C-172 C Engine Management Questions

[jsstevens]

I'm flying a club owned C-172 C with the Continental 0-300 engine. The club & plane owner has given me some very specific instructions about managing the engine. Never idle below 1000 RPM. Run full rich below 6000 feet. Don't run it in the 2000 RPM range (there is a bit of vibration there).

I find I'm having to adjust some of my pattern habits to meet these instructions.

When I trained (in a C-172N with the Lycoming 0-320) if my downwind was extended, I'd throttle back to 2000 RPM and just slow fly until they cleared me to turn base. There's no need to hurry away from the airport just to fly back again, right? But that engine setting is right in the vibration zone prohibited by the owner.

Likewise, I find idling at 1000 RPM makes for an uncomfortably fast taxi speed. Or I have to ride the brakes. Also, it adds a noticeable bit of thrust on final. I'm used to pulling the engine all the way back to idle on short final.

The full rich below 6000 feet is not how I was trained, but I haven't flown that way enough to see what it's doing to fuel consumption. I rent dry so I do care.

Are these kinds of things normal for the 0-300? My impression is that this is a very well maintained airplane and it performs reasonably well.

John

 

[Tom-D]

I'm flying a club owned C-172 C with the Continental 0-300 engine. The club & plane owner has given me some very specific instructions about managing the engine. Never idle below 1000 RPM. Run full rich below 6000 feet. Don't run it in the 2000 RPM range (there is a bit of vibration there).

I find I'm having to adjust some of my pattern habits to meet these instructions.

When I trained (in a C-172N with the Lycoming 0-320) if my downwind was extended, I'd throttle back to 2000 RPM and just slow fly until they cleared me to turn base. There's no need to hurry away from the airport just to fly back again, right? But that engine setting is right in the vibration zone prohibited by the owner.

Likewise, I find idling at 1000 RPM makes for an uncomfortably fast taxi speed. Or I have to ride the brakes. Also, it adds a noticeable bit of thrust on final. I'm used to pulling the engine all the way back to idle on short final.

The full rich below 6000 feet is not how I was trained, but I haven't flown that way enough to see what it's doing to fuel consumption. I rent dry so I do care.

Are these kinds of things normal for the 0-300? My impression is that this is a very well maintained airplane and it performs reasonably well.

John

The 2000 RPM is a direction of the prop/engine manufacturer, but all the other restrictions are with out merit

 

[Rob Schaffer]

I'm flying a club owned C-172 C with the Continental 0-300 engine. The club & plane owner has given me some very specific instructions about managing the engine. Never idle below 1000 RPM. Run full rich below 6000 feet. Don't run it in the 2000 RPM range (there is a bit of vibration there).

I find I'm having to adjust some of my pattern habits to meet these instructions.

When I trained (in a C-172N with the Lycoming 0-320) if my downwind was extended, I'd throttle back to 2000 RPM and just slow fly until they cleared me to turn base. There's no need to hurry away from the airport just to fly back again, right? But that engine setting is right in the vibration zone prohibited by the owner.

Likewise, I find idling at 1000 RPM makes for an uncomfortably fast taxi speed. Or I have to ride the brakes. Also, it adds a noticeable bit of thrust on final. I'm used to pulling the engine all the way back to idle on short final.

The full rich below 6000 feet is not how I was trained, but I haven't flown that way enough to see what it's doing to fuel consumption. I rent dry so I do care.

Are these kinds of things normal for the 0-300? My impression is that this is a very well maintained airplane and it performs reasonably well.

John

I agree with Tom,... the O-300 is a great engine overall. Startup, lean out properly, taxi like normal. 1000 rpm and leaned may be ok for sitting and waiting to taxi, but once you are moving, you'll be holding on the brakes and just grinding away your money. I would be full rich below 2500 here in PA, but once level at or above 2500, I'd lean out accordingly and she purred nicely. I recall the 2000 rpm zone written down someplace too, but cant recall off the top of my head. the one I flew seemed to ahve a slight vibe between 1900-2000 if I was entering the pattern at that rpm.

