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Uneven Cylinder Wearing

RogerH

RogerH

Member
On my flights to & from OSH 2023 and home SLC, UT my IO-360 was using progressively more oil, eventually almost the Lycoming max limit of 1 qt per two hours Subsequent compression tests were good but borescope inspection on the left (pilot) side cylinders #'s 2 & 4 showed significantly less cross-hatching. This was producing some blow-by evidenced by oil residue on the exhaust valve stem and left underside of the aircraft. Those two cylinders are now removed and heading to Western Skyways for rework with the expectation oil consumption should return to the roughly 8-10 hours per quart after break-in I was experiencing previously.

What has me baffled is the right side cylinders #'s 1 & 3 have good cross-hatching, no sign of oil loss, and look to be good to remain on the engine. Since all four cylinders are operated in the same manner in flight I'm curious if others have seen lopsided wear on horizontally-opposed cylinders -- is this normal, ABnormal or ???

Background: The previous owner had all new Lycoming cylinders installed during a major overhaul by Poplar Grove in 2016. He subsequently put about 100 hours on the engine and I've since put another 200 on. Not a lot of hours but winter weather permitting regular flights. All Blackstone oil analysis reports have been good, no red flags, not making any metal.. Regular oil changes with CamGuard since I bought the plane (typically annual or every 30 hours ish) with normal CHT & EGT readings (380F/1350F typically in cruise).

Anyone have any similar experience or good theories of the cause?

Thanks
 
Do you know what glazing is? It fills in the cross hatch and to the untrained eye, it looks like the cross hatch is gone. Cyl walls seem to be coated with a tan colared opaque coating instead of shinny metal. Glazing cause oil burning and the greater the extent of the glazing, the more oil burned. I am not sure that two glazed cylinders could cause an oil burn rate as high as you are seeing. glazing happens when the cylinders get too hot during break in.

Larry
 
What wrist pins were in the cylinders? The pins with the loose button heads (lycoming) have caused issues in the past. Most people get rid of them on a cylinder change and go with the Superior 13444 wrist pins. They have pressed in button heads and a relief hole in wrist pin. Also, you said you engine was overhauled. Just because you get Yellow tagged con rods and a yellow tagged Crankshaft, doesn't mean you cannot have a combination of parts that can fall out of tolerance once assembled. Con Rods to Crankshaft in 320/360/540's should be around Max .016". A place like Poplar should be measuring these tolerances and recording them. You have to put the bearings on and torque up the con rods bolts to measure this. Most places don't like to pull that apart once it's been torque up and on IO-360's with stretch bolts, its more expensive to do that and throw those away if you fail that clearance.
With that being said, if you were at max tolerances, you can have forces exerting side force on the con rods during a compression stroke that can push the piston around and also wear out the bottom side walls of the con rods. That may be a stretch and glazing is more likely an issue and just keeps getting worse with more hours on the engine.
 
Some excellent advice provided here by the others.

One other thing you might like to consider as a "bigger picture" kind of thing is the cooling of the engine. Sometimes it's very difficult to measure the effects as the visible results can take several hunderd hours to become apparent, but poor baffling, poor sealing, incorrect airflow, cracked or missing baffles - all these things can influence wear on the cylinders.

To illustrate the point, I witnessed an occasion where a shop installed an engine after overhaul and they had missed fitting a small baffle at the rear of the engine. This allowed a higher level of cooling to the aft side of the rear cylinder. The excessive cooling caused tighter tolerances on that side which in turn resulted in excessive wear on that side where it was colder. The barrel was literally oval in operation by a few thousands of in inch. It took 500 hours of operation to show up and cost the owners a new cyclinder.

Never underestimate the work your baffles are doing to maintain your engine in good condition. Pay attention to them.
 
lr172 said:
Do you know what glazing is? It fills in the cross hatch and to the untrained eye, it looks like the cross hatch is gone. Cyl walls seem to be coated with a tan colared opaque coating instead of shinny metal. Glazing cause oil burning and the greater the extent of the glazing, the more oil burned. I am not sure that two glazed cylinders could cause an oil burn rate as high as you are seeing. glazing happens when the cylinders get too hot during break in.

Larry
Click to expand...
Thanks for your comment, no glazing evident.
 
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