Citing Valve Damage, UND Drops Unleaded Fuel And Returns To 100LL

[RV8JD]

Well this is an interesting development, from AvWeb. From the article, it seems that UND had a good monitoring program in place, and is working with Lycoming to evaluate the data and parts.

"Citing Valve Damage, UND Drops Unleaded Fuel And Returns To 100LL"

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

"After an extensive trial, the University of North Dakota’s flight school has dropped Swift UL94 fuel and resumed use of 100LL. The school said ongoing maintenance monitoring of aircraft using UL94—almost exclusively Lycoming-powered Piper Archers and Seminoles—resulted in measurable exhaust valve recession. The school made the switch back to 100LL on Oct. 27.
..."​

OTOH, later in the article (but no mention of their maintenance monitoring system):

"Another operator we’ve been monitoring for more than two years is Rabbit Aviation Services in San Carlos, California. The company oversees maintenance and fueling of a pair of flying clubs totaling nearly 10,000 hours of flight per year. Rabbit CEO Dan DeMeo said experience with UL94 has been universally positive with less spark plug fouling and cleaner oil. Rabbit has been offering UL94 for two and a half years."​

 

[gasman]

The propane industry found this out in the 60's when doing conversions that the valve would beat itself into the head.

When lead was removed form gas, the auto industry went with hardened seats to solve the problem, as did the propane conversions to solve the problem of the missing lead cushion.

 

[rv8ch]

This is gonna be good. Wait until the GAMI boys get a look at this. Getting out my popcorn!

 

[StuBob]

This is gonna be good. Wait until the GAMI boys get a look at this. Getting out my popcorn!

Nope. I predict, if he says anything, George will say that some Old Wives’ Tales never die, and that the “valve damage” is exaggerated or due to something else.

And he could be right. Were they on this monitoring program before they started on UL? If not, they don’t have a control and have no idea whether this is something they would’ve found on 100LL.

 

[plehrke]

Interesting but too little sample size to form a conclusion.

Article says
“ Lycoming addressed this issue in its cylinders during the 1990s and was believed to have valve seats and guides suited for unleaded fuels.”
But article never says if these Lycoming engines at UND had those hardened seats.

 

[Bill Boyd]

Pardon me; would you please pass the seasoned butter salt? Thank you.

I suspect a lot of mogas users will be silently and respectfully munching our popcorn as this story unfolds.

 

[airguy]

I suspect a lot of mogas users will be silently and respectfully munching our popcorn as this story unfolds.

1500 hours on unleaded in my 360 so far, and the engine looks very clean inside, no valve recession that I can see on a borescope, compressions are all 77+.

Sample size of one means just about nothing, positive or negative.

 

[rv6ejguy]

One big user has issues, another doesn't. Will be most interesting what Lycoming determines here.

Greg, you are not far from the usual TBO now. If the engine makes it there producing good power and sound compressions, that's a useful data point.

Doesn't Pete Howell have over 2600 hours on mostly mogas now?

 

[Freemasm]

Question for consideration

I have no idea so I'll throw this question out.

It was my understanding, right or wrong that lubricity of gasoline was one of the least controlled properties. It varied greatly between suppliers.

While both the Swift fuel and 100LL would have to meet the spec (ASTM D910???) is lubricity even specified? Would be easy to conceive that the lead in 100LL would help that fuel exceed any spec value or at least that of truly unleaded fuel.

Yes, the subject sample size is limited but still curious.

Anybody? Thanks

 

[KatanaPilot]

One big user has issues, another doesn't. Will be most interesting what Lycoming determines here.

Greg, you are not far from the usual TBO now. If the engine makes it there producing good power and sound compressions, that's a useful data point.

Doesn't Pete Howell have over 2600 hours on mostly mogas now?

One big user, one huge. UND flies around 10,000 hours in a month. Having seen their operation up close, I trust their data.

 

[lr172]

The propane industry found this out in the 60's when doing conversions that the valve would beat itself into the head.

When led was removed form gas, the auto industry went with hardened seats to solve the problem, as did the propane conversions to solve the problem of the missing lead cushion.

+1

Hardened seats were a cure to the missing lead and today seeing engines going 200-300K on original heads. I had always assumed that th Lyc seats were hardened. Does anyon know definitively? Sounds like too small of a sample size to declare this fuel as a cause.

 

[lr172]

1500 hours on unleaded in my 360 so far, and the engine looks very clean inside, no valve recession that I can see on a borescope, compressions are all 77+.

Sample size of one means just about nothing, positive or negative.

the recession wouldn't be seen with a borescope. A better test is dry tappet clearance. If you recorded the dry tappet clearances when you built the engine, a new clearance measurement will tell if your valves have been receding, and how much over those 1500 hours. Challenge here is that it also accounts for tappet face and cam lobe wear. valve recession reduces the clearance and the other two increase it. In a healthy engine, the lobes and tappet faces do not see much wear and why most cams can be polished and put back in service. Tappets are just re-ground for the concave break in shape.