 

[Dan Thomas]

1000 rpm and leaned may be ok for sitting and waiting to taxi, but once you are moving, you'll be holding on the brakes and just grinding away your money.

And sucking up all the small stones that chip up a propeller, too.

Dan

 

[TMetzinger]

On the one hand, some of these instructions make little sense - as others have noted.

On the other hand, it's the owner's airplane, and if he wants you to operate it a certain way, you should.

Oh, you should be paying a wet rental rate if the owner wants you to burn fuel like that, instead of saving some money by leaning.

 

[gismo]

I'm flying a club owned C-172 C with the Continental 0-300 engine. The club & plane owner has given me some very specific instructions about managing the engine. Never idle below 1000 RPM. Run full rich below 6000 feet. Don't run it in the 2000 RPM range (there is a bit of vibration there).

I find I'm having to adjust some of my pattern habits to meet these instructions.

When I trained (in a C-172N with the Lycoming 0-320) if my downwind was extended, I'd throttle back to 2000 RPM and just slow fly until they cleared me to turn base. There's no need to hurry away from the airport just to fly back again, right? But that engine setting is right in the vibration zone prohibited by the owner.

Likewise, I find idling at 1000 RPM makes for an uncomfortably fast taxi speed. Or I have to ride the brakes. Also, it adds a noticeable bit of thrust on final. I'm used to pulling the engine all the way back to idle on short final.

The full rich below 6000 feet is not how I was trained, but I haven't flown that way enough to see what it's doing to fuel consumption. I rent dry so I do care.

Are these kinds of things normal for the 0-300? My impression is that this is a very well maintained airplane and it performs reasonably well.

John

It's clear that the owner doesn't know how to operate an aircraft engine and that you know considerably more than he does, but it's his airplane. If I were you I'd try to find a way to get him to learn more about engine management (preferably from someone else) but agree in the meantime to operate per his "rules". If the rental has a wet rate, you're only loss is the range reduction (significant), the increased potential for fouled plugs, and higher than necessary club expenses. If it was a dry rate, I'd go somewhere else if the owner's mind is closed on this.

And whoever you solicit to enlighten the owner might benefit by starting with the very true fact that by imposing a "no leaning below 6000" rule he's invalidating the POH range and endurance data significantly enough to result in a fuel exhaustion incident, for which he could be held liable.

 

[Tom-D]

It's clear that the owner doesn't know how to operate an aircraft engine and that you know considerably more than he does, but it's his airplane. If I were you I'd try to find a way to get him to learn more about engine management (preferably from someone else) but agree in the meantime to operate per his "rules". If the rental has a wet rate, you're only loss is the range reduction (significant), the increased potential for fouled plugs, and higher than necessary club expenses. If it was a dry rate, I'd go somewhere else if the owner's mind is closed on this.

And whoever you solicit to enlighten the owner might benefit by starting with the very true fact that by imposing a "no leaning below 6000" rule he's invalidating the POH range and endurance data significantly enough to result in a fuel exhaustion incident, for which he could be held liable.

There are several old Cessna POHs that specify that the engine should not be leaned below 5k. I believe all the C-145/0-300 equipped Cessna have that in the POH. It was the word of the time, but things change.

I operate the 0-200-0-300 at WOT full rich during climb and 2450 as lean as it will run, at all cruise altitudes, If the Carb is set correctly it will not need leaning on the ground nor will it be required to run over 500 RPM for idle.

there are no less than 20 versions of the Marvel Shebler carb on the series of Cessna aircraft all of which are subject to 4 major ADs, but the best of all the carbs are the ones that have never been messed with.

metal float, two piece venturi, standard fuel nozzle, will run 6.5 GPH lean as the engine will run.

