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Lycoming - What is this noise?

J

johnpaul44

Member
Lycoming 0-360 with about 1000 hours. Recently replaced a cylinder with a new superior cylinder and I have about 4 or 5 hours on that cylinder. I noticed when the engine is hot if the prop is rotated i hear this strange creaking sound (see video). I only hear this when the engine is hot once it cools down a little bit the noise goes away. The propeller spins freely just like before, i borescoped the new cylinder and it looks perfect inside.

I asked my mechanic about this and he said sometimes superior cylinders make noises like this for the first 10 or 20 hours? is this really normal?

https://imgur.com/a/miMmdE1
 
Orlando engine shop.

Don George is in your home town and is a great engine shop. I would ask them.
 
Strange noise

Is there a vacuum pump on the engine? It appeared that the creaking happened when you turned the engine backwards. It’s a long shot, but it kinda sounds like pump vanes dragging the wrong way in a vacuum pump.

If no vacuum pump: Disregard.
 
What mine does..the belt

I have a Lycoming O-320 and when mine is hot and the prop is turned the belt makes a pretty strong creaking growl..I wasn't able to listen to what you posted (cant open file due to my firewall), but I have no vacuum pump. Never does it cold, but will always do it hot when I reposition the prop after a flight..forward less noised than backward. Alignment is spot on,tension normal, no unusual wear on the belt. 350 hrs. and always does it.
 
Do you have a Plane Power alternator?

The rear bearing enlarges the bore in the aluminum cover, which allows the rotor to scrape. Does it hot, after shutdown, when the flywheel grows a bit due to heat.

Remove the alternator, clamp the pulley in a solid vice, and rock the brush end. If it has any freeplay, it's bad. Ask Hartzell for a new one, free. They know about it.
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  • Alternator Rear Bearing Test.jpg
    Alternator Rear Bearing Test.jpg
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thank you for the comments

I do have a vacuum pump and i hadn't thought it could produce such a noise. The noise started after i replaced the cylinder but the vacuum pump is on its way out (low vacuum at full throttle with regulator turned all the way up) any way to inspect this?

No push rode tube scraping, i replaced all push rod tubes with brand new ones recently.

I don't think the noise is from the alternator, i hear it coming from the engine itself not near the alternator. My alternator is also brand new as well.
 
Make a mechanics megaphone stethoscope. Take a 1 gallon plastic jug (like the ones used for windshield washer fluid) and cut off the bottom.

Take a long screwdriver and tape the handle into the mouth of the bottle. Poke around the suspected areas while moving the prop.
 
I listened and it definitely sounds external. It can't realistically be the rings, as with that kind of sound, the the cyl would be trashed by now. Not sure where to direct you to find it, but pretty sure it is not the new cyl. It does sound like a rotating part that is binding. Can hear the tension build and then snap as it releases. vac pumps have sliding vanes that require centrifugal force to pull them into contact with the cyl, so doubt that is it.
 
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Creaky Spinning Things...

This is a two person job -- with the ignitions OFF and the fuel supply OFF, have a helper grab and rotate the prop to replicate the noise. Then, while it's creaking, put your hand on or near various spinning things that are attached to the engine -- such as (in no particular order):

1. Vacuum Pump
2. Standby Alternator
3. Propeller Governor
4. Oil Pump
5. Fuel Pump
6. Magnetos
7. Tach cable
8. Alternator
9. Baffling front ramps behind ring gear
10. Starter Housing (hung pinion gear)
...what did I miss?

With a noise that pronounced, you will be able to feel the corresponding vibration in one of the aforementioned items.
 
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I had this problem.....

I had almost the same exact sound (heavy squeaking - not clicking) it was the choke on the cylinders that was too tight. My noise was quite a bit worse than this.... About 10 mins after shutting the engine off - the internals are still hot but the cylinder is cooled. When rotating the prop to get pistons to top dead you would hear the squeak. The choke is too tight on the cylinder and there is no ring gap at top dead. Someone told me Superior had a bunch of cylinders that were "tight". When the engine is hot or cold it would not do it - only after shutting the engine down and waiting for the cylinder to cool a bit.

I don't know that I have the right solution for you but I'm highly confident that's what your issue is.

My noise was a lot worse than this - Lycoming treated me right - took the thunderbolt engine back and replaced the cylinders, pistons, etc.
 
RyanWhite said:
I had almost the same exact sound (heavy squeaking - not clicking) it was the choke on the cylinders that was too tight. My noise was quite a bit worse than this.... About 10 mins after shutting the engine off - the internals are still hot but the cylinder is cooled. When rotating the prop to get pistons to top dead you would hear the squeak. The choke is too tight on the cylinder and there is no ring gap at top dead. Someone told me Superior had a bunch of cylinders that were "tight". When the engine is hot or cold it would not do it - only after shutting the engine down and waiting for the cylinder to cool a bit.

