M20J Top Overhaul

[hnorber]

I've been watching with alarm a significant increase in oil consumption (and tons of oil on the belly of my plane) over the past year or so.  I'm up to about 1 quart per every 2.5 hours.  My mechanic has been recommending a top overhaul based on the symptoms and oily spark plugs.  Yesterday, I took the plane to another shop to adjust my mag timing and to get a second opinion on the cylinders (including identifying which of the cylinders was causing the problem, since I disagreed with my regular mechanic about replacing all 4 instead of just those that are problematic).  

The new shop showed me that all 4 cylinders were glazed and that I do, in fact, need a full Top Overhaul (quoted me btwn $5K and $8K to overhaul my existing cylinders - I think that the higher end of the range would be for replacing the pistons, if necessary).  I currently have 1950 hours on the engine - so I'm inclined to overhaul they cylinders rather than replace them with new ones.

I'd be grateful for any thoughts from the group here - particularly on the following questions:

1. I'm have a flight planned from Chicago to the east coast next week.  My understanding is that this condition isn't really a safety issue as long as I can ensure that I maintain enough oil in the engine - so I'm inclined to take this flight (the cylinder repair will probably be late Sept or early October) - but I'd like to pressure-test this notion with the group.  

2. My engine is high-time (over 1900 hours) and so I'm inclined to overhaul my existing cylinders (quoted btwn $5,200 and $8K depending on whether or not I need new pistons), rather than buy factory new cylinders.   Again - I'd be grateful for any thoughts on that decision.

 

Thanks in advance for all responses!

 

-Howard 

 

[Andy95W]

With that much time on the engine, why even bother with overhauling the cylinders?  Just have them IRAN them (Inspect and Repair As Necessary).

I suppose there's a good reason for not overhauling the whole engine, so I won't ask.  (But since you're the one who is also having magneto problems, I'll just point out that your engine is trying to talk to you about how it's doing.  You should listen.)

[CaptRJM]

How do you know they are glazed?  Borescope?  Was a compression check performed?  If so, what were the compressions?  If they were low, where did you hear the air leaks?  Crankcase (piston ring leakage)?  Exhaust (valve leakage)?  Often if cylinders are just glazed you can break the glaze with a honing tool and install new rings.  But, you have nearly the same labor cost as installing overhauled or new cylinders.

I wouldn't throw money into an engine with that many hours. Spending $5-8 AMUs now when you'll probably have to go for overhaul in the near future doesn't sound prudent to me. 

If you are committed to not overhauling the motor in the near term, I'd go with the least costly route to minimize your financial exposure at overhaul.  But, you really need to be certain of the problem before you start.  If you pull a cylinder and it has a worn bore you are into a new ballgame.  Overhauled or new cylinders will be required and the AMUs will start adding up! Also, when you pull the cylinders you should do a cam and lifter inspection.  If they are not in great shape you'll be forced into pulling the engine and at 1950 hours you'll be doing an overhaul anyway.

[alextstone]

I suggest you read Mike Busch's books in your spare time.  He has a more modern approach to when to overhaul engines, etc.  Basically, the premise is:  Use all analyses tools at your disposal (modern engine monitor with data collection, data analysis service, oil analysis, borescope inspections, etc) then based on data, repair as necessary.  If you apply this method to your issue, it might be reasonable to do the top overhaul or a complete overhaul but TBO is not the deciding factor...

[KSMooniac]

If your goal is to minimize cost and improve oil consumption, I would just plan to hone the cylinders and install new rings. As already mentioned, you should get the cylinders inspected to make sure they're within limits in the bore, check the valves, etc. I think pistons are only ~$150 each if you have to replace them. Lifters and cam should definitely be checked as well.

You might get away with just rings and honing and fly hundred of hours more, or you could find a worn-out mess when you start disassembly. Be prepared for both scenarios.

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[hnorber]

2 hours ago, Andy95W said:

With that much time on the engine, why even bother with overhauling the cylinders?  Just have them IRAN them (Inspect and Repair As Necessary).

I suppose there's a good reason for not overhauling the whole engine, so I won't ask.  (But since you're the one who is also having magneto problems, I'll just point out that your engine is trying to talk to you about how it's doing.  You should listen.)

Thanks, Andy.  My thought is that I'd overhaul the engine only if, after pulling the cylinders, I discover issues in the cam that lead to an overhaul (in which case, I'd switch course and go with new cylinders) - but I'm really hoping that the cam is fine.   

What is the connection between cam health/overhaul and the need to adjust mag timing?

Thanks!

 

[jetdriven]

1 hour ago, KSMooniac said:

If your goal is to minimize cost and improve oil consumption, I would just plan to hone the cylinders and install new rings. As already mentioned, you should get the cylinders inspected to make sure they're within limits in the bore, check the valves, etc. I think pistons are only ~$150 each if you have to replace them. Lifters and cam should definitely be checked as well.

