Boroscope Concerns on a '55 PA-22 O-320

[jasongould]

Hi fellow Short Wingers:

I purchased a '55 PA-22-150 about 4 months ago (from Southern Illinois, now in Grand Prairie, TX) which was mostly restored (with a beautiful Superflite recover) and had field overhaul of it's original O-320-A1A. Unfortunately the guys doing the overhaul decided to use the original cylinders during the overhaul, though they had the crankshaft repaired (by AEA), and used new one-piece camshaft, tappets, plungers, oil pressure relief valve, bearings, oil pump, pistons, exhaust valves, etc.. Connecting rods, rocker arms, etc were inspected and re-bushed by G&N aircraft.



After they finished the restoration, they put about 2 tach hours on the motor before both lost their medical which led to it sitting for 4 years. Over the 4 years they would start it, do a long ground run up, and taxi it around every 2-4 weeks (so they said...), as well as added Avblend to the oil after to help prevent corrosion. The compressions before flying it down to TX were all around 76/80, but I was an idiot and didn't have them do a boroscope inspection when I picked it up (big lesson learned!)

I've been having a few last bugs worked out of it over the last 4 months, so including the flight down from IL, I've only put about 14 tach hours on the motor. This puts it right at about 16 hours since the field overhaul, and about 3300 hrs total since new. Then recently I thought I'd do a boroscope inspection just to investigate how the cylinders and valves are holding up, and what I found was a bit concerning and I thought I'd get some opinions on what's going on.

My number 1 cylinder was chromed back in the 70's, and is actually still in pretty good shape, and all the exhaust valves all show a good symmetric pattern. However all the other cylinders show what looks like scratching, and my #4 cylinder has stripes! I'll attach a few of the examples, and link to a shared Dropbox folder with all the images from the boroscope inspection.

Images: https://www.dropbox.com/sh/55fkjbm7b9uphdj/AADnWbntN0pKIenoWJp-V7eMa?dl=0

Cylinder 4 stripes on the fore side of the cylinder wall:



Aft side of Cylinder 4:


Wear on cylinder 3:


Possible corrosion (and a small pit?) on cylinder 3:



Cylinder 2 wear:




The engine runs great other than a slight vibration that I can't figure out where it's coming from (even had the prop dynamically balanced.) Cylinder 4 runs the hottest at about 430-440 deg F on climb out on a 65 degree day, for example. I do have an Aerospace Logic 4 channel EGT/CHT and have been monitoring it closely. My mechanic friend is most concerned with cylinder 4, and wants to pull that one and see if we can either hone it back, or worst case replace it. Oil usage is around 1/4 Qt per 1-2 hours right now.

Anyone seen anything like the striping? Also, how concerned should I be with the state of the other cylinders? Any advice is immensely appreciated!

 

[Steve Pierce]

I would send the pictures to G&N and see what they think. I have never seen anything like that. You also have Sal Buentello of Sal's Cylinders up in Prosper who does great cylinder work. 972-346-3339.

 

[andya]

Something to remember about break in, that two hours they flew is not necessarily long enough to seat the rings on normal factory cylinders.
the ground runs after that certainly didn't help seat the rings, ie need at least 70-75 percent power and plenty of airspeed for cooling, which won't
happen with ground running in the airplane. Regard the pics, steve has the best advice, contact G&N

 

[DaleLindstrom]

It looks like the rings were not fitted to the cylinders. The end gap on the rings needs to be checked before installing them on the pistons. If they are too tight, they are filed to the correct end gap.
On #4, especially, you can actually see the cooling fins from the inside of the cylinder! That is caused by too tight of a fit of the components inside of the cylinder "pushing" the cylinder walls outward when things heat up. I'm pretty sure that those cylinders are junk.
I would also be worried about the steel and chrome scraped from the cylinder walls contaminating the bearing surfaces within the engine.
As an A&P/IA, if I owned it, I would tear it completely down and do an IRAN. (Inspect & Repair As Necessary)

 

[Pacer42Z]

One quart of oil every 4 to 8 hours is also quite high. I'm surprised the compression checked in as high as it did. I think your mechanic friend is correct. If it would be my engine, I would have the cylinders pulled for closer inspection.

Juergen
Pacer N3342Z

 

[Steve Pierce]

I ran my Clipper past TBO and iot always burned a quart of oil every 4 hours and had compressions in the mid 70s. When I took it apart it had worn the oil control rings out. I think a quart every 4 hours is at about the bottom of the limit from Lycoming.

 

[DaleLindstrom]

After reading the first post again, it could have just been overheated on the ground runs. Especially if high power was used for extended periods.

 

[jasongould]

Thanks everyone!

I also reached out to the infamous Mike Busch's firm, who recommended pulling the worst (#2 and #4 cylinders) and sending them of to a reputable shop. This way I can also get a better look at the cam and lifters, which I've been told to be prepared to find corrosion pits. My fingers are crossed that I somehow get lucky on the bottom end corrosion...

So #2 and #4 should be going to (infamous in the DFW area) Sal's Aircraft Cylinders sometime later this week. I'll post pics of the cam and bottom end to complete this post as a look at what happens when someone makes bad mistakes and lets an engine sit un-pickled for an extended period of time.

Definitely learned my lesson: never buy an aircraft without a boroscope inspection! Especially if it's been sitting. Even if everyone seems very trustworthy and tell you that corrosion isn't a problem in their area!

 

[Pacer42Z]

Good luck with the examination of your cylinders. I had to do a top end overhaul after just 1,100 hours on a newly rebuild engine done in 2007 (I own my Pacer since 1999). I fly my Pacer regular all year long at least 100 hours and still ended up with a top overhaul. It was about $6,500 for brand new Lycoming parts. Worse case, you have to spend the money, but then you will have a really nice Tri-Pacer. As far as I'm concerned, it's much better than finding airframe corrosion that requires repair and then new fabric and paint.

Juergen
Pacer N3342Z

 

[Gilbert Pierce]

Juergen, I had a similar situation averaging 100+ hours a year on a rebuilt engine with new Millennium cylinders.
Pulled them at 1400 hours for excessive oil consumption and took them to Sal’s. Worn valve guides and cylinders barrels.

Were new cylinders installed on your engine at the 2007 rebuild?

Jason, take your cylinders to Sal in person. He is an interesting guy.

 

[Pacer42Z]

Gilbert, yes, brand new Millennium cylinders. After 1,100 hours I had high oil consumption and low compression on two cylinders. Plus on the #4 cylinder the rocker shaft bearings started to move since the hole in the cylinder heads for the bearings were over sized (out of spec).
I had a full top end overhaul done with brand new Lycoming parts. Now I have over 200 hours on the new cylinders with very low oil consumption and a strong running engine. Last October I flew 48 hours in 10 days and only had to fill in one quart of oil between the oil change (every 50 hours).

Juergen
Pacer N3342Z