Valve Stem Seals, or maybe throw in the towel

[storm 64]

Rich, just give a shout out if you need anything.
I have a valve spring if you need it.
I even have a 1100e engine if you're interested in the 7/11 swap! ...

[Cipher]

I still had 'em beat running on 3 cylinders.
Though, they were riding 2-up on 883's.

For now, all parts are being bagged, tagged, and boxed till I get some time, a valve spring compressor (a buddy at work has one maybe I can borrow), and some winter weather. Will measure all and put the best head together from the 3 that I have.

Its good to work in winter there's no point in rushing.

[rphillips]

Aren't extra parts handy? Hoping you've got most all you need... Waiting for more on the Tiger can imagine, and completely understandable, the TZ being slid back for a little while.

[Rich82GS750TZ]

Say, how far did you leave those HDs behind?

I still had 'em beat running on 3 cylinders.
Though, they were riding 2-up on 883's.

For now, all parts are being bagged, tagged, and boxed till I get some time, a valve spring compressor (a buddy at work has one maybe I can borrow), and some winter weather. Will measure all and put the best head together from the 3 that I have.

[pdqford]

Rich, check the valve seat width.
Too wide a seat width and those carbon deposits to get stuck into the seat and keep the valve from sealing properly.
Too narrow a seat width will prevent valve head from transferring heat into the block.
Seat width should be about 0.040”

And a worn valve seat leaves the valve margin too thin and invites high temps that can melt the valve edge, much like yours looks.
Valve margin should be at least 0.02”.
Say, how far did you leave those HDs behind?

[KiwiAlfa156]

Ah, a burnt valve. Not unheard of. Did exactly the same thing to an exhaust valve in 2.0 Alfa Romeo 156. High rpm and foot flat up a hill with 4 folks in the car. The edge was melted away exactly like yours. I souvenir-ed it, will snap a pic of the melted area if I find it in the souvenir box. That thing had hydraulic lifters and clearance seemed ok. But I replaced the lifter with the valve just in case. Sometimes it's just wear that causes this. A tiny part of the valve not sealing against the seat enabling super-hot high-pressure combustion gases to leak past causing localised heating, and eroding the valve lip. Eventually can destroy the valve in a catastrophic event under high load and rpm.

The valve seats generally come though this pretty well as they are sitting in a big heat sink. From memory I just lapped the new valve in on the Alfa as the seat was good.

Water testing for leaks with compressed air is a good way to ensure you have good valve sealing. If it leaks or you can blow bubbles with compressed air with the valve held against the seat with the springs, you know don't have the best seal.

[Rich82GS750TZ]

Well, I guess if that’s the only explanation, I suppose I must have gotten that adjustment wrong. Or, I the words of Sherlock Holmes “… when you have eliminated the impossible, whatever remains, however improbable, must be the truth".

Will take it slow on the rebuild. If all goes well, I way have a new(er) bike to ride by the weekend”. Stay tuned. And thanks for watching.

[rphillips]

Yep, what he ^^^^^ said. That's why I's wondering about the clearances on that cyl. If it had got too tight we know what caused the damage, if it was still within spec. we're still scratching our head. Hopfully the seat don't look near as bad as that valve.

[Rich82GS750TZ]

Yes. Was certain of clearances when I put this engine back together in spring 2020, and checked/adjusted valves and retorqued head about 1000 miles later.

[Nessism]

Were you keeping up with valve adjustments? It's unusual for a valve to burn and break apart that way under normal circumstances.

You may be able to use a valve from one of your other cylinder heads. Or, use the best parts from all and make one good head.

[Rich82GS750TZ]

And now back to our regularly scheduled program:
Had a few hours in the garage tonight to pull valve cover, exhaust, airbox, and finally, the head

Tadahhh! # 4 exhaust.

[Rich82GS750TZ]

In my destroy-rebuild thread, I tell of how i got this '81 engine from Norm storm 64 when I broke all the rockers off the intake side on the '82 engine. When I showed up at Norm's shop, he had the head off an was milling out some broken exhaust bolts and chasing the threads for me. Glad he did too. Saved me a ton of work. It also meant that I had to take off the jugs and replace from the base gasket on up. One piston's rings were stuck fast, so rather that fool with it, I took the pistons out of the '82 with their rings and put them in the '81 engine. I did put a fresh hone on the cylinders. There was nothing that I could see that could have been wrong with the head/valves at that time. Says the inexperienced guy who had never gone past valve adjustment into an engine before. If I had taken the time, at that time, to pull the valves and replace seals, inspect seats, I may not be where I am today. But here we are.

I did enjoy that work, and I'll enjoy doing a better job of it this time,

I'll get it done. Not in a hurry this time. Thanks for the vote of confidence.

I'm test riding a Triumph next week. Don't tell my GS.

[93Bandit]

You'll get it fixed

Just take your time and be methodical with disassembly. Makes it go back together easier.

As previously mentioned, rebuilding engines is fun. Part of the fun of an old bike if you ask me.

[Rich82GS750TZ]

Won’t know for sure till I pull the head off. Next week. Maybe Sunday evening. I’ll be away all weekend at kid’s college parents weekend stuff.

[93Bandit]

Yes, I can see a bit of the exhaust valves that are open in cylinder 4, a bit out of focus, but enough to see that one of them is pretty clearly deformed.

Is that deformation or is it wet with oil? Oil globs/drips can make it appear deformed, especially if the picture isn't clear.

But with compression that low, I would suspect valve issue as well. Usually worn rings will still have some compression. 15psi is essentially 0 in my opinion, which would indicate an apparent leak, like damaged valve or a hole in the piston (which you don't have thankfully).