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#353308 - 01/16/11 11:49 pm Trying to diagnose hot exhaust on one cylinder  
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yellow_cad Offline
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Folsom, CA
Just redid the top end on my 70 Bonny. In the process, I installed new exhaust pipes and mufflers. This time to ward off the blue exhaust pipes I painted the inside of the pipes with high temp paint. After torquing head and adjusting valves, I ran it for a bit, retorqued head and adjusted valves. When I ran it again, left pipe (no crossovers on the new pipes) smoked some but I put it to oil on the outside. The previous running was with bike moving but this time I ran it a bit with two fans on it and it was clear that the left pipe was trying to blue even through the paint. At that point I posted on this board and got some great suggestions. A lot of the suggestions were about running lean but one, sort of a first step, was to check exhaust valve clearance. I let the bike completely cool down (day or so) and sure enough the left exhaust valve had no clearance. It was not very tight as it only took a little over 1/8 turn to get it with correct clearance. I would hope that I would have found the source of my hot exhaust pipe but it doesn't seem that small amount of adjustment would cause it. I am also puzzled because my left plug does not look as though it is running hot at all which might say that it was just the valve clearance. Since I am trying to find out and fix the hot exhaust without any harm to the motor (valves, etc), I am trying to determine the best way to diagnos this. Should I when I do run the bike to test for the hot cylinder use a point and read heat guage and if I should, would it be best to check my readings on the first exhaust pipe bend out of the cylinder and if so, how much difference in temp would be excessive and shut off time? Thanks for any help on this.

Last edited by yellow_cad; 01/18/11 1:48 am.

Jim

1970 Triumph Bonneville
1973 Commando Interstate
1971 OSSA MAR
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#353415 - 01/17/11 3:58 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Vic. Australia
I wouldn't expect the plug temperature to be higher on the "hot" side.Combustion temperature is only likely to increase if there is more mixture in the cylinder or its compressed more when the plug fires.A slightly lean mixture could also increase combustion rate and cylinder pressure,and plug temperature.
The plug doesn't know what happens to that hot mixture after it fires.If the burning mixture is leaking through the exhaust valve,the exhaust pipe will know what happens.
You could still have valve leakage,even after you adjusted the clearance.Rev it up a few times with no exhaust pipes fitted (about 30 seconds running),and check the clearance again when it cools down.See if that fixes it.

#353422 - 01/17/11 4:30 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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btour Online content
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Hi YC,

Hold on. Stop a minute. Are you saying you just got done with the top end? So now you have heat-cycled it twice without riding it? That will probably be fine. But you have to ride it soon. Get some real compression behind the rings for them to seat ASAP., or you are tempting fate to have the cylinders glaze before the rings are seated.

I understand you do not for some reason want a blue pipe. But priorites first.

I have blue pipes. Nothing is wrong. It is just the make of pipe. It is thinner, and copper is used in the plating process. Trying to prevent them from bluing would be futile, and the fiddling to do so, may cause another problem.

It is not clear, if you found no valve lash clearance before you re-torqued the head (also base, and rocker boxes, I assume), or after you re-torqued the head. That makes a difference as to whether or not there is a "situation".

If you have already ridden the bike and "seated" the rings, then ignore this.

Last edited by btour; 01/17/11 4:35 pm.

Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
#353478 - 01/17/11 8:16 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Ahhh, memories of leaving half my glove on the left cylinder pipe...I'll NEVER forget that smell....


If you love it, let it go. If it comes back, you've highsided!"

1971 Triumph T120
2005 Triumph "America"
1976 BMW R90/6
#353480 - 01/17/11 8:21 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: btour]  
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yellow_cad Offline
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Folsom, CA
Originally Posted By: btour
Hi YC,

Hold on. Stop a minute. Are you saying you just got done with the top end? So now you have heat-cycled it twice without riding it? That will probably be fine. But you have to ride it soon. Get some real compression behind the rings for them to seat ASAP., or you are tempting fate to have the cylinders glaze before the rings are seated.

I understand you do not for some reason want a blue pipe. But priorites first.

I have blue pipes. Nothing is wrong. It is just the make of pipe. It is thinner, and copper is used in the plating process. Trying to prevent them from bluing would be futile, and the fiddling to do so, may cause another problem.

It is not clear, if you found no valve lash clearance before you re-torqued the head (also base, and rocker boxes, I assume), or after you re-torqued the head. That makes a difference as to whether or not there is a "situation".

