Indicator of blow by and chrome cylinders

Over the last 50hrs I have graphed a rise in CHT's on one of my cylinders causing me to look for problems in my plenum and instrumentation. The change was not outrageous but could be be described as a 30 deg higher temp during climb (high power) while nearly equal to all other cylinders in cruise. I was thinking along the lines of airflow and AOA for a few months but it now appears to be blow by. I could not get one cylinder above 60/80 (retested after a flight). Last year that same cylinder was 74/80

Should this be another indicator we can key on when assessing our engines? Even with this one cylinder leaking, the WOT speeds on the AC were close enough to not notice where the CHT stuck out.

Scoping the cylinder the valves look great but lots of air flow from the crankcase vent so that leads me to ask, what are most shops recommending for 500hr chrome cylinders with ring problems?

jdeas said:

Over the last 50hrs I have graphed a rise in CHT's on one of my cylinders causing me to look for problems in my plenum and instrumentation. The change was not outrageous but could be be described as a 30 deg higher temp during climb (high power) while nearly equal to all other cylinders in cruise. I was thinking along the lines of airflow and AOA for a few months but it now appears to be blow by. I could not get one cylinder above 60/80 (retested after a flight). Last year that same cylinder was 74/80

Should this be another indicator we can key on when assessing our engines? Even with this one cylinder leaking, the WOT speeds on the AC were close enough to not notice where the CHT stuck out.

Scoping the cylinder the valves look great but lots of air flow from the crankcase vent so that leads me to ask, what are most shops recommending for 500hr chrome cylinders with ring problems?

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I would not expect blowby to increase CHTs. The barrel may get hotter, but I don't think that heat would migrate to the head. The heat in the upper barrel area is mostly influenced with combustion heat. With the head, it is all about combustion temps and I would expect them to be a bit lower with the lost compression, not higher.

Maybe other can chime in with personal experience. WHen I had excess blowby, I don't recall the CHTS being high. However, it happened at the beginning of my engines life, so didn't have a reference to compare.

I have no experience with chrome cylinders, so cannot offer any advice on that front.

Larry

I'm nobody, but if you have a large amount of ring blow by, it can be ring ends in alignment, or worn/stuck rings or broken rings.
Loss of ring seal means hot gas along the cylinder wall, making it hot. That heat can migrate to the cylinder head temp probe on the bottom of the head, you may see an increase in temperature.
If the oil on the cylinder gets hot from the gas, it will cook on, and you can see it as brown areas on the cylinder. If rings are broken you will get scratches. A bore scope may see these when the piston is down at the bottom.
If the engine has been run hot and the pistons grew to the bore, you will have piston and cylinder galling. It's possible to have piston galling if the oil has been blown down from hot gas leakage and the piston lost lubrication.
A loose intake hose or gasket can cause a lean condition in one cylinder that causes the oil to cook on the inside of the piston crown; look for carbon particles when you change the oil and inspect the oil screen.
I run chrome bores and accept the slightly higher oil consumption. They are tough and resilient, last a long time.
Mike Busch, the savvy aviator has some comments on 'The Jug Jungle' article, might be worth reading.
https://www.avweb.com/news/maint/182902-1.html
A Pull:
"Bad things also happen if too much oil is allowed to reach the compression rings due to a loose oil control ring or an excessively rough cylinder barrel. The compression ring grooves may fill up with oil, the oil may be cooked into varnish by the heat of combustion, and ultimately the compression rings may become stuck and unable to flex or rotate.
Stuck rings are usually revealed as a sharp and sudden increase in oil consumption, and often accompanied by oily top spark plugs. If caught early, rings can sometimes be unstuck without cylinder removal by means of a penetrant soak. Sometimes pulling the cylinder is unavoidable."