How bad can a valve clearance be and still live?

[Big T]

You'll have to take it all apart and check it out first

Then, decide from there

A used head might be cheaper - still would need lapping and new valve stem seals

[MisterCinders]

Case study of why you always break down used heads, check everything out, change the valve stem seals, and adjust the valves before installing.

How do you adjust valves in a head before installing them onto the bike? Just curious.

[Nessism]

How do you adjust valves in a head before installing them onto the bike? Just curious.

I did it by turning the cams with vise grips, but truth is I misspoke with my comment. Meant to say the head should be gone though and the valves adjusted before trying to run the bike.

[chef1366]

That's a drag.
If the seat isn't too damaged it can be cleaned up and install a new valve.
With zero compression I bet it ain't pretty.

[86turbodsl]

I still have to do a compression test to verify, one of the guys I know said it could be a dead carb, but I'm not hopeful. I just rebuilt all the carbs. The exhaust pipe wasn't very warm. Maybe 85-90 degrees when running.

[Nicholaschase29]

why would that cylinder fire while the valve was held open a tad and now it doesn't run when it's seated?

[86turbodsl]

I don't think it was ever running.

[spchips]

Well, I got my answer tonight. A valve cannot be held open 0.5mm and survive, no matter how easy you run the engine. Put it all back together and ran it, started harder now with more clearance, and #4 is cold. No compression. Running on 3 cylinders. I guess the head is coming off this winter...

Any advice on repairing valves?

How cheap are you? You can spread a little lapping compound on the valve through the spark plug hole, attach a drill to the valve stem, and start spinning.

This is considered a cheater job when done with the head removed, and I've never heard of anyone doing it attached, don't know where the compound will go...

[hampshirehog]

How cheap are you? You can spread a little lapping compound on the valve through the spark plug hole, attach a drill to the valve stem, and start spinning.

This is considered a cheater job when done with the head removed, and I've never heard of anyone doing it attached, don't know where the compound will go...

Grinding paste will shoot up the valve stem / guide; then you've got extra work. DON'T DO IT!

[86turbodsl]

Ok, now I dont know what's going on anymore.

Did the cranking compression test :

#1 - 137 psi
#2 - 115 psi
#3 - 125 psi
#4 - 127 psi ---> the "cold" cylinder.

The exhaust pipe on #4 was cold enough I could comfortably hold my hand on it.

I have verified spark too. #4 wire with plug sparks strongly when laid on valve cover.

Carbs are fresh rebuilt.

Any ideas? Bueller?

I tried revving it up around 5-6000 rpm and didn't get any heat out of the #4 cylinder then either. I figured that would be enough to get it onto the main jet if the idle circuit was plugged.

[chef1366]

Is the spark plug wet?

[86turbodsl]

Ok, now I'm baffled. All it did was sit for a couple days. Now I have it firing on #4.
Ran it till it warmed up, LOTS of backfiring.

Reran the compression test on #4, it was about the same.

Did it fix itself? Seems so. Maybe a stuck float bowl valve?

Only thing I can think of is I put it on the center stand tonight rather than side stand.
But the funnel I was using has always been at least 8+ inches above the floats.

But as far as this thread goes, it SEEMS to be fixed. Perhaps the valve didn't burn because it
wasn't firing on #4 for a time? One things' sure, the valvetrain is a LOT noisier. sounds like spinning bearings now.

My guess is do a carb sync next and try and get the AWFUL idle mixture settings correct.
It's got a nasty bog then rev at idle. Doesn't really get responsive until you get it up around 4K rpm.
Still doing tons of popping in exhaust and a bit of fire in the vacuum line to petcock.
Mixture screws all set about 3.5 turns out.

[spchips]

wait a minute... you do have the airbox installed, air filter in place, and the cover on, right???

This bike will NOT run in a usable way without all of the above installed.

[hampshirehog]

wait a minute... you do have the airbox installed, air filter in place, and the cover on, right???

And if you have then you have got dirty carbs. Your compression numbers are fine.

[86turbodsl]

Airbox in place, new K+N filter, fresh foam seals on both end caps, new airbox boots and carb boots, new orings.

Carbs were completely disassembled and soaked in berrymans multiple times for over 24 hrs, then removed from the cleaner and sprayed with carb cleaner and all orifices were cleared and sprayed/soaked. I followed the guides.

All new o-rings putting it back together.

Floats set with digital caliper. Even made a bowl screw with tube to double check float heights assembled. (only used it on one bowl though as I set all the floats the same height and the one I checked was EXACTLY at spec with fuel in it.