 

[jsstevens]

I took a friend and his two young boys on a sightseeing flight this morning. I flew from Orlando Executive (KORL) to the west bank of the Indian River, north up the river bank to look at the space coast from ~4nm south of Titusville (KTIX) until ~2nm north of Dunn Airpark (X21) then back into KORL for a total of .88 on the tach and 1.1 on the Hobbs. With outside air temps in the upper 40s to the low 50s (F) and cruising at 2500 feet, we burned 9.3 gallons. THis seems higher than necessary, so I;m going to speak to him about it. His comment when he said to run full rich was immediately post annual and he said it's running lean.

Anyway, thanks for the advice.
John

 

[Areeda]

Have you looked at the POH recommendations for this plane?

I don't have one earlier than an L model but there after the recommendation is not to lean in a full power climb below 3,000'. This is often interpreted to mean run full rich at all times below 3000.

Granted it's not clear but the don't lean is in the climb section and lean is in the cruise section.

The better argument is to look at the plugs and/or borescope the cylinders at the next oil change to look for carbon/lead deposits. Or report the need to "burn off carbon" to complete the run-up mag check. If I was renting a plane dry the fuel cost to the pilot would be ..ugh.. a low priority item.

We have a club procedure to idle at 1000 rpm with mixture leaned aggressively (tired of cleaning plugs) but taxiing and final approach are not idling.

Joe

 

[dmccormack]

I don't even have a mixture control but plan on adding one.

Many of the older engine manuals recommended full rich up to some altitude (I *think* the O-145 says under 5,000). Idle is also recommended to not exceed 5 minutes on the ground and idle should be between 800-1000 RPM to keep the oil circulating.

Of course fuel was cheaper and so was engine overhaul labor. Plugs were pulled and cleaned every 100 hours or even more frequently.

We've learned a few things since the 1930s yet not everyone has caught up.

 

[Dan Thomas]

I don't even have a mixture control but plan on adding one.

Many of the older engine manuals recommended full rich up to some altitude (I *think* the O-145 says under 5,000). Idle is also recommended to not exceed 5 minutes on the ground and idle should be between 800-1000 RPM to keep the oil circulating.

Of course fuel was cheaper and so was engine overhaul labor. Plugs were pulled and cleaned every 100 hours or even more frequently.

We've learned a few things since the 1930s yet not everyone has caught up.

The oils used in the 1930s coked a lot faster than the oils we use now, so plug fouling was much more common. In our flight school we pull and clean the plugs every 50 hours due to the lead content of 100LL (four times what the 80-octane engines were designed for) and too much circuit work adds to the fouling.

Continentals have a weak top end. Their exhaust valves make trouble much more quickly than Lycomings, so running richer in the climb helps cool them. It's typical for a Lyc to reach TBO without valve trouble, while the small Continentals often need a top OH at mid-time or so.

Dan

 

[Tom-D]

The oils used in the 1930s coked a lot faster than the oils we use now, so plug fouling was much more common. In our flight school we pull and clean the plugs every 50 hours due to the lead content of 100LL (four times what the 80-octane engines were designed for) and too much circuit work adds to the fouling.

Continentals have a weak top end. Their exhaust valves make trouble much more quickly than Lycomings, so running richer in the climb helps cool them. It's typical for a Lyc to reach TBO without valve trouble, while the small Continentals often need a top OH at mid-time or so.

Dan

That may be true for the old OEM cylinders but not the new after market.

I doubt there are any of the old version OEM cylinders still running.

we aggressively lean and have for a long time and I have 2, 0-200s over TBO with nothing but routine maintenance during their life.

 

[Rob Schaffer]

In the 67-H model I flee I regularly burned 7 - 7.5 GPH on the typical 1 hr local flights with TO/LNDgs at local airports. XC flights could get down below 7 GPH if above 5000 feet it seemed and leaned out.

 

[jsstevens]

In the 67-H model I flee I regularly burned 7 - 7.5 GPH on the typical 1 hr local flights with TO/LNDgs at local airports. XC flights could get down below 7 GPH if above 5000 feet it seemed and leaned out.

In the N model I trained in we frequently got 7.2-7.5 GPH on IFR cross country flights. But that was leaned out and I really don't know wether we were treating it well or not.

