Engine Vibration and Exhaust Noise at Low Power Settings

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Rich
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Rich »

Matt, some comments on the CHT deal:
1. EGT#4: what's up with that???
2. I've never cruised with EGT's that high. ROP, somewhere in the mid 1400's generally.
3. What RPM? Higher RPM does mean higher CHTs.
4. OAT impacts CHTs. I don't generally see the problem you mentioned except when OAT is abnormal. One flight last year I had the same experience as you at 8K with OAT at 25 DegC (far above normal for that altitude - DA 10.5K)
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by mhoran »

Rich wrote: Thu Jul 01, 2021 4:21 pm Matt, some comments on the CHT deal:
1. EGT#4: what's up with that???
2. I've never cruised with EGT's that high. ROP, somewhere in the mid 1400's generally.
3. What RPM? Higher RPM does mean higher CHTs.
4. OAT impacts CHTs. I don't generally see the problem you mentioned except when OAT is abnormal. One flight last year I had the same experience as you at 8K with OAT at 25 DegC (far above normal for that altitude - DA 10.5K)
1. The EGT #4 probe was bad; it's since been replaced and is in line with the others as you'd expect.
2. Interesting. We've tried both the "lean until rough and enrich" and running 50 degrees ROP and this is where things land. This past Sunday I was debugging and landed at about 1450 EGT at 8k but CHT #1 was at 413 (the rest were 385-386). I enriched to get CHT #1 down to 404 and EGT was around 1400 or a bit less. Fuel flow was at 10.1 GPH.
3. I had been running at 2500; last weekend I tried 2450.
4. Unfortunately cylinder #1 runs hot even in winter. But recently it has been around 60 degrees at cruise.
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Rich »

mhoran wrote: Thu Jul 01, 2021 4:42 pm
1. The EGT #4 probe was bad; it's since been replaced and is in line with the others as you'd expect.
2. Interesting. We've tried both the "lean until rough and enrich" and running 50 degrees ROP and this is where things land. This past Sunday I was debugging and landed at about 1450 EGT at 8k but CHT #1 was at 413 (the rest were 385-386). I enriched to get CHT #1 down to 404 and EGT was around 1400 or a bit less. Fuel flow was at 10.1 GPH.
3. I had been running at 2500; last weekend I tried 2450.
4. Unfortunately cylinder #1 runs hot even in winter. But recently it has been around 60 degrees at cruise.
I would be surprised if this is a factor but what you describe about #1 being hottest is exactly the behavior we had when we got our plane. Subsequently we installed the unfortunately named "Arizona Baffle" and it brought #1 CHT in line with the other 3. I thought said baffle became standard somewhere along the line, but certainly don't know when that happened. Check this link out. It also has a note about an obstruction I discovered below #3 cylinder, which I suppose could happen with #1 also: viewtopic.php?f=8&t=7231
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by mhoran »

I thought we could be missing the Arizona baffle, but we have a 2007 and I think it was standard by then. Looking at the hole in our cowling, it seems a bit larger than the original hole. Good point about the obstruction though, that could well be it. I'll take a look. I've also heard a poorly installed EGT probe can blow hot air on the CHT probe, so I'll check for that too.
PXL_20210628_020541057.jpg
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by mhoran »

Latest thought on the cause of the roughness is bad mags. I've noticed RPM drop during mag checks getting progressively worse over the past few flights, and analyzing the last year of engine data there's a definite trend on the left mag (oddly, I thought the right mag was misbehaving.) We've ordered a pair of overhauled mags and will try that out this week.
Mag drop.png
CHT #1 is still baffling (no pun intended.) I do think it could be a bad reading, or perhaps something else (like an obstruction) in the cowl setting the temperature off. EGT seems fine on cylinder 1 and the higher CHT makes no sense. The cylinder also isn't misbehaving in any other way. I've read that others have seen anomalous CHT due to failure of the fire proof cowling paint (ours is failing too, again) as well as baffle seals. I'm having the fire proof paint replaced soon, and will have the seals checked.

One other suspicion my mechanic had around the vibration is my alternator. It looks like a rock got sucked through recently which roughed up the cooling fans. However, they all look to be intact. We decided to go with the mag replacement first, but he was going to try and run the engine with the alternator belt disconnected as well to see if that is the source of the bad vibes.
PXL_20210615_151751576.jpg
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Rich »

Have you tried a mag check in flight? This was how I identified an issue to Surefly.
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by mhoran »

Rich wrote: Sun Jul 04, 2021 4:31 pm Have you tried a mag check in flight? This was how I identified an issue to Surefly.
I have not. I didn't suspect the mags until I dug deeper into the engine logs. Unfortunately the plane is in my mechanic's hangar at this point so I likely won't get to do one before the mags are swapped.
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by mhoran »

Replaced the mags today and the vibration is still there. The right mag still shows significant drop and roughness; the left mag seems to be fine. We now suspect the wiring harness or the plugs. I did perform an in flight mag check but nothing really stuck out. I suspect I didn't run on each mag for long enough; I only went around the pattern once so didn't have much time to test.
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Pilot55 »

Did your mechanic check the resistance in your plugs? If they are more than 5000 ohms resistance through them out. When I had my DA40 i used tempest fine wire plugs. If mags seems to run rough always check plugs and wires first. Champion plugs will fail much quicker than tempest do to the type of resister circuit. The IO 360 should be run at around 12 -12.2 air/fuel ratio which will give you @ 2450 rpm 11 gph @ 21MP, 11.6gph @ 22" and 12.6 @ 24MP. This should put the egt's at around 100 ROP. If your engine can run lop it should be around 17-17.7 a/f. Also check the prop balance on these engines. The four cylinder engines have much more vibration than six cylinders and any added out of balance do to the prop makes it much worse.
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Re: Engine Vibration and Exhaust Noise at Low Power Settings

Post by Steve »

I'll second the recommendation to check the plugs and harnesses. I had a number of failed Champion massive electrode plugs when I used them. In my case there wasn't much vibration, but I had uncharacteristic difficulty with cold starts. Switching to Tempest fine wires did the trick, and that is what I use now.
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