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Thump-thump vibration through the floor of my RV-10 after an engine (re)install

vas4vans

vas4vans

Well Known Member
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As I have shared in other posts, I had the engine overhauled in my -10 and it was reinstalled about 3 weeks ago with new shock mounts. I have been doing break-in flights since then and I am up to about 11 hours or so on it. What seems to be different now (compared to before the overhaul) is that when I reduce the RPM to 2500 and below, the amount of vibration that I can feel through the soles of my feet seems to be higher. It's a fast thump-thump as opposed to a continuous vibration and the frequency seems to change with the RPM.

The A&P and I took off the cowls and tightened up everything (exhaust pipes, oil breather tube, etc.) and the vibration didn't change. I had the prop balanced (IPS went from .49 to .02) earlier this week. On the flight yesterday, it seemed a bit less but it's still very perceptible.

Any other ideas from the braintrust in terms of what else we should be looking for?

Thanks.
 
vas4vans said:
As I have shared in other posts, I had the engine overhauled in my -10 and it was reinstalled about 3 weeks ago with new shock mounts. I have been doing break-in flights since then and I am up to about 11 hours or so on it. What seems to be different now (compared to before the overhaul) is that when I reduce the RPM to 2500 and below, the amount of vibration that I can feel through the soles of my feet seems to be higher. It's a fast thump-thump as opposed to a continuous vibration and the frequency seems to change with the RPM.

The A&P and I took off the cowls and tightened up everything (exhaust pipes, oil breather tube, etc.) and the vibration didn't change. I had the prop balanced (IPS went from .49 to .02) earlier this week. On the flight yesterday, it seemed a bit less but it's still very perceptible.

Any other ideas from the braintrust in terms of what else we should be looking for?

Thanks.
Click to expand...
What prop are you using?
 
Couple thoughts. Was the prop put back on in the same index position as it came off? The 540 is sensitive to prop clocking, at least with the hartzel. No experience with ww.

Lycoming has several different counterweights and a few different bushings that can go in them, as well as different pin sizes. Might want to get the detailed parts list for what went back into the engine. Often the weights go to asi and they rebush them and new pins are ordered, as these are wear able parts. If any of these changed, it could cause vibration issues.

Finally, exhaust drumming on the lower skin can match your symptoms if the exhaust alignment changed.
 
lr172 said:
Couple thoughts. Was the prop put back on in the same index position as it came off? The 540 is sensitive to prop clocking, at least with the hartzel. No experience with ww.

Lycoming has several different counterweights and a few different bushings that can go in them, as well as different pin sizes. Might want to get the detailed parts list for what went back into the engine. Often the weights go to asi and they rebush them and new pins are ordered, as these are wear able parts. If any of these changed, it could cause vibration issues.

Finally, exhaust drumming on the lower skin can match your symptoms if the exhaust alignment changed.
Click to expand...

I am not sure about the index position. I'll have to check. If I can figure out that the new index position is different than the old one, would it require the prop to come off to be put back on in a different position and would that be recommended?

I am pretty sure the exhaust pipes are not hitting the cowl or the bottom of the firewall but I'll check again when I go to the hangar tomorrow.

The attached document has the list of parts that went in per engine shop. But I am not sure what came out of the old engine. Also, the case is different as is the crankshaft. My original case was going to take longer to refurbish so they sent a different refurbished case. My original crank was out of spec so I landed up having to buy a refurbished crank.

Thanks.
 

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vas4vans said:
I am not sure about the index position. I'll have to check. If I can figure out that the new index position is different than the old one, would it require the prop to come off to be put back on in a different position and would that be recommended?
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Yes, the prop would need to come off. As mentioned, the 2 blade metal props seem to have a favorite position. The 540 seems have more of a "thumpier" feel than a 4 banger. (I re-clocked my WW 3 blade on my 390 to see which one felt better) You probably have seen 10's with exhaust extensions, pretty common. I also re-clocked the WW 300 on my 10 to see which one "felt" better.

Is your WW a 2 or 3 blade? The props with wider chords both WW (Now Hartzell) and Hartzell designs (Raptor design) seem to have more of the floorboard thump-thump. Pics of the prop might help the group. I did not recognize or know WW made a model "RV-10" prop. More familiar with the HRT, 300 and 330 model.

When you had it rebalanced the newer devices will give 1st and 2nd order harmonics and might give you a lead what to look for.
 
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vas4vans said:
I am not sure about the index position. I'll have to check. If I can figure out that the new index position is different than the old one, would it require the prop to come off to be put back on in a different position and would that be recommended?

I am pretty sure the exhaust pipes are not hitting the cowl or the bottom of the firewall but I'll check again when I go to the hangar tomorrow.

The attached document has the list of parts that went in per engine shop. But I am not sure what came out of the old engine. Also, the case is different as is the crankshaft. My original case was going to take longer to refurbish so they sent a different refurbished case. My original crank was out of spec so I landed up having to buy a refurbished crank.

