Be Afraid

[Alan Maurer]

Hello Mooney People, I have six brand new cylinders , boxes not opened yet. My Ovation has over 1000 hours since factory new and adding a quart of oil around every three hours or more. Decided to take the plunge and top the engine. I have read Mike Busch's essay " Be Afraid" I have read all about

lubrication, torque, cleaning ad nauseum but still nervous about it. I believe everything comes assembled in the box from Continental. ( piston  rings

already in cylinders etc. Thought alot  of fellow Mooniacs have done this and would be glad to have some suggestions of anything to keep an eye on. 

Sarasota Avionics will do this and I thought I might hang around  I did have one cylinder changed at the last annual and told cam looked fine. 

The rebuilt cylinder from last year has been fine also. The new cylinders do not include new nuts and I asked about not re using the old nuts. 

I have stocked up on Xanax

Alan

[M20F]

9 minutes ago, Alan Maurer said:

Thought alot  of fellow Mooniacs have done this and would be glad to have some suggestions of anything to keep an eye on. 

I would have read more Mike Busch before I bought six brand new cylinders.  

[MikeOH]

Six new cylinders!?!! For high oil consumption???

I think you should investigate a bit further; it may be just one cylinder with an issue.  If so, you can return at least 5, maybe even 6, cylinders and the Xanax!

[KSMooniac]

Not to increase anxiety, but if I had new Continental cylinders to install, I'd send them to Powermasters in Tulsa to get the valves fixed.

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[N201MKTurbo]

Just find all the TCM service bulletins about changing cylinders, and make sure your shop is complying with all of them.

[A64Pilot]

1 hour ago, KSMooniac said:

Not to increase anxiety, but if I had new Continental cylinders to install, I'd send them to Powermasters in Tulsa to get the valves fixed.

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This,

So far as worrying about pulling jugs, it’s been done frequently for way over 60 years, a qualified knowledgeable mechanic won’t screw up, plus you have new jugs, so it’s pull one, replace it. Sure someone who isn’t can cause problems, so use a good engine shop or be darn sure the A&P is good, don’t go to someone your not sure about.

The problem comes when the jugs are off, without the studs being retorqued and the aircraft sits for quite awhile while the jugs are being overhauled etc and someone moves the prop. Or possibly an unknowing mechanic rotates the engine with cylinders off to position it to remove pistons on the other cylinders.

Simply relaxing the torque and retorqueing without turning the prop won’t cause any issues, the bearings won’t move unless the crank is turned.

I would however have a good engine shop rework the valves and possibly guides though, maybe even port and polish them. I’d call Gann Aviation and ask if he would.

Conti was notorious for sloppy valve guides as in very poor finish, don’t know if that’s old news or not, maybe they fixed that long ago.

So far as treating just the offending cylinder, it works for some, but also some end up spending way more money in the long run and buying lots more down time having the airplane in the shop to replace the next jug that goes bad, the one after that etc. Sure sometimes a jug goes bad and the other 5 are pristine, but more often I think one goes bad and the rest are not too far behind, if you flew infrequently and not that many hours per year, maybe one at a time is the way, but if you fly a lot and don’t want to eat down time, I think removing cylinders as a problem for several years may be a better bet. 

Edited May 11, 2025 by A64Pilot

[dkkim73]

3 minutes ago, A64Pilot said:

sure sometimes a jug goes bad and the other 5 are pristine, but more often I think one goes bad and the rest are not too far behind, if you flew infrequently and not that many hours per year, maybe one at a time is the way, but if you fly a lot and don’t want to eat down time, I think removing cylinders as a problem for several years may be a better bet. 

I've wondered about this. After getting the airplane out of annual-as-prebuy (1400hrs SNEW), a few months later a new mechanic recommended replacing all 6. Did a lot of legwork and consultation, lapped valves and flushed rings (with good results for a few months), then replaced those cylinders, then replaced another several months later. So 3 new cylinders in. With higher prices for shorter lead-times, no re-working of valve guides, etc. 

The last time, I did have the rotocoils on the other 3 cylinders replaced (including the oldest, about 1000 hrs in). Got a yellow flag from Savvy's automatic data analysis shortly afterwards (about 15-20 hrs in), borescoped it myself, all fine. Planning on continuing on in this mode. The oldest cylinder is now an outlier at about 1000hrs of life. 

In *retrospect* I don't think it would have been crazy to get 6 new cylinders, have the valves re-worked as above (insurance), and topped the engine. I am probably going to go on-condition past the TBO of 2200 hrs anyway, so I might well have saved on some down time and got some peace of mind. I spent a lot of time managing the uncertainty around this, and speaking to several mechanics. OTOH maybe there would be infant mortality on a new cylinder. 

