G80CS... and the saga continues

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G80CS... and the saga continues

Postby Matchymarty » Sat Sep 15, 2018 10:09 pm

Hi all,
Well my issues continue with my '55 G80CS. I've ridden the last 2 weekends at rallies, and both, were in hilly areas.

First things first. My oil burn continues on overrun, and, consumption is still out of control - 70ml per 70miles. I can only assume this is a combination of intake valve guide and blow by the rings.

So, that out of the way - my last rebore and new piston resulted in a +40, and my Amal 389 is set with a 30 pilot, 420 main and usual 106.

Now, Timing is set using the stick in the hole, but, I take the time to get it just right to 1/2" BTDC. The bike is usually a little hard to start, as it floods easily with the 420 main, but I was advised to use that main, by a guy who's worked with Matchy's for many years and has actual information from the factory with carb settings with compression ratio and cam combinations.

So, generally, the bike performs 'well', although I don't have a baseline of how it 'should' perform. Since going to the big main, I can cruise at 50mph ok, and 55 if I want to. That said, it still doesn't pull up hills unless you drop a gear and keep the motor spinning.

I've had the bike up to 70mph along the flat, and it didn't seem like it'd explode or whatever... but certainly took it's time to get to that speed. I still think it struggles to hold 50mph over ant hills - ie, rolling rises in country areas.

So to the last 2 rallies. I've always had issues with hills. Last weekend, was up and over a small mountain range a number of times. When going up one of the long drags uphill , running in 3rd, then second, it wasn't labouring, but I could feel it getting hot on my right leg. I decided to drop speed, and engage 1st, and let it spin up the hill.

It got hotter, and spark broke down a number of times, Missing and banging. I thought that must have been pre-ignition. No pinging though. That said, I backed off let it regroup, then it I made it to the top of the hill in one bit, and it started to cool down as I rode along the top. This happened on both saturday and sunday runs, on different roads.

To this weekend.
Rode yesterday, and it was up over 2 mountain ranges. - Why the rally staff use these mountain roads for old bike rallies is beyond me... The first part of the run was up a long drag, which would be an 7-8mile run to the top, with a few downhills and flat sections inbetween obviously.

Ignition broke down twice, and it began to get VERY hot, and I could feel it getting tight. The last steep pinch, I had to engage first gear and pray I go up. I did, and despite the hill, sort of felt ok and 'normal' after that and on the way down the hill.

THen we went along another 20 miles along the flat and it went ok.

Till the next hill. Which is very steep and winding but only a few miles to the top. 1st gear was engaged early due to the incline, and the bike got really hot, smoked a lot from around the engine etc. I got passed by a M21 like I was standing still, little 2strokes, A B31 plunger and 2 350 matchy's like, I was standing still. It should be said, I also cannot go up hills generally any better than my father in laws 350 compy which is just flogged out like you wouldn't believe.

Quite demoralizing.

I got to the top, but I was so close to fully nipping it up. I had to will it to the top in a cloud of smoke and oil coming from everywhere.

So, WHAT THE HELL?!

I just had an idea... Is it the plug? Could it be that simple? I use NGK B7ES. Are they reliable at high temp and load? (I've swapped out plugs regularly with new B7ES's and don't seem to have any different results)
see photo below. (just pulled plug) I've just ordered some new Bosch plugs - W5CC and W7CC's to try.

As soon as it gets under a decent amount of load, it starts to break down and heat up. I'm feeling like sending the Mag back to the guy and getting him to check it, but he's already had it twice... It should be mint.

Long and the short is, I think i've blown the head gasket or, at least the head has loosened off due to the over heating, as I couldn't start it after the beer stop yesterday, without bump starting it, (very low compression) and had very little power on the return trip to camp. Luckily it was all down hill. When accellerating though, I could hear it choofing - which I'd say is a head gasket.

ANY IDEAS GUYS?? Going to throw this compy in the ocean before much longer! I wanted to ride this and my '56 at the november JAMPOT Rally, and its looking like it won't make the distance!!!

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Re: G80CS... and the saga continues

Postby Mick D » Sun Sep 16, 2018 7:27 am

Hi

How's the exhaust valve tappet setting? if it's a little tight it could be holding the valve open when hot.

Excess heat is usually indicative of a weak mixture, are your jets clean / needle in the desired position / strainer clean?