Thanks.
Click to expand...
If someone did not take note of the prop oreintation relative to the crank, you will probably never know how it was before. There is a standard position, but many of us with the hartzel 2 blade re-clock it to reduce vibrations. It makes a meaningful difference on the 10. I have flown both with balanced props and the difference is definately noticeable even though it is not harsh. That is a more involved discussion though. Looks like they overhauled the weights, but didn't see new pins on the parts list. You can probably assume this was done correctly with a shop like lycon. With the exhaust, I was not referring to the pipes hitting anything. On the early 10's with the shorter pipes, belly drumming was common from the pulsing exhaust hitting the belly. Worth a look to see if they did something different when reinstalling yours. Probably not likely.
 
vas4vans said:
As I have shared in other posts, I had the engine overhauled in my -10 and it was reinstalled about 3 weeks ago with new shock mounts. I have been doing break-in flights since then and I am up to about 11 hours or so on it. What seems to be different now (compared to before the overhaul) is that when I reduce the RPM to 2500 and below, the amount of vibration that I can feel through the soles of my feet seems to be higher. It's a fast thump-thump as opposed to a continuous vibration and the frequency seems to change with the RPM.

The A&P and I took off the cowls and tightened up everything (exhaust pipes, oil breather tube, etc.) and the vibration didn't change. I had the prop balanced (IPS went from .49 to .02) earlier this week. On the flight yesterday, it seemed a bit less but it's still very perceptible.

Any other ideas from the braintrust in terms of what else we should be looking for?

Thanks.
Click to expand...

Sounds similar to an issue I had with my RV-6. The issue ended up being caused by a fractured exhaust hangar. Or, rather, the motion of the exhaust pipe in flight as a result of the broken hangar.

Here's the thread, and it includes some audio that might help you determine if your thumping sound was anything like mine:

Engine knocking sound

I recently noticed what I will call a knocking sound from the engine and can't seem to identify what's going on. I thought perhaps the collective knowledgebase here might be able to help. Here's a link to a sound file which I recorded with my phone. (Apologies for the fact that you can hear...
vansairforce.net

--Ron
 
Attached are photos of the exhaust pipes. Are they too close to the cowl?

Thanks.
 

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vas4vans said:
Attached are photos of the exhaust pipes. Are they too close to the cowl?

Thanks.
Click to expand...
yes. Over time that will start wearing your cowl IMO. 1/4" is probably adequate, depending on how rigid or loose your exh hanger set up is.

This could be the source of your vibration. I know many that don't cut down the baffling enough to avoid contact with the upper cowl get noticeable vibrations, though that is a more rigid part. It shouldbe addressed either way.
 
vas4vans said:
Attached are photos of the exhaust pipes. Are they too close to the cowl?

Thanks.
Click to expand...
The pipe to cowl clearance does look a bit tight to me.

One thing you might check:
In those pictures I can't see the lower cowl pins. How are they secured? During flight test on my RV-10, on one flight I noticed similar vibration, which I localized to the floor under my feet. Upon investigation I found one of the lower cowl pins had worked itself loose. Still attached, but had worked itself partway out. When I resecured the cowl pin, the vibration went away.
 
Tweetr said:
The pipe to cowl clearance does look a bit tight to me.

One thing you might check:
In those pictures I can't see the lower cowl pins. How are they secured? During flight test on my RV-10, on one flight I noticed similar vibration, which I localized to the floor under my feet. Upon investigation I found one of the lower cowl pins had worked itself loose. Still attached, but had worked itself partway out. When I resecured the cowl pin, the vibration went away.
Click to expand...
Surprising how many little seemingly unrelated things can cause vibrations under the right conditions l
 
Thanks for all the suggestions!

After moving the exhaust pipes, the vibration seems to be much better though it's not completely gone at all RPMs. Perhaps we need to move it a bit more the other way and also secure them more tightly.

I'm told that there is a more sophisticated dynamic prop balancer which has two sensors which are installed at different parts of the engine. Any thoughts on whether that may help?

Thanks.
 
vas4vans said:
Thanks for all the suggestions!

After moving the exhaust pipes, the vibration seems to be much better though it's not completely gone at all RPMs. Perhaps we need to move it a bit more the other way and also secure them more tightly.


Thanks.
Click to expand...
If you think it is still making contact, put a piece of tape on the cowl where you think it is contacting and go fly. If it is, you will see witness marks in the tape.
 
vas4vans said:
I'm told that there is a more sophisticated dynamic prop balancer which has two sensors which are installed at different parts of the engine. Any thoughts on whether that may help?

Thanks.
Click to expand...
Measuring the vibs at the rear of the engine is a bit of a waste of time as there is nothing you can do to specifically correct it. It could point out an engine problem in rare cases if you compare it to the front vibs, in my experience a spectrum analysis at the front will basically do the same thing.
 
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