A contrary view (from an experienced broker) was that I wouldn't get the recognition of money spent on a top (vs. something that can be logged as an overhaul). So this would also depend on whether you think might sell it in the new few years... If keeping it, I would think you'd get value out of what you're doing. 

The internet consensus wisdom certainly supports maintaining everything on condition. The aforementioned Mike Busch has gotten a very long time out of some of the cylinders on his dual IO-520's. 

 

[Alan Maurer]

Hi Everyone, Thanks for the replies. I believe Sarasota Avionics has excellent mechanics. But having read Mike Busch, he does not like top overhalls.  I think he did top his 310. I will speak to the shop about the quality of the valve guides on new cylinders. I would hope that Conti is doing better and that it is old news. I absolutely do not want to sell the airplane. It is a member of the family, but I am an old fart and concerned each year about renewing my insurance. I re attend our Mooney MAPA training every year and I hope the real training and flying 100 hours per year helps.Have never  had an insurance claim in over 50 year of flying.  Ovation is a 2008 with just over 1000 hours.

Alan

KVNC 

 

[PT20J]

It seems pretty common for big bore Continentals to need cylinder work around mid-TBO. I don't know if Continental has improved its valve alignment issues or not. But a few  calls to overhaulers should let you know. Sure, if you are on a budget, you can replace them on condition one at a time, but that's going to be playing a game of whack a mole and end up costing more in the long run. If you want to fly more than be in the shop, once and done is not a terrible idea.

The problem with magazine articles and forums like this one is that they can cause us to worry about stuff that's not worth worrying about. Aircraft engine cylinders were designed to be replaced in the field. Done correctly by a competent shop it shouldn't be a big deal. Pick a good shop and don't lose sleep over it.

[Utah20Gflyer]

 I recently removed and reinstalled a cylinder to repair a broken cylinder hold down stud.  When the mechanic and I reinstalled the cylinder we applied torque seal to each nut as it was torqued to spec.  Now whenever I have a part of the cowl off I can visually inspect the hardware to confirm nothing has lost torque.  
 

The hardware loosing torque is the big risk in doing cylinder work so this seems like extremely cheap insurance.   I’d imagine lots of others are doing this already but thought I’d mention it because it is great for piece of mind.   Without torque seal that nut that should be at 50 ft lbs looks exactly the same at 50 ft lbs as it does 10 ft lbs.  

[Bartman]

13 hours ago, KSMooniac said:

Not to increase anxiety, but if I had new Continental cylinders to install, I'd send them to Powermasters in Tulsa to get the valves fixed.

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I would consider this, but you have to weigh the equation's benefit/cost/time components.  

You already have 6 new cylinders that will get you back in the air quicker than playing whack-a-mole, which is a significant benefit too.  Even if you don't send these new ones off, I would definitely send the ones you remove for rebuilding.  Store them properly and you have 6 ready for the overhaul a few years down the road.

[GeeBee]

9 hours ago, Utah20Gflyer said:

 I recently removed and reinstalled a cylinder to repair a broken cylinder hold down stud.  When the mechanic and I reinstalled the cylinder we applied torque seal to each nut as it was torqued to spec.  Now whenever I have a part of the cowl off I can visually inspect the hardware to confirm nothing has lost torque.  
 

The hardware loosing torque is the big risk in doing cylinder work so this seems like extremely cheap insurance.   I’d imagine lots of others are doing this already but thought I’d mention it because it is great for piece of mind.   Without torque seal that nut that should be at 50 ft lbs looks exactly the same at 50 ft lbs as it does 10 ft lbs.  

The method of torquing is critical and if you are going to hang around to observe the work, this is the one thing you do not want to miss. First the torque wrench should be calibrated, most shops do this and FAA Repair stations are required, but you never know when Vern pulls out his personal wrench. You want to make sure the torque to final spec occurs in one smooth swing and of course the torquing method (wet) is complied with.

[kortopates]

The method of torquing is critical and if you are going to hang around to observe the work, this is the one thing you do not want to miss. First the torque wrench should be calibrated, most shops do this and FAA Repair stations are required, but you never know when Vern pulls out his personal wrench. You want to make sure the torque to final spec occurs in one smooth swing and of course the torquing method (wet) is complied with.

