Valve Stem Seals, or maybe throw in the towel

[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.

[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]

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.

[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.

[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?

[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.

[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.

[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.

[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! ...

[rphillips]

OOhhh, that's dirty...

[Rich82GS750TZ]

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! ...

Oh, buddy. Don't tempt me!
Thanks for the offer.
If I get the Tiger, that will fulfill my liter bike jones.

[93Bandit]

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.

Ayo! Called it lol. Glad you found the issue. Now you have a fun winter project. Hopefully you have heated shop space?

[Rich82GS750TZ]

My garage is attached to the house. I've added an electric heater in the wall. It takes the chill off. It's not bad.

[Redman]

.
.
If I get the Tiger, that will fulfill my liter bike jones.

Oh Oh!
Tiger 1050
Liter bike, yes, but 3 cylinder, so low end torque.
What my son has (and had before). I rode it and learnt to have it pointed straight down the road before crank the throttle (cuz I didnt know how to steer without front wheel on pavement).
But that is another story.

Seems like you made quick work on the diagnosis and dissasembly.

.

[Rich82GS750TZ]

The Tiger comes in lots of cc configurations and road/dirt biases. The one I’m looking at is 1215cc road biased but very dirt capable. Specs here.