Not a great day...help with diagnosis

Lachlan said:
That was a nice guess, @weirdjim, but you were off the mark. ;) Hlad to hear the OP got the problem taken care of relatively easily!
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If a major league batter makes one correct guess out of three (s)he goes to the Hall of Fame. I'm entitled to miss one every now and again. No big deal AND I"m happy too that the problem is solved.

Now the aftermarket questions ... why does a leaking intake valve gasket make a lot of noise? Vibration, sure, from a lean mixture and resultant (probable) slight detonation, but that doesn't make a hell of a lot of noise.

?????
Jim
 
I am thinking there is more to this story than an induction leak. That noise is saying "help me"!
 
weirdjim said:
If a major league batter makes one correct guess out of three (s)he goes to the Hall of Fame. I'm entitled to miss one every now and again. No big deal AND I"m happy too that the problem is solved.

Now the aftermarket questions ... why does a leaking intake valve gasket make a lot of noise? Vibration, sure, from a lean mixture and resultant (probable) slight detonation, but that doesn't make a hell of a lot of noise.

?????
Jim
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I concur. Induction leaks usually don't have much affect at high RPMs. Lower RPMs, they certainly do.
 
Ray Eaker said:
I concur. Induction leaks usually don't have much affect at high RPMs. Lower RPMs, they certainly do.
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That would make sense with what the OP posted. In the video the aircraft was shaking and the noise more pronounced at 1000 and 1300 RPM. The one cylinder was probably so lean it would not light off. It was not quite as bad when he ran it up to 1800. And the OP said he had a smooth and uneventful takeoff and flight to the service airport, at even higher power settings.
 
I spoke too soon. I wrote my post about the intake gasket after I got the call from the mechanic letting me know he "fixed" the issue. Well, I can say he did do some work that needed to be done on that intake gasket, but I don't know what he did after that. Apparently it wasn't test running the engine. When I went to fly the plane home it sounded exactly as it did before. Although, I did notice the RPM to be somewhat more stable. So, I'm back to suspecting an exhaust leak somewhere in the system. Tomorrow I'm working with my regular mechanic to pull the pipes and exhaust. We're going to replace all the exhaust and intake gaskets (except for the one) and make sure they all seat properly as well as inspecting the muffler carefully. I have a strong suspicion that weirdjim is going to be inducted into the diagnosis hall of fame after all...
 
hish747 said:
I spoke too soon. I wrote my post about the intake gasket after I got the call from the mechanic letting me know he "fixed" the issue. Well, I can say he did do some work that needed to be done on that intake gasket, but I don't know what he did after that. Apparently it wasn't test running the engine. When I went to fly the plane home it sounded exactly as it did before. Although, I did notice the RPM to be somewhat more stable. So, I'm back to suspecting an exhaust leak somewhere in the system. Tomorrow I'm working with my regular mechanic to pull the pipes and exhaust. We're going to replace all the exhaust and intake gaskets (except for the one) and make sure they all seat properly as well as inspecting the muffler carefully. I have a strong suspicion that weirdjim is going to be inducted into the diagnosis hall of fame after all...
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No-Blo exhaust gaskets for that sucker are around triple the price for a "regular" gasket and worth ten times the price. You will NEVER replace another exhaust gasket for the life of the engine. But I'm thinking you are doing "shotgun" repairs. Why would you replace perfectly good intake gaskets before you drop the exhaust stack(s) and look inside? That's just a waste of intake gasket money.

Well, haul (sic) of fame perhaps, but I've been inducted into the haul of shame more than once, so perhaps they will level out after a while. By the way, Tom is my guru on this board. He's spilled more gasket cement than I've ever used. He is a cantankerous old ba$+@rd, but he knows more about airplane in his little finger than I know in my entire body. LIsten to him.

Jim
 
The intake pipes were rusty and the gaskets were not in good shape. I suspected that the bad gaskets were the cause of rpm fluctuations. So, I cleaned up the rust, primed and painted the intake pipes. Jim got it right again as I did buy No-Blo gaskets. I also took Tom's advice and inspected the muffler and the rest of the exhaust system carefully. Turns out the muffler is less that 2 years old.