If you have already ridden the bike and "seated" the rings, then ignore this.


Bob, I took your advice from another post and rode it for a few miles early in the process. The ride consisted of keeping the revs and back pressure up. My concern over the blue pipe is that I have painted the inside of these pipes so if it wants to blue, I would think that that is even hotter than when pipes are not coated with high temp paint. After riding the bike, I have run it once with fans to try and determine if I have one cylinder running a whole lot hotter than the other. Also after riding the bike, I retorqued the head, base and rocker boxes, reset the valve clearance, then ran it with the fans. After running it with the fans and letting it cool, the left exhaust valve had no clearance so I readjusted it and checked the others.

Last edited by yellow_cad; 01/17/11 8:24 pm.

Jim

1970 Triumph Bonneville
1973 Commando Interstate
1971 OSSA MAR
#353481 - 01/17/11 8:26 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: DPO]  
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yellow_cad Offline
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Folsom, CA
Originally Posted By: DPO
Ahhh, memories of leaving half my glove on the left cylinder pipe...I'll NEVER forget that smell....


So, is it not so unusal to have one cylinder running quite a bit hotter than the other with things set right?


Jim

1970 Triumph Bonneville
1973 Commando Interstate
1971 OSSA MAR
#353493 - 01/17/11 9:03 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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btour Online content
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Originally Posted By: yellow_cad
[
Bob, I took your advice from another post and rode it for a few miles early in the process. The ride consisted of keeping the revs and back pressure up. My concern over the blue pipe is that I have painted the inside of these pipes so if it wants to blue, I would think that that is even hotter than when pipes are not coated with high temp paint. After riding the bike, I have run it once with fans to try and determine if I have one cylinder running a whole lot hotter than the other. Also after riding the bike, I retorqued the head, base and rocker boxes, reset the valve clearance, then ran it with the fans. After running it with the fans and letting it cool, the left exhaust valve had no clearance so I readjusted it and checked the others.


OK YC. At least you rode it once. That is good. 50 miles minimum I would expect. It takes some to really seal them.


With my new pipes, first one side "blued" and then the other. I am more concerned that you are chasing something that is not relevant. I mean the blue may or may not indicate that is running too hot. Just how far down the pipe does the "blue" extend? John mentioned that he would not be concerned about the color unless it extended down to and past the lower bend in the pipes. Pipe color being blue, is kinda of a "street" adage. If they use copper in the plating process, 3 stage plating, which is good, you are gonna get blue color in the chrome. It just means a good plating job. If the pipes are thin, they may even glow at night under certain atmospheric conditions. Scary sure e'nuff, but mine have done so intermittently for many tens of thousands of miles, and nothing bad has happened yet. smile

If you are really concerned about it, get a temperature sensor and check it. Some new timing guns come with one.

I am not sure just how much some paint will make the pipes "cooler". I think the paint will just help prevent corrosion from the inside.

Why you had no valve lash clearance, I do not know. You mentioned that you set the clearance after a ride. It is not clear. Did you let the bike cool overnight before setting them? The clearances indicated are for a cool engine. You let it cool, then re-torque everything, and then set the lash. I always like to check lash, before everything else, just to see where it was, just out of curiousity. But I would not adjust it it before retorquing, if I were breaking it in.

You are alot like me. You want everything to be as good as it can be, and worry about things. But be careful not to over do it, and over fiddle things. How does that thing go that John always said. Better being the enemy of the good?


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
#353496 - 01/17/11 9:10 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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btour Online content
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PS. It has been a struggle for me to unlearn, a lot of the things that were said by so called "experts". So that I am not sure all the time, which things in memory are correct.

So, thank God for John Healy. Wish we could clone him. One to run his business. One to write a book. One to Make a really good rebuild video. And one to have fun! ,of course. Although that one would probably never be really content, just having fun.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
#353501 - 01/17/11 9:23 pm Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Maui Hawaii
I've put quite a few Triumph engines together and it has been rare that one would have both sides the same temperature. Even with single carb and solid state ignition. In fact the ones that were closer to the same were those that had twin carbs. So, that points to things like port biasing and other mysterious things to most of us.
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
#353569 - 01/18/11 5:00 am Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Honda and others found that often the only way to cure this "problem" was to use dual-wall exhaust pipes.

Don't know if high-temp paint will do any good, but you could get the inside of the pipes coated. There are various ceramic and other treatments out there that might help.

The quality of the chrome plating is just one of many factors to consider.