Exactly right and improper torquing, the real
concern, comes from not lubricating the threads/nut for a wet torque, not torquing in stages , not the correct order as outlined by TCM, not using new nuts to get proper torque, not cleaning the mating surface to be free of paint, sealant, dirt etc (that might have been used to treat a leaky bolt), and a big one is not torquing thru-bolts from both sides which is often missed because it requires a lot more disassembly from the opposite side to gain access.
This is why Mike says Be Afraid, paying attention to the details is critical but when a mechanic who’s boss tells him he only has X hours to complete the job can have him/her hurrying to get it done.
Me on the other hand i could never afford because i am slowest mechanic ever, triple checking because i have no one to do so for me. but I’ve never had an issue or failure to start right up because i can afford to take my time before i am ready for that return to service flight to verify all is good. But time is a luxury in the real world and virtually every one is over $100 an hour yet the vast majority are still under what a car dealership charges. And try finding a dealership that can actually fix a broken part that easily fixable but is only willing to replace it! It’s pretty amazing what a good GA mechanic can do.


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[Alan Maurer]

On 5/10/2025 at 10:57 PM, PT20J said:

It seems pretty common for big bore Continentals to need cylinder work around mid-TBO. I don't know if Continental has improved its valve alignment issues or not. But a few  calls to overhaulers should let you know. Sure, if you are on a budget, you can replace them on condition one at a time, but that's going to be playing a game of whack a mole and end up costing more in the long run. If you want to fly more than be in the shop, once and done is not a terrible idea.

The problem with magazine articles and forums like this one is that they can cause us to worry about stuff that's not worth worrying about. Aircraft engine cylinders were designed to be replaced in the field. Done correctly by a competent shop it shouldn't be a big deal. Pick a good shop and don't lose sleep over it.

Hi Skip, Thank for the note. The mechanics here at Sarasota Avionics are very competent and careful. I believe a set of new cylinders will keep me flying throught the suggesed TBO and maybe

 

 

 beyond.  Thank you]

Alan

N913ND

KVNC 

[Alan Maurer]

18 hours ago, kortopates said:

Exactly right and improper torquing, the real
concern, comes from not lubricating the threads/nut for a wet torque, not torquing in stages , not the correct order as outlined by TCM, not using new nuts to get proper torque, not cleaning the mating surface to be free of paint, sealant, dirt etc (that might have been used to treat a leaky bolt), and a big one is not torquing thru-bolts from both sides which is often missed because it requires a lot more disassembly from the opposite side to gain access.
This is why Mike says Be Afraid, paying attention to the details is critical but when a mechanic who’s boss tells him he only has X hours to complete the job can have him/her hurrying to get it done.
Me on the other hand i could never afford because i am slowest mechanic ever, triple checking because i have no one to do so for me. but I’ve never had an issue or failure to start right up because i can afford to take my time before i am ready for that return to service flight to verify all is good. But time is a luxury in the real world and virtually every one is over $100 an hour yet the vast majority are still under what a car dealership charges. And try finding a dealership that can actually fix a broken part that easily fixable but is only willing to replace it! It’s pretty amazing what a good GA mechanic can do.


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Hi Paul, great advise, Thanks,, I will watch out for every retail. I have a question. Thinking that the thru bolts are not the deck bolts that attach the cylinder but just hold the case together. Should they not just have their original torque or should  they be removed, relubricated and then put back in and re-torqued. .Are they not located in between the cylinders? Seemed like they shoud be left alone or should they have a torque wrench  put on them to ? re tighten??

Thanks

Alan

[kortopates]

3 hours ago, Alan Maurer said:

.... I have a question. Thinking that the thru bolts are not the deck bolts that attach the cylinder but just hold the case together....

Thanks

Alan

No these aren't just case bolts. Surely you've heard of a danger of bearing slipping when when the torque is relaxed after all or multiple cylinders are removed? This is because each cylinder is secured not only by 7 studs in the case but also by 2 thru bolts that help secure a cylinder on as well as a opposite side cylinder AND the crankcase bearing between the cylinders! When you relax the torque on end of these 2 thru bolts to removed a cylinder, as part of the re-torquing process you need to be dissemble the other side enough to get a cylinder wrench on the opposite side of these thru-bolt nuts and make sure they are torqued from both sides.  Since your doing a Top, the process requires that as each cylinder is removed that they retorque in particular those 2 thru bolt 1/2" nuts (along with the 7 stud nuts just to keep the pressure even) so that the crankcase bearings can't possibly loosen up as the prop is rotated. Its necessary to rotate the prop to get each cylinder off since each piston has to be moved to top dead center in order to get the clearance to push the piston through to get the piston off. Its not a guarantee that a bearing will slip or the thru bolts will lose torque by not following this procedure but it has happened many times, including by good shops. 

