Loud Pop, Vibration and Partial Power Loss C172

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bearitus
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Loud Pop, Vibration and Partial Power Loss C172

#1 Post by bearitus » Tue Jul 12, 2016 4:06 pm

I had a flight recently where in cruise in my C172 I heard a loud bang followed by a strong vibration with considerable power loss. Needless to say it was a scare and was I relieved to land safely at the airport. In the air I tried checking the mixtire was leaned properly, the mag's, the fuel selector and the alternate air and nothing helped the engine symptoms. Engine gauges were in the green too. Not sure what it could be, is it just a simple case of spark plug fouling or could it be more severe?

Thanks
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crazyaviator
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Re: Loud Pop, Vibration and Partial Power Loss C172

#2 Post by crazyaviator » Tue Jul 12, 2016 5:21 pm

Stuck valve or magneto failure ?
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ahramin
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Re: Loud Pop, Vibration and Partial Power Loss C172

#3 Post by ahramin » Tue Jul 12, 2016 5:33 pm

Broken exhaust valve? Failed cylinder? Why ask here? Surely an AME could inspect the engine and find the problem?

How big a bang? How big a vibration? How much power loss? Which engine gauges were in the green?
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lownslow
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Re: Loud Pop, Vibration and Partial Power Loss C172

#4 Post by lownslow » Tue Jul 12, 2016 9:04 pm

Do you have a cowl-mounted landing light? Actually, make that do you still have a cowl-mounted landing light?
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bearitus
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Re: Loud Pop, Vibration and Partial Power Loss C172

#5 Post by bearitus » Wed Jul 13, 2016 5:50 am

I just did a ground run-up this morning and I am thinking its a stuck valve from the symptoms. Time to get an AME to look at it.
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Re: Loud Pop, Vibration and Partial Power Loss C172

#6 Post by AirFrame » Wed Jul 13, 2016 6:53 am

The same symptoms happened to a friend of mine while I was flying with him. Result was an ingested Exhaust valve, and an overhauled engine. I recommend you DO NOT RUN IT on the ground or otherwise until it's been checked out by someone competent.
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Re: Loud Pop, Vibration and Partial Power Loss C172

#7 Post by rigpiggy » Wed Jul 13, 2016 9:20 am

I had a similar issue years back, just a light unknown engine vibration. Ended up being a lose valve seat, only happened once up to temperature, so hard to trace.
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digits_
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Re: Loud Pop, Vibration and Partial Power Loss C172

#8 Post by digits_ » Wed Jul 13, 2016 9:33 am

lownslow wrote:Do you have a cowl-mounted landing light? Actually, make that do you still have a cowl-mounted landing light?
How would that cause a partial power loss ?
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Re: Loud Pop, Vibration and Partial Power Loss C172

#9 Post by PilotDAR » Wed Jul 13, 2016 10:50 am

I just did a ground run-up this morning and I am thinking its a stuck valve from the symptoms. Time to get an AME to look at it.
Time to get an AME to look at it.
Yup!
Ended up being a lose valve seat, only happened once up to temperature
:shock: :shock:
The same symptoms happened to a friend of mine while I was flying with him. Result was an ingested Exhaust valve, and an overhauled engine. I recommend you DO NOT RUN IT on the ground or otherwise until it's been checked out by someone competent
+1

It's kinda cool and techy sounding to say "stuck valve", but make sure you understand what that means as you say it. Stuck open is one thing, stuck closed is very much something else - how would you know which? Usually by how much of the internals of the engine must be replaced when you get it taken apart!