Is the timing fully advancing?

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Re: G80CS... and the saga continues

Postby clanger9 » Sun Sep 16, 2018 7:47 am

Excess heat / lack of power sound like symptoms of retarded timing. It's not running lean, from the photo of your (oily!) plug.
Is the exhaust header getting excessively hot and/or blue? That would be another indicator.

It should certainly pull better than that.

I'm not a fan of using "factory" methods for setting ignition timing. The correct timing depends on the fuel grade, the compression ratio and to some extent the gas flow in the head. All these things can vary considerably from how things were when it left the factory. The original timing settings were determined by trial and error, and that's still the right way in my opinion. On a coil ignition bike, you can just rotate the points plate while it's running to find the "sweet spot" when idling (i.e. advanced as far as it'll go just before it stumbles, but I think this method may be more of a faff on a magneto ignition...)

Suggestions:
1. Check your auto advance mechanism is working / has the right springs etc (if it's got one)
2. Try advancing the timing in stages. If you go too far, it'll be a pig to start and might pre-ignite under load. If you get that, you know you've gone too far so back it off a bit...

PS: here's a great guide on reading the ignition timing from the spark plug. With a new plug, the little telltale heat mark on the plug electrode is easy to see and a great way to check everything is right: https://honda-tech.com/forums/forced-in ... A-3063102/
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Re: G80CS... and the saga continues

Postby ajscomboman » Sun Sep 16, 2018 9:17 am

I think I'd be ready to throw it in the sea too but I can't help feeling your going in the wrong direction carb wise. That plug is rich,as it would be with a 420 main. That's in shortstroke territory and way way too big, not far short of double the factory jet.

I take it that you have tried all the usual things like testing the compression with a guage, if not I'd start there and make sure you have around 145psi

1/2" BTDC is as per book but with modern fuel you could knock it back to 7/16th. Check the valve settings after 2-3 mins running and make sure the rods spin freely.

Carb settings according to the book are 240 main, number 3 slide, 106 needle jet and needle in central notch. Your plug is in the correct range as are the Bosch.

If you've tried all the above and not strayed too far from the recommended settings then I'd seriously start to look hard at the mag.

I've long and shortstroke comps and none vary too far from factory and run well except the 500 CS which hates being stiffled by the exhaust silencer. Actually that might be worth checking as well. Ensure your pipe enters the silencer (if you have one) by just enough for the silencer to clamp on. In the silencer is a baffle approx 6" in and if the pipe goes in too far it'll choke the motor as the back pressure builds. I've also knocked out the very end baffle to ensure free flow. It certainly helped but still doesn't run as well as it did with the silencer off (takes off like a scolded cat without it!)

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Re: G80CS... and the saga continues

Postby clive » Sun Sep 16, 2018 9:30 am

"So, generally, the bike performs 'well', although I don't have a baseline of how it 'should' perform. "

I don't have a CS but I have ridden 500 singles for some years. The performance you are describing sounds worse than my 54 AJS model 18 which had a Busmar double adult sidecar attached usually with 3 kids and the camping gear.
This year I rode two up to Portugal on a 55 G80 temperature in the mid 30s across a mountain range and I doubt I changed below 3rd for any hill.
Do you have an auto advance or manual advance. Sounds like timing is retarded (poor power and overheating). If auto advance what are the springs like, is the chain drive loose enough to allow the operation of the advance? If manual are you sure you have got the advance retard sorted in terms of which is which, tight or loose cable depending on which side of the mag the cable enters?
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Re: G80CS... and the saga continues

Postby clanger9 » Sun Sep 16, 2018 9:55 am

ajscomboman wrote:...except the 500 CS which hates being stiffled by the exhaust silencer. Actually that might be worth checking as well.

Oh, good suggestion! A partially blocked exhaust will also give very similar symptoms (without necessarily blueing the exhaust manifold). Worth a check, I 'd assume a bike like this really needs a straight-through exhaust...
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Re: G80CS... and the saga continues

Postby Matchymarty » Sun Sep 16, 2018 10:23 am

Thank you all for your comments I'll keep this going by answering you all one by one. :)

Mick D:
Valve tappets are free with no discernable tightness or 'looseness' after running.
Jets are clean, I run good filters also. Needle is in stock position. I have raised it, and it made no difference other than making it run much too rich.
I have run the timing fully advanced, and, have fettled on the move to find the 'sweet spot' whilst making the bike pull in top gear, and twiddling the adv/ret lever to find where it pulls hardest. - Result: over heats up hills either way.

