After an uneventful flight from Berry Hill Airport (South of Atlanta) to Norfolk, Va the C-145 on my "new" '52 started "ticking" at lower RPMs, namely below 800 or so(bottom idle is set around 500.) The oil pressure is steady 30-40, the RPMs do not fluctuate, there is no hesitation/misfiring and the temperature on the trip was good during cruise and climb....even better when I got the new cowl pressure seal "trained" a little. Being new to C-145/O-300s I have no idea what this could be.
Some of the ideas from local A&Ps and IAs familiar with the 145s are: sticking valve, noisey impulses on a mag (noise appears to be on the right side (cyl 1,3,5 side), counterweights?, shear on the generator, generator itself....... The noise appears to be metallic but, it goes away at RPMs above 900 and at 2450 everything looks, feels, sounds great.
Ideas? Thoughts? Troubleshooting tips? It had been a while since it was flown (5 years) but the compressions were all above 76, no major leakes (a little leak around the generator shaft, etc...
Thanks in advance for thinking about this and all of the free "Advice"
Do not run the engine again until you have inspected your impulse couplings on your magnetos.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Impulse couplings can be pretty loud as they snap, and if one is failing, I can imagine they might make all kinds of racket. I was only thinking of the fact they disengage around 600 rpm normally, and I figured you probably already knew the sound of a collapsed lifter (which is the only other thing I could think of....but a lifter would likely also contribute to a rough idle...which you don't describe.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
Thanks for the clarification! I'll see about getting them checked out. I don't think it's a lifter either, then again, my experience is with C-220s and car engines but, I would imagine they sound about the same. I wonder is the idle is set too low...450-500? Perhaps it takes a moment for the couplings "spool up?" Also, if the mags are not modded (spring) would they be more prone to "ticking?" I think that there is an inspection interval on mags which are not modded and meet the "1/8 or 30 drill bit" gap test.....do you know?
After closely listening to your post several times my ear tells me it is probably the impulse coupling. 450-500 rpm is a bit low and I would think you might hear the impulse couplings. I can hear them on my Cub at this RPM.
Having recently had a mag bearing failure which sounded like an impulse coupling in the moments before it failed I would recommend at the very less a log search to determine the last time the mags where removed and inspected. Assuming that wasn't in the last 100 hour or so i would remove them and inspect them. Mine failed 370 hours after remanufacture. To be honest with my experience if I had any question I'd pull and inspect the mags.
If you find nothing you won't be sorry you did it cause you'll know their OK and if you find an problem be happy you found it on the ground before more damage from a failed mag can happen.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Here is something from "Harry Fenton's Hints and Tips for Small Continental Engines" Harry Fenton is an A&P and has owned numerous airplanes over the years. He's been providing a lot of good advice on maintaining Continental engines to the Fly Baby mailing list. This can be found at:http://www.bowersflybaby.com/tech/fenton.htm
This is contained in an article entitled: "Trouble-Shooting Low RPM"
"You don't mention the mag type, but it is impulse coupled , the impulse coupling spring, or springs, could be broken and most definitely cause rpm loss. Wood props with an idle set below 450 rpm will cause this problem as the impulse coupling will click continuously until the spring fails. When the prop is pulled thought, you should hear a solid click for each impulse coupled magneto. "
This supports some of the ideas above. In my 170 manual, it says not to idle the engine below 600 RPM for any length of time, however the reason given is lack of lubrication. I've never heard my magnetos "click" at minimum idle, but it sounds like if they do, I would consideer George's advice.
There use to be an AD which required inspection of certain mags impulse couplings at every 500 hours. That AD has been superseded with another limiting the mags to just a few on certain engines and the C-145/0-300 is not one of them. So there is no AD any more that applies.
Based on my experience of a total mag failure which could have lead to at the least engine gear replacement or engine overhaul or worse, I am planning on inspecting my mags every 300 hours.
I will do this regardless of manufacturer. Mine happen to be brand new Slicks.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
I will get them inspected. I found the idle info in the manual as well, 600 RPM. So, first I'll warm the engine and then I'll adjust the idle up to 600 and see how that does. Then, inspect the mags!
Working with an IA I think we found the problem. Got a couple leaks, generator shaft and right mag. Those will be done this weekend. The big noise maker (so far is the #5 cylinder. BOTH lifters are not quite coming up when the RPMs are low. When the engine is brought up on the power, no noise so they must be pumping up more under the slightly greater oil pressure. So, I put some Rislone in it and will run it for a few hours to see if the lifters might clean up and work properly. IF not, then the cylinder will have to come off
Any other things which might get them working correctly again? Exhaust is about a credit card's width and the intake is slightly less.
Suggestion.
Before you try to remove the lifters, bleed them down and check the dry tappet clearance. Seems to me it's .030 to .110 inches, but best you check the manual. You may need other than standard length push rods.
It would be hell to split the cases to chage out the lifters and then find that it was a dry tappet clearance problem.
I have this same problem I have always noticed it while taxing around......I usually try to keep the rpm around 800 to 1000 while on the ground.......When the rpm is up I dont here the clicking noise.... My wife was standing by the hangar when I taxied up one day and she could here the noise from the outside........I askes my Mech. but they were not too concerned.......The engine was rebuilt by Mena aircraft engines about 40 hours ago..............Let me know what you find out
Weird, same noise...... I've been flying mine with no issues for about 12 hours (out on the ship now, no flying 170s) with no change in the noise or perfromance. My "new" radios go in on the 1st and then I'm having another local IA do a new weight and balance and check into the noise a little more. He seemed to think it was nothing to worry about either but, I want him to dig a little deeper anyway. I'll post what I find out either way.
If you get anything, I'd like to know as well (probably others too!)
any luck on your eng noise? I was flying mine this evening, after I landed I took off my headsets and man......that noise is driving me crazy There is another 170 on the field, I took a ride in his the other day............quiet as a mouse..........maybe he will leave his hangar unlocked so I can trade noises one night.... Nobody seems to be too concerned with the noise.....I know its not the generator because I got a different one installed..........long story.........
Oh well
Good luck
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to your post several times my ear tells me it is probably the impulse coupling. 450-500 rpm is a bit low and I would think you might hear the impulse couplings. I can hear them on my Cub at this RPM.
I have always noticed it while taxing around......I usually try to keep the rpm around 800 to 1000 while on the ground.......When the rpm is up I dont here the clicking noise.... My wife was standing by the hangar when I taxied up one day and she could here the noise from the outside........I askes my Mech. but they were not too concerned.......The engine was rebuilt by Mena aircraft engines about 40 hours ago..............Let me know what you find out
There is another 170 on the field, I took a ride in his the other day............quiet as a mouse..........maybe he will leave his hangar unlocked so I can trade noises one night.... 
Nobody seems to be too concerned with the noise.....I know its not the generator because I got a different one installed..........long story.........