First Annual Done

How to keep the Cessna 170 flying and airworthy.

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IP076
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First Annual Done

Post by IP076 »

Hey all,

Had the first annual completed on the new to me 53 170B I purchased this summer. The annual was signed off and things are reasonably well, the airframe is nice and clean and got complements from the IA. The engine showed signs of some future work needed.

As it's my first airplane, a lot of this is new to me. Also, I'm a pilot...I fly for a living...I'm not a mechanic...I'll tinker on my old jeep, but definitely not the most mechanically inclined person out there.

I'm looking at compressions and just wondering a few things. Here's the data:

Engine was O/H at 1149.03 Tach Time, over 30 years ago. #6 cylinder was replaced 7/2015 at 2533.5 Tach.

12/18 Annual, Tach: 2557.89, #1-68, #2-72, #3-72, #4-72, #5-65, #6-77
12/19 Annual, Tach: 2559.00, #1-67, #2-70, #3-75, #4-72, #5-66, #6-77
Last Annual (1/21), Tach: 2655.80, #1-65, #2-67. #3-55, #4-69, #5-51, #6-75

Obviously #3 and #5 are the lowest. #5 was investigated and is leaking at the exhaust valve. It's tough to make a trend out of just this year, but is there anything to them all being lower? I would have thought flying it nearly a 100 hours might have helped the situation a bit.

I bought the airplane knowing an overhaul would likely be in the not too distant future. I'd like to get a few years out of what I've got before doing such, simply because I'd like to evaluate options of keeping the C145 or dropping the coin on an STC option.

What do you guys think about the data? Anything to do immediately? Fly it and see if anything comes up? For the record, the IA didn't seem too concerned about anything other than #5 and that was simply fly it until you notice a difference, and be ready to maybe swap the cylinder next year. What, if anything, should I be doing to help in my case?

Appreciate your feedback.
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johneeb
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Re: First Annual Done

Post by johneeb »

Hello IP,
Did the inspector Borescope the cylinders? The concern level of mediocre compressions goes up if the exhaust valve has an area that appears to be getting hot and causing the lower compression. Have a look at the below link it has useful information regarding valve appearance.

https://www.aopa.org/news-and-media/all ... _ownership
John E. Barrett
aka. Johneb

Sent from my "Cray Super Computer"
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IP076
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Re: First Annual Done

Post by IP076 »

John,

Thanks for the link. Informative.

Unfortunately no, it wasn't scoped at the time. Sore subject, I wish that would have happened, but there was a bit of a communication issue and I wasn't available at the right times...

Probably worth doing that now...
hilltop170
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Re: First Annual Done

Post by hilltop170 »

Did the same inspector do all the compression tests? There are approved techniques for compression tests and if done differently may give different results. Since all the cylinders are lower, something might have been done differently.

Was the same differential tester used for all the tests? Different gauges can show different results.

Sometimes trash can get under valves showing leakage that might clear up if the engine is run awhile. Or sometimes mechanics will “stake” the leaking valve while pressure is on by carefully tapping the valve rocker/stem with a soft hammer which will momentarily open the valve slightly and let it slam shut again.

Usually exhaust valve leakage is disqualifying as a true exhaust valve leak will not heal itself, only get worse, unless there was trash under the valve holding it open that works its way out while running.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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c170b53
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Re: First Annual Done

Post by c170b53 »

Agree with everything Richard adds. The exhaust valve leaking isn’t normally something most signing I think would live with. Hopefully its just carbon otherwise the cylinder should be pulled which might lead to the start of your new top.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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IP076
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Re: First Annual Done

Post by IP076 »

Thanks guys!

No, the recent test was done by someone differently than the first two points. I was thinking along the same lines, it just seemed odd that all were a bit lower.

I think I'll go down the road of investigating a little further, see if we can get a look at the valve itself and take anything away from that.

Honestly, I hesitate to doing a full top overhaul at this time since last major, would have to think you might as well do the whole overhaul...but that's getting a little ahead of where I'm at right now I think.
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c170b53
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Re: First Annual Done

Post by c170b53 »

I think it wise on your part to ascertain exactly why air is getting past the valve. As for your engine’s future, I believe a 30 year old smoh engine won’t come apart well. I would just put a new cylinder on if it indeed needs it but once you look into the hole in the case you might be looking down the rabbit hole.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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GAHorn
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Re: First Annual Done

Post by GAHorn »

The compressions on a high time engine are not too concerning, but the exhaust valve leak should be addressed. “Low” compressions can still be airworthy but not an exhaust-valve leak. You said your inspector indicated that also? If so, follow his lead on that.

