun Sep 16, 2018 12:35 pm

Matchymarty wrote:
Ajscomboman:
I take your point with the carb comments. I had run a 260 main and all 'book' settings. I cooked 3 pistons on that setting. The fella I know who has some factory information that lists cams,CR's, and carb settings, read it and showed me where it said 400-420main. And yes, was '55 Long stroke. So I'm at a loss there, as the manuals say 260. IN any event, it does perform much better on the 420 than it ever did on the 260. Will it cook a piston on a 420? As you've read, I was very close 3 times in the last 2 weeks.

I may well try the 7/16". This will advance it yes? If this is so, why does my bike 'pull better' in it's 'sweet spot', when I retard the lever by around 3/8" of lever travel? I'm totally lost on this one. It doesn't make sense.

My exhaust header is longish (about 1" before the baffle) however the end of the baffle has been cut out of the silencer.
Perhaps I should run it without and see what happens? Marty


Definitely run it without the silencer and see if that improves the breathing. If your pipe was within 1" of the internal baffle of the silencer I'll tell you now it was running as flat as a turd! Also running hot. It's exactly what I experienced with the shortstroke. I'd find road models easily pulled away from me at low to mid speed as the motor was being strangled. I've cut the pipe so I have enough to get the clamp on with maybe 1/2" extra for safety and now the thing easily stays with a 650 CSR. The oil burning is definitely another issue you have and either it's due to guides being worn, inlet oil feed adjuster too far out (you can almost shut it off without any serious issues) or rings are buggered again either too sloppy in the grooves or end gap too big.

The jet is way too big despite what you're being told. All my bikes have SH scrambles cams and they are down on power compared to road models at low speeds but really start to pick up at over 20 mph when roads models can't get anywhere near them.

You'll get there eventually, keep at it and really takes pictures of everything and anything as you're doing it then post them it's easier for us to diagnose if we can see.

Member
Online
Posts: 1358
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: G80CS... and the saga continues

Postby Mick D » Sun Sep 16, 2018 12:42 pm

Hi

You say the bike floods easily and put this down to the 420 main - this is a false assumption, the main jet has no effect on the propensity of the carb to flood. If the carb is flooding it is probably a fault with the float or it's valve - have you checked the fuel level in the float chamber aligns with the cast dot on the float chamber cover? Use a short length of clear plastic hose on the pilot jet. Does the carb flood if the bike is on the centre stand with the fuel supply switched on?

If you are putting that much oil through the combustion chamber and have a blown head gasket you would have a fair old oil slick over the barrel fins. Are you sure the oil loss is through the chamber?

A sticking inlet valve would result in a lot of spitting back in the carb.

A sticking exhaust valve would give you a loss of power and banging in the exhaust - are you sure the valve is the correct length, are the springs in good order?

As regards the amount of heat / power, in my experience:

Rich mixture = less heat and power

Weak mixture = more heat and power, (up to the point of pre ignition).

Retarded timing = less power, (in the cruising and 'pushing on' ranges) less heat in the engine, but more heat in the exhaust.

Advanced timing = more power and heat in the engine.

Regards Mick

Member
Posts: 197
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

Re: G80CS... and the saga continues

Postby Matchymarty » Tue Sep 18, 2018 2:15 am

Andy:

As this 'problem' is re-occuring and involves a number of damaged pistons, I've tried all variations of oil feed screw positions. None seems to make much difference, in the sense that there is still loads of oil consumption - read: Not burn. I only get oil smoke on overrun.

Crank case breather works well, but in fact always sprays loads of oil all over everything behind the breather hose.

My Compy is 1 tooth up on engine sprocket, but will not 'Cruise' at 60 or higher. It 'cruises as long as you keep on it to regulate up and over any shadow or cats eye or micro hill. If you hunt it along, it'll cruise at 55, but it's not exactly happy.

Spriddler: Again thank you for chiming in. I'm beginning to think you hit the nail on the head with the fouled plug. The excessive oiling and richness (though it does not blow black smoke - EVER) may well be fouling the plug. I clean the plug after 2 or 3 rides, maybe like every 200 miles or so. Perhaps, I should pop a new one in after sorting the lack of compression and run it straight up a long hill.

I tend to agree with your comment on the timing. Just about everyone I know uses the stick in the hole method, and never has any issues. And they are half blind, and have shakey hands. I'm VERY particular with my 1/2" measurement and, ensure it is vertical. Any minor discrepencies in the timing, can be twiddled with the manual ADV/RET lever anyway ... am I right?

AJSCombiman:

I will run it without the silencer. I'll also remove the little that is left of the baffle.
I have replaced the oil feed screw with a new one some time ago to ensure that that might not be the issue.


Mick D:

My carb holds fuel well. Doesn't normally 'flood'. Iguess what I mean is that to start my bike, i've always had to be quick to open the throttle directly after the kick. If she does not fire, it then gives a bit shot of fuel into the chamber - flooding it in that respect.

Yes, I have oil all over the fins. So much so, when it was over heating on the weekend, I was engulfed in smoke from the burn off.