If there is any possibility this threat is real, it wouldn't be a bad idea to do this in your case. If they are receding and your clearances were on the min side of the range, you could have issues down the road. If an exh valve is left open even a thou, it will start to burn and warp.

All of these issues make me wonder how much precision was applied by the UND folks when determining that the valves were receding. Only real way to know is if someone put a dial indicator on each cyl and measured installed stem height for each valve both at install and tear down. Not tools the average A&P uses. The cyl overhaul guys I am sure do this but doubt they keep records of it. Stem height has a fairly wide tolerance and each is a bit different, as grinding valve seats is not precision work in most cases. It is just a guy using a drill with a piloted stone on the end of it. He just keeps grinding until the stem height is in the range. Lyc gives guidance on measurements at the seat itself, so stem ht doesn't have to be measured, though suspect that good shops use a go/no go block of some sort to confirm stem ht is in range.

Larry

 

[lr172]

I have no idea so I'll throw this question out.

It was my understanding, right or wrong that lubricity of gasoline was one of the least controlled properties. It varied greatly between suppliers.

While both the Swift fuel and 100LL would have to meet the spec (ASTM D910???) is lubricity even specified? Would be easy to conceive that the lead in 100LL would help that fuel exceed any spec value or at least that of truly unleaded fuel.

Yes, the subject sample size is limited but still curious.

Anybody? Thanks

Fuel and all of their additives have very poor lubricity and don't believe that anyone measures that, as no one is counting on it. If you need lubrication in your fuel (e.g two stroke engines), you mix oil in with it. There are standards for that, though the engine makers specifies the ratio based upon their needs. Lead has decent lubrication properties and back in the day, engine makers used non hardened steel for valve parts because the lead provided a protective layer and lubrication. When the lead went away, they had to move to harder steel in order to survive.

 

[rv6ejguy]

Assuming hardened seats and valve faces, a systemic problem with valve recession caused by no lead would show up across the Lycoming fleet. It doesn't seem to be.

Petersen Mogas STCs have been around for decades. UL fuel use in Lycomings is nothing new.

Pete here on VAF has around 2700 hours on his Lyc using mostly mogas if I am not mistaken.

Swift and GAMI have done years of testing themselves and under FAA supervision. Wouldn't have been approved if they saw this issue in testing.

Is UND operating ancient engines with non-hardened components?

A borescope will show serious recession since you have around .050 available in lifter plunger travel available. That would be a lot of wear on the valve face and seat. When you reach zero clearance, a burnt valve will result pretty quickly which is easily evident with a borescope and compression test.

The Swift 94 is basically 100LL without the lead from what I have read on the subject.

 

[BillL]

Until the seat/valve materials and geometry are documented there is little in the way of universal conclusions that can be made here regarding UL potential to replace 100LL, but it certainly shows that universal replacement in the field without proper data and specific tests, and endorsement by manufacturers is going to cause trouble.

Let's not throw propane into the mix for any reason. Propane A/F for combustion has a much higher adiabatic flame temperature and that has an adverse effect on valve recession life. This is based on being project leader for a propane and NG conversion of a specific diesel engine. Valve events, seat angles, materials and other engine design parameters also have effects on durability that don't get reported in entertainment magazines.

 

[KatanaPilot]

Is UND operating ancient engines with non-hardened components?

Not unless Piper is installing ancient engines on new airplanes. UND refreshes their fleet pretty often. They used to operate mostly Cessna singles, Piper twins. A few years ago they replaced the Cessna fleet with Piper. They do have a few other makes for specialized training.

According to my son who attended UND (and worked as a mechanic and parts room attendant while a student) - UND gets 10-15 new engines at a time and replaces 3-4 a month. Each airframe flies 1200-1500 hours a year.

It will be interesting to see what Lycoming says.

 

[petehowell]

Interesting Study

A nice, controlled comparison study here It only goes for 150 hrs tho.:

I Just overhauled my O-320 as part of a prop strike inspection at 2725 hrs. At time of overhaul, my valves looked fine - pics here. I had the ECI AD cylinders vintage 2005 that could not be reused, or they would have been.

Sample size = 1, all caveats apply. I run LOP with a carb and use a splash of MMO (I know, I know)in my mogas. I'm doing the same with the overhauled engine - 40 hours on it now.

 

[rv6ejguy]

2725 hours! Most excellent Pete.

 

[Mike S]

Well this is an interesting development, from AvWeb. From the article, it seems that UND had a good monitoring program in place, and is working with Lycoming to evaluate the data and parts.

