Piper Cherokee cylinder replacement

jmarine225

Pre-takeoff checklist
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Jmarine225
This is a bit of a change from my last post so I figured I’d start a new thread. My Cherokee O320 is using more oil than usual. I have the numbers and I’m going to plot them out to see the usage increase. With that, the AP pulled all the plugs and my number 3 cylinder has oil on the bottom plug. He borescoped the cylinder and stated it looks black inside. Did a compression check prior to running the engine up and the check was in the 70’s. The AP indicated to keep flying the aircraft but the cylinder will need to be replaced at some point. I have no issues with power or performance in the aircraft. He said it appears oil is getting past the rings.
 
This is a bit of a change from my last post so I figured I’d start a new thread. My Cherokee O320 is using more oil than usual. I have the numbers and I’m going to plot them out to see the usage increase. With that, the AP pulled all the plugs and my number 3 cylinder has oil on the bottom plug. He borescoped the cylinder and stated it looks black inside. Did a compression check prior to running the engine up and the check was in the 70’s. The AP indicated to keep flying the aircraft but the cylinder will need to be replaced at some point. I have no issues with power or performance in the aircraft. He said it appears oil is getting past the rings.

My best bud has a cherokee with a 0-320 in it. I helped him and his IA do his annual this past Aug. His motor is using 1 qt every 4 hours. His compression's were in the mid 70s with one at 70/80. That cly had a oil fowled lower plug in it. His motor is running well with normal power. His IA is a 40 year personal friend and has been a IA that long. My best bud is 22 year SW captain and both of them have been in aviation since they were teenagers. So he can trust his IA.

He said to fly it, don't worry about it until the oil consumption gets worse. You could take that cly off and checkout the rings but he did NOT recommend that until the oil usage got worse.

On the other hand, I have a 0-320 H2AD motor that had 1650 hrs on it all original. It was using 1 qt per 4 hrs. Last Xmas I removed all four clys to checkout what I had. 2 of mine were down in the 50s compression. I found 3 out of 4 clys had the rings lined up to one another. I have done a lot of motor rebuilds in cars and trucks and have NEVER seen that. I found no other problems. I spaced the rings out, the original rings and put it back together. I flew it for another 100 hrs and it ran great, maybe a little better than before I took it apart. But the big take away was the oil consumption improved to 1 qt to 8-9 hrs.

Jim my buddys IA said he has seen that before when he took pistons out to find the rings lined up. I have never noticed before on motors I have rebuilt. True story...
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Just so you don't think I am BSing you.
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I did find minor spalling on some lifter/tappets. Not enough to keep me from putting it back together. The one still showed the rockwell test marks on it as you can see.
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The AP did mention the rings may be lined up now and can possibly correct themselves. I have the formula for the oil consumption but did he happen to say at what point is too much?
 
The AP did mention the rings may be lined up now and can possibly correct themselves. I have the formula for the oil consumption but did he happen to say at what point is too much?
1 qt per 1-2 hours would be when action should taken.

Jim the IA seemed to think for some reason the compression holds the rings in place when they are lined up on airplane motors? He said he has no technical evidence of that and was just speculating. But have seen rings lined up when removing jugs. Jim maintains a fleet of chieftains that do aerial surveys. He remove jugs on those things with his eyes closed.
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1 qt per 1-2 hours would be when action should taken.

Jim the IA seemed to think for some reason the compression loss holds the rings in place when they are lined up on airplane motors? He said he has no technical evidence of that and was just speculating. But have seen rings lined up when removing jugs. Jim maintains a fleet of chieftains that do aerial surveys. He remove jugs on those things with his eyes closed.
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Thanks for the info. So I’m curious why are the compressions still good but increasing oil consumption? Does the cylinder still need to be changed with good compressions?
 
Thanks for the info. So I’m curious why are the compressions still good but increasing oil consumption? Does the cylinder still need to be changed with good compressions?
Jim said he replaces clys and pistons when the oil consumption get too high. Not by compression.

I cleaned my used pistons and rings before putting it back together to insure nothing is stuck. Definitely made a difference in oil consumption, not so much performance.

Jim said some of his cheiftains motors use 1qt per 2 hours and can predict when oil must be added by the number of hours each plane fly's .
 
