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  #11  
Old 10-24-2020, 08:27 PM
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skylor skylor is offline
 
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Quote:
Originally Posted by Scott Hersha View Post
I agree with Rocketbob that this looks like glazing, but I don’t agree that the Lycoming recommended break-in procedure is not right. They caution about not letting the CHT’s to get too hot (>400*). But they recommend an agressive power setting (75%) so there is enough pressure to force the new rings outward against the cylinder walls to break them in. Unfortunately, the only way to fix a glazed cylinder is to hone it. I think you should consult a reputable engine shop before you pull a cylinder.

https://www.lycoming.com/content/har...t-engine-break

Cylinder #3, and usually #4, has a cooling challenge because of the cylinder fin casting in conjunction with our standard baffle, that prevents cooling airflow to migrate to the lower barrel fins where the rear baffle is mounted (discussed on this site in detail - see the DanH remedy). This challenge would be most evident during engine break-in when cylinder head cooling is critical because of excess piston ring friction for this period.
The original poster indicated that he ran at 75 degrees ROP while at 75 percent power or above. 75 degrees ROP is just about the worst possible place to run an engine while at high power settings as far as cylinder temperatures are concerned!

Skylor
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  #12  
Old 10-24-2020, 08:42 PM
Scott Hersha Scott Hersha is offline
 
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Yep, I missed that detail in the original post(75* ROP). Lycoming recommends “best power” after the initial couple hours at full rich, which would be 100-150 for this phase of break-in. If the cylinders get too hot prior to break-in due to a too lean mixture, approaching peak EGT (high temp, high pressure), you could have a problem, especially on the most stressed cylinders - #3 & #4.
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  #13  
Old 10-24-2020, 11:27 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by hgerhardt View Post
That really looks like rust to me. Look at the left side of the close-up. That stuff looks more brown than black there.

If this was "oil coal", I'd expect it to be uniformly around the cylinder, not localized in one area. Plus, you can see where a ring sat for a while; there's more rust in that area.

Have you cut open an oil filter yet?
The other clue that points away from glazing is the affected area is on top, which is the coolest part of the barrel. I have only seen glazing on the sides or bottom of the barrel. It is also odd to have zero glazing on the other three jugs. If one was that bad, I would expect at least light glazing on another jug or two.

It looked black to me, but the edge shaping does resemble corrosion.

Larry
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  #14  
Old 10-25-2020, 02:31 AM
Touchdownzone Touchdownzone is offline
 
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Thanks for all replies and opinions.

I agree its hard from the blurry pictures to see whether its corrosion or baked oil.
Before first engine start I did a borescope inspection as well and found all cylinder corrosion free (might have missed that particular spot though).

I did cut open the oil filter, did not find anything unusual.

Running the engine 75 ROP is according Superior Airparts XP-360 operators manual for break-in. I checked my engine monitor and found cylinder #1 and #3 to run about 10F cooler than #2 and #4, with #3 often showing the coolest temperature (I did the baffle mod suggested by DeeCee and DanH).
During the first couple of hours I did not see CHT above 420f during climb out and during cruise the CHT stabilised in the 380F region.

Tomorrow I will try to scrape the cylinder wall with a small tool I made out of some scrap aluminium to find out more. Wiil keep you informed..
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  #15  
Old 10-25-2020, 07:44 AM
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75 ROP vs 150 ROP is unlikely to be an issue here. Concern for operation in the 50~75 ROP region is based on being near/at the detonation limit, assuming CHT is near 475, hot intake air, poor fuel, etc.

That scope photo is too fuzzy to tell much of anything.
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  #16  
Old 10-25-2020, 11:05 AM
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Snowflake Snowflake is offline
 
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Is this black area on the bottom (ie. closest to the ground) of the cylinder? The edges of this look like corrosion to me. The pattern looks like what you'd get if there was some moisture collected in the bottom of the cylinder while it was stationary for a while.

You can even see two lines that run circumferentially out of the affected region. That immediately says "rings" to me, suggesting that's where the cylinder was sitting. Moisture started corrosion in the lowest part of the cylinder, and moisture wicked up along the rings starting corrosion along those lines around the circumference.

How long did the engine sit before first start? And where was it stored?
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  #17  
Old 10-25-2020, 01:00 PM
Touchdownzone Touchdownzone is offline
 
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the blackened sector is furthest away from the ground, so it's the top section.

The engine has been sitting for a while, but was well conserved and looked after.

In the mean time I found some pictures that I took before first engine start. Although not the same detail, I can clearly see that there was no corrosion present then.

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These shots are from the 18th May 2020. I have flown 25h since then.
I think its very unlikely that this is corrosion on #3..
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  #18  
Old 10-25-2020, 03:27 PM
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rv8ch rv8ch is offline
 
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Default anything else?

Daniel - do you have any other issues with the cylinder besides the borescope concerns? EGTs or CHTs running differently? Might also do a compression check to see if the rings are leaking.

What kind of oil? Are you running 100LL or UL91 or mogas?

Anything strange with the spark plugs?
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  #19  
Old 10-25-2020, 04:44 PM
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skylor skylor is offline
 
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Default Ground Run

Did this engine see much ground run time and high-power run ups without the cowling before it was flown?
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  #20  
Old 10-26-2020, 08:51 AM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by Touchdownzone View Post
the blackened sector is furthest away from the ground, so it's the top section.
...
The engine has been sitting for a while, but was well conserved and looked after.
...
These shots are from the 18th May 2020. I have flown 25h since then.
I think its very unlikely that this is corrosion on #3..
Hmm... Well, the only other thought i'd have then is condensation... Which may form at the top first. But I admit i'm reaching here. I can't get my mind to stop seeing the witness marks where the rings sat.

Could that cylinder have been "less well" preserved? Could there have been moisture in there before it was preserved, and the prop not moved while it was sitting?

Are you 100% sure of the orientation of the cylinder, I know I have trouble tracking which is "up" when i'm using my borescope.

Could this be residue from any preserving oil that was fogged into the cylinder while it was parked?

Trying the buckshot approach here... Hopefully something triggers some further ideas/suggestions...
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