Clanger9:
I highly doubt its running lean. I run 95RON unleaded, and yes the plug is black, even before it oils up. I can't tell if the header is discoloured, as it is ceramic coated and never changes colour.

My mag is manual advance.
Thank you for the link to plug readings. I'll read that thoroughly.

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?

Clive:
I'd agree. I've seen many 350 iron matchy's run rings around my compy. Totally upsetting and I have no end of issues with it.
My Mag is Manual advance - loose wire advance.


I have since put the plug back in and kicked it over. It has little compression, so I'm going to have to pop the top off.
I suspect one of the valves is either hanging up, gunked up or the head gasket is blown.

Incidently, as it consumes huge amounts of oil, would anyone consider that the fouling of the plug could be causing me these issues? Most of the guys at the club tell me it shouldn't make any difference, and 'just keep riding it'... but it's terrible, and I keep having these issues.

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Re: G80CS... and the saga continues

Postby clive » Sun Sep 16, 2018 10:49 am

Like comboman I am sure you have the wrong main jet. 440 seems to be for the short stroke motor or at least a much later model than yours. Hope this photo of the carb settings page of the Roy Bacon book helps.

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Re: G80CS... and the saga continues

Postby Andy51 » Sun Sep 16, 2018 11:09 am

Hi Marty, I run a '54 18S fitted with compy cams and a JP 8.5 to 1 piston, so I am not that far off what you have. I used the standard mod 89 1 5/32in carb, with the same settings as the roadster, as per the book. My silencer is a Armour's one with no internal baffles, but the pipe has a blanked off end and lots of holes drilled in the sidewalls. It seemed too long so I sawed off the blanked end and it goes well, albeit a bit noisy. I recently changed carbs to a 930 30mm one, with a 210 (I think, it was a while ago) main jet as the 89 was worn out. It goes just as well but I now have a tick-over!. Have you checked the inlet valve oil screw in the head? Too far out and it could let too much oil into the combustion chamber. I have had to adjust it out on my G80 because the valve squeaked, so they can get out of tune. I think it should be 1 1/2 turns out, but check the book. Is the breather OK? Too much pressure in the crankcase can raise oil consumption. In my experience, the book settings for everything are best and, if not, are still a very good start point - your main jet seems very large. With regards to performance, top speed should be well into the 80s on roadster gearing with good acceleration and cruising happily in the high 60s. It should run down to under 40 in top gear, but is happiest round town in 3rd. All the best, Andy

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Re: G80CS... and the saga continues

Postby SPRIDDLER » Sun Sep 16, 2018 11:14 am

Matchymarty wrote:Incidently, as it consumes huge amounts of oil, would anyone consider that the fouling of the plug could be causing me these issues?


My first thoughts were also that the main jet is waaay too large and having to use first gear on a run (even up steep inclines) wasn't right unless the bike is seriously over-geared. I think we previously established that it isn't over-geared. We have already established that you have the correct inlet valve metering screw and there is no excessive wear on the valve guides. It was recently rebored, presumably with the correct clearance and new piston and rings so provided that the c/case breather is operating it's a mystery how the oil is getting into the combustion chamber. (Unless, daft thought, it is being drawn in between a loose valve guide and the head casting. Nah, surely not?).

I may well try the 7/16". This will advance it yes?

No, 7/16" BTDC is less advanced than 1/2" BTDC
TBH I don't think that whether you have timed it at 1/2" or 7/16" BTDC it would make such a difference. Besides, you have twiddled the A/R lever whilst riding with little effect.
Curiously, the plug appears to be simultaneously oily (shiny around the Earth body/rim) and yet sooty on the central insulator. This fouling would certainly cause the misfire.
I've no experience of the symptoms you describe but assuming that you have the correct carb to start with (bore size correct and matching the spacer and head) I would guess that the excessive amount of oil entering the combustion chamber could be weakening the mixture enough to make it run 'better' by substantially increasing the size (i.e. petrol flow) of the main jet. Hence you have both over-oiling and richness.
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