My local guy keeps suggesting i'm running too retarded. You say, Retarded timing = less power and less heat. Therefore, over heating is not necessarily high on the list. I also, can't see that its running retarded, as I've mentioned before, to find it's sweet spot, I have to retard it about 1/2" of lever pull.


Thank you again guys. I'm going to pull the head off when I can. and at least get it checked out.

I'm really wondering now, if the fouled plug (which fouls very quickly - within 30-50 miles of being cleaned) is causing my lack of power, over heating and subsequent pre-ignition and near seizures.

Member
User avatar
Posts: 913
Joined: Sat Jun 20, 2015 8:38 am
Location: Chester, UK

Re: G80CS... and the saga continues

Postby clanger9 » Tue Sep 18, 2018 7:26 am

All sensible, just one point: if the fuel is going in, less power always means more waste heat.
So, retarded timing produces more heat.

The timing lever just retards the timing to less than 1/2" (39 degrees) to help with starting - fully advanced is where the sweet spot should be. It sounds retarded to me, and/or the exhaust is restrictive.

Final thought: does it crackle & bang a lot on the overrun? That's a sure sign of retarded timing. A correctly-timed engine should run "clean" on the overrun.

I do hope you find the cause!
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

Member
Posts: 6049
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: G80CS... and the saga continues

Postby SPRIDDLER » Tue Sep 18, 2018 8:05 am

Matchymarty wrote:The excessive oiling and richness (though it does not blow black smoke - EVER) may well be fouling the plug.

Yes, I have oil all over the fins. So much so, when it was over heating on the weekend, I was engulfed in smoke from the burn off.

Is oil leaking externally, e.g. from the rocker box or top of the pushrod tubes?

I clean the plug after 2 or 3 rides, maybe like every 200 miles or so.

Modern plugs will soon become knackered with cleaning. The central insulator isn't glazed nowadays.

I also, can't see that its running retarded, as I've mentioned before, to find it's sweet spot, I have to retard it about 1/2" of lever pull.

Are you setting the timing on full advance? Are you absolutely certain you know which way to move the lever to obtain full advance? Could it be that when you are 'retarding' the lever to get the sweet spot you are in fact advancing the timing?
I poke badgers with spoons.

Member
Online
Posts: 1358
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: G80CS... and the saga continues

Postby Mick D » Tue Sep 18, 2018 8:34 am

Hi

clanger9 wrote: just one point: if the fuel is going in, less power always means more waste heat.


Not true in my opinion:

At the optimum mixture and timing all of the fuel is burned on the power stroke - max heat / power and clean exhaust

Richen the mixture and combustion on the power stroke is incomplete and less efficient resulting in less power and heat, unburnt fuel is seen in the form of carbon from the exhaust

Retarded timing results in incomplete combustion within the power stroke - less power and heat, combustion continues after the exhaust opens and hence the exhaust gets hotter

It may help to compare this to an oxy/acetylene flame - yellow / cool and very sooty on pure acetylene, (rich mixture). As the oxygen flow is increased the flame becomes hotter and less sooty until at the optimum mixture there is a clean blue /white cone of flame at it's maximum heat.

Marty - Are you sure the valve timing is correct?

Regards Mick

Member
User avatar
Posts: 2499
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: G80CS... and the saga continues

Postby ajscomboman » Tue Sep 18, 2018 9:08 am

On which side of the mag does the cable enter your mag, is it at the front or at the rear of the points housing? Is it a comp mag with screw on wader end? If it enters at the front and you're having to pull the lever back towards you whilst running it's too advanced, however if the cable enters at the rear and you're having to pull the lever back then its to retarded.

Also you mention oil all over the barrel fins. That indicates that either it's leaking from the pushrod seals or the lapped head joint is poor and this will not only allow oil to piss out but also give low compression and allow oil into the combustion chamber. If you haven't already done so I'd suggest that when you've pulled the head, check the seals and also use a copper head gasket on the rebuild, that eliminates the poor lapped joint. One of the Essex members had the same issue with his joint and the only solution to his oiling issue was the use of the gasket. Since then his bike has been oil tight and he only has to sort out the missing gear from his gearbox!!!

Keep the updates coming and I'm sure we'll get you there in the end.

Member
Posts: 197
Joined: Sun Oct 25, 2015 8:19 am
Location: AUSTRALIA

Re: G80CS... and the saga continues

Postby Matchymarty » Tue Sep 18, 2018 10:10 am

Clanger:

I agree, the 'sweet spot' should be @ full advance, but does not seem to be.
See attached photo of Mag. When contact is closed near the top there, lever is 'fully loose wire'. If i open the lever, ie, tighten the wire, the contacts open, hence retarding it?

As for the banging and crackling on overrunn, well, no. I wouldn't say it's 'much'. on a very steep hill, it might 'boom boom boom a few times' but, certainly not a crackle or 'bang' ever.

Spriddler:
Oil is leaking externally from head gasket, around plug hole, bottom pushrod tubes - WHEN under load. It has been, and should be noted, quite a lot of oil comes out of the C'Case relief valve also, and when stopped, it drips from the hose.