If you look at the cylinder securing nuts around each cylinder, you'll see 7 nuts of one size (7/16") a two larger 1/2" nuts on one side, top and bottom, of the cylinder for a total of 9 nuts. These large nuts are on the thru bolts that secure the crankcase bearings in the center of the crankcase that need to remain under tension as as the prop is rotated while working on the engine.

[MikeOH]

1 hour ago, kortopates said:

No these aren't just case bolts. Surely you've heard of a danger of bearing slipping when when the torque is relaxed after all or multiple cylinders are removed? This is because each cylinder is secured not only by 7 studs in the case but also by 2 thru bolts that help secure a cylinder on as well as a opposite side cylinder AND the crankcase bearing between the cylinders! When you relax the torque on end of these 2 thru bolts to removed a cylinder, as part of the re-torquing process you need to be dissemble the other side enough to get a cylinder wrench on the opposite side of these thru-bolt nuts and make sure they are torqued from both sides.  Since your doing a Top, the process requires that as each cylinder is removed that they retorque in particular those 2 thru bolt 1/2" nuts (along with the 7 stud nuts just to keep the pressure even) so that the crankcase bearings can't possibly loosen up as the prop is rotated. Its necessary to rotate the prop to get each cylinder off since each piston has to be moved to top dead center in order to get the clearance to push the piston through to get the piston off. Its not a guarantee that a bearing will slip or the thru bolts will lose torque by not following this procedure but it has happened many times, including by good shops. 

If you look at the cylinder securing nuts around each cylinder, you'll see 7 nuts of one size (7/16") a two larger 1/2" nuts on one side, top and bottom, of the cylinder for a total of 9 nuts. These large nuts are on the thru bolts that secure the crankcase bearings in the center of the crankcase that need to remain under tension as as the prop is rotated while working on the engine.

Thanks for the details.  While the cylinder is removed, I understand re-torquing the 2 thru-bolts,  I'm not too clear on the need to tighten the 7 cylinder head studs; you say 'just to keep the pressure even' but I'm not following how that has anything to do with the main bearings as all the force would just be within the case-half, not between the cases??

Also, do aircraft main bearings not have 'tangs' to 'lock' them in place?  Every auto engine I've rebuilt has both main and rod bearing insert shells with tangs.

[EricJ]

2 hours ago, MikeOH said:

Also, do aircraft main bearings not have 'tangs' to 'lock' them in place?  Every auto engine I've rebuilt has both main and rod bearing insert shells with tangs.

They do, but just like in cars they can get unregistered and spin.   Letting pressure off the bearings during cylinder removal seems to increase the likelihood of this, so it is recognized procedure to not let the case relax too much.    Cars also have the benefit of main bearing caps and much more rigid blocks than we have.    We have two essentially relatively floppy aluminum case halves to keep the bearings in place.  

[Bolter]

On 5/10/2025 at 3:19 PM, MikeOH said:

Six new cylinders!?!! For high oil consumption???

I think you should investigate a bit further; it may be just one cylinder with an issue.  If so, you can return at least 5, maybe even 6, cylinders and the Xanax!

I can relate to the OP's decision process.  In my old J, I replaced all 4 cylinders with new while chasing a major oil consumption issue at around 1200 hours SMOH.  Since I cannot do my own labor, after the best efforts to identify the "Bad" cylinder with compression testing, data trends, and borescoping, we were left with removal and peeking.  Of course, it was the 4th cylinder to remove that showed a smoking gun of a trashed oil ring.  The labor costs were such that it just made sense to replace all the cylinders rather than just return them to service after overhauling the one that we found had the broken ring.  If I was my own A&P, I would have considered cleaning up the 3 good cylinders, but if spending 8 AMU's, I might as well spend 12 AMU's and never worry about cylinders for the rest of my ownership.  I flipped the old cylinders, which I could not do if I had overhauled them, getting some costs back.

My 310 STC'ed Ovation has 3 original cylinders and 3 overhauled at 2300 hours.  If I remove a cylinder now, it is probably weighed against an overhaul of the entire engine.  

-dan

[goodyFAB]

i recently topped my tsio520. why are you topping your engine ? do you have excess crankcase pressure ? oil on the belly ? or just burning some oil? thats well within limits if there was not contributing factors. there is a ton of options to decrease oil consumption before the top.

with that being said, theae things get topped every day. use an a&p thats capable and follows directions. follow the manufacturers guidelines with no exceptions and you will be fine. i found this was the time to do lifters, rockers, gaskets, hardware, and just about everything old and rubber. turns into quite the adventure.