John

 

[dmccormack]

The oils used in the 1930s coked a lot faster than the oils we use now, so plug fouling was much more common. In our flight school we pull and clean the plugs every 50 hours due to the lead content of 100LL (four times what the 80-octane engines were designed for) and too much circuit work adds to the fouling.

Continentals have a weak top end. Their exhaust valves make trouble much more quickly than Lycomings, so running richer in the climb helps cool them. It's typical for a Lyc to reach TBO without valve trouble, while the small Continentals often need a top OH at mid-time or so.

Dan

Dan -- how would oil coking lead to plug fouling?

 

[Dan Thomas]

In the N model I trained in we frequently got 7.2-7.5 GPH on IFR cross country flights. But that was leaned out and I really don't know wether we were treating it well or not.

John

The N model has a Lycoming in it and can stand aggressive leaning. Lyc says you can anything you like with the mixture when at 75% power or less in a naturally-aspirated Lycoming.

Dan

 

[Dan Thomas]

That may be true for the old OEM cylinders but not the new after market.

I doubt there are any of the old version OEM cylinders still running.

we aggressively lean and have for a long time and I have 2, 0-200s over TBO with nothing but routine maintenance during their life.

Lycoming converted to a chrome-bronze valve guide in 1999. I don't know if Continental did anything similar, but I'll bet the aftermarket guys are using better stuff for their guides. Lycoming's valve issues diminished sharply with the new guide material.

However, with the problems the aftermarket guys have had with their cylinders, I'd be reluctant to use them.

Dan

 

[Dan Thomas]

Dan -- how would oil coking lead to plug fouling?

Old oils had lower flash points so they burned off the cylinder walls more quickly. They thinned out more at higher temps so more got past the rings to get burned in the cylinder and form soot. Soot, being carbon, is conductive and shorts the sparkplug's tip to ground. When additives were developed to modify oil behavior, things got better. Less oil got past the rings and less of the microsopically-thin film on the cylinder walls flashed off when exposed to combustion flame. The rings don't scrape it all off, see. Impossible, and the rings themselves need something to keep them from making metal-to-metal contact with the the cylinder or they'd wear out in about thirty seconds.

Dan

 

[Tom-D]

Lycoming converted to a chrome-bronze valve guide in 1999. I don't know if Continental did anything similar, but I'll bet the aftermarket guys are using better stuff for their guides. Lycoming's valve issues diminished sharply with the new guide material.

However, with the problems the aftermarket guys have had with their cylinders, I'd be reluctant to use them.

Dan

I thought we were talking about small bore 0-200/0-300 engines. it doesn't matter what The big "L" is doing,

ECI has the STC to place a valve rotator on each Exhaust valve, thus eliminating most all of the valve problems.

TCM has never been able to get the choke right in its 50Ci cylinders, but Superior and ECI never had any problems in that area.

If you are operating ANY of the C-series engine up thru 0-470 and want minimal problems this is what you need to do

1 dump any Aeroshell multi-weight oil you are using, the aeroshell oils that comply with the snake oil AD are harmful to the C-series because it contains TCP which is a polishing agent. the Continentals do not require this additive, nor do they like it.

If you are a aeroshell addict, run the Straight 40 or 50 weight and cam guard.

2. place the after market oil filter on the engine, there are several out there that work really well. and change oil and filter every 35 hours.

3. Start using phillips 20-W-50 and Cam Guard, Your little C-Series will love you for it, and run to TBO every time.

I overhaul several C-Series every year, none have any problems with this formula. I have 1, 0-200 that I built in 1990 that is coming up on 3000 hours with superior cylinders and the set up I described, the last annual the compressions were 77/80 across the 4.

And Always read and understand " Oil Talk For Dummies" on the ECI web page

http://www.eci.aero/pdf/BreakInInstructions.pdf

 

[Tom-D]

The oils used in the 1930s coked a lot faster than the oils we use now, Dan

We have always used a light crude oil, that's always,,, there is no difference between what was used in the 30s and what we used today, it is all a light crude oil.

