Low CHTs and lead deposits on rings - any connection?

Is there any correlation between low CHTs and lead buildup on the rings? I came to the RV community after flying a Cirrus SR22 for 6 years. In LOP cruise our CHTs usually ran 285-300 degrees. We had a recurring problem with lead deposits building up on the rings which kept the rings from rotating freely thereby increasing oil consumption. The solvent ring wash procedure never worked, so we re-worked four cylinders in a three year span. It seemed like the cooler running cylinders had the bigger problem with deposits, hence my question. Any thoughts?

Cirrus or RV?

Hi Chris,

Just a quick question, was the lead issue on the Cirrus or on the RV? I could not quite tell from your post(My wife will tell you I can be very dense - so it might just be me....) Nevermind, I googled and see this was on the Cirrus.

I have 10 years and 1550 hrs running LOP with CHTs in the same range on my O-320 and have not seen this. One caveat, I have run a pretty high % of mogas the last 2.5 years - but saw no issues prior to this while running 100LL.

Just one data point.

Thanks, Pete. Yes, I was talking about the Cirrus. Big bore Continental, IO-550. At 10,000 or greater we could lean it back to 12.7 gal/hr at 165 kts and get these CHTs. Great cooling designed into that airplane. As long as we leaned brutally on the ground we never had a problem with fouling, except oil fouling when we had a ring problem.

We also used Camguard religiously. I still do in the RV6A. Cooling has been an issue for our RV. We have to watch CHTs closely in the climb. It is a challenge to keep them below 400 degrees, even after sealing the top of the engine well with RTV.

cht

Run the recommended by manufacturer of Marvel Mystery Oil I do and my pistons are very clean.I run in gas.
Bob

Perhaps it is a Continental issue. There are thousands of RV's flying with Lycoming engines and this type of ring problem is absent.

I recall reading about build up of lead balls on spark plugs in engines with low CHT in a technical article somewhere; can't recall where. The lower temperatures prevented it's burn off I believe. Doesn't seem like a stretch to also have it on the rings.

Erich

You are in luck - I had the article saved on my iPad and it looks like it has some suggested remedies
Here ya go :

http://www.shell.com/business-custo...mljYWwtdGFsay90ZWNoYXJ0MTgtMzAwNzE2MDAuaHRtbA

I can't figure how that would be caused by low CHT's. First, CHT's don't directly related to the Cylinder barrel temp (where the rings are). Second, most auto engines run with block temps under 200 and I don't recall lead fouled rings as a common problem with them (back in the days of leaded fuel). It was usually carbon and usually caused by excessive oil burning (i.e. poor ring interface).

I would think excessively rich mixtures would be a leading cause.

Larry

Read the article -it's short and informative. As stated there, lead is present in Av gas at 5 times the levels that were present in auto fuel.
Regards
Erich

100/130 referenced in the article

Isn't that the green stuff? Not very common now days. Isn't the blue stuff 100/110? Less lead in the blue stuff.

Recommended cruise CHTs are around 380f. TCM warns of ring fouling at temps less than 320f or so...and warns of lower RPM cruising causing the same problem (fouled rings) - they want 2400 and up for cruise..

Carry on!
Mark

Octane ratings

Gasoline octane is usually measured using the "motor" or "research" test method or an extension thereof. This produces a motor or research octane number for the tested fuel in "RON" or "MON" with the motor method being the more conservative and lower number producing test. The local gas station averages the two methods using the formula R+M/2. The octane rating of gasoline and long term storage stability, can be dramatically increased by adding tetraethyl lead (TEL).
I believe 100 Avgas "green" and 100LL Avgas "blue" share the same "Motor" class octane Rating(AKA aviation lean) of 100 and an 'Aviation Rich" rating of 130. The main difference between the fuels is the octane rating of the fuel base stock before the TEL is introduced, 100LL using a higher quality more refined base fuel and the amount of TEL added (100LL has about half the TEL of 100). The final octane rating of both products is the same "100/130".
The key to preventing unwanted lead buildup is heat. If combustion temps are high enough the lead remains in a vapor state and goes out the exhaust. If temps are too low the lead condenses as a solid on rings, plugs, valves etc. and leads to engine trouble. Good luck, Russ