Ultimately, it's the poor, low-production-cost design of the Triumph exhaust that's to blame. Better (more costly) designs isolate the exhaust pipe from the head. For example, Ducati singles, Honda 305s, etc.


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
#353581 - 01/18/11 9:35 am Re: Trying to diagnos hot exhaust on one cylinder [Re: Nick]  
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Originally Posted By: Nick
Better (more costly) designs isolate the exhaust pipe from the head. For example, Ducati singles, Honda 305s, etc.


They do, but that is to stop the pipe heating the head, not the other way round.

Blue pipes isn't a big problem, but if you think one cylinder is much hotter than the other, try these:

If the bike has points ignition, double check the timing on both sides with a strobe, up to all rpm. Check all joints in the inlets for air leaks by spraying WD40 on them with idling engine. If it's not that, enrich the carburettor on the hot side and see what effect that has. Enrich it in the throttle range where the pipe roasting occurs. If it's at idle, adjust the mixture screw and check the metering bush is clear. If it's at fast idle, the slide cutaway might be too big. If it's when you ride the bike, I'd suspect throttle needle height. The notches on the needle are a coarse adjustment and shimming the needle up half a notch might work.

I assume you've already made some attempt at the AMAL tuning procedure.


Amateur Loctite enthusiast.
#353584 - 01/18/11 10:34 am Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Emsworth, sunny south of Engla...
I agree with Triton. The most common reason for over hot exhaust headers is retarded ignition timing.

The pipes usually end up going blue at some stage.
Dave


Last edited by dave jones; 01/18/11 10:37 am.
#353885 - 01/20/11 3:13 am Re: Trying to diagnos hot exhaust on one cylinder [Re: triton thrasher]  
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[/quote] Originally posted by Triton Thrasher

They do, but that is to stop the pipe heating the head, not the other way round.

Blue pipes isn't a big problem, but if you think one cylinder is much hotter than the other, try these:

If the bike has points ignition, double check the timing on both sides with a strobe, up to all rpm. Check all joints in the inlets for air leaks by spraying WD40 on them with idling engine. If it's not that, enrich the carburettor on the hot side and see what effect that has. Enrich it in the throttle range where the pipe roasting occurs. If it's at idle, adjust the mixture screw and check the metering bush is clear. If it's at fast idle, the slide cutaway might be too big. If it's when you ride the bike, I'd suspect throttle needle height. The notches on the needle are a coarse adjustment and shimming the needle up half a notch might work.

I assume you've already made some attempt at the AMAL tuning procedure.

[/quote]

It is true that I painted the inside of my new pipes so they wouldn't blue but my primary concern with one side trying to blue right after my top end job was not the discoloration of the pipes but to determine if the hot exhaust on one side indicated some problem such as running lean, etc. The bike has electronic ignition and I did strobe it. The carbs are fairly new and ran fine before but I am adjusting from scratch since the top end job. Neither side had the blue exhaust issue before the top end job so my most likely culprit seems to be carb adjustment. I will probably do as Bob suggested and forget the exhaust color for now and concentrate on getting some miles on the new rings. That being said, before I start the bike next I will go through the left carb checking what you say Triton Thrasher. It would certainly help me if you could elaborate on a couple of points you made. When you say, "check the metering bush is clear" are you referring to idle jet? When you say, "the slide cutaway might be too big" I'm not sure what you are saying except this same slide and carb worked fine before so I believe this would not be the problem. Thanks for any help on this.

Last edited by yellow_cad; 01/20/11 3:25 am.

Jim

1970 Triumph Bonneville
1973 Commando Interstate
1971 OSSA MAR
#353893 - 01/20/11 4:46 am Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Check to make sure the engine didn't inhale a manifold gasket and float levels are correct. Just to be sure ride at night and see if one side glows and not the other. Good luck on this.

#353914 - 01/20/11 10:41 am Re: Trying to diagnos hot exhaust on one cylinder [Re: yellow_cad]  
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Yes when I said metering bush I meant the pressed-in hidden pilot jet.

Mixture just above idle is partly controlled by the cutaway size. If you can't correct it with the pilot screw, a smaller cutaway might help. You shouldn't have to tune your carbs differently from each other but sometimes it happens. Air leaks or fuel restriction faults of some kind are probably more likely.

Did you renew needle jets in both carbs? They are very wear-prone and also affect mixture at small throttle openings. Although of course they wear richer not leaner.


Amateur Loctite enthusiast.

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