Engine Top End - New Set or Overhaul?

[WDD]

So, I need to work on 3 of my cylinders - leaking oil. Continental 0470 O

I could order all new - each set will have new cylinder, new piston, new rings.

Or I could have them overhauled - machined cylinders, new valve seats and guides, and new rings.

What say you who have walked this path before?

 

[AV8R_87]

If you have a reliable shop with a quick turnaround, overhaul them.

Sent a couple to Columbia Aircraft for valve work. One was salvageable, the other one had a crack in the intake port. They had a similar used but good one on the shelf, sent me that one for not much more over the overhaul cost. And it was an 8 day turnaround.
That was almost 400 hours ago. Still running good.

Now, if the turnaround time is months, I'm buying new. Too much money spent on hangar, insurance and so on just to have the plane sit.

 

[WDD]

Last time it was 2 weeks to get overhaul done. Shop was local. Note to self - if 3 cylinders need work, just do the remaining three as well.

 

[mondtster]

With no more information than has been given, I’d fix the oil leaks and not replace or overhaul anything unless there is a truly compelling reason to do so.

 

[WDD]

Engine is using oil. Oil is pooling on tops of three pistons. Compressions good, so probably leaking valve guides.

No external oil leaks.

 

[Dan Thomas]

Engine is using oil. Oil is pooling on tops of three pistons. Compressions good, so probably leaking valve guides.

In flight, when the MP is well below ambient pressure, the low pressure in the cylinder during intake can pull oil past the oil control rings, even if compression is good. Once past the oil rings, it finds its way around the compression rings and ends up in the cylinder. This is because there are no drain holes back to the case in the ring grooves of the compression rings, except sometimes for the bottom compression ring if there are three of them.

So the oil rings might be worn, or maybe carboned up and stuck in their grooves.

Worn bearings can cause excessive oil consumption, too, unfortunately. The clearance between the crank's journals and the main and rod bearings is tiny, and that controls the oil flow from the crank into that interface. The oil that escapes out from the edges of the bearings is thrown into the cylinders to lubricate the pistons and rings, and it takes only a small amount to do that. When the bearings wear, clearances increase and too much oil is thrown into the cylinders and the oil ring has trouble scraping it off, so the rings end up "hydroplaning" on it and it gets past the rings.

A cold engine and cold oil can also result in hydroplaning and oil consumption. The oil is thick and not easily controlled.

 

[Half Fast]

Depends on what the cylinders need. Three of mine had cracks and required welding, and the cost of repair was within a couple of hundred dollars of buying new Superiors. I decided to bite the bullet and buy four new cylinders.

 

[bonefishpete]

How much is it burning? How much time on engine? My O-470 U drank oil but always ran good.
Allowable oil use is measured in quarts per hour I believe.

 

[Steamflyer]

If at least one of the three is on the opposite side consider doing all six since you'll be pulling the entire exhaust. Personally consider cylinders disposable and hence like new ones.

 

[WDD]

Learning as I go along. I replaced 3 cylinders last November. Should have replace all 6 at same time, because 2 of the “old ones” that I didn’t replace are now leaking/burning oil.

I’m now replacing/rebuilding the three old ones. Which means I’ll end up with a complete top end - in a more expensive and time consuming way of course.

 

[Jim K]

I wouldn't replace them unless I was doing a major. Even then, everyone i talked to said overhaul once, then replace; assuming they measure okay. The concern is the head separating from the barrel with enough heat cycles/stress. I think i remember hearing somewhere that Lycoming cylinders were less prone to that, but i might be making that up. Point being i know just enough about lycomings to be dangerous, and nothing about continentals, so you should probably ignore anything i say.

Especially after two beers

How much more are the new ones? What's the availability? For my engine, OH was literally the only option. The labor & parts are not insignificant.

If it really is just the valve guides, maybe you could get away with just replacing those and cleaning the crap out of the piston ring grooves, and save a bunch of time & money.