I will say the new additive packages are different.

There is no such thing as a detergent aviation oil.
There is no such thing as a synthetic recip engine oil.

There are additives that produce a "EP" oil.
There are additives that produce an oil that will prevent sludge build up "D"
there are additives that claim a lot of things, but there is no chemical that will put the metal back once it is worn off.

 

[Tom-D]

However, with the problems the aftermarket guys have had with their cylinders, I'd be reluctant to use them.
Dan

Show me one AD or problem area with any Continental 50Ci Cylinder (0-200/0-300) made by any after market manufacturer.

 

[Tom-D]

In the N model I trained in we frequently got 7.2-7.5 GPH on IFR cross country flights. But that was leaned out and I really don't know wether we were treating it well or not.

John

If it were leaned and running 7.2-7.5 you are doing the correct thing.,

ATTA BOY keep it up.

 

[Tom-D]

The N model has a Lycoming in it and can stand aggressive leaning. Lyc says you can anything you like with the mixture when at 75% power or less in a naturally-aspirated Lycoming.

Dan

"N" model 172 = Lycoming 0-320-H2AD
"N" model 150 = Continental. 0-200-A

BIG difference

but lean the he-- out of both, pull it until it stutters and push it till it is smooth. any throttle setting, any altitude.

 

[Tom-D]

Dan -- how would oil coking lead to plug fouling?

It won't

 

[Tom-D]

The N model has a Lycoming in it and can stand aggressive leaning. Lyc says you can anything you like with the mixture when at 75% power or less in a naturally-aspirated Lycoming.

Dan

It has been proven many times over and over, you can cool any engine better by removing fuel than you can by adding fuel.

When you run full rich, there is more fuel in the cylinder than can be burned by the amount of O2 in the air/fuel mixture, thus you have unburned fuel to wash the cylinder walls and a higher temp than had you run leaned to a EGT lower than full rich.

That in a nut shell is the lean of peak theory, It works.

you should read several articles by Lycoming, they have bought on to the LOP theory, lean at any throttle setting at any altitude.

want to prove the theory? if you were at Leadville Co and you wanted best climb, would you lean to get it?

 

[flyingcheesehead]

If you are operating ANY of the C-series engine up thru 0-470 and want minimal problems this is what you need to do

1 dump any Aeroshell multi-weight oil you are using, the aeroshell oils that comply with the snake oil AD are harmful to the C-series because it contains TCP which is a polishing agent. the Continentals do not require this additive, nor do they like it.

I'm still trying to figure out "why?"

We just ran a Conti O-470 951 hours past TBO on Aeroshell 15-50... Seemed to like it just fine!

Absent a really good reason not to run Aeroshell 15-50, one good reason to run Aeroshell 15-50 is that you can find the stuff darn near anywhere. Phillips XC 20W-50 comes in second. Exxon Elite? Better carry a spare case in the baggage compartment.

 

[Tom-D]

I'm still trying to figure out "why?"

We just ran a Conti O-470 951 hours past TBO on Aeroshell 15-50... Seemed to like it just fine!

Absent a really good reason not to run Aeroshell 15-50, one good reason to run Aeroshell 15-50 is that you can find the stuff darn near anywhere. Phillips XC 20W-50 comes in second. Exxon Elite? Better carry a spare case in the baggage compartment.

Finding Phillips has never been a problem for me. but you can find engines running on every kind of oil out there, that have been run way past TBO. During the 30/40/50s we all ran Straight weigh oil and it was not uncommon to see TBO on no filter/no Additive package oil of all kinds.

but in today's world of additive packages we see AeroShell using a polishing agent as a method of polishing their cams to rid them selves of a cam and lifter problem, So why would you run a polishing agent in an engine that has no cam or lifter problem?

 

[flyingcheesehead]

but in today's world of additive packages we see AeroShell using a polishing agent as a method of polishing their cams to rid them selves of a cam and lifter problem, So why would you run a polishing agent in an engine that has no cam or lifter problem?

