Need engine guru advice...

I am considering a 1996 RV-6. It has 295 TTAF. It has an O-360-A4A with 1602 SMOH. I am told this (paraphrasing a couple of e-mail's):

--- In Feb 2000 at 113TT it suffered a prop strike on a grass strip on take-off. I went to the far north end and turned to the south for takeoff. I gave it full power and when I could lift the tail the landing gear dropped into a hole and the prop struck the turf shattering it on impact. The engine continued to run and I had to shut it down.

I put a dial indicator on crankshaft. Absolutely no run-out.

The first prop was a Bernie Warnke Almost Constant Speed prop. I bought the replacement prop from his daughter. ---

I think I can assume that the engine was not torn down for inspection. It also sounds like the engine has about 180 hours on it since the prop strike.

So, my questions:

- Should I just walk away?
- If the engine has run fine for 180 hours since the incident is it safe to assume that no damage was done to the crank or accessory case parts?
- Any other questions I should ask?

Thanks,

IMO it is not safe to assume no damage was done. Lycoming is very clear on what to do when a prop strike occurs. Personally, I would walk away or negotiate a price that would allow for an immediate teardown inspection.

Old school of thought was that if the flange dialed good, it was safe. More experience has shown that a sudden shock to the drive train can loosen the bolt at the back end of the crankshaft. If that ever comes out, the gear comes off, and the whole accessory case stops - and, of course, the engine stops running. The problem is that without a teardown, you don't know if the bolt has cracked loose or not - and if it does, it can work free somewhere down the line.

I'd negotiate for a teardown - they'll call you a wimp, in which case you have to wonder about what else they are "old school" on....

One "big deal" in addition to the flange runout is the other end of the crankshaft. There is a drive gear that mounts on the crankshaft and it is oriented by means of a dowel pin. If the dowel pin cracks or shears, then there is little to prevent the gear from moving out position. Then, everything downstream (camshaft, mags, fuel pump, etc.) either stops or doesn't happen at the appropriate time.

Just the other day I was speaking with another pilot who had a similar episode and not too long after had the crankshaft actually fail. Another Cherokee that I'm aware of had a prop strike with the same engine type and it was put back in service. Within 200 hours, it was making metal and grinding up the case. I never did hear whether it spun a bearing or not.

The A4A crankshaft should be the solid crankshaft, but there is nevertheless a lot of energy to be absorbed.

So, on the front end of this transaction, I'd have to say that there is an AD and a Service Bulletin specific to Lycoming prop strikes and, setting aside the regulatory interpretation of whether ADs apply to experimental aircraft, it would be a very bad idea to ignore the guidance provided for the standard airworthiness aircraft.

FWIW - just another data point.

Dan

Thanks for the info so far.

Since I have no engine experience I would have to have someone do the teardown and inspection. Any idea what that might cost?

Thanks again,

teardown

I bought several engines that were prop strikes. One was running full rpm when the fiberglass prop hit the dirt. Another was a "slow" wood prop strike. Both got teardowns. Both had some issues here and there. Before I tore them down, "old-school" pals said to run them after the crank checked ok. The high rpm strike ended up having a good crank and got a yellow tag. However, I found pitting on cam (imagine that) and experts said I had about 100hr before it was going to need ohaul. Also found two lifters seized and not rotating. Also, both mags wouldn't pass without teardown. Drivetrain shock is a coin toss. Engine had 250 SMOH, 800 TTSN. Weird.

The other engine with the "slow" wood prop strike had a crack in the crank. I guess my takeaway from this is that if you have a strike, follow mfg recommendations.

As far as teardown cost, a lot of folks want to do stuff and replace stuff once the case is split open. I had prices given to me from 2K to 8K depending on what they find.

The paranoid part of your brain says that engine makers and engine shops are just there to make $$ and you don't need to do all that inspection stuff. Experimental means experimental and you can do what you want, right?

Hopefully the rational part of your brain says follow mfg recommendations and let the liability fall on them instead of you. Since you are in FL, you certainly have a lot more options.

ccsmith51 said:

Thanks for the info so far.

Since I have no engine experience I would have to have someone do the teardown and inspection. Any idea what that might cost?

Thanks again,

Click to expand...

Id recommend JB Aircraft in Sebring. I trusted him with my motor. Call him and discuss your particular story and get his advice and pricing.
http://www.jbaircraftengines.com/

suspect

I would be wondering what else in the airplane "is probably OK" if the seller is willing to blow off a prop strike inspection.