"Citing Valve Damage, UND Drops Unleaded Fuel And Returns To 100LL"

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

"After an extensive trial, the University of North Dakota’s flight school has dropped Swift UL94 fuel and resumed use of 100LL. The school said ongoing maintenance monitoring of aircraft using UL94—almost exclusively Lycoming-powered Piper Archers and Seminoles—resulted in measurable exhaust valve recession. The school made the switch back to 100LL on Oct. 27.
..."​

OTOH, later in the article (but no mention of their maintenance monitoring system):

"Another operator we’ve been monitoring for more than two years is Rabbit Aviation Services in San Carlos, California. The company oversees maintenance and fueling of a pair of flying clubs totaling nearly 10,000 hours of flight per year. Rabbit CEO Dan DeMeo said experience with UL94 has been universally positive with less spark plug fouling and cleaner oil. Rabbit has been offering UL94 for two and a half years."​

One big user has issues, another doesn't.

Am I the only one noticing that one quote is from a user, and the other from a user who is also a vendor?

 

[BillL]

Pete - thanks for that paper. Although the conclusion says the auto-gas and 100LL exhaust valves had the same stabilized VSR, figure 7 would seem to dispute that claim. After about 60 hrs there is a steady recession of ~ .004"/100 hrs for 3 of the 4 exhaust valves.

As Pete points out, is only the standard FAA 150 hr test. Maybe the auto-gas would have stabilized later or maybe not, but certainly not stable by 150 hrs to satisfy this engineer.

All in all seems like a pretty thorough test protocol.

Based on Krea's 1200-1500hrs per year (UND) let's assume 1500. That might average 500 hrs for 4 months. .028" /.004" X 100 is 700 hrs. based on the test report. Certainly in the range of variance. Cylinder pressures, valve seating velocity, and temperature (note exhaust vs intake difference) are variables in the result. Consequently, it certainly will be interesting "to hear what Lycoming has to say".

Caveat - -one does not know if it take only one tank in 20 of 100LL or what fraction of lead it would take to prevent the wear. Or just MMO

 

[rmarshall234]

There’s a guy on the Bonanza forum named Lew Gage - in fact he is “Mr Bonanza” as far as the older E-Series Bonanzas go. He literally wrote the book on flying and operating them. Engineering, manufacturing, A&P/IA credentials, etc. He has burned 45,000 gals of unleaded fuel in his Bonanza. One data point but a pretty impressive one.

 

[Canadian_JOY]

The UND experiment leaves much to be desired in terms of scientific method. There's no control group of aircraft which continued running 100LL. There's no "before and after" data samples to measure recession. To the best of my knowledge there's no documentation of rigor in fueling - how many airplanes got some 100LL while operating away from home base?

All of these points lead me to believe there is much more study which needs to be applied to the use of unleaded fuels.

I'll return you to your regular programming as I head out to the local gas station to pick up a bunch of jerry cans of MOGAS to burn in my airplanes.

 

[scsmith]

When lead was removed form gas, the auto industry went with hardened seats to solve the problem, as did the propane conversions to solve the problem of the missing lead cushion.

I ran Volvo B-20 engines with plain old iron heads with no hardened seats, just ground into the iron, on unleaded premium for many hundreds of thousands of hours. Never had to do a valve job. Just a light lapping when apart to replace a cam (B-20s had a cam-wear problem)

 

[rv8ch]

People inside and outside the US have been running unleaded for decades without problem, but perhaps they just never measured exhaust valve recession.

I saw this in a Flying article:

What Is Valve Recession?
According to Richard Scarbrough, A&P mechanic and contributor to FLYING, “exhaust valve recession is when the valve sits too low in the seat.” If the valve is not properly seated, there can be “blow-by” that can result in an uncommanded loss of engine power and compression and, in worst cases, valve failure.

“Exhaust valve recession can result in valve discoloration—first red, green, then purple. It can also erode the guide,” said Scarbrough, adding that at this time no one has attributed exhaust valve recession to a lack of lead in the fuel.

and

UND director of maintenance Dan Kasowski said the Lycoming-specified minimum clearance is 0.028 inch, and some of the cylinders exceeded this limit.

Is this something we should be measuring regularly? Do I need to add this to my OCM checklist?

I think we are going to learn a lot more about "exhaust valve recession" in the coming days and weeks!

 

[Tandem46]

The UND experiment leaves much to be desired in terms of scientific method… there is much more study which needs to be applied to the use of unleaded fuels.

I agree 100%!!!
Something else that hasn’t been addressed that I think is huge. Look at the pilots flying these airplanes. They are extremely low-time, low-experienced pilots… both the students and the instructors. Essentially children teaching children. I guarantee they do not have the engine management skills (leaning techniques, operating temp management in terms of EGT/CHT, etc) that an average aircraft owner has developed. Being flight school aircraft, these engines are most assuredly abused on a daily basis.