 

[WDD]

Spoke with my A&P, and the game plan is to pull the cylinders and send to local shop that did my others. Good reputation, good work. If in specs, will overhaul. I’m going to order a new cylinder set just to have at the ready should one of the old ones not be rebuildable. It’s returnable for a 10% core charge and shipping.

A new cylinder set/piston set is $1800 + shipping. A rebuild that includes new valve seats, guides, rings is about $800 a cylinder and about 1-2 weeks. The only parts my A&P adds are new piston wrist pins. Heck, they even paint it.

Work starts June 2, be done by June 27.

 

[FORANE]

I'm done with cylinder overhauls. False economy pulling them to not replace with new, in my admittedly limited experience.

 

[WDD]

I'm done with cylinder overhauls. False economy pulling them to not replace with new, in my admittedly limited experience.

Maybe an important variable is the shop quality; sounds like you had a bad experience.

I’m going with the overhaul for now based on the past work they’ve done for my A&P. He would know if it was a good or bad overhaul shop. My A&P has been around for decades, large shop, lots of work, no one has complained of bad work, etc. Shop is clean, organized, his wife works there doing the books and his son works on the floor as well; that kind of place. And they have their dog there as well - what’s not to like about that?

Like I said, I’m learning as I go here, only being a plane owner since last June. Hence the questions to the “POA brain trust”.

 

[FORANE]

Maybe an important variable is the shop quality; sounds like you had a bad experience.

I’m going with the overhaul for now based on the past work they’ve done for my A&P. He would know if it was a good or bad overhaul shop. My A&P has been around for decades, large shop, lots of work, no one has complained of bad work, etc. Shop is clean, organized, his wife works there doing the books and his son works on the floor as well; that kind of place. And they have their dog there as well - what’s not to like about that?

Like I said, I’m learning as I go here, only being a plane owner since last June. Hence the questions to the “POA brain trust”.

I've used Gibson's a couple of times and an unknown shop my a&p got a cylinder from once.

 

[Jim K]

At overhaul I'd probably go new at that price delta, but for a mid time repair, I can't see any reason to spend the extra $1000/hole. I think Lyco parallel valve cylinders are similar because there's aftermarket options. Angle valve is a different story.

I'm a little surprised that he replaces wrist pins. Must be a continental thing. Near as I can tell my pins are 1976 originals through 4 major overhauls now.

 

[EdFred]

If you overhaul them, don't use Harrison in Indiana. Due to their ineptitude and "**** you" attitude I ended up paying them to overhaul AND having to buy new.

I had chrome cylinders. Had 2 that were an issue. Why do two when you can do all 6 right?
So I sent 6 down there. 5 of them they could overhaul, one was beyond. Bought that one from somewhere else - this one wasn't chrome. Get all 6 put back on. Do the break in as stipulated. Fly less than another 50 hours. All 5 cylinders Harrison did looked like someone took a metal fork and scratched the hell out of them. Now they are beyond repair. Call them up, talk, send pictures.

"You did the break in wrong."
"Then why does the one not from you look perfect?"
" - - - "

Basically Harrison told me to **** off, refused to pay for new cylinders, wouldn't even give me my money back for the **** job they did.

So I ended up buying new cylinders anyway. If I had to do it again, I would just skip the getting ****ed over part, and buy new cylinders from the get go.

 

[WDD]

Damn - sorry to hear. Might need a new Sticky for Machine/Overhaul Shops Recommended and Machine/Overhaul Shops Not Recommended..........

 

[bonefishpete]

3 new OH and 3 old cylinders. Do you use mineral oil for break in or regular oil?

 

[WDD]

3 new OH and 3 old cylinders. Do you use mineral oil for break in or regular oil?

Used Phillips XC. From what I've read and the A&P's experience, it works just fine. Flew max green on MAP and RPM on some nice long X Country. After 40 hours, new cylinders have no oil leaks, no oil pooling, good compressions, etc. I have confidence they were broken in correctly and will run well in the future.