Because it doesn't really matter? That's what I'm wondering - How does it cause harm? Sure, it may not *help*, but that's different from causing harm.

Of course, we'd probably run the Aeroshell anyway. We have three engines:

Lyc O-360-A4M
Lyc IO-360-M1A
Conti O-470-U

And, it'd be more likely that someone would grab the wrong kind and dump it in the Lyc than it would be for the Aeroshell to harm the Conti.

 

[Tom-D]

Because it doesn't really matter? That's what I'm wondering - How does it cause harm? Sure, it may not *help*, but that's different from causing harm.

Of course, we'd probably run the Aeroshell anyway. We have three engines:

Lyc O-360-A4M
Lyc IO-360-M1A
Conti O-470-U

And, it'd be more likely that someone would grab the wrong kind and dump it in the Lyc than it would be for the Aeroshell to harm the Conti.

You will see high metal in your oil samples, copper and chrome being the most worrisome. and at overhaul time you will be replacing the cam and lifters.

Aeroshell 15W50 is an "EP" oil, so is phillips20W50 with a different additive package that's all.

I would check to see if your Lycoming Engines are required to have the snake oil. some do some don't.

 

[flyingcheesehead]

You will see high metal in your oil samples, copper and chrome being the most worrisome. and at overhaul time you will be replacing the cam and lifters.

Except none of that actually happened. Oil analyses were normal right up until the end. The only anomaly on the overhaul was that the crank had to be re-ground, and that was probably due to the metal that got passed around the engine when the #1 cylinder shredded something, which is what prompted the overhaul.

But I still don't understand *why* TCP would cause such a thing...

EDIT: Sorry I'm such a pain in the ass, but this is how I learn.

 

[Tom-D]

Except none of that actually happened. Oil analyses were normal right up until the end. The only anomaly on the overhaul was that the crank had to be re-ground, and that was probably due to the metal that got passed around the engine when the #1 cylinder shredded something, which is what prompted the overhaul.

But I still don't understand *why* TCP would cause such a thing...

remember what's normal for one engine isn't always be normal for another, that's why we trend the oil samples.

We have discovered the the little Continentals have less problems with Phillips than Aeroshell, because both the 0-200, and the 0-300 have slip clutches for starters. when we used the aeroshell 15W50 we changed starters on a 500 hour cycle, on Phillips we got the life of the engine with out changing a starter clutch.

I don't sell oil, but I have noticed a few things over the years.

OBTW no oil would have saved your crank, metal in the oil doesn't care what kind of oil carries it.

 

[flyingcheesehead]

We have discovered the the little Continentals have less problems with Phillips than Aeroshell, because both the 0-200, and the 0-300 have slip clutches for starters.

So it's not as big of a deal on the 470 if we use Aeroshell?

OBTW no oil would have saved your crank, metal in the oil doesn't care what kind of oil carries it.

Yup. That's why we went for the overhaul - They said that the metal would have gone through the oil pump, the prop governor, and pretty much everywhere else before it got to the oil filter.

In fact, where it first appeared was in some questionable operation of the prop governor. My CFI flew it with David (a very infrequent poster here) and called me afterwards asking about the prop governor. Then I flew it to see if it was normal (with David aboard to make sure that the weirdness happened the way it did on his flight) and it was most certainly NOT normal - It lagged significantly on both prop and throttle changes. After conferring with the MO, we grounded the plane, and a few days later got a look at what was in the filter.

 

[Tom-D]

So it's not as big of a deal on the 470 if we use Aeroshell?

the 0470 has a clutch starter. So the TCP will polish the clutch until it quits working. or you get tired of it requiring two or three tries to get the engine to turn over.

 

[flyingcheesehead]

the 0470 has a clutch starter. So the TCP will polish the clutch until it quits working. or you get tired of it requiring two or three tries to get the engine to turn over.

Wow! OK, now we might be on to something!

If things happen as you're describing above, what exactly would the symptoms be? And what part would you replace to get it working again?

 

[Tom-D]

Wow! OK, now we might be on to something!

