paulsmeds Posted August 10, 2021 Report Share Posted August 10, 2021 I got some unexpected and bad news on two cylinders in my 680 SMOH IO-360A1A 15 years ago. One shows very low compression 25 and another 50. Last two in the 70s. Prior year all 4 in the 70s. No sign of power loss or engine roughness and ran 70 hours this year. A&P thinks the engine is run out and needs a top overhaul on the two cylinders at the least and he can’t do it. Any recommendations for a reputable shop\mechanic in Northern CA? Wasn't looking to break the bank for another 10 years so this is a shocker and also don't really know where to take it. 1967 M20F Quote Link to comment Share on other sites More sharing options...
MB65E Posted August 10, 2021 Report Share Posted August 10, 2021 Lycon! Visalia CA. -Matt Quote Link to comment Share on other sites More sharing options...
paulsmeds Posted August 10, 2021 Author Report Share Posted August 10, 2021 I was hoping for somewhere we could fly it in and have it worked on and avoid the remove and re-install costs. Maybe that's just a pipe dream. Quote Link to comment Share on other sites More sharing options...
ilovecornfields Posted August 11, 2021 Report Share Posted August 11, 2021 Did you try Top Gun? Quote Link to comment Share on other sites More sharing options...
markgrue Posted August 11, 2021 Report Share Posted August 11, 2021 Where is the pressure leaking? Is it going past the rings or valves? If it is going past the valve perhaps it is just a stuck valve. Perhaps some investigation is in order before changing cylinders. If you do have to have them changed any mechanic can do that in a couple days. Just my opinion mind you. Mark 3 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 11, 2021 Report Share Posted August 11, 2021 Welcome aboard Paul. Lets see if we can figure out what you have first… 680hrs on the engine… mechanic thinks it is run out… Why? Two cylinder’s have low compression…. Why? Have you not been using the plane for a year? (70hrs this year, how about the year before?) When the air escapes while doing the compression test… did it leave through the exhaust pipe, or engine case vent? How was the engine running? Oil usage? Does the oil turn black, smell like exhaust, get foamy, and start to disappear? Most people reporting low compressions take pics of the cylinder walls and the valves… They make this little device called a dental camera for taking pics inside the cylinder… Get pics of the valves… Get pics of the cylinder walls… Be on the look out for normal patterns… If the normal patterns are not there… then decide on what cylinders you want to replace or OH… Find a mechanic with a dental camera… Or buy one yourself… You need a mechanic with basic mechanic skills… Why is your existing mechanic unable to pull a cylinder? Plenty of homework you can do, or have done, before doing a top OH because somebody said so… Do you have an engine monitor? Have you ever looked at the data? Fortunately, Aviation has come a long way since the Wright brothers… I’m not a big fan of flying a plane with unknown problems to go see a different mechanic miles away…. PP thoughts only, not a mechanic… Best regards, -a- 2 Quote Link to comment Share on other sites More sharing options...
MB65E Posted August 11, 2021 Report Share Posted August 11, 2021 I’m sure Lycon will do the work locally at the airport. They may still have their hangar. -Matt Quote Link to comment Share on other sites More sharing options...
ShuRugal Posted August 11, 2021 Report Share Posted August 11, 2021 See the following for some very good information about the value (or lack thereof) of compression tests: Important notes...Continent has an AD out saying that any time you do a compression check, you must do a boroscope. Lycoming has a service bulletin advising the same.There are lots of harmless reasons you might have a compression leak. Don't start tearing the engine apart until you know what the cause is.Tearing engines apart for no reason is not the best of ideas: Sent from my Pixel 3a using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
paulsmeds Posted August 11, 2021 Author Report Share Posted August 11, 2021 Lots of good info guys thank you. Still settling in this isn’t going to be a normal annual year and cost a lot more $$$ I don’t have to spare. Oil consumption is up a little from prior years but not bad. Run 20 to 30 hours a year prior to this year. This year about 70 as we are planning on using it more and never missed a beat or acted up. Oil is not burnt looking or smells bad. Changed at 35 hours prior to now and all was normal. No power drop off, no odd running, no odd starting, no drop off in climb or cruise, all normal. If not for low leak down on two cylinders wouldn’t know anything was up. No engine monitor – I know I should have one. Leak down we could not tell where the air was going. Used a borescope, valves all moving so not stuck and look okay. Getting a better camera in a couple of days. Going to take a step back, big breath and check it over again. See if we can determine where the air is going because it has to go somewhere. Get some better pictures inside and go from there. A&P is getting up there in age and is reluctant to get into a cylinder replacement. If it goes that direction, might have to find some more options locally. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 11, 2021 Report Share Posted August 11, 2021 Listen to find where the air is going… You found air leaking, finish the job…. You took pics inside the cylinders…. Post the pics. Valves moving is nice… but doesn’t tell you if they are stuck or sticky…. Or seating properly When discussing valve pics, do they look like nice pizzas? Are they rotating as they are supposed to. Have the valves turned into tulips? Are they missing any pieces? air leaks out of cylinders two common ways… through valves and rings… If you know what the challenge is… you can go about fixing it… If you guess about what the challenge is… you can swap out some pretty good parts and not make any headway… If you had to write down the objectives of today…. What would that list look like? PP thoughts only, not a mechanic… all issues that have been shared around here before… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted August 11, 2021 Report Share Posted August 11, 2021 15 hours ago, paulsmeds said: Lots of good info guys thank you. Still settling in this isn’t going to be a normal annual year and cost a lot more $$$ I don’t have to spare. Oil consumption is up a little from prior years but not bad. Run 20 to 30 hours a year prior to this year. This year about 70 as we are planning on using it more and never missed a beat or acted up. Oil is not burnt looking or smells bad. Changed at 35 hours prior to now and all was normal. No power drop off, no odd running, no odd starting, no drop off in climb or cruise, all normal. If not for low leak down on two cylinders wouldn’t know anything was up. No engine monitor – I know I should have one. Leak down we could not tell where the air was going. Used a borescope, valves all moving so not stuck and look okay. Getting a better camera in a couple of days. Going to take a step back, big breath and check it over again. See if we can determine where the air is going because it has to go somewhere. Get some better pictures inside and go from there. A&P is getting up there in age and is reluctant to get into a cylinder replacement. If it goes that direction, might have to find some more options locally. If possible, you might try running it until fully warmed up (or around the pattern if it’s airworthy) and reaccomplish the compression check. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 11, 2021 Report Share Posted August 11, 2021 16 hours ago, paulsmeds said: Lots of good info guys thank you. Still settling in this isn’t going to be a normal annual year and cost a lot more $$$ I don’t have to spare. Oil consumption is up a little from prior years but not bad. Run 20 to 30 hours a year prior to this year. This year about 70 as we are planning on using it more and never missed a beat or acted up. Oil is not burnt looking or smells bad. Changed at 35 hours prior to now and all was normal. No power drop off, no odd running, no odd starting, no drop off in climb or cruise, all normal. If not for low leak down on two cylinders wouldn’t know anything was up. No engine monitor – I know I should have one. Leak down we could not tell where the air was going. Used a borescope, valves all moving so not stuck and look okay. Getting a better camera in a couple of days. Going to take a step back, big breath and check it over again. See if we can determine where the air is going because it has to go somewhere. Get some better pictures inside and go from there. A&P is getting up there in age and is reluctant to get into a cylinder replacement. If it goes that direction, might have to find some more options locally. Your guide to compression testing in a Lycoming engine. Values as low as you’re reporting should be evident somewhere. https://www.lycoming.com/sites/default/files/Cylinder Compression.pdf Clarence Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 12, 2021 Report Share Posted August 12, 2021 @paulsmeds… As crummy as the news sounded at first…. See the input of Doc and Rags above… They are describing the normal things that happen regarding compression tests… The advice you had received sounds like it came from a resource that doesn’t really know the compression test procedure… Overseeing the compression test being done is the quickest way to know how good your cylinders really are before taking pics of them… PP thoughts only, not a mechanic… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
ShuRugal Posted August 12, 2021 Report Share Posted August 12, 2021 Wasn't there a service bulletin somewhere detailing how to assess ring health by measuring outflow from the crank breather with an airspeed indicator?Measuring how much combustion gas is actually leaking while the engine is running seems like a much more useful diagnostic point than pumping 80psi air into the cylinder of a cold engine... Cylinder rings are designed to seal thousand-psi pressure ranges, at 400 degrees, while moving very rapidly. Testing 80 psi at 200 degrees, or colder, while static seems like it would never give trustworthy results.Sent from my Pixel 3a using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
paulsmeds Posted August 12, 2021 Author Report Share Posted August 12, 2021 (edited) Thanks everyone for the sound advice. It was an unexpected shocker and clearer heads always prevail. We quickly scoped the cylinder and it does show a burned valve on the questioned cylinder. We can’t do anything for about a week but the plan is: 1. Redo leak down on all four (both cold, then warm it up and do it again) and identify where the air is going (exhaust or case). 2. Re-scope all four cylinders and get clear pictures of the valves, piston and walls (so shiny hard to see any scorching). From here we should have a clearer picture if we are talking just one problem cylinder or more. At this point, I’m resolved to replacing the problem jug with new providing the others are still in good shape. After talking with a couple good shops, they are saying overhauling a cylinder is going to take weeks or more and the cost will be just slightly less than purchasing a new jug from AirPower. But I’m getting ahead of myself again. Thanks again everyone for the excellent input. Edited August 12, 2021 by paulsmeds 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 13, 2021 Report Share Posted August 13, 2021 That valve is showing signs of distress… light color around the 10:00 position in the pic… Typical of a valve that has stopped rotating… Often called a sticky valve… When they stop rotating that one spot gets very hot, and the seal stops happening as the seat gets affected… If you have a JPI engine monitor…. A specific pattern to look for in EGTs is called a saw-tooth pattern… Somebody posted a video just the other day of how the valve rotator works… Seeing if @M20Doc is in the neighborhood… (sticky valve pic, discussing next steps…) Best regards, -a- Quote Link to comment Share on other sites More sharing options...
drapo Posted August 14, 2021 Report Share Posted August 14, 2021 On 8/12/2021 at 1:25 PM, paulsmeds said: At this point, I’m resolved to replacing the problem jug with new providing the others are still in good shape. After talking with a couple good shops, they are saying overhauling a cylinder is going to take weeks or more and the cost will be just slightly less than purchasing a new jug from AirPower. But I’m getting ahead of myself again. Thanks again everyone for the excellent input. m I went through the overhaul process in 2019 and the price of a new IO360A1A cylinder assembly was close to $3000 and they were not in stock. I ended up using overhauled cylinder assemblies made available by the numerous low time R44 parts on inventory (Due to mandatory overhaul after a timeline). The O540 uses the same cylinders as my IO360A1A, mine were first run with less than 500hrs and we had them overhauled at a cost of around $1000 apiece. 1 Quote Link to comment Share on other sites More sharing options...
MB65E Posted August 14, 2021 Report Share Posted August 14, 2021 Some engine shops will buy cylinders in bulk from Japan. They have an 800hr life limit over there. I would buy a reconditioned 800hr cylinder all day. probably better than having infant mortality with anything new from lycoming. Also better than having cracked, welded, heat soaked, 5000hr cylinders. -Matt Quote Link to comment Share on other sites More sharing options...
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