Before I bought the plane, the previous owners had some engine work done on the top end. It turns out they didn't hone the cylinders, no cross hatch visible. Which means they probably cheaped out on other needed overhaul work on the top, such as valve guides. So I bought some bad overhaul work.

BTW, while getting the first set of three cylinders worked on last November I also "got" to install a new muffler, repair a crack in the exhaust manifold, and pull the oil pan to put in a new gasket to stop an oil leak there. Muffler I new needed replacing sooner than later, the other was "surprise!".

Since last June when we bought the plane, there are other things I had to fix, but the trips to the A&P shop and the avionics shop are getting fewer and farther between. I might be soon approaching the point of getting it sorted out to just endure the normal financial pain vs the enhanced version LOL.

 

[Pinecone]

I'm done with cylinder overhauls. False economy pulling them to not replace with new, in my admittedly limited experience.

Except that some quality shops overhaul NEW ones to get things right.

 

[Dan Thomas]

I'm done with cylinder overhauls. False economy pulling them to not replace with new, in my admittedly limited experience.

Yup. There will be wear to the cylinder wall, and in rehoning, the piston-to-cylinder clearances increase further. Once near the wear limits, the rings will have more trouble controlling the oil. Now you're faced with new cylinders, or resizing of the old ones to .010" oversize, meaning new pistons and oversize rings. That costs money and you still have an old cylinder.

Back in the old days when labor was cheaper, it made sense. It doesn't now, especially with the shortage of skilled machine workers. An aircraft engine shop in my hometown had an expensive cylinder resizing machine sitting there, unused, either because they could find no one to operate it, or it was cheaper to just buy new cylinders.

I didn't tell them that I had thousands of hours, over 11 years, of experience on an identical machine.

I'm a little surprised that he replaces wrist pins. Must be a continental thing. Near as I can tell my pins are 1976 originals through 4 major overhauls now.

That's a very long time for piston pins. No wonder he wants them out of there. Pin failures are not unknown, and those pins will also be worn somewhat and there's no way to fix that.

 

[WDD]

Except that some quality shops overhaul NEW ones to get things right.

Yeah - I’m in that camp as well, that a good shop will give you a product checked over and maybe in better specs than new out of box.

Maybe I’m that way from working with my dad many many years ago. He was a high school ag teacher, and a big part of that was fixing engines. One of his “tests” was to overhaul a small engine. One kid wanted to use starting fluid on his project. Dad thought that was funny. No, if you did it right, it will start first pull.

 

[Eldorado]

I’m way more concerned with finding a trustworthy engine repairman, close to home, with a long record of satisfying customers, than I am which cylinder repair shop, new vs old. If I trust him to put it back together, I’ll certainly trust his opinion on who is good or bad. Mine said this is what we will do, this is who I’ve worked with etc. If I have problems, I will go back to him and let him deal with the factory/rebuild people. By the way, he did major firewall forward overhaul and did not charge a penny till I picked up the plane. I feel more comfortable dealing with those I am comfortable and letting them make the decisions.

 

[WDD]

I’m way more concerned with finding a trustworthy engine repairman, close to home, with a long record of satisfying customers, than I am which cylinder repair shop, new vs old. If I trust him to put it back together, I’ll certainly trust his opinion on who is good or bad.

Copy that. I've had this guy do a number of things, and I've dealt with another shop for our flying club. I like who I'm working with. Other shop didn't find a leak from the pan, this guy did. Other shop couldn't fix the flap problem I had, this guy knew instantly what it was (limit switch). And a few other things.

He's also looking for ways to save you money when possible.

He reminds me of your old High School shop teacher who could build a house over the weekend with only a saw and he may or may not need a hammer.

 

[chemgeek]

On my previous Lycoming engine, I replaced cylinders with overhauled or exchanged/overhauled from a very reputable shop. Those cylinders never had an issue for the life of the engine. They broke in great and had low oil usage. I would not replace a cylinder except on condition. On a prior plane I had a motley collection of steel, chrome, and cermichrome cylinders (technology changed over time). They seemed to play together just fine.