Thanks for the info. So I’m curious why are the compressions still good but increasing oil consumption? Does the cylinder still need to be changed with good compressions?

Oil helps ring seal which can in turn boost cylinder leakage numbers.
 
There are many ways that oil can get into the combustion chamber and be consumed. I’d be taking the engine apart to figure out what’s wrong with it but with the given description I can’t fault the mechanic for making the recommendation to leave it alone for now.

I have taken apart a lot of engines of various types. The ring gaps being lined up occasionally happens but it is the least of my concerns. I’d say the most likely place the oil is coming from is either past the rings or from the valve guides. Nobody on the internet will be able to pinpoint the problem without seeing the engine so my recommendation would be to get an aircraft engine expert that you trust to assess things and make a recommendation.
 
My best bud has a cherokee with a 0-320 in it. I helped him and his IA do his annual this past Aug. His motor is using 1 qt every 4 hours. His compression's were in the mid 70s with one at 70/80. That cly had a oil fowled lower plug in it. His motor is running well with normal power. His IA is a 40 year personal friend and has been a IA that long. My best bud is 22 year SW captain and both of them have been in aviation since they were teenagers. So he can trust his IA.

He said to fly it, don't worry about it until the oil consumption gets worse. You could take that cly off and checkout the rings but he did NOT recommend that until the oil usage got worse.

On the other hand, I have a 0-320 H2AD motor that had 1650 hrs on it all original. It was using 1 qt per 4 hrs. Last Xmas I removed all four clys to checkout what I had. 2 of mine were down in the 50s compression. I found 3 out of 4 clys had the rings lined up to one another. I have done a lot of motor rebuilds in cars and trucks and have NEVER seen that. I found no other problems. I spaced the rings out, the original rings and put it back together. I flew it for another 100 hrs and it ran great, maybe a little better than before I took it apart. But the big take away was the oil consumption improved to 1 qt to 8-9 hrs.

Jim my buddys IA said he has seen that before when he took pistons out to find the rings lined up. I have never noticed before on motors I have rebuilt. True story...
022_5.jpg

Just so you don't think I am BSing you.
008_6.jpg

I did find minor spalling on some lifter/tappets. Not enough to keep me from putting it back together. The one still showed the rockwell test marks on it as you can see.
066.jpg
one little thing that is a real pet peeve of mine, I hate seeing a rod laying on the case like that. rods are one of the most stressed parts in an engine and it only takes a slight nick in one to set up a stress riser in it. lycoming states in the overhaul manual

CAUTION
After the removal of a cylinder and piston
the connecting rod must be supported to
prevent damage to the rod and crankcase.
This is done by supporting each connecting
rod with torque hold down plate ST-222,
rubber band (discarded cylinder base on
seal rings) looped around the cylinder base
studs or using plates as shown in figure
6-2.
 
Thanks for the info. So I’m curious why are the compressions still good but increasing oil consumption? Does the cylinder still need to be changed with good compressions?

Oil in the cylinder will help it seal better, thus higher compression readings.

The oil burn is what you should focus on.
 
It appears you have both a good Tech and good advice.

Hope you don’t mind if I add some comments.

Oil consumption per hour can be skewed if most of the oil is going through 1

cylinder. You can tell which one by removing top plugs and checking for “Ponding”

in the cylinders. Your A & P may have already made a note of this. ( #3 )

It may also show up as an excessive mag drop.

A good time to check this is during a POST FLIGHT RUNUP as burning off plugs

is easier on a hot engine. Good time to check circuit breakers also.

You may want to check and see if your engine makes “ Minimum Static RPM”

at Full Throttle. This is a check to verify your engine is producing the

proper power. You can look it up in the FAA Type Certificate Data Sheets for

your aircraft or post it here and folks will comment.

The reason you would do this is when the cylinder comes off the Tech will

likely look at the Cam. Worn Cam Lobes will not permit full power

so you may wind up with a Major Overhaul.. If your Static RPM is low on the

aircraft tach is not reason to panic. Recheck with a hand held tachometer.

There are also other reasons for low Static RPM.

