The interesting question is why this does not happen in those places in Europe where unleaded fuel has been used for decades
It was always hypothesized that if the same car or motorcycle engine is run on leaded fuel initially and occasionally thereafter, the same problems do not occur.
On many other types including many developed before unleaded fuel existed, problems don’t occur regardless and the UND testing program is on only a limited number of aircraft engine types.
As a follow on to my previous post 21, it was pointed out to me that both of the once-popular 1980s FAA auto-fuel STC holders recommend running a newly assembled engine on leaded fuel initially before running unleaded. These FAA STCs were widely used on both Lycomings and Continentals for decades before non-alcohol unleaded fuel became mostly unavailable in the US, and no valve recession problems were reported when following this recommendation.
Silvaire wrote:
it was pointed out to me that both of the once-popular 1980s FAA auto-fuel STC holders recommend running a newly assembled engine on leaded fuel initially before running unleaded.
It would be interesting to know if UND has engines that have never seen leaded fuel. Normal flying you can’t avoid leaded fuel all the time, but I can see if these aircraft fly 100% of the time from their base, then they could have perhaps stayed “pure” unleaded.
Silvaire wrote:
it was pointed out to me that both of the once-popular 1980s FAA auto-fuel STC holders recommend running a newly assembled engine on leaded fuel initially before running unleaded. These FAA STCs were widely used on both Lycomings and Continentals for decades before non-alcohol unleaded fuel became mostly unavailable in the US, and no valve recession problems were reported when following this recommendation.
Lycoming requires the use of an oil additive when using unleaded AVGAS with engines originally intended for 100LL. I assume that UND would have used it, bit do you know if this autofuel STC had a similar requirement?
Lycoming requires the use of an oil additive when using unleaded AVGAS with engines originally intended for 100LL. I assume that UND would have used it, bit do you know if this autofuel STC had a similar requirement?
No, I haven’t reviewed them in detail but don’t think either of the two auto fuel STCs have that requirement. I also think the recommendation to run leaded fuel occasionally is a recommendation not a requirement. Some details here under ‘Lead’.
Are they lycoming cylinder heads or superior? Or are their engines the continetial O-370 which is what I think you get when you get a new pa28 from the factory.
Either way it’s disappointing.
Shame piper haven’t put the Rotax 915 in the pa28. They could of run on ethanol 10% then.
That school did fly 46,000 hours in 4 months.
They also conducted specific checks to find recessed valves, they caught the issue well before the engines got even close to lower compression.
According to the article, only some aircraft were affected.
So both observations are not contradictory.
It would be interesting to have a control group – in a better experiment, they would have run half the fleet on 100LL and monitored it the same way
The basic tappet clearance on these engines is fairly generous and I would bet most mechanics would not notice because it is probably forgotten at the Annual 
With hydraulic tappets a lot of people would go for the max amount of 0.080" and you would need a huge amount of valve seat recession to take that up. And even if it falls to zero, the engine will still “run” and almost nobody does a borescope check so the burning of the valves (caused by them not sitting down on the seat) won’t be noticed…
Airborne_Again wrote:
Lycoming requires the use of an oil additive when using unleaded AVGAS with engines originally intended for 100LL. I assume that UND would have used it, bit do you know if this autofuel STC had a similar requirement?
Do you have more details on this additive? Not sure I recall hearing about that requirement. Thanks!
