Prop Strike Poll--what would you do??

lancef53 · Post by **lancef53** » Fri Apr 04, 2008 12:36 pm

I just bought a wrecked RV 8A to use for parts for my RV-8. It ran out of fuel, and landed off airport, with a nose over to finish it off. The prop was bent back on both blades, but the engine was not turning. We checked the crank, and it is true--zero runout. I am leaning to tearing it down.

Would anybody on here just run it? The engine has 192 hours since new, and 75 hours on new cylinders(superior recall).

Any Thoughts??

http://www.ntsb.gov/NTSB/GenPDF.asp?id= ... 007&rpt=fa

svanarts · Post by **svanarts** » Fri Apr 04, 2008 1:50 pm

There are many shortcuts I'm willing to take on an airplane but the engine and prop are not among them. I'd tear it down just to be sure.

cjensen · Post by **cjensen** » Fri Apr 04, 2008 2:45 pm

Tear it down to be sure. I would not risk anything with an unknown such as this.

I think it's great that you're asking the question, but I think you'll find that the answers will agree with one another...

Wicked Stick · Post by **Wicked Stick** » Fri Apr 04, 2008 3:08 pm

If there's zero run-out and the crank is true. It would appear the engine was already stopped before it crash landed.
I'd say odds are pretty good the engine is fine given the zero runout of the crank.

Perhaps there may be other things to check though.
I'd consult with Mattituck/Mahlon to see what his opinion is.

painless · Post by **painless** » Fri Apr 04, 2008 4:33 pm

If it were me and I didn't tear it down, that little voice in the back of my head would be asking the question, "Is it REALLY Ok???"

dynamicjohn · Post by **dynamicjohn** » Fri Apr 04, 2008 6:49 pm

Just because there is zero run out and it looks fine, doesn't mean it's good to go. Even if the engine was stopped, it bent the blades which means the engine got stressed. Have it torn down and mangafluxed or dye pen'd, for cracks. Reusing parts that are still good is great, its A LOT cheaper than a new engine. And infinitely better than a small crack enlarging and leading to a failure.

captain_john · Post by **captain_john** » Fri Apr 04, 2008 7:09 pm

Wicked Stick wrote:If there's zero run-out and the crank is true. It would appear the engine was already stopped before it crash landed.
I'd say odds are pretty good the engine is fine given the zero runout of the crank.

Perhaps there may be other things to check though.
I'd consult with Mattituck/Mahlon to see what his opinion is.

DAVE!

I am stunned and amazed that you would think such atrocities!

No, no, no... crank runout is just one indicator of a potential problem with the powerplant. You could have many other potential problems.

*bad wrist pins
*stressed bearing surfaces
*separated case halves

Who knows?

Me? I would rip 'er down.

My vote is cast.

What cha gonna do?

CJ

lancef53 · Post by **lancef53** » Fri Apr 04, 2008 8:33 pm

These were the responses I figured I would get. I am holding off making a decision on the teardown until I can talk to a friend who builds engines for 180 hp SuperCubs, he has seen LOTS of prop strikes.

Can someone explain what it is on an engine that needs to be checked after a prop strike/stoppage? I understand that there is a gear or dowel that can fail. Could someone explain what exactly it is I am talking about? Thanks--

By the way, what would I gain by installing 10:1 pistons? I am planning on running ethanol for fuel, and think the 8.5:1 might be a little on the low side.

Thanks for the replies!!

captain_john · Post by **captain_john** » Fri Apr 04, 2008 9:02 pm

Dunno anything about the dowels. Usually dowels are placed between cases to help in alignment during assembly. Are these the dowels you speak of?

High compression engines are more prone to preignition than their low compression counterparts.

This obviously necessitates high octane fuel (ie. 100LL). In and of itself that isn't really a bad thing, aside from the money.

Pound for pound, high compression is your best "hop-up".

There is no lighter way to get more ponies than pumping up the volume of air transferred through the engine.

Personally, I wouldn't go 10:1. When engines get out there on the ragged edge they can be fickle beasts. I had a really hot sled once. It was 800 cc with about 150 horsepower and went like the hammers of Hell. It had poor trail manners and didn't like to start in really cold (~20 degrees F below zero) weather. When the temperature changed, I would have to redo the jets. It was just too finicky, but ALOTTA FUN when it ran right!

Getting back to planes, I am going with moderate compression (8.7:1) in my 390. It is the standard compression for that engine and I am throwing displacement at the problem instead of compression.

There is no replacement for displacement. If you want a powerful engine, make it big!