You might get away with just rings and honing and fly hundred of hours more, or you could find a worn-out mess when you start disassembly. Be prepared for both scenarios.

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Definately this.  Hone and re-ring can go a long time and its pretty cheap as engine repairs go.  I wouldnt have a shop that has a white floor and turbine airplanes in it do this, have some local curmudgeon semi-retired A&P do it.

 

[Andy95W]

1 hour ago, hnorber said:

 

What is the connection between cam health/overhaul and the need to adjust mag timing?

 

Nothing whatsoever on the surface.  

It goes back to when I was working for an old curmudgeon of an IA who taught me what TBO means and doesn't mean.  His point was that even though 2,000 hours in itself isn't important, you have to look at everything together.  Little things start breaking, little oil leaks become slightly bigger oil leaks, cylinders start needing replacement, oil pressure needs to be adjusted, etc.  Now when you throw in a big SMOH number, he would have said that the engine was trying to tell you something.

That's why I suggested the cheapest course of action- just repair what you have- exactly like Byron said, above.  It would suck to drop $5k+ on overhauled cylinders and then have your fuel servo take a dump 50 hours from now.  Or to have your engine start making metal 50 hours after that.

[OR75]

looking at everything but you need to start somewhere .... what are the 4 compression numbers like ?

 

[carusoam]

Starting with the easy stuff first...

1) compressions? Post some data...

2) Dental camera  check of valves and cylinder walls? Post the pics...

3) if the cross hatches are missing in places.... Hone and rings, makes a ton of sense...

4) Got an engine monitor? Post some graphs...

5) when a lot of oil is leaving the engine, it is going to leave one place more than the others... a JPI can probably point that out.

 

Nothing cooler than flying beyond TBO with all the information to support it....

No information? That becomes a study of discomfort...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Yetti]

Leakdown compression test is the first step.

OH cylinders are $500

New are $2000

History of the Engine is the second determining factor.   1 OH  1 Top

If the last thing was a full OH.  then replace cylinders as necessary.

 

[kortopates]

On 8/8/2019 at 9:28 AM, hnorber said:

My thought is that I'd overhaul the engine only if, after pulling the cylinders, I discover issues in the cam that lead to an overhaul (in which case, I'd switch course and go with new cylinders) - but I'm really hoping that the cam is fine.   

I think that's exactly the right approach to go. With the cylinders off you can get a good idea of the Cam and bottom end by checking one of two of the crank rod bearing and then decide your next steps. You might also check your engine logbook to see if the at the last overhaul the crankshaft was machined to its final undersize and if so you'll be aware that you could need a new crank which makes a Lyc rebuilt/overhaul exchange suddenly more attractive when factoring in a new crankshaft. 

[jkarch]

I chose to go with a factory remanufactured engine at 1250SMOH when oil started leaking from the through bolts. Once a cylinder was pulled the bad cam came through. At 1950, consider an overhaul. I mean you could do an on condition top overhaul too but if you find a bad cam or lifters it’s game over.

[INA201]

1.  Im concerned that all your cylinders are glazed. What is your standard operating technique?

2.  Was timing somehow integral to your situation?

3.  Are you comfortable with 1qt per 2.5 hours? I’m personally not but some folks are.

 

[tigers2007]

What are the duration of the flights that have the 2.5qt per hour consumption?

I was scratching my head at what I thought was higher than normal consumption then I realized it was for my short (less than one hour) flights. For flights greater than two hours my consumption is one quart per 9-10 hours.

 

M20D with O-360-A1D

 

 

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[INA201]

13 hours ago, tigers2007 said:

What are the duration of the flights that have the 2.5qt per hour consumption?

I was scratching my head at what I thought was higher than normal consumption then I realized it was for my short (less than one hour) flights. For flights greater than two hours my consumption is one quart per 9-10 hours.

 

M20D with O-360-A1D

 

 

Sent from my iPhone using Tapatalk

 

 

That doesn’t sound exactly accurate in my opinion. My guess is touch and goes with a lot of power changes along with climbing at a steep angle may cause a higher burn rate. I would have a hard time believing you would go from 2.5 hours a quart to 9.5/10 or rather a 400% increase in consumption unless there is something really unique going on. I might consider a third opinion from possibly a highly reputable engine shop before jumping into a conclusion based on the information presented here. 

[M20F]

Keep in mind the engine is 1950.  If at some point you elect to do a major overhaul you will need to redo the cylinders again.  I did my bottom with 2 new cylinders (one about 100hrs and one about 25).  I have a repair return which is every bit as good as a major in purpose. Because I didn’t feel like overhauling 2 new cylinders though it cannot be considered a major.  This is fine for my purposes but if you want the words major overhaul in your book keep in mind you might be doing them again sooner than you think. 

