Silvaire wrote:
Based on Shell’s description of the additives, I think it’s interesting to consider how the additive is beneficial for use with unleaded fuel – valve seats are not oil lubricated.
Indeed, sure seems difficult to imagine a way that these additives could help harden valve seats. They are essentially anti-scuff agents.
@Peter_Mundy, not sure what you mean?
In four months of flying totaling 46,000 hours, the school found evidence of significant valve recession in some of the Archers.
I read that as that they flew these 46k hours in 4 months.
I did a quick sanity check – the school has over 120 aircraft, so let’s say 100 are on 94UL, 400 aircraft-months of flying means 115 hours per month, or less than 4 per day, so this looks plausible.
In practical terms, the LW16702 additive requirement only means using e.g. W100 Plus oil instead of W100, or the multigrade equivalent noted by Airborne_Again. The additive oil is slightly more expensive and likely wouldn’t otherwise be used unless the engine is a Lycoming O-320H, O-360E or TIO-541 series engine. Based on Shell’s description of the additives, I think it’s interesting to consider how the additive is beneficial for use with unleaded fuel – valve seats are not oil lubricated.
According to some there are issues in using Camguard with the additive oils, but nothing earth shaking IIRC.
eurogaguest1980 wrote:
Do you have more details on this additive? Not sure I recall hearing about that requirement. Thanks!
From the Lycoming service instruction 1070AB:
“WHEN USING THE UNLEADED FUELS IDENTIFIED IN TABLE 1, LYCOMING OIL ADDITIVE P/N LW-16702, OR AN EQUIVALENT FINISHED PRODUCT SUCH AS AEROSHELL 15W-50, MUST BE USED.”
But then the lyco O-360 and O-320 as used in the PA28 not that prone to lead fowling.
The O-200 and O-235 (low compression) are a different matter
Cobalt wrote:
That school did fly 46,000 hours in 4 months.
I did not read that – In addition to data sent to Lycoming, UND is also sending both cylinders and engines for further analysis. Kasowski said after 46,000 flight hours, the school had about the same replacement rate for spark plugs as on 100LL, nor was spark plug fouling noticeably reduced.
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!
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…
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
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.