If you suspect a valve problem, get the help to the engine, rather than the engine to the help - if you would like to reuse the engine. Loose exhaust valve seat! Don't run the engine until that cylinder is repaired. You will hear stories about engines which were operated in this condition. Yup, I can't deny that. And you'll hear horror stories of galled cam and lifters, broken lifters, broken rocker bosses, and bend pushrods.... Hmmm..... Cause and effect in many cases...
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photofly
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Re: Loud Pop, Vibration and Partial Power Loss C172

#10 Post by photofly » Wed Jul 13, 2016 1:16 pm

Credit where it's due ... I think it's kind of ballsy to go and do ground runs on an engine that went POP and lost power in flight. I mean, I wouldn't have the nerve :-)
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Re: Loud Pop, Vibration and Partial Power Loss C172

#11 Post by Choppermech1986 » Wed Jul 13, 2016 6:42 pm

I'm going to assume it's a Lycoming so another vote for stuck exhaust valve. Watch for bent pushrods, I've had to send an engine for overhaul after a pushrod bent and the lifter busted it out of the case, that was an expensive stuck valve (admittedly the engine had gone over 1700hrs TSO). Get your AME to carry out Lycoming Service Bulletin 388C to confirm your suspicion and then hone/ream the valve guides to the appropriate diameter to get rid of the carbon build up. Best to get them to drop the exhaust valve into the cylinder and do a complete job of it, a good piston AME worth their salt should only take a few hours to do this once the exhaust is off.

Moving forward, Lycoming Service Instruction 1425A details the preventative maintenance to minimise the likelihood of valve guides sticking.

For the sake of the thread, please keep us up to date with what you learn!
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Re: Loud Pop, Vibration and Partial Power Loss C172

#12 Post by bearitus » Thu Jul 14, 2016 3:13 am

It ended up being a stuck open exhaust valve in one of the cylinders. The cylinder showed no compression and the AME is in the process of repairing it. Luckily there were no bent pushrods or cracks to the engine mount or any other damage. The engine was a rather new Lycoming O-360.
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Re: Loud Pop, Vibration and Partial Power Loss C172

#13 Post by crazyaviator » Thu Jul 14, 2016 9:52 am

The engine was a rather new Lycoming O-360.
You may want to seriously consider inspecting the other cylinders for the same problem before flying
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Re: Loud Pop, Vibration and Partial Power Loss C172

#14 Post by cgzro » Thu Jul 14, 2016 7:36 pm

[quote="crazyaviator"] inspecting the other cylinders [/quote]

Good advice, all the exhaust guides likely need to be honed out a bit, I doubt only one of them got gummed up.

Hopefully the cylinder did not strike the open valve otherwise its a whole lot more expensive!

Peter
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Re: Loud Pop, Vibration and Partial Power Loss C172

#15 Post by CFR » Sun Jul 17, 2016 7:38 pm

cgzro wrote:
crazyaviator wrote: inspecting the other cylinders
Good advice, all the exhaust guides likely need to be honed out a bit, I doubt only one of them got gummed up.

Hopefully the cylinder did not strike the open valve otherwise its a whole lot more expensive!

Peter
I assume you meant piston did not strike the open valve. My question is can a piston touch an open valve?
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Gyroscopic
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Re: Loud Pop, Vibration and Partial Power Loss C172

#16 Post by Gyroscopic » Sat Sep 17, 2016 9:48 am

Not under normal circumstances, in any other case, if a piston is striking a stuck open exhaust valve... "A lot more expensive" is an understatement, LOL
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Re: Loud Pop, Vibration and Partial Power Loss C172

#17 Post by cgzro » Sat Sep 17, 2016 1:21 pm

If the valve does not close fast enough (its just a spring that closes it) it can be hit by the piston.
If the valve does not open fast enough (its pressure from the cam/rod/rocker) then one
or all of the things pushing or the valve itself will bend/break.
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Re: Loud Pop, Vibration and Partial Power Loss C172

#18 Post by Big Pistons Forever » Sat Sep 17, 2016 6:50 pm

Engines don't usually fail without giving some warning. A "loud pop, vibration and partial power loss" is your engine telling you

"Dude, Pay Attention I Am One Unhappy Engine !!!"

When an engine does that land ASAP and don't mess with it without professional help.
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