[larryb]

If it were me and I was going to keep the plane I would just get a new engine now and be done with it. If I was going to sell it soon I would sell it now as a runout with a heavy discount. You will have to pay either way. Buyers will not value any repairs in a high time engine. It is still runout.

 

I would not overhaul a cylinder. If it comes off the plane it is replaced with new. The only exception to this is if the cylinder was low time TTSN and I knew for certain it had never been abused. Perhaps I feel this way because I had a cylinder head separation in my J on the takeoff roll. Cylinders lead a hard life.

[tigers2007]

That doesn’t sound exactly accurate in my opinion. My guess is touch and goes with a lot of power changes along with climbing at a steep angle may cause a higher burn rate. I would have a hard time believing you would go from 2.5 hours a quart to 9.5/10 or rather a 400% increase in consumption unless there is something really unique going on. I might consider a third opinion from possibly a highly reputable engine shop before jumping into a conclusion based on the information presented here. 

No touch and goes; just much higher oil burn noticed after short hops. I’m the sole owner and operator and the person who checks and refills the oil. Engine has almost 2300 SMOH and I don’t fly it all the time. Another hypothesis could be that the time between use along with oil leaks could explain missing oil. Mine leaks oil but not quarts of oil. (I keep mine at 6qts).


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[DXB]

On 8/8/2019 at 9:29 AM, hnorber said:

The new shop showed me that all 4 cylinders were glazed and that I do, in fact, need a full Top Overhaul (quoted me btwn $5K and $8K to overhaul my existing cylinders 

I may have learned something here - I thought glazing was mainly a concern if running low power settings during breakin, not a cause for increased blowby on an aging cylinder.  Is this accurate?  How does one diagnose "glazing" in your situation?  I also wonder why there isn't a solvent fix for glazing - it's just combusted oil residue and carbon after all.  One reads about Seafoam and such in the automotive world.  

When deciding to IRAN cylinders vs. major overhaul, the number of years since last overhaul might also be an additional consideration - i.e. 10 years might favor IRAN, 30+ might favor overhaul.  Also it's not uncommon to pull a cylinder and pay labor to sandblast it clean before rehoning, only to find a minute crack that makes it unservicable and requires replacement - so the costs keep going up and those resources might be better put toward an overhaul.

[laytonl]

On 8/8/2019 at 12:28 PM, hnorber said:

Thanks, Andy.  My thought is that I'd overhaul the engine only if, after pulling the cylinders, I discover issues in the cam that lead to an overhaul (in which case, I'd switch course and go with new cylinders) - but I'm really hoping that the cam is fine.   

What is the connection between cam health/overhaul and the need to adjust mag timing?

Thanks!

 

This is my recommendation too. If the cam is good have an engine shop overhaul your cylinders.  The Removal and replacement labor is about half the cost of a top overhaul.  Honing the cylinders, rings, valves are about $600 per cylinder, so about $3,600 plus about that for R&R.  Lee

[aidanf]

I was in a similar situation last year, but in fact the high oil use was because of wobbly valves, cylinders lead hard lives and overhauling them is stressful as well, in the end new cylinders are the way to go - I went with continental prime Nicr cylinders for my J and I am really happy with them - they ran in really quick, the EGTs are balanced right across the board and it now runs like a clock.

It expensive(1900 per cytlinder) but to be honest I enjoy flying more now because I am confident in the engine - oil use, strange noises, stumbles, and parts overhauled by "some guy" just lead me to spend more time looking at the engine monitor than looking out the window or talking to my passengers.

[aidanf]

Actually I tell a lie - just checked the prices again and they are down to 1725 dollars

[hnorber]

Well, after much delay, I've overhauled my cylinders and am going to pick up the plane tomorrow.   The shop instructed me to run it at low altitude (less than 5K MSL), high manifold pressure and btwn 65%-75% power for several hours to properly break in the cylinders.

Wondering if anyone has more specific advice - and thoughts on how long the break-in period should be?

Thanks.

[KSMooniac]

Run it as hard as you can, and keep it cool. Hopefully you have an engine monitor. I flew around at 2500'/1000' AGL in a triangular pattern between airports while breaking mine in last time. I ran ~80% LOP with cowl flaps open. Some ROP as well...your choice. You should see CHT drop at some point in time, and oil consumption stabilize. Likely within a few hours.

My procedure was a minimal ground run/run-up, quick flight around the pattern a few times (not touch n go's!) and then land for an inspection and leak check. Next flight was a couple hours locally as described above. Next flight was low altitude/high power XC, or just repeat the local orbits until everything stabilizes.

Use the regular oil you plan to run, no Camguard or other additives until well past break-in!

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