I don't know that I have the right solution for you but I'm highly confident that's what your issue is.

My noise was a lot worse than this - Lycoming treated me right - took the thunderbolt engine back and replaced the cylinders, pistons, etc.
Click to expand...

Thanks that actually makes alot of sense. Did Lycoming ever say what the long term issue with this could be ? If this issue only appears during cool down would it not affect a running engine ? I'm guessing the miss match between cylinder and piston temp when cooling exacerbates the issue
 
I've had that noise in my O320-H2AD for the last 500 hrs or so. Only noticeable when the engine is shut down. My AI years ago diagnosed it as the camshaft bearing clearance. Did not seem overly concerned. Said he has seen it in a number of Lycoming engines.
 
One data point

A rivnut holding baffling to my lower cowl came unscrewed once, and the baffling and associated aluminum rubbing on the ring gear sounded just like this.

bjdecker said:
This is a two person job -- with the ignitions OFF and the fuel supply OFF, have a helper grab and rotate the prop to replicate the noise. Then, while it's creaking, put your hand on or near various spinning things that are attached to the engine -- such as (in no particular order):

9. Baffling front ramps behind ring gear
Click to expand...
 
johnpaul44 said:
Thanks that actually makes alot of sense. Did Lycoming ever say what the long term issue with this could be ? If this issue only appears during cool down would it not affect a running engine ? I'm guessing the miss match between cylinder and piston temp when cooling exacerbates the issue
Click to expand...

If the ring gap isn't big enough for the choke area (that would be an installer error, as the superior rings need to be sized by the installer - all of mine needed to be filled down some) the ring is mostly likely to crack the first time it got hot. If the gap is too small but ring not yet broken, there would be obvious signs of wear and distress on top inch or so of the cyl walls. You said you did a borescope and assume you wouldn't have missed this; Maybe that was an error on my behalf. If the ring is cracked, it wouldn't make this noise and compression would be low.

ring gap is an issue at high temp, NOT when cold. It is the expanding ring we are concerned with not the expanding cyl, when it comes to ring gap. The ring expands much more than the cyl does, so if there is not a gap to take up that growth (at least 15-20 thou), then the ring snaps. IIRC these rings need .0075 in the choke (this part of the barrel expands a lot) and .025 in the remainder of the bore (this part doesn't expand much).
 
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Dad's RV-10 said:
Make a mechanics megaphone stethoscope. Take a 1 gallon plastic jug (like the ones used for windshield washer fluid) and cut off the bottom.

Take a long screwdriver and tape the handle into the mouth of the bottle. Poke around the suspected areas while moving the prop.
Click to expand...

Funny, I was just telling my wife the other night that a screw driver is also called a mechanic's stethoscope. :D
 
Many scenarios here now..

Now that this thread has expanded in suggestions, and I finally figured out how to see the OP's video with sound, my sound is nearly identical. I have always attributed it to my alternator belt because it sounds like a creaking belt..And to Dans post,I have a Denso alternator from Vans way back store and not a Plane Power product. I have never had my engine un-cowled and duplicated it. It goes away pretty quickly as the engine cools. My engine is an O320H2AD, which I re-built myself (350 hrs. on it)and did my ring gapping per spec...interestingly from the other H2AD post a cam bearing is referenced. Not much the engine builder can do to alter those dimensions best I recall when I built mine. I will be keeping an eye on the additional responses here, as I am always looking for the "smoking gun" type answer. As an AP/IA, I haven't seen this on any other engines, but then I don't move a lot of "hot" props looking for it, except every time I pull mine in the hangar after flying.
 
As mentioned previously I had a very similar noise when moving the prop with the engine hot. Found it when turning the prop slightly to remove top cowl for an oil change. It ended up being the Plane Power alternator rear bearing. Just started to move in the housing. Hartzell replaced quickly under warranty.
 
Thank you all for the suggestions so far, i bought a mechanic's stethoscope to try to identify the exact noise location. The vacuum pump theory is interesting, the noise started after the replaced cylinder but my vacuum pump is indeed on its last legs, i will see if i cant isolate the noise location
 
Dad's RV-10 said:
Make a mechanics megaphone stethoscope. Take a 1 gallon plastic jug (like the ones used for windshield washer fluid) and cut off the bottom.

Take a long screwdriver and tape the handle into the mouth of the bottle. Poke around the suspected areas while moving the prop.
Click to expand...

much easier than that, skip the jug.... hold the handle of the screwdriver against your cheek bone just in front of your ear. (or any long stiff metal rod/tube, etc...)

It's amazing what you can hear through conduction
 
Jetmart said:
A It ended up being the Plane Power alternator rear bearing. Just started to move in the housing. Hartzell replaced quickly under warranty.
Click to expand...

I would start here as Dan suggested. This is a known and common failure point on the PP alt.
 
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