If it were me, I'd just factor in the cost of an overhaul. 1600 hours SMOH, and it only flew 180 hours in the last 14 years? Never mind the prop strike, how about corrosion?

Paige

Where to stop

The bigger issue to me is not if you are going to tear it down, but where are you going to stop? The economics of it may well be that it is more efficient to overhaul it once the cost of disassembly/inspection/reassembly is factored out. Since you have to spend that money anyway, adding in the cost of the remaing parts and machine work may be any easy decision, at least for the bottom end.
Good luck on it.
Tim

Prop strike

ccsmith51 said:

Thanks for the info so far.

Since I have no engine experience I would have to have someone do the teardown and inspection. Any idea what that might cost?

Thanks again,

Click to expand...

I bought one that tipped over so a prop strike. I had Premier at KTTD do the teardown and mandatory parts per Lyco. Turnied out not to have needed same but $3k for parts/labor anyway and worth the peace of mind. Dialing the crank may be fine for some, just not me or the guy who I may sell it to.

Prop was a new Sensenich twisted like a pretzel so guess it absorbed the energy just fine.

I would suggest you figure the price with engine core value only. That way you could just sell the engine and replace with a known quantity. Call up Wentworth and they can tell you what the core is worth.
http://www.wentworthaircraft.com/engines.html

Jerry

While a prop strike with a wood prop is an excellent negotiating point for a buyer, my attitude is that most of the hand-wringing is caused by both legal protection techniques and $profit$ visions by the manufacturer(s).

Many of these engines were in service for decades following prop strikes with no adverse effects prior to that draconian AD being issued. What changed? Where are the numbers on the total number of prop strikes, and the total number of actual issues found? Do those numbers (assuming that they are available) also show the numbers of metal vs wood props, and the numbers under power vs at idle or even not running prior to impact? How many AD's would be issued if the law (Congress) mandated the same thing that they did with the ATP age 60 rule (show evidence of real risk instead of picking an arbitrary number)?

I suspect that for every cracked crank that's found after a wood prop strike, there's another found during a normal overhaul with *no* prop strike on record. Now, we can either assume that everybody in the second case was lying by omission, or assume that a significant percentage of those found in the 1st case were already cracked, prior to the prop strike. Since both Lyc & Cont have significant records of actually causing crank defects by changing manufacturing specs, I know which I agree with.

If Lycoming's 'mandatory service bulletin' were complied with in literal terms, those of us operating off grass would be doing a complete bottom end & accessory drive system overhaul any time we take off or land when the grass hasn't been mowed in a week, and so would *everyone* who flies in the rain, every time that happens.

Charlie

AD

Draconian ADs are usually issued after someone ended up dead. The other opinion (watch the news after plane crash) is that they don't issue enough ADs.
It's a sudden engine stoppage inspection not a mowing the lawn inspection.
If you want to bet your life on a statistical chance that it is OK go ahead.
But you should have a single place airplane.

Prop strike

Another concern with this type of event would be an overspeed condition. "Full throttle, shattered prop, continued to run" sounds like a overspeed inspection is needed.

Chris

Have them take off $20k or find another plane...

Overspeed

brooksrv6 said:

Another concern with this type of event would be an overspeed condition. "Full throttle, shattered prop, continued to run" sounds like a overspeed inspection is needed.

Chris

Click to expand...

1000 hours in a Pitts, 0 360 run most of the time at 3300-3500 r/m. There is zero evidence that anyone ever had problems operating the fixed pitch Pitts this way.

Poor boy inspection

Ironflight said:

Old school of thought was that if the flange dialed good, it was safe. More experience has shown that a sudden shock to the drive train can loosen the bolt at the back end of the crankshaft. If that ever comes out, the gear comes off, and the whole accessory case stops - and, of course, the engine stops running. The problem is that without a teardown, you don't know if the bolt has cracked loose or not - and if it does, it can work free somewhere down the line.

I'd negotiate for a teardown - they'll call you a wimp, in which case you have to wonder about what else they are "old school" on....

Click to expand...

Paul's advice is best but keep in mind removing rear accessory case and replacing bolt and locking tab that bolts gear to crank is not terribly difficult. We will do tear-down and inspection then maybe field overhaul would be $3500-4000 plus parts at Titan.

Just sayin'

I personally have seen crankshaft failures after minor prop strikes. The most common being the bolt holding the gear on.

I have also seen others that went for many hours without a teardown. I would not take the chance.

Not a guru but

I'd walk away from this airplane. Take your time and find another RV-6.