There is a huge difference in the cost of 1 cylinder and a Cam Replacement

or Major Overhaul.

I hope it goes well. Unexpected large maintenance bills are not fun.
 
one little thing that is a real pet peeve of mine, I hate seeing a rod laying on the case like that. rods are one of the most stressed parts in an engine and it only takes a slight nick in one to set up a stress riser in it. lycoming states in the overhaul manual

CAUTION
After the removal of a cylinder and piston
the connecting rod must be supported to
prevent damage to the rod and crankcase.
This is done by supporting each connecting
rod with torque hold down plate ST-222,
rubber band (discarded cylinder base on
seal rings) looped around the cylinder base
studs or using plates as shown in figure
6-2.

Good advise and I was ignorant to that fact when I did the work. My IA helped me put it back together who is not my buddy's IA.
I work here in Cincy.
Magman offered good advise when I was learning about my H2AD motor, thanks for that Magman.
My buddy's IA is up near Cleveland Ohio. This was the second year I flew up there to help do his annual.
His cherokee in for his annual.
IMG_0503.JPG

I got to fly in a chieftain during a checkout. That is my buddy who does checkrides for the chieftain pilots. Love aviation.
IMG_0506.JPG
 
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Gary. You might say you went through some “ challenging” times?
 
If the compressions are good, don't mess with it. Been flying an O320 a long time that uses a bit more oil than desired, its finally getting close to TBO hours now, 53 years since it was put into service.

If compression gets weaker, and weaker its gotta be cracked or valve seating issues.

All flat lycomings will pull oil into the combustion chamber through the valve guides. Oil wet valve stems observed through the exhaust and intake ports (exhaust and intake system removed) is normal.
 
My best bud has a cherokee with a 0-320 in it. I helped him and his IA do his annual this past Aug. His motor is using 1 qt every 4 hours. His compression's were in the mid 70s with one at 70/80. That cly had a oil fowled lower plug in it. His motor is running well with normal power. His IA is a 40 year personal friend and has been a IA that long. My best bud is 22 year SW captain and both of them have been in aviation since they were teenagers. So he can trust his IA.

He said to fly it, don't worry about it until the oil consumption gets worse. You could take that cly off and checkout the rings but he did NOT recommend that until the oil usage got worse.

On the other hand, I have a 0-320 H2AD motor that had 1650 hrs on it all original. It was using 1 qt per 4 hrs. Last Xmas I removed all four clys to checkout what I had. 2 of mine were down in the 50s compression. I found 3 out of 4 clys had the rings lined up to one another. I have done a lot of motor rebuilds in cars and trucks and have NEVER seen that. I found no other problems. I spaced the rings out, the original rings and put it back together. I flew it for another 100 hrs and it ran great, maybe a little better than before I took it apart. But the big take away was the oil consumption improved to 1 qt to 8-9 hrs.

Jim my buddys IA said he has seen that before when he took pistons out to find the rings lined up. I have never noticed before on motors I have rebuilt. True story...
022_5.jpg

Just so you don't think I am BSing you.
008_6.jpg

I did find minor spalling on some lifter/tappets. Not enough to keep me from putting it back together. The one still showed the rockwell test marks on it as you can see.
066.jpg
I have a rule: if you can see the piston rings, you replace the piston rings. Did that at ~240 since major on my 0-300.
 
Jeeeeezzzezzzz! If my old mentor saw connecting rods laying like that, he would have torn me a few new ones!! "Did they drop? Are they marked? What the %$^& are you doing, young man? Jeeezzzzeeeezzz!" The whole time his cigarette hanging from his mouth, ash almost up to his lip, fishing for another cause his young apprentice is stressing him out! Learned a lot from him, both positive and negative. ;)
 
Jeeeeezzzezzzz! If my old mentor saw connecting rods laying like that, he would have torn me a few new ones!! "Did they drop? Are they marked? What the %$^& are you doing, young man? Jeeezzzzeeeezzz!" The whole time his cigarette hanging from his mouth, ash almost up to his lip, fishing for another cause his young apprentice is stressing him out! Learned a lot from him, both positive and negative. ;)

I will try to make this a short story.
I pulled the lifters to check their condition because I could. They were somewhat questionable and I had 2 low clys.