(The problem with an exhaust valve leak is that the hot gases will act like a cutting-torch and the valve can break-up sending parts loose. A valve head inside the cylinder WILL get your attention...and WILL cause considerable damage.)

If it were an INtake valve then operating it a few hours then a re-check would be appropriate, but not an exhaust valve. Some mechanics have had success with “staking” the valve to reseat it, but if the exhaust valve cannot be sealed from leaking the cylinder must be repaired.
'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. ;)
counsellj
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Re: First Annual Done

Post by counsellj »

That engine has seen very little operation over it's last two years. Fly the hell out of it. Change oil every 25 hours and do an analysis. It just might need to be "exercised" to get it back to better compressions. 100LL or Mogas? Any fuel additives being used?
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Vertical
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Re: First Annual Done

Post by Vertical »

I'm in the process of going through this currently. Two low cylinders with exhaust leaks. Did a borescope with the mechanic. Then I bought my own scope off amazon for ~$50. I scoped all cylinders again and catalogued photos. Then I researched, asked around and studied valve/cylinder health issues, until I felt I could make the safest, most informed decision.-Its my butt in the air after all.

I bought two new cylinders and am in the process of installing them. At the same time I'm doing an IRAN on the exhaust system, baffles and powder coating the cylinder head covers.

During the IRAN I found a hard see but very cooked/cracked exhaust riser on the cylinder with the worst exhaust leak. There was also a couple cracked exhaust riser clamps. -Definitely glad I didn't just keep flying it hoping for better news later.
hilltop170
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Re: First Annual Done

Post by hilltop170 »

When borescoping a cylinder and exhaust valve, rotate the engine until subject valve is fully open. Note: DO NOT ROTATE THE ENGINE WITH THE BORESCOPE INSERTED INTO THE CYLINDER!!!! That crunching sound is very expensive!

Look for a yellow-ish, orange-ish, or green-ish discolored area on the valve itself near the edge which may indicate where the leak/hot exhaust gas escape path is located. Inspect the valve and valve seat sealing surfaces for any distress. If none is seen, it might have been trash holding the valve off-seat.

You and your IA will have to decide to continue running the engine or R&R the offending parts. Carbon or precipitated lead particles breaking off inside the combustion chamber and temporarily getting caught in the exhaust valve seat surfaces is a common occurrence.

If you go with new cylinders, buy the ones with valve rotators if they are still available. That definitely helps reduce the valve sticking and burning problems. I bought ECIs in 2006 with rotators but ECI is gone now so I don’t know if any are still available.
Last edited by hilltop170 on Wed Jan 20, 2021 8:28 am, edited 1 time in total.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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c170b53
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Re: First Annual Done

Post by c170b53 »

Well of opinions is, what it is but a tap on the valve stem is also a common occurrence and would or should have been done right then to determine if debris was causing a leak.
I'll counter Jughead's comments based on the time out of operation (maybe if I had his off airport landing skills I might think differently), that leaking valve might just be doing you a favor.
I'm doing little to assuage your thoughts on the engine's condition but I've seen this story unfold before and all I can say is I'm hoping that Jughead is right.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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Bruce Fenstermacher
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Re: First Annual Done

Post by Bruce Fenstermacher »

hilltop170 wrote:If you go with new cylinders, buy the ones with valve rotators if they are still available.
Only OEM Continental and Superior are available. No rotators.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
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mmcmillan2
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Re: First Annual Done

Post by mmcmillan2 »

Subscribed
170B owner, KCFD, CFI(I), ATP Multi
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IP076
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Re: First Annual Done

Post by IP076 »

Thanks for all the info guys.

To speak to Jughead's points, I kind of had those thoughts early on in owning the airplane. I half expected the situation to improve with the amount it's flown since the last annual...nearly 100 hours, and from what I've come to understand, that's probably above average. An oil change is about 8 hours away (maybe just do it early), and I've got the kit to send a sample off now...it will happen this time. I've changed the oil at 25 hour increments and there's no signs of metal in the ADC oil screen.

I'm going to go down the road of a cylinder inspection with a borescope and see what we can see.
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