I'm letting things settle in and will go start up the plane in the morning and see how things go. I'm optimistic...
 
Well...the sound of the engine is still off. So much for optimism. I will say that the RPMs are now consistent and not fluctuating due to the intake leak. The vibration is also better. The sound is almost backfire like. Is it time to just overhaul the engine? Seems like a shame with great compressions, normal oil use and no metal. I'm taking a Borescope to the cylinders next week to have a look. The mystery continues...
 
hish747 said:
Well...the sound of the engine is still off. So much for optimism. I will say that the RPMs are now consistent and not fluctuating due to the intake leak. The vibration is also better. The sound is almost backfire like. Is it time to just overhaul the engine? Seems like a shame with great compressions, normal oil use and no metal. I'm taking a Borescope to the cylinders next week to have a look. The mystery continues...
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Borescope, look for a stuck valve, man it is taking a long time to get this fixed.
 
PaulS said:
Borescope, look for a stuck valve, man it is taking a long time to get this fixed.
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Part of the problem may be that the valve isn't totally stuck, it may just be tight. That can lead to troubleshooting difficulties and still yield good compressions if the valve closes and seals when the test is performed.

My opinion is that the OP needs to get a real engine guy to look at this and diagnose the problem. it seems like parts are just getting thrown at it in an attempt to fix things.
 
mondtster said:
Part of the problem may be that the valve isn't totally stuck, it may just be tight. That can lead to troubleshooting difficulties and still yield good compressions if the valve closes and seals when the test is performed.

My opinion is that the OP needs to get a real engine guy to look at this and diagnose the problem. it seems like parts are just getting thrown at it in an attempt to fix things.
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Believe me, I've been trying to get "a real engine guy" to look at it. The one I know says he's too busy, and this is the guy who "fixed" the problem by replacing the intake gasket. Others won't travel to the airport where the plane is based and I'm not real excited about flying it to another mechanic in it's condition. After the borescope test this week however, I will either be more comfortable flying it to another mechanic if the valves look good or perhaps resign myself to an overhaul.
 
hish747 said:
Believe me, I've been trying to get "a real engine guy" to look at it. The one I know says he's too busy, and this is the guy who "fixed" the problem by replacing the intake gasket. Others won't travel to the airport where the plane is based and I'm not real excited about flying it to another mechanic in it's condition. After the borescope test this week however, I will either be more comfortable flying it to another mechanic if the valves look good or perhaps resign myself to an overhaul.
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In this case, I have my doubts that a borescope will yield much useful information. It is simply one of several tools I'd be using to determine engine health. I'd scope the engine but don't stop there.

Sounds like your "engine guy" either didn't take much time to really look at your engine last time (perhaps because he was busy) or may not be the guy to help you out here.

An overhaul is an awfully expensive route to fixing this. Find the real problem first, and depending on what the real problem is you can decide if an overhaul is necessary or not. It may not be a quick diagnosis and may cost several hours of shop labor to properly troubleshoot but it is worth the time and money spent to figure it out.
 
An overhaul isn't my first (or even second) choice but a consideration is that the engine is already at 2400 SMOH and an overhaul would add some value I think. That said, I'd really love to diagnose the issue.
 
An overhaul to fix a slight roughness is like amputating your arm and getting a prosthetic because you have a hangnail.

FWIW, our club's old Archer was at 3200 SMOH when we sold it and still going strong.
 
Im not an AP but the youtube video sounds like a sticking valve to me. If so, its beating your cam lobe up. Maybe the mech can do a wobble test on the rocker arms just to make sure.
 
Any more updates Hish? Just curious if you've found the culprit. I owned a similar Cherokee for a number of years and can't say that I've experienced a similar issue before. From your YT vid it does sound like an exhaust leak. I've had my share of leaky exhaust and intake gaskets but never had a noise like that when the gaskets failed. I've also had the flame tube collapse inside the muffler but that didn't produce a vibration or noise. The only indication I had was that my static RPM dropped by about 120 due to bits of the flame tube clogging the exit to the down pipe.

Any possibility that the noise is from something banging / rattling against the firewall? IIRC the muffler on my old Cherokee is very close to the firewall and is held there by a couple of supports. If they have some slop the muffler may rattle enough to strike the firewall?