 

[MacCool]

The UND experiment leaves much to be desired in terms of scientific method. There's no control group of aircraft which continued running 100LL. There's no "before and after" data samples to measure recession. To the best of my knowledge there's no documentation of rigor in fueling - how many airplanes got some 100LL while operating away from home base?

All of these points lead me to believe there is much more study which needs to be applied to the use of unleaded fuels.

I'll return you to your regular programming as I head out to the local gas station to pick up a bunch of jerry cans of MOGAS to burn in my airplanes.

Maybe I misunderstood. In UND's switch to Swift, I didn't see any thing that suggested that this was an "experiment". I viewed it as an aviation company with a fairly large fleet of piston airplanes that elected an operational change (Swift), then monitored. Based on their subsequent maintenance findings, they elected to change back. AvWeb caught wind, and now people are pissed at UND for undertaking a poorly-designed "experiment".

I want to hear what Lycoming has to say. Supposedly they hardened their valve seats in 1994 and they have formally said that unleaded fuels are OK in at least some of their engine models.

 

[KatanaPilot]

I agree 100%!!!
Something else that hasn’t been addressed that I think is huge. Look at the pilots flying these airplanes. They are extremely low-time, low-experienced pilots… both the students and the instructors. Essentially children teaching children. I guarantee they do not have the engine management skills (leaning techniques, operating temp management in terms of EGT/CHT, etc) that an average aircraft owner has developed. Being flight school aircraft, these engines are most assuredly abused on a daily basis.

Most of what you say regarding the experience of the students and instructors is fairly accurate. That has been the case at UND (and most flight schools) for many years. However, the only thing that changed recently was the fuel being used.

UND runs a top flight (pun intended) organization and the folks that are in charge are pretty experienced.

 

[plehrke]

Economics

My guess it is all about cost and it is significant.

I could not find on AirNav the cost of 100LL vs UL94 were UND is at GFK airport in grand forks but did find the closest airport to carry both fuels is Fleming Field (KSGS) in South St Paul. 100LL is $0.70 per gallon cheaper than UL94. UND said they flew 46,000 hours in 4 months in Archers and Seminole. I don’t know their burn rate but for easy math let’s guess 10 gal per hour. That is 460,000 gal they burned. Paying $0.70 extra per gal that is an extra cost of $322,000 for four months or $966,000 for an entire year.
I would switch back to 100LL no matter what was going on with the exhaust valve.

 

[PilotjohnS]

Why?

If they were paying more for UL94 why would they every go that route in the first place? I hope they were getting the UL94 for the same price as 100LL. Maybe their accountant finally realized how much this “experiment” was costing them? But why throw “valve recession” under the bus unless there is a warrenty claim or other monetary motive? Something is rotten in Bismark.

 

[plehrke]

If they were paying more for UL94 why would they every go that route in the first place?

And there is the question we will all be asking from now until 100LL is no longer available.

My guess is Swift gave UND a deal on the price of UL94 since they are a University and it appears it is not for sale at Grand Forks Airport. Two other schools, Purdue and Utah Valley Universities, are using UL94 according to Swift’s website.

 

[cactusman]

I'm guessing UND operates their airplanes much more roughly than the average builder/flyer here.

There used to be a time when instructors taught folks techniques to be smooth and gentle with things mechanical...sighhhhhhh.

Although in fairness in primary instruction there are lot of things done that are rough on engines...shock cooling...hard go arounds...things that us normal folks don't normally do.

 

[PilotjohnS]

Huh?

Although in fairness in primary instruction there are lot of things done that are rough on engines...shock cooling...hard go arounds...things that us normal folks don't normally do.

Speak for yourself. The plane flies better than I do.

(Just joking)

 

[rv8ch]

...

Although in fairness in primary instruction there are lot of things done that are rough on engines...shock cooling...hard go arounds...things that us normal folks don't normally do.

There are some folks that say shock cooling is an OWT.

https://www.avweb.com/ownership/shock-cooling-time-to-kill-the-myth/

 

[airguy]

There are some folks that say shock cooling is an OWT.

https://www.avweb.com/ownership/shock-cooling-time-to-kill-the-myth/

For a turbo, I might can believe in shock cooling or at least avoiding rapid temp swings. For a cylinder, not so much.

 

[MacCool]

I'm guessing UND operates their airplanes much more roughly than the average builder/flyer here.

There used to be a time when instructors taught folks techniques to be smooth and gentle with things mechanical...sighhhhhhh.

Although in fairness in primary instruction there are lot of things done that are rough on engines...shock cooling...hard go arounds...things that us normal folks don't normally do.

A previous poster appropriately noted that students are likely no harder on engines now than they were before UND switched to Swift. It's unlikely that their experience with valve recession can be blamed on the people flying the airplanes.

Not sure that shock cooling is an actual thing.