Curious Boresocpe - Crazing ?

[pjc]

Seeking wisdom ...

Three of my 0-320 chrome cylinders have >2000 hrs and look something like the first picture below.

80 hours (and one year ago) I changed out one cylinder for a "repaired" unit (new piston, wristpin, iron rings, valve guides, serviceable valves), also chrome, which now looks like the second photo.

Engine runs fine and all compressions (warm) are in the 70s. The "new" cylinder broke in fine and oil consumption is < 1qt/10 hrs.

Clearly one of these cylinders is not like the others. Is this:

a). A BAD thing. Flakes of chrome are about to come off and eat your cam and most of your crank bearings ?

b). A GOOD thing. This cylinder was artfully re-chromed with this harmless crazing which helps the cylinder wall hold oil ?

c). Nothing ? A demonstration of my poor borescope skills perhaps.

d). Something else ?

Thanks in advance,
Peter

 

[Mike S]

Digging deep in the old memory banks here----channel chrome IIRC.

What color paint is on the fins between the pushrod tubes?

 

[Freemasm]

Agreed. Looks like channel chrome. What are the relative "birthdays" of the two cylinder types?

IIRC, the move to channel chrome was done because that feature made for a more oil "wet-able" surface -> low cylinder temps, longer ring life, etc. Been a long time since I've thought about this as well.

 

[pjc]

Agreed. Looks like channel chrome. What are the relative "birthdays" of the two cylinder types?

All four cylinders are ”chrome” with the orange stripe on the fins of the cylinder barrels.

The three “smooth” ones are quite old. Engine was last overhauled in 1990 and the cylinders we not new then. Original date of manufacture for the engine was in the 1960’s, and it had been overhauled twice before 1990. All have 2-3k hrs in operation. I’d have to dig into the logbooks to be more precise on dates.

I don’t know the vintage of the new one, it was installed 14 months ago, but was a repaired (not new) unit from a reputable local engine shop. Could be of any vintage, and who knows when/if it was re-chromed at some point. I didn’t borescope it on installation (before running the engine) but I don’t recall seeing crazing in the barrel when I installed it. Perhaps the break in, or oil soak, has enhanced the visibility of the crazing. Also, the oil analysis trend shows chrome (and iron) still moderately high but DECREASING since the cylinder replacement last year.

Would very much like to believe all is well. Anyone else have direct experience?

Peter

 

[hgerhardt]

I have 4 overhauled cylinders just like that one on a shelf. That's indeed channel chrome, which is a process done to retain oil on the surface. As I remember it, during the chrome plating process, they reverse the electric current near the end which causes those micro cracks in the surface of the chrome. Perfectly normal.

 

[Freemasm]

All four cylinders are ”chrome” with the orange stripe on the fins of the cylinder barrels.

The three “smooth” ones are quite old. Engine was last overhauled in 1990 and the cylinders we not new then. Original date of manufacture for the engine was in the 1960’s, and it had been overhauled twice before 1990. All have 2-3k hrs in operation. I’d have to dig into the logbooks to be more precise on dates.

I don’t know the vintage of the new one, it was installed 14 months ago, but was a repaired (not new) unit from a reputable local engine shop. Could be of any vintage, and who knows when/if it was re-chromed at some point. I didn’t borescope it on installation (before running the engine) but I don’t recall seeing crazing in the barrel when I installed it. Perhaps the break in, or oil soak, has enhanced the visibility of the crazing. Also, the oil analysis trend shows chrome (and iron) still moderately high but DECREASING since the cylinder replacement last year.

Would very much like to believe all is well. Anyone else have direct experience?

Peter

Seems to line up with what I can remember. The wide move from "straight" chrome to channel chrome was around 1990 IIRC; about the time (possibly a market reaction to) the release of Cerma-chrome and later Cerma-Nil treated barrels. I believe these were ECI products. Good thing is they could restore barrels back to new limits with the aforementioned processes. Unfortunately, neither lived up to the hype; though I personally didn't have the common wear step issues with the CC barrels that killed the product.

Back to your point, nothing that I see suggests any current or pending related issue.

 

[pjc]

I have 4 overhauled cylinders just like that one on a shelf. That's indeed channel chrome, which is a process done to retain oil on the surface. As I remember it, during the chrome plating process, they reverse the electric current near the end which causes those micro cracks in the surface of the chrome. Perfectly normal.

Excellent, that’s what I was hoping. Thanks for the confirmation.

Peter

 

[SPB W10]

Peter, seeking wisdom ...
You're doing very good with 2000 hours flying those chrome cylinders, doing oil analysis and posting, topside up, your clear borescope photos.
Keep doing the same.
As others have pointed out, there have been a variety of names and processes, through the years, for chroming cylinders back to standard bores.
Steven B

 

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All is well!
I concur you have one Channel Chrome cylinder.
I have 4 on an 650 hour 0-360 and it burns a quart in 6.5 hours.
Actually wished now I didn't have them but such is life.
Fly and don't worry about it.
Art