Is the noise audible outside of the cockpit?
 
Thanks for asking. The sound doesn't seem to be something banging against the firewall. If I had to locate, I'd say the area of the #2 Cylinder. It is audible outside the cockpit but I've only heard it from inside the cockpit so it's hard to pinpoint a location. The muffler is quite solidly mounted and only a couple of years old.

This has been most frustrating. The problem is still not fixed and no one seems to be able to properly diagnose it. I've had 4 different mechanics look at it. How can it be this hard to diagnose such a prominent issue. Here's what we've done so far:
Done compression tests: Good
Replaced all exhaust and intake gaskets.
Replaced the ignition harness (the old one was fraying)
Rechecked mag timing (it was a little advanced by a degree or so)
Adjusted the Carb/mixture (It was a little lean)

Perhaps what's most annoying is the suggestion to continually replace components that end up not fixing the issue. What kind of diagnostic process is that?
Where's Mike Busch when you need him! (No offense Tom, I really appreciate the help!)
 
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You said leakdown checked out. Rings and valves probably fine at TDC on compression stroke.

Did you do a borescope inspection of the cylinders? Inspected the fins? Look for signs of a cracked cylinder.

Funky acting valvetrain? Disconnect both plug wires on individual cylinders to find the bad cylinder (obviously all cylinders are firing and mag drop shows both plugs are working).

Use a heat gun on the cylinders and exhaust and intake tubing to find a discrepancy.

That’s all I got.
 
hish747 said:
...How can it be this hard to diagnose such a prominent issue...
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While I share your frustration, sounds can be very difficult to identify the cause.

For example, I recently had a sound that, on the interior of my truck could only be heard at a certain speed and was clearly on the driver side.

Took a mechanic for a drive and he felt the same as I did.

Nothing wrong with the driver side, front or read.

So, last week I decided I had enough of the sound. Put the truck on a lift and checked all components. Turns out the pax front wheel bearing was beginning to degrade.

Had to remove the tire and turn by hand the hub to diagnose.

Swapped the hub and all is well.
 
455 Bravo Uniform said:
You said leakdown checked out. Rings and valves probably fine at TDC on compression stroke.

Did you do a borescope inspection of the cylinders? Inspected the fins? Look for signs of a cracked cylinder.

Funky acting valvetrain? Disconnect both plug wires on individual cylinders to find the bad cylinder (obviously all cylinders are firing and mag drop shows both plugs are working).

Use a heat gun on the cylinders and exhaust and intake tubing to find a discrepancy.

That’s all I got.
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I really appreciate the diagnostic advice.
No signs of a cracked cylinder that the mechanics could find. Fins look good.
Can you be more specific about what to do with the heat gun? Also, what am I looking/listening for when I disconnect the potentially bad cylinder? Wouldn't the disconnected cylinder still move and make the odd sound? If it was rod related for example. Or are you thinking that lack of a weird sound when disconnected would mean the cylinder is cracked and only produces the weird sound under the pressure of combustion?
Anyway, thanks again!
 
Yes, was thinking that stopping combustion in one cylinder would act or sound different than stopping it in the others. You’d then narrow your diagnostic search down to that one. Whether the sound was combustion or a mechanical sound that only occurred or didn’t occur during combustion is also what you may find.

Same with the heat gun. You’re looking for one that’s not like the others, either intake, exhaust, or cylinder. Do that while all are firing.
 
Get an IR thermometer and compare exhaust stack temps after a run-up or even while running if your comfortable doing that. Not able to determine for certain from the video but it almost sounds like you’re running a 3 banger there. The thermometer will at least get you down to the culprit cylinder if that’s it.
 
I’d put a quart of MMO in the oil, take it up for a short flight, if it is a stuck valve this will likely unstick it. Change the oil afterwards, check for metal in the filter and the drained oil.
 
hish747 said:
Sorry, I'm still not sure what to do with the heat gun...
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I think he means a laser temp gun/sensor, not a heat gun. Since you don't have EGT/CHT per cylinder, it may show a discrepancy.

I listened to the video and it thought it could just as well be some part of the cowling or a fairing flapping in the prop blast.
 
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