Stuck Valve??

[Frank DeBartolo]

I have flown my BC12-D with Continental A-65 engine regularly the past month (over 20 hours), use Avblend in the oil and MMO with auto fuel (25% avgas). I have been adding the MMO with almost every fill--4 ounces to appx ten gallons. Tonight when I started the engine, the engine ran somewhat rough. I thought it might be a fouled plug. However at the run up--1700 RPMs, the mags checked out OK and the carb heat was ok. On takeoff I could only get 1800 RPMs with full throttle and I aborted the take off. Static RPMs are appx 1800 RPMs. (usually over 2000). One cylinder is real weak when pulling the prop through. The engine has been running good up till tonight. I last flew it Monday June 28 1.7 hours and made multiple takeoffs and landings and experienced no problems with the engine.

Question is--has anyone out there experienced this problem. Could it be a stuck valve--or something else?

Frank DeBartolo
N43684

[Robert Lees]

If it was a stuck valve, one cylinder's compression would be non-existent. Your "real weak" cylinder does sound as if it has at least some compression, so it is probably something else.

[alwaysoar]

Stuck valve

If you pull the prop through, do you hear blowby, and if so, where is it coming from? I would next do a compression check to find out which cylinder it is. Once you find out, take off the rocker box cover and see what the valves are doing? Go from there.

[Frank DeBartolo]

Stuck Valve

The A&P looked at my A-65 and it appears that the exhaust valve to the #1 cylinder is bent. We will be removing the cylinder and replacing the valve and valve guide. Question is--what causes exhaust valves to bend? Could it be excessive heat? Or is is just that the engine is old? My engine baffles and the rubber baffling is pretty sad looking. Could it be that refreshing the baffling would prevent bent valves and other similar problems?

Any comments would be appreciated.

Frank DeBartolo
N43284
BC12-D

[crispy critter]

Bent Valve

Check your mag timing.I have been told by those older and wiser that if your timing is off it can cause the engine to fire a little harder than it should which could cause a valve to warp or bend after time.Also,if the engine backfires can bend them too.

[Frank DeBartolo]

Stuck Valve

By backfiring do you mean when swinging the prop that sometimes it will abrubtly go backwards?

This has happened several times while trying to swing the prop. It seems to happen more when using autofuel.

Also, does anyone have any advice regarding mag timing.

Thanks,

Frank DeBartolo
N43684
BC12-D

[alwaysoar]

stuck valve

Damage can be caused by detonation which is an explosive hammering in the cylinder. It is the result of an excessively lean mixture or lower than specified fuel octane which causes overheating. It sounds like knocking but it's hard to hear over the sound of the engine. Backfiring is also caused by a lean mixture that burns so slowly fuel can still be burning when the intake opens on the next cycle. You've heard cars backfire--that's what it sounds like. Timing could also be off but you need someone knowledgeable to time it. Mags should be timed at annual--when was your plane annualed?

Ed@BTV VT
TF 527

[Frank DeBartolo]

Stuck Valve

Plane was annualed in May. I flew it approximately 20+ hours in June and approx 12 hours in May. Apprx 32 hours since annual. It could be that my mixture is too lean because fuel burn is appx 3.7 to 4 gallons per hour. I do not have a recording tach and use my watch to record time. Should I install a recording tach? But again as is suspected the mag timing could be oiff. The IA that did the annual is on vacation but will be back next week. I will definitely have the mag timing checked and the fuel mixture checked. We believe that course of action on the cylinder now is to remove the cylinder and if the cylinder is OK, install a new valve and valve guide and seat the valve. At that time install new new rings. I wonder how the other valves are? The other cylinders tested 72/80, 72/80 and 75/80. If the other valves were in process of being bent would the cylinders have tested that good?

Thanks,

Frank DeBartolo
N43684

[alwaysoar]

stuck

That fuel burn is normal and who's to say for sure it was detonation or backfiring or timing problems. And I'm not sure you can tell for certain if the valve stem is actually bent without taking it out--I don't know what kind of check your A&P did to find that out. The first thing that occured to me when you lost compression suddenly like that is that a piece of carbon was the culprit.

[Frank DeBartolo]

Stuck Valve

We removed the rocker cover and the rocker arm and struck the valve to release it. It will not release. We assume it is bent because the spring is compressed and will not release. The IA is on vacation and the young A&P that got us this far does not have the tool that compresses the valve to remove the keeper. So we have to wait till next week to remove the keeper and possibly the cylinder if the valve is bent. Hope it is only carbon.

Thanks,

Frank DeBartolo
N43684

[jgerard]

I vote it's just a stuck valve, not a bent one.

Jason
N43643

[alwaysoar]

stuck valve

I second Jason's vote. I would not be taking off the cylinder yet!

Ed@BTV VT
TF 527

[mhorowit]

And you think it's a carbon deposit that's causing it to stick? - Mike

[jgerard]

Not like pulling a jug is hard to do, It probably leaks oil from some gaskets anyhow.

Did you try tapping on the valve with your "B.F.H." to knock it loose. Always make sure the cylinder is at bottom dead center first! In the past I have put rope into the cylinder through a spark plug hole, pulled the engine through, and pushed the valve back up. You may have to do this if the valve spring is fully compressed before you can get the keepers of the valve stem. Or pull the jug and tap it back up with a block of wood and the "B.F.H."

Jason
N43643

[Frank DeBartolo]

Stuck Valve

Hit the valve with BFH but I do not believe that the A&P put the cylinder at bottom dead center--he might have and I will call him to find out if he did. He tried the BFH several times but the valve did not loosen. Will try it with cylinder at bottom dead center and hope it loosen the valve. If not we will remove the cylinder. Will let you know more next week. Question--What does having cylinder at bottom dead center do to help loosen the valve?

Thanks,

Frank DeBartolo
N43684