If things happen as you're describing above, what exactly would the symptoms be? And what part would you replace to get it working again?

Symptoms are a slipping of the starter clutch. and it requires several attempts to get the engine to crank over.

The parts that would be required to resolve that would be the starter clutch. which is the part between the starter motor and the engine. as seen below.

these are usually about $12-1300 for a overhauled one.

 

[flyingcheesehead]

Symptoms are a slipping of the starter clutch. and it requires several attempts to get the engine to crank over.

The parts that would be required to resolve that would be the starter clutch. which is the part between the starter motor and the engine. as seen below.

these are usually about $12-1300 for a overhauled one.

I ask because this plane does not like to start, never has. It acts like the battery is low - It won't even turn all the way over the first time you hit the key. The second time, it'll turn over just fast enough to get started.

We went through everything - New batteries, starters, yadda yadda - Nothing worked... Until they replaced the starter adapter (which I'm guessing is what contains the clutch). Worked great for a few months, and quickly deteriorated back to its previous level of performance.

Based on what you're saying, it sounds possible to me that the clutch could have been damaged by the Aeroshell oil, and that's why the new starter adapter went bad so quickly? Or are these symptoms indicative of something else?

 

[Tom-D]

I ask because this plane does not like to start, never has. It acts like the battery is low - It won't even turn all the way over the first time you hit the key. The second time, it'll turn over just fast enough to get started.

We went through everything - New batteries, starters, yadda yadda - Nothing worked... Until they replaced the starter adapter (which I'm guessing is what contains the clutch). Worked great for a few months, and quickly deteriorated back to its previous level of performance.

That is typical of TCP at work, remember, polishing is wearing. and in the process of protecting the cam and lifers the TCP polishes the cam and lifters it is also polishing the rings and clutches in the whole engine.

Based on what you're saying, it sounds possible to me that the clutch could have been damaged by the Aeroshell oil, and that's why the new starter adapter went bad so quickly? Or are these symptoms indicative of something else?

Nope that is precisely what happens.

 

[flyingcheesehead]

Nope that is precisely what happens.

Just one more thing - FWIW, it doesn't ever feel like something is slipping. When the engine doesn't turn over on the first try, there is no whirring of the starter motor at all. Like I said, it just acts like a weak battery... But the second time it always cranks over.

Wouldn't a worn clutch that was slipping allow the starter motor to continue to spin?

 

[Tom-D]

EDIT: FWIW, it doesn't ever feel like something is slipping. When the engine doesn't turn over on the first try, there is no whirring of the starter motor at all. Like I said, it just acts like a weak battery... But the second time it always cranks over.

this clutch is a coiled spring wrapped around a shaft, which when turned in one direction it expands, if turned in the opposite direction it contracts and grabs a shaft which turns the engine over, after the Aeroshell polishes/wears the internal ID of the spring it will no longer receive enough drag to cause the spring to shrink and grab the shaft, then the motor runs but the engine does not turn over.

THe best method of determine what's happening is to un cowl the engine then use a inductive ampmeter and hold it to the cable to the starter while some one tries to start the engine.

If the battery is low, the amp meter will go to a high reading and stay there while the engine does not rotate,

If the engine starts to rotate and then stops because of a worn spring, the ampmeter will show a high reading at first and then drop to a lower reading after the clutch slips and unloads the starter motor.

Read http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1409C.pdf

And consider that this Snake oil is in Aeroshell 15w50 and many other oils, but not Phillips 20W50.

 

[flyingcheesehead]

Thanks Tom!

The starter motor, if it is still running, is completely inaudible, so I'm not sure if this is really our problem, but it certainly warrants a look.

I was also surprised at how few engines require the additive:

Lycoming Engines (Lycoming) O-320-H, O-360-E, LO-360-E, TO-360-E, LTO-360-E series engines

So, with our only Lyc carbureted engine being the O-360-A4M in the Archer, it would appear that we don't need the additive in any of the planes. But, at least it doesn't appear harmful to the A4M... Or is it?