You don't know how many 'unknowns' there are here. Bottom line - what's your life worth? Mine is worth a lot more than $20,000 - and how about your passengers? Why risk it? Whether or not this engine is ok, you may never know - then again, you may find out some day when you don't have options except to put her down in a field somewhere. Aircraft power plants are not a good place to guess or hope.

I think that if you have to ask the question about the reliability of this engine, then you already know the answer. Be

who built the airplane

Who built the airplane? Was it built in Iowa?

If its the airplane I am thinking of, it would be a very well built airplane built before all these super hi dollar airplanes and paint jobs we see today.

cm

overspeed

jrs14855 said:

1000 hours in a Pitts, 0 360 run most of the time at 3300-3500 r/m. There is zero evidence that anyone ever had problems operating the fixed pitch Pitts this way.

Click to expand...

This is not just a potential over speed but a unbalanced condition. I sure wouldn't buy a engine that has been routinely run past 2700. See lycoming sb 3691.
You wear a parachute in the Pitts?

I suspect Lycoming has the largest data set concerning their engines.

E. D. Eliot said:

Bottom line - what's your life worth? Mine is worth a lot more than $20,000 - and how about your passengers? Why risk it? Whether or not this engine is ok, you may never know - then again, you may find out some day when you don't have options except to put her down in a field somewhere. Aircraft power plants are not a good place to guess or hope.

Click to expand...

Take $20k off the purchase price ...
Order and install a NEW engine.
Sell the installed engine as a core.

Christopher Murphy said:

Who built the airplane? Was it built in Iowa?

If its the airplane I am thinking of, it would be a very well built airplane built before all these super hi dollar airplanes and paint jobs we see today.

cm

Click to expand...

Chris,

PM sent.

MauiLvrs said:

Have them take off $20k or find another plane...

Click to expand...

The engine has 1,600 hours on it I think the OP said. Forgetting the issue of corrosion (put in new oil/filter, get them to fly it for 10 hours, send oil sample to Blackstone), the engine is approaching TBO anyway.

Assuming a 2,000 hr TBO and a $20,000 overhaul, and also assuming the age of the engine is already factored into the equation, this issue only warrants a $4,000 price reduction.

Overspeed

paul mosher said:

This is not just a potential over speed but a unbalanced condition. I sure wouldn't buy a engine that has been routinely run past 2700. See lycoming sb 3691.
You wear a parachute in the Pitts?

I suspect Lycoming has the largest data set concerning their engines.

Click to expand...

This completely ignores the GSO and IGSO Lycomings that turn 3400 r/m. These engines have a history dating back to the late 40's early 50's. yes they are different than the O 360 but not that different regarding the basics.
Unbalanced condition-I have no idea what you are talking about.
Overspeeding the four cylinder Lycomings dates back to the early history of the Pitts. Curtis Pitts started out with Lycoming GPU's converted for aircraft use.
Four cylinder Continental engines have an overspeed history that goes back to the first Goodyear Midget Race in 1947. In that era they were turning 3200-3400 rpm for racing. Many in that era were flying cross country at 2900-3000 rpm. Today nearly all are trailered.
Steve Wittman liked to tell the story of the owner of a near new Cessna 140 who babied his engine. At TBO teardown the engine was in terrible shape. Wittman tore down his racing engine just to see what it looked like and it was in near perfect condition.
I just reread an article on Nemisis I, talks about 300 degree oil temps and mid to high 500's CHT. NO they will not last long at those temps but they do hold up for a few races. 4200 rpm on the 0 200 in todays racing environment.

When I first flew my RV4 in 95, almost twenty years ago, it had a beautiful Warnke wooden prop. The prop was not really pitched properly for the I0-360 that I had in the plane and you could run the rpm up to 2900 straight and level.
Many people told me that is was ok to go over 2700rpm. I wanted to hear that it was ok to go over 2700rpm. I ended up in a soybean field with a totally trashed engine after a setting of 2900 rpm. I had just got done saying to my passenger, see how smooth it runs at this rpm when there was a very loud bang.
Since that time I have never run a Lycoming past 2700rpm. Even when I was racing I never crossed that line, preferring drag reduction, as my major area of speed increase.
If you want to go faster then get a bigger engine.

