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M20J Top Overhaul


hnorber

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The key is to run them hard at high power low altitudes for as long as it takes to bring the CHTs down and stabile. I only replaced one cylinder. Instead of using straight mineral oil, they used a Phillips oil. Watch the oil consumption early on. They will go through oil quickly early on.

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Nitride cylinders (blue stripe) break in fairly fast. The others take longer. I was told if the oil consumption didn’t stabilize in 10 hours, I may have glazed the cylinder. Oil consumption stabilized for me by the 8th hour.

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See if you can find the Lycoming break-in procedure...

Essentially, new cylinders and rings are going to go through the same break-in procedure as new engines...

The advice given by MSers above is perfect, and comes from people that have done this before...

There just may be some small detail that you find from reading what the factory thinks is a good idea...

 

I used the procedure written by the Continental guys... the first two flights were short and over the airport, leak checking...

The long break-in flights were a blast... high speed down the jersey shore @1k’ agl... (not 50’ agl...)

Cold air, Max FF, altering rpm every 15minutes...

 

It helps to have a second pilot with you scanning either traffic or engine details... and confirm your thoughts when something goes funky...

Review the JPI data for CHTs... looking for step changes as the rings wear in... it may happen quickly.  Between factory engine runs, and the first two hours of flight the break-in must have been 90% complete... I didn’t capture any stepwise change in CHTs...

PP thoughts only, not a mechanic, I overhired a pair of Mooney specific CFIIs to help with the flights... No chance to do it a second time... the finance administrator is a tough cookie... engine outs were not part of my plan A, B, or C... :)

Best regards,

-a-

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Cylinders have a tendency to crack after 2000 hrs. I would go with new cylinders or engine overhaul.

On every power stroke a cylinder looses a few molecules due to tensile stress on the wall, at 2000 hr operating hours this would lead to at least 120 million molecules lost. If they are in line it would lead to a crack that could lead to cylinder separation on the next power stroke:o.

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6 hours ago, Gagarin said:

Cylinders have a tendency to crack after 2000 hrs. I would go with new cylinders or engine overhaul.

On every power stroke a cylinder looses a few molecules due to tensile stress on the wall, at 2000 hr operating hours this would lead to at least 120 million molecules lost. If they are in line it would lead to a crack that could lead to cylinder separation on the next power stroke:o.

alens.jpg

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On every power stroke a cylinder looses a few molecules due to tensile stress on the wall, at 2000 hr operating hours this would lead to at least 120 million molecules lost.

To put that in perspective, those 120 million molecules amounts to 0.00000000000001 grams. The cylinder wall lose magnitudes more than that when they are honed. I wouldn’t sweat it.


Tom
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On 11/7/2019 at 2:54 PM, hnorber said:

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.

In case you haven’t started the break in yet, here is the Lycoming version.  Finishing the top on mine and was looking at various documents.  Seems fairly detailed compared to the usual basic advice.  The one thing that I am a little uncomfortable about is the suggestion of a two hour first flight.  I’ve always kept them to about an hour so I can get eyes on things.  Wonder what others think?

https://www.lycoming.com/content/service-instruction-no-1427c

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In case you haven’t started the break in yet, here is the Lycoming version.  Finishing the top on mine and was looking at various documents.  Seems fairly detailed compared to the usual basic advice.  The one thing that I am a little uncomfortable about is the suggestion of a two hour first flight.  I’ve always kept them to about an hour so I can get eyes on things.  Wonder what others think?

I did 2 hours, but spent it going in circles above the airport.


Tom
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1 hour ago, ArtVandelay said:


To put that in perspective, those 120 million molecules amounts to 0.00000000000001 grams. The cylinder wall lose magnitudes more than that when they are honed. I wouldn’t sweat it.


Tom

A stronger reason to get new cylinders instead of honing them.

Edited by Gagarin
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13 hours ago, Gagarin said:

Cylinders have a tendency to crack after 2000 hrs. I would go with new cylinders or engine overhaul.

On every power stroke a cylinder looses a few molecules due to tensile stress on the wall, at 2000 hr operating hours this would lead to at least 120 million molecules lost. If they are in line it would lead to a crack that could lead to cylinder separation on the next power stroke:o.

Any data on that? I’ve heard they tend to crack after 6-8k hours, but two TBO cycles were ok. 

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4 hours ago, ArtVandelay said:


To put that in perspective, those 120 million molecules amounts to 0.00000000000001 grams. The cylinder wall lose magnitudes more than that when they are honed. I wouldn’t sweat it.


Tom

I've lost more brain cells than that reading his posts.

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21 hours ago, Gagarin said:

Cylinders have a tendency to crack after 2000 hrs. I would go with new cylinders or engine overhaul.

On every power stroke a cylinder looses a few molecules due to tensile stress on the wall, at 2000 hr operating hours this would lead to at least 120 million molecules lost. If they are in line it would lead to a crack that could lead to cylinder separation on the next power stroke:o.

More likely to have a cracked head on a Continental than a Lycoming, in fact I don’t think I’ve ever seen a Lycoming with a cracked head.

Clarence

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On my old 1966 M20C I had a 45deg circumference crack on the steel part of the Lycoming cylinder. I first noticed due to the oil mark on the cylinder between the fins. I pulled the cylinder and look inside and the crack was visible to the naked eye. The engine had 1700hrs since new.  The plane was based at TJIG (next to the San Juan Bay) and all the cylinders showed signs of corrosion on the fins. I was lucky the cylinder did not separated in flight.        

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9 hours ago, ArtVandelay said:


Regarding Continentals, have you seen any on normally aspirated engines?


Tom

Yes on the cylinders on IO550’s cracks from fuel injector hole to upper spark plug hole and on TSIO-520’s between the cooling fins toward the cylinder barrel.  I don’t think I’ve ever seen one on a IO-360 cylinder though.

Clarence

 

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  • 2 weeks later...

Hey @hnorber how about an update ?

I am in a similar situation but instead of burning I’m leaking.  My IO-360 has about 1950 as well, but after the last rebuild it had some case work at about 500 hours and cylinders IRAN at that time. My issue is a leaking case stud and we are gonna either fix it with an oversized stud as recommended by several in this thread or it’s going for overhaul or exchange. Anyway we agreed to remove the cylinders and inspect the cam and lifters thoroughly. If it looks good then we IRAN the cylinders and reinstall with new rings. 

Edited by Bartman
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  • 4 weeks later...

Apologies for the delay in providing an update.

I had my cylinders repaired a Poplar Grove Airmotive.   I've put about 6.5 hours on the engine since picking up the plane, and the difference in performance is definitely noticeable!  I'm actually getting about 50-75 more RPM in my takeoff run (shop confirmed that they didn't adjust the governor - so the difference seems to be attributable to the cylinder repair!) - and my cruise speeds seem to be about 3-5 knots faster (although it's hard to tell, since I'm running the engine much harder than my typical SOP for break-in purposes).  I'm also happy to say that there doesn't seem to be any fresh oil on the belly after these flights.

I thought the price was reasonable (paid more to disassemble/reassemble than the actual cylinder work itself).

Unfortunately, now my attitude indicator seems to be failing (will post about that separately).

Happy to answer any specific questions.

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