exhaust valve leaking

[lktiller]

Seems the exhaust valve on #2 is leaking. Compression check 50/80.
Guide not stuck. Just valve won't seat. Don't think it is burnt but don't have it apart enough to tell yet.
Easily compressed the springs and pulled the rocker arms, put the rope in the cyl but can't compress the spring to get the keepers off the valve stem!
Should it take a lot of effort? Should I soak it in MMO? (dissolves carbon)

[Ragwing nut]

Re: exhaust valve leaking

Make sure the piston is at the bottom of the stroke when you put the rope in and fill it up, then roll the piston to tdc. Once the rope is compressed it will not rotate and you can compress the springs.

Mike

[lktiller]

Re: exhaust valve leaking

Hummm...Maybe my problem is too much rope.... Can't rotate the piston to TDC.
I've been holding the prop and trying to compress the spring at the same time.

thanks,
Larry

[Ragwing nut]

Re: exhaust valve leaking

Hummm...Maybe my problem is too much rope.... Can't rotate the piston to TDC.
I've been holding the prop and trying to compress the spring at the same time.

thanks,
Larry

Keepers are more than likely well seated to the retainer. I have found over time it is just easier to pull the cylinder and fix it right.

Mike

[3Dreaming]

Re: exhaust valve leaking

Sometimes it takes a light rap on the spring cup with a mallet to break the cup loose from the retainers. It works best to do this with pressure on the valve from the rope. Did you just have the one low compression check, or have you been tracking a problem? I've had one check low like that only to have it come up after a quick run up. I've also used shop air pressure built up in the cylinder, and released through the exhaust valve to remove trash from the valve surface. Tom

[lktiller]

Re: exhaust valve leaking

keepers came loose, gave it 'enough rope'. and enough pressure.
looked the valve over as best as I could, saw nothing that would indicate a burnt valve. Wee bit of compound and spinning the valve in the seat, then flushing, did nothing for the leakage.
No, I was not tracking anything. had 78/80 comp about 6 mos ago. less than 800 hrs smoh which included new cyls.
last ran 2 hrs about two weeks ago, no problems.
When cranking this past weekend, noticed the exhaust huffing past one compression stroke. Ran good except maybe 50 rpm less at static. Ran engine 1/2 hr, no change.
compression test confirmed exhaust valve leaking on #2.
90# air on cyl, tapping on valve stem did not help.
spark plug with about 100 hrs looked as good as when installed. head of piston has no carbon to amount to anything. Valve stem definitely not sticking in the guide.
soooooo.... looks like the cyl comes off!!!!!

[Armstrong]

Re: exhaust valve leaking

Did you find the problem ?

[lktiller]

Re: exhaust valve leaking

yes, it needed more than the rope trick!
The 2nd compression ring was stuck, in addition to carbon on the valve seat.
cleaned, ground valve seat, replaced rings, gaskets, reassembled, and away we go!

Hindsight:
I had been noticing quite a bit of oil under the cowling, seeping out from under every gasket. Attributed it to old age, etc. But it came on rather rapidly.
After replacing the rings, no more oil seepage!
Obviously, the stuck ring was contributing to crankcase pressure.

retrospect:
I believe 100LL is the biggest culprit in carbon buildup in these old engines. But a contributing factor in my case is the carb is (was) running rich.