When I first flew my RV4 in 95, almost twenty years ago, it had a beautiful Warnke wooden prop. The prop was not really pitched properly for the I0-360 that I had in the plane and you could run the rpm up to 2900 straight and level.
Many people told me that is was ok to go over 2700rpm. I wanted to hear that it was ok to go over 2700rpm. I ended up in a soybean field with a totally trashed engine after a setting of 2900 rpm. I had just got done saying to my passenger, "see how smooth it runs at this rpm", when there was a very loud bang.
Since that time I have never run a Lycoming past 2700rpm. Even when I was racing I never crossed that line, preferring drag reduction, as my major area of speed increase.
If you want to go faster then get a bigger engine.

geared

I ignored geared engines because we are not discussing them.
Imbalance usually occurs because I doubt a prop breaks exactly evenly.
You want to run your engine past red line go ahead, I could care less.
Ancedodal evidence is worthless. Like I said I think Lycoming has a better grip on what their engines are capable of than anyone else.
The overspeed limits are there for a reason.
I tend to not take advice from some guy on this forum that promotes something that is contrary to the manufacturers recommendations.

Overspeed

I though we were talking about engines. Propellers are an entirely different issue. Just an example, the Hartzell constant speed props on a four cylinder Lycoming have known issues above 2700 r/m. Not so with the fixed pitch Sensenich.
The point I was trying to make is that there is NO convincing evidence that overspeeding a four cylinder Lycoming, normally aspirated, direct drive engine will cause any problems.
The Lycoming HIO 360 D1A helicopter engine has 10:1 compression. It is rated at 3200 r/m. The TBO is reduced to 1500 hours vs the normal 2000 hours. I believe that this is conclusive evidence that a PROPERLY BUILT(vs some shade tree overhaul) Lycoming will not have a problem resulting from continuous overspeed. It will wear out faster. The two significant issues with wear are piston speed and bearing loads. The TBO for extremely high compression engines can be very low. 13:1 compression ratios are not uncommon and I doubt these go much past 500 hours. Piston speed is far less important. The general consensus on the normally aspirated 0 360 parallel valve in the Pitts S1 was that the engine would last 1200 hours without a problem.
An unrelated problem on both the four and six cylinder aerobatic engines is crank flange failure, as well as some very rare failures behind the flange area. This is directly related to gyroscopic loads. Flat spins, torque rolls, tumbles etc. Lycoming has never solved this problem despite a much heavier flange on the aerobatic engines. Wood composite or all composite prop blades greatly reduce the chances of a crank failure.
I would challenge anyone who would make a few phone calls to find anyone involved in cross country racing, operating a fixed pitch prop, who is not "overspeeding" their engine for the duration of a race.
During 21 years of involvement in IAC aerobatic competition, I don't remember a single case of a fixed pitch Pitts being operated below 2700 r/m. Likewise I don't remember a single case of an engine failure on a S1 Pitts during a contest that was caused by a catastrophic internal failure.

prop

The propeller is connected to the crankshaft. In the case of a engine continuing to run with a broken, unbalanced propeller I wouldn't think it would be good for the crankshaft.
Just because you haven't heard of engines failing unless you have seen the internals of those engines I would consider your anecdotes meaningless.
All I am suggesting is that you don't promote the overspeeding of engines to the uninitiated.
I'm going to ignore ths thread, I'm done with it.
Do as you like with your engine.

When I first flew my RV4 in 95, almost twenty years ago, it had a beautiful Warnke wooden prop. The prop was not really pitched properly for the I0-360 that I had in the plane and you could run the rpm up to 2900 straight and level.
Many people told me that is was ok to go over 2700rpm. I wanted to hear that it was ok to go over 2700rpm. I ended up in a soybean field with a totally trashed engine after a setting of 2900 rpm. I had just got done saying to my passenger, "see how smooth it runs at this rpm", when there was a very loud bang.
Since that time I have never run a Lycoming past 2700rpm. Even when I was racing I never crossed that line, preferring drag reduction, as my major area of speed increase.
If you want to go faster then get a bigger engine.[/QUOTE]

Recommended reading:
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=corelation%20vs%20causation

Charlie

I have the privilege of a friend who was an engineer on the "core" design team for a new Detroit engine. He is also a pilot, so he is familiar with Lyc's. Some years back, he cleared up the apparently inconsistent results from one prop strike to another.

The issue he raised is one of timing - of the strike. If the prop contact coincides with an engine firing pulse, the "loads go to Valhalla" [quoting my friend] The next issue is Magnaflux is only good for about 3/8" depth (bummer me, I had just purchased a 3000A magnaflux) and you can have fractures deeper in the crank metal than 3/8".

According to my friend, the best (only?) method to "really" test a crank is by X-ray.

FWIW