American flight school switches to unleaded. And back again

[danny_galaga]

https://www.avweb.com/aviation-news/citing-valve-damage-und-drops-unleaded-fuel-and-returns-to-100ll/

[RFguy]

article .. I guess when they mean 'dry tappet' they mean they remove and bleed the hydraulic lifters right down. Since it's not like a solid lifter engine.  Thruster ?????

 

could just be they ran the engines hot ?  or ran high CHTs ? I wonder. will be interested to see if Lycoming releases the numbers, since the Lycoming factory  guidance is different to this results

 

UL94 is a bit different to the proposed GAMI100 unleaded. 

(Lycomign O-360) I run 100LL for TO, climb  and landing (left wing) , and Premium98 (right wing) for other (cruise) ops at 70% of max HP.

Edited November 10, 2023 by RFguy

[Thruster88]

Yes dry tappet means remove tappet, disassemble and clean with solvent. Normally only done when installing new or overhauled cylinder on to engine. Lycoming dry tappet clearance 0.028 to 0.08 thou. The worry (for rotax 912 people) is how the air gets out of the tappet/ hydraulic lifter when the engine starts. 🤔😂 

[danny_galaga]

1 hour ago, RFguy said:

article .. I guess when they mean 'dry tappet' they mean they remove and bleed the hydraulic lifters right down. Since it's not like a solid lifter engine.  Thruster ?????

 

could just be they ran the engines hot ?  or ran high CHTs ? I wonder. will be interested to see if Lycoming releases the numbers, since the Lycoming factory  guidance is different to this results

 

UL94 is a bit different to the proposed GAMI100 unleaded. 

(Lycomign O-360) I run 100LL for TO, climb  and landing (left wing) , and Premium98 (right wing) for other (cruise) ops at 70% of max HP.

Interesting idea with the two different fuels RF. I never would have thought of it. 

[facthunter]

In principle, I don't like hydraulic lifters on an aeroengine. When you check them manually you get to know if there's something amiss. It also nearly killed me causing the only engine failure I've had on any GA "little" motor. A Continental 0-300. in a C-172.  Nev

[facthunter]

Reading the comments related to that fuel matter gives you an insight as to how little people really know about Valve seating, guide wear etc. When a cylinder head heats up the heating is very uneven around the exhaust port and the valve and seat will inevitably distort and seat less well than it did when cold. Arranging the valve spring to have special washers under it would cause them to rotate slowly and even out the wear on the valve  at least. Better head cooling can reduce distortion there. Side valves are notorious for this because of the positioning of the exhaust port close to about 1/3rd of the cylinder.  Nev

[onetrack]

I don't understand why a valve seat recession protection additive wasn't used by the flight school. MMT (Methylcyclopentadienyl manganese tricarbonyl) is a Manganese-based fuel additive that provides excellent protection against valve seat recession - and it boosts the octane rating of the fuel by 2 or 3 numbers at the same time.

In addition, MMT has been in use in Canada for over 40 years, with no detrimental health or environmental effects. Manganese is a naturally occurring element in Nature and is needed in trace levels by plant life to improve nutrient uptake.

In the U.S., Millers VSP additive is readily available, and I'm sure a big flight school could have acquired the product at a discounted price for bulk purchases.

[facthunter]

Some of any additive is always going to end up in the oil.  Some  anti scuffing additives have caused stuck exhaust valves on hot running aircooled motors.   Nev

[onetrack]

That may be the case with some "alternative" dubious additives, but MMT has an excellent track record as a fuel additive over a generation or more, enough time to find any problems.

The car manufacturers wouldn't approve additives simply because they claimed they'd damage catalytic converters. No CC, no problem.

[facthunter]

There are lot's of additives in modern oils. As you say, some of the older ones are not  permitted anymore. These days it's difficult to get an oil for a mini  and a lot of cars with non roller cam followers.   Nev

[RFguy]

valve seat recession : I'm sure there is more to this story..... Seems  valve recession  had coincidence with use of UL94. But  that's all we have right now, the controls on their 'experiment ' are NOT tight enough to deduce causality. IE that UL94 caused the recession.

Danny- dual fuel- yeah when available it's how I roll...(it does have a MOGAS STC). There is no detectable change in EGT, CHT, RPM  when switching between fuels at ANY power level.... A change in the burn rate would show up as EGT change...

[facthunter]

 Right . the burn rate with change of octane doesn't change enough to be at all relevant. Rich or lean will alter burn rate and effective OCTANE figure. IF you detonate, your temps will go up. More likely if you are lean.  Nev