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Discussion Starter · #1 ·
So here is the story, I have about 500 miles on my bike since rebuild and for some reason I could not get it to start the other day. I went through everything, electrical, timing, carbs, etc. So I looked down into the juggs and my right side piston has an unusual amount of carbon buildup while the other side is very minimal. I had reset the valve adjustments three times already so was thinking that may not be what is wrong. So I tore of the head and found this. The left side of the jugg seems to be getting more oil on the walls while the right side with the buildup is drier. The buildup is on the exhaust end of the piston and is like a 16th of an inch thick. I am looking for some suggestions before I do anything unnecessary. Can i just clean the piston off, please tell me there is an easy fix. Any help would be appreciated.
 

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Check the rings they may have shifted and have to be reindexted....
 

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valve /guide is probably the suspect. I am not saying the rebuilder was a hack but sometimes even the best builder misses the mark on one. or perhaps the valve itself got bent or otherwise not able to perform it's job. a bad seal would cause escaping compression gasses to cool the charge at an increased rate and maybe sort of condense the carbon onto the piston?

looking at the picture of the head says the same. one of these valves is not like the other. except it is the intake valve. this still may point to the exhaust valve as the intake is not getting as hot as the other valves because the combustion is compromised.

are the cam lobes ok? there is only so many places for failure.
 

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Yeah like threeston mentioned, remove the springs and check the guides on that side. Make sure one hasn't come loose and no slop in the valve stems. You can put some kerosene around the base of the guide and see if it leaks through.

There are some good threads on the britbike forum on how to fix leaky guides without removing and replacing them.
 

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perhaps the piston ring gaps line up at the exhaust side ... that acts like a scrach on the cylinder wall and let the oil trough
 

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You said you had to re-set the valve adjustments 3 times....was it ALL or just the one (shiny) valve....
You said "re-build"...what work was done?
 

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Discussion Starter · #8 ·
Ok here are some more specifics. The head was rebuilt by a professional, all new valves stems and guides. I should have mentioned that the reason that one valve looks cleaner than the others is because i rubbed on it with some gasoline and it cleaned it up. I was just unsure what was causing the carbon buildup on the right piston. I figured that not to be normal with a fresh motor with less than 500 miles on it. I figured this should be addressed before it got any worse, because obviously something is not right. I do not have any of the special tools for the head nor do I feel very comfortable digging into it since this is the only part of the motor that I did not do, and I figured that it should be ok. The reason I reset them three times is because I had my first adjustment, then retorqued the head after a couple hundred miles reset them again, and then after I had everything painted I bought some new bolts for the head so when I put those on I reset the clearances again. The bike was running good so far then all the sudden would not start at all. All I could get was a pop out of the left exhaust and that is when I inspected the pistons through the spark plug hole and found the excessive carbon buildup. I could only see the buildup getting worse and something catastrophic happening so I am addressing the issue. For the most part the cylinder walls are good still very smooth with minimal wear. Thanks for all the input so far.
 

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roll the pistons to dead bottom center and post a pic of the cylinder walls ....especially where the carbon is built up.....also get pics of inside the intake and exhaust ports of the head if you cant pull it apart.
Have you shown this to your professional head re-builder? and why was the head re-built??
 

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Oil. It's either going up past the rings or down through the guides (my guess would be rings, but check the guides anyway). One of the most problematic areas of any Triumph rebuild is preparing the cylinder and getting the rings to seat properly. There's a lot of information about this on this site and elsewhere.

Regarding ring indexing, the rings are constantly rotating in their lands, so that's probably not the issue.
 

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put new spark plugs in you may have a bad plug.sometimes life is that simple.probably not but you never know
 

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new plugs being bad.....I have first hand experience of this...
 

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A rich air/fuel mixture can cause excessive carbon build up too. Maybe one of your carb's has a leaky needle and seat, flooding that cylinder, fouling the plug, won't start, etc. An easy way to clean carbon without disassembling an engine is to run the bike about 1500-2000 rpm and gently mist water in the carb. with a spray bottle. Auto parts stores also sell special cleaners that you inject into the intake while the engine is running. Just be careful not to hydro-lock the engine while doing this and also not to get crazy with those special cleaners and have the header glowing red ( I've seen it). Then, swap carb's from side to side and see if the other side carbon's up real bad. Not saying fuel is definately your issue, but it could be. Could also be a valve guide, rings, cracked cylinder wall, etc. Did you staggar the rings when you install them? did you have to force the cylinders over the pistons? Could have damaged the rings during installation.
 

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I also just finished rebuilding a T120 engine, the only part I didn't do was the head. It was built by a "professional" Guess what? the exhaust guide is leaking.

You can remove the valve springs without pulling the head. Just takes a chunk of steel plate and a 13/16 wrench. You need 2 long 1/4" bolts (about 2-1/2") to replace the long rocker-box bolts. You drill 2 holes in the plate the same distance apart as the rocker bolt. Screw it to the head with these bolts. Then you can use the closed end of the wrench to lever against the plate to compress the valve-spring. Put the engine at TDC so the valve doesn't fall into the cylinder. Hook up air hose to cylinder to replace springs.

OR have the guy that rebuilt it check it out for you. Have you done a leak down or compression test? Did you break the engine in with non detergent 30wt oil? Helps bed the rings in.
 

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Discussion Starter · #17 ·
I I think I found the problem with the carbon build up, my piston with the carbon build up was loose in the jug. Took the old rings out and gaps were also a bit off. So just got new rings and all the gaskets and re-rebuilt the top end. I think this may have been due to the prob of trying to get my old carbs working before I bought the new ones. I spent prob about a week of idling and reving and never got them good enough to ride right, but once I got the new carbs it was good to go.

However now I have a new dillema. This is what made me catch the carbon build up problem. I was having an electrical problem. My bike ran fine for 2 months then all the sudden I started it it was idling for a min then I turned the lights on and it died and would not start back up. I am running batteryless with pazon ignition and coils, new sparks rotor, new stock stator, and sparks eliminator. I have volt metered everything, from the stator I have about half meter on the dial, after the eliminator the dial is maxed out and at the coil the meter is still maxed out. I put the meter in the spark plug caps and hardly a charge, not sure if this is because its different ohms or not accurate or if my coil is gone. I took all lights and switches out of the equation and still no luck on getting it started. When I hook a battery up it fires first kick and sounds great, WHAT AM I MISSING HERE. I have about 2 months of riding on this bike and now this just started and I am dumbfounded. I really do not wanna run a battery since I just got everything back from paint a few weeks ago and do not wanna have to weld on any mounts. Any help would be greatly appreciated.
 
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