TX500 smoking on right side after rebuild

[bhchefyoder]

I have 1973 Yamaha TX500 that I just finished rebuilding the top end. I lost compression on one side. After rebuild, which I had to redo some stuff multiple times since it was my first rebuild. Well, I finally got it back together again and the right cylinder (parallel twin) is smoking bad. Compression is equal on both sides. A leak down test doesn’t show anything.

I was told I may have put the oil control rings in upside down and the bevel is sucking oil into the cylinder. Well, mine aren’t beveled.

Next I was told that a valve seal may be bad. New valve seals on the intake side. My exhaust didn’t look like it had seals at all. That seems weird to me but that’s what it looked like.

So 2 things I’m looking for.
1- Should I have valve seals on the exhaust side?
2- Any suggestions on what is going on and how to fix it.

 

[adventurco]

It does not look like your exhaust valves have a valve seal.

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[adventurco]

Check the valves fitment in the seat and ensure there is no lateral movement. Grab the valve and try to move it side to side. Especially in the exhaust side with no seal, any clearance can cause oil from the top end to enter the combustion chamber.

What are the actual numbers for the compression reading on the cylinders?

Did you pull the heads and barrels off and check that you installed the rings correctly? They have an up, and the gap on the rings should be 120 degrees apart so none of the gaps align.

What side is smoking? Is it the kickstand side and smoking while running on the kickstand?


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[bhchefyoder]

Going from memory I think the compression was 120 on both sides. A little low but both sides were the same so I wasn’t going to fuss about that too much if I didn’t need to. Runs fine except for the smoke.

Smoking on the right side so opposite of the kickstand. Also, it was up on its center stand so it is level.

When I originally rebuilt it I did the ring’s. The first time one of the oil control rings got stuck when I was putting it back together and bent. So I ordered a new set of rings. None of the oil control rings have any writing on them. The top 2 rings did and I’m pretty sure I did those correct as far as orientation. I did make sure they were offset the 120 degrees. Whether they moved or not is unknown.

 

[adventurco]

It sounds like you need to open it back up and find out what is wrong. Obviously something that you thought was done correctly, is not to spec or not assembled correctly.


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[Streetfighterkz]

I worked on a Kz1000 for a guy that smoked like a freight train and spit oil out the exhaust. Did compression checks, leak-down tests, replaced valve stem seals etc. Turned out the oil rings’ expander spacer ends were overlapping and not butting up on a couple pistons. It basically turned the engine into an oil pump. I’d double check and triple check those if I were you.

Later, Doug