So the original plan was to have the motor overhauled by a local shop. So I removed the motor from the airframe to take it across town. I asked the shop if I could have the old cyls back for some hangar swag as my buddy calls it. They said no they can't return the clys unless they make them unusable. They suggested if I wanted the cyls to remove them before I bring them the motor for overhaul.

So I put the motor back on the plane and removed the clys not expecting to ever put it back together.

I was having second thoughts about the overhaul because it was going to need a crank because of pits in the crank snout. FAA AD 98-02-08. They said it would take 7 weeks to overhaul, this was Jan 2020 the beginning of covid19. I knew it would take longer to overhaul especially if I needed a crankshaft.

So after some thought and price comparisons I decided to order a zero time rebuilt motor from Lycoming because I knew I would get a fresh crankshaft. Lycoming said it would take 7-9 weeks to get the rebuilt motor but I did not believe that. I knew it would be longer and it was, took 12 weeks to get it in April 2020.

So I decided to put the old motor back together so I could keep flying while waiting for the rebuilt motor from Lycoming. The old motor ran great and the oil consumption got way better. Now I was sorry I ordered the rebuilt motor. I flew the old motor as much as I could which was right at 100 hours in 5 months time. I had to get my core back within 90 days, otherwise I would have flown the old motor more. The motor was 41 years old.

So during the 4th of July weekend 2020 I swapped motors and now have 289 hrs on the new motor. I did install new vibration mounts and a few other things at the same time. Things like oil and fuel hoses, scat hoses, starter etc were replaced in the previous year.

So that is why those poor rods were abused. As it turned out the old rods and cam and lifters, rings held up just fine for another 100 hrs. I am pretty sure the old motor would have made it to TBO and probably 2400 hrs. I ran the old motor to 1772 hrs. I even sent a oil sample out to be tested with 100 hrs on it when I took the old motor out for the final time. I didn't bother to change oil at 50 hrs and ran it to 100. They said the oil was fine even at 100 hrs after I put it back together. Oh well live and learn.

My rebuilt motor burns 1 qt every 12 hours now. I try to fly 4-5 day a week. Last fall I flew 23 days in a row.

I did 98% of the work myself in a 95° hangar in 5 days after work. My IA did inspect all of it and he did all the safety wire and was there for the original fire up and break in.
IMG_8174.JPG

I did get full credit for my core motor from Lycoming even with a pitted up crankshaft. The motor had to be together running within the last 12 months. So that was another reason I had to put the old one back together and fly it. Bragging again I put the old motor back together in a just a few days during Xmas week 2019 with new o rings and valve cover gaskets. Did you know that new silicone valve cover gaskets cause your silicone numbers to be high right after installation on your oil analysis?
IMG_8214.JPG
 
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Question for the OP-What oil is being used? If you see high consumption using 15-50? Switch to
20-50.
 
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What oil is being used? If you see high consumption using 15-50? Switch to
20-50.
aeroshell 15W50 is what I use. This H2AD motor was broke in with it also. Not mineral oil. BTW the old motor did not have the T mod done to it.

I did not just "shoot from the hip" when I took that motor apart. I read this service manual front to back before turning a wrench. I missed the part about protecting the rods.
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Well this gets a bit more interesting now. I have not had a chance to fly the aircraft since this encounter. Today the AP calls e and said my number 3 cylinder is out of spec, making the aircraft unairworthy. Curious how he came to that conclusion? No obvious damage, cracks. Compression is in the 70’s. Now trying to figure out my next move. Any suggestions?
 
Well this gets a bit more interesting now. I have not had a chance to fly the aircraft since this encounter. Today the AP calls e and said my number 3 cylinder is out of spec, making the aircraft unairworthy. Curious how he came to that conclusion? No obvious damage, cracks. Compression is in the 70’s. Now trying to figure out my next move. Any suggestions?

It seems like you should go there and have him show/explain the situation to you and then you will have better information for us?


What is his recommendation?
 
It seems like you should go there and have him show/explain the situation to you and then you will have better information for us?


What is his recommendation?
I’ll get more info tomorrow when I stop and look at it again. He said I need a cylinder replacement for that cylinder.
 
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