CJ

jim_geo · Post by **jim_geo** » Fri Apr 04, 2008 9:39 pm

Tear it down for peace of mind. I would have the crank looked at by a shop. If the engine isn't under power it's not going to have a big problem with the accessory case gears, bolts and pins but you still get a chance to look at it all and you can do your own work if you want. It wouldn't have to cost much if the crank really is in good shape which it probably is. While your looking around you can replace the bearings and rings and have a good look at the valves. Still a cheap partial overhaul if you do it yourself.

4kilo · Post by **4kilo** » Fri Apr 04, 2008 10:18 pm

lancef53 wrote: I understand that there is a gear or dowel that can fail. Could someone explain what exactly it is I am talking about? Thanks--

The gear on the back end of the crank (inside the accessory section) can break the spline which causes it to turn with the crank. If that goes, you loose magnetos, oil pump, fuel pump and prop governor, not to mention the cam shaft. Its fairly important.

Pat

Thermos · Post by **Thermos** » Sat Apr 05, 2008 9:48 am

4kilo wrote:The gear on the back end of the crank (inside the accessory section) can break the spline which causes it to turn with the crank. If that goes, you loose magnetos, oil pump, fuel pump and prop governor, not to mention the cam shaft. Its fairly important.

Based on what I learned at a Mattituck engine building workshop, accessory drive gear ratios mean that they turn faster than the crank. That extra momentum due to faster turning means that they're under more stress should the engine experience a sudden stoppage.

As others here have rightly noted, you won't discover these problems by checking crank runout. If you don't know how the engine was stopped, seems like there's only one sound option - tear it down.

Dave

Wicked Stick · Post by **Wicked Stick** » Sat Apr 05, 2008 9:07 pm

CJ,
I wasn't saying "just run it" base on the crank runout alone.

It was my understanding that the engine was stopped in the air before it landed, and the prop got bent from getting tipped over.
I don't see how the accessory case gears would be an issue if it wasn't spinning when it landed.

Perhaps the thrust bearing, etc... would need to be checked, and I did remember saying that he should seek out experts advise on the subject.

captain_john · Post by **captain_john** » Sat Apr 05, 2008 9:09 pm

Aight...

CJ

lancef53 · Post by **lancef53** » Sun Apr 06, 2008 6:47 am

The engine was not turning when it landed, the blades are bent because of the tip-over, not from striking the ground under power or while rotating.

Thanks for the replies!!

captain_john · Post by **captain_john** » Sun Apr 06, 2008 6:51 am

Lance, you are welcome.

Do you have a picture of the prop?

CJ

lancef53 · Post by **lancef53** » Sun Apr 06, 2008 7:56 pm

I added some pictures to my user gallery, I will try to link them here:

http://www.rivetbangers.com/forums/gall ... temId=4698

http://www.rivetbangers.com/forums/gall ... temId=4701

http://www.rivetbangers.com/forums/gall ... temId=4704

http://www.rivetbangers.com/forums/gall ... temId=4707

Lance

weezbad · Post by **weezbad** » Sun Apr 06, 2008 8:13 pm

Welllllll, I was looking at buying a salvaged piper for the 0 360 on it.
It suffered a little more than a prop strike and when I posted info about it I got private e-mails from 3 professional engine builders that said. When they tore down for "sudden stoppage" they rarely found any damage. IF this happened as you say it is likely that it would be just fine. However there is no way I could bring myself to install this engine without a tear down. I might run it, but I wouldnâ€™t fly it.

I have witnessed (through accident reports with pictures) a Cessna 172 that broke the crank off at the flange. The prop departed the aircraft and a forced landing was successfully performed. Not only would I not want to be flying the plane but man where does the prop land. My luck it would hurt someone.

jim_geo · Post by **jim_geo** » Sun Apr 06, 2008 10:19 pm

Your luck! Think about the luck of the poor slob it hit. Talk about luck.

captain_john · Post by **captain_john** » Mon Apr 07, 2008 3:37 am

Lance, yes... That prop was not spinning when it was bent. It probably would be okay to use.

Mahlon, are you watching this thread? What do you think?

The question is, would I just bolt it on and use it? Naw, I would probably tear down most any used engine before I put it on the nose of my plane. It is just the way I am.

I would want it looked at anyways. To go through all the work of fitup, plumbing, wiring and what not to just find out it is using oil or something would be a real hassle.

Looks like you got a good hub there too!

CJ

RivetBangers.com

Prop Strike Poll--what would you do??

What would you do??

Prop Strike Poll--what would you do??