Thanks for the heads up on the plugs. I've actually got a few new Bosch plugs today that I'll swap out the NGK with.

Advance /retard, - see above comment to Clanger. I HOPE I've been setting the timing right! Otherwise, I'm a complete boob and should be shot!

MickD:
I've been trying to wrap my head around whether I think retarded ignition produces more or less heat too. I'm uneducated in this, but my logic agrees with yours. If fuel is unburnt, one would expect less heat. Also, more unburnt fuel in the chamber COULD lead to 'cleaning' the cylinder walls of it's lube- which then, would increase friction and potentially additional heat?

I believe the valve timing is set correctly. Ie, it is as per the book. THat said, gawd knows whos' done what to the cams and whether or not they are the correct shape I have no idea. They are SH cams, but, with all the years of use, only the lord knows what they are like. Maybe just maybe they are shot too!

I know, that I've recently been working on a B31, and Couldn't get it started or, once going, I couldn't get it to idle. I swapped out the cams for some M20 cams (which are the same as B31 cams) which were MUCH better condition and, importantly MUCH POINTIER in profile to the cams that were in the motor when we got the bike. Ran well instantly with the M20 cams in it with standard carb settings. ???

This is the problem with these old bikes, got no idea what components are in them when you buy them. I've been chasing this problem for 2.5 years now, 4 (and probably now 5 ) pistons cooked and destroyed due to what ever this issue is!

AJScomboman:
See photo attached. Cable enters at front. And It is a comp mag.
SO yes, I believe, it's too advanced. That said, it's set to 1/2" as absolutely accurately as I can. I have good eyes and feel. And if it's a poofteenth out, I take the sprocket off the exhaust valve and re-time until it's spot on.

This bike is the '55, so, long stroke. I've always used a copper head gasket and the oil seems to be coming from there at the moment. I'll pull the head tomorrow night.

Thank you again guys. I really appreciate this help. I don't have anyone around me with your combined experience! I really am desperate to get to the bottom of this, it's costing me way too much in oil and new pistons and rebores! If I have to rebore again this time, it'll be +60.

Also, don't forget, that, I wasn't always running on the 420 main. That only happend this piston. the previous 3 pistons were run on a 260 main. So, rich mixture, I believe is not at fault . I'm heading towards the oil in the combustion chamber being the major concern.

But then, the oil would mean the mixture is not fully burnt, and in that case, if MickD is correct, combustion chamber temps are lower, therefore, how does that cause overheating?

Judging by comment that, if I have to retard the ignition to 'find sweet spot', meaning it's too advanced, that would mean I'd need to set the timing to say, 7/16" BTDC ?? Or even less?

Cheers. Marty

20180918_193437 (Medium).jpg
You do not have the required permissions to view the files attached to this post.

Member
User avatar
Posts: 913
Joined: Sat Jun 20, 2015 8:38 am
Location: Chester, UK

Re: G80CS... and the saga continues

Postby clanger9 » Tue Sep 18, 2018 10:35 am

Mick D wrote:
clanger9 wrote: just one point: if the fuel is going in, less power always means more waste heat.

Not true in my opinion


It's just physics. I should have said " if the fuel is going in and being burned, less power always means more waste heat". Your oxy-acetylene analogy is talking about complete/incomplete combustion (which does affect heat output, as you say.)
For ignition timing, the situation is different. The fuel-air mix still burns! It just burns at the wrong time (or place, when the exhaust valve opens) . Think about it: you don't get black smoke when the timing is wrong...
What changes is whether the peak pressure in the cylinder happens at optimum downward part of the stroke. Too late (i.e. retarded) means the energy of the expanding gases isn't converted to mechanical force on the piston, so it's wasted as heat. That's why the timing needs to be advanced as the revs increase for maximum efficiency. It's also why retarded engines run hotter.
Last edited by clanger9 on Tue Sep 18, 2018 10:49 am, edited 1 time in total.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

Member
User avatar
Posts: 913
Joined: Sat Jun 20, 2015 8:38 am
Location: Chester, UK

Re: G80CS... and the saga continues

Postby clanger9 » Tue Sep 18, 2018 10:46 am

Matchymarty wrote:Clanger:
As for the banging and crackling on overrunn, well, no. I wouldn't say it's 'much'. on a very steep hill, it might 'boom boom boom a few times' but, certainly not a crackle or 'bang' ever.


Fair enough - that sounds about right. Badly retarded engines are usually noticeably "crackly" on the overrun. Sounds good, but does nothing for the power output. ;)
From your description, your timing doesn't sound too far off, but you could still have the advance/retard the wrong way around. I'll leave it to the magneto experts to puzzle that one out!

Does it kick back if you try to start it with the timing fully advanced? It should. Not something you want to really try, 'cos these things can do you an injury...

I'd definitely try it with an open exhaust. I'm fairly certain that's what CS bikes had originally.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

PreviousNext

Return to Competition / Racers

Who is online

Users browsing this forum: No registered users and 3 guests