The International Cessna^® 170 Association

Our aeroplane was recently involved in a ground incident when it swung into the refueling pumps under quite high power after the wing struck a vertical vent pipe.Fortunately no one was injured .
The propellor demolished a set of refueling steps and eventually stopped when it struck the fuel hose reel.One tip was severed and has not been recovered.
The engine shop have advised the crankshaft has a 4 thou TIR run out and the maximum permitted is 5 thou.
I am convinced this can only be as a result of the incident and I know I may just be worrying over nothing but is it likely to cause future problems or early failure ?

Thanks

Bryce

I seen an ad for a 0 time O-300D with all accessories rebuilt for $11K. If anyone is interested I'll figure out where I saw it.

Joe

IS this engine disassembled? Is this measurement just taken at the flange with the crankshaft still in the case?

Bryce,... checking a crank for "runout" after a prop strike... instead of properly complying with the mandatory TCM Service Bulletin.... is false economy. And it's also invalid as a method of determining airworthiness.
Any shop that will encourage you to rely solely upon such is unknowlegeable or unqualified or both. If any certificated repair station or repairman will rely upon that method... then you should make absolutely CERTAIN they will put it IN WRITING that they approve it for return to service. Then store that document in a safe place so your survivors can use it in court.

I think I responded to you once before privately about this incident. You should make an insurance claim for a sudden stoppage if you have insurance. If you don't, you should pay for the inspection yourself. You cannot afford the liability if you later sell this airplane to anyone who might be injured by your failure to have the engine properly inspected. IMHO.

George and Mod Cessna.
Thankyou foryour responses.
The engine has been stripped and inspected as the service bulletin and no damage found that could be attribted to the propeller strike incident other than a cracked engine mounting bracket .They have carried out penetrating dye crack tests.
They advised that the crankshaft had run out close to the permissible maximum value of 5 thou but it remained srviceable.

All the repairs are being carried out under our insurance and I have written to them requesting they consider allowing a replacement crank because the run out must surely be as a result of the incident and I wont feel comfortable knowing it is so close to being unservicable.
I am concerned that the 4 thou runout could lead to early failure and perhaps internal damage not found through dye testing will develop.
Thanks
Bryce

Bryce,

I would not be happy KNOWING the run out exceeded that allowed for new limits. If this crank has run out that exceeds that for new limits then at some point I'd think it had to be damaged. This may very well be a case of if you never knew it, it wouldn't hurt you. But you do know and that will never change.

I would have to talk to a lot of engine people I really trusted and they would all have to have no problem putting their kids in the plane with the engine before I started to feel comfortable. I would have to spend a lot of time convincing myself that the limits TCM set are acceptable and set with good reason and experience. I'm not sure I could convince myself and feel comfortable.

I'd feel different if this was my lawn mower or weed waker but it's not.

Hmmmm. Here I am wondering if I'd like flying behind this crank that is within tolerance yet I fly helicopters for a living where there are thousands of parts that are always in a state of wear causing vibration and stress, yet I think nothing of it. Aren't we humans a funny lot.

Yea Bruce, we humans are a funny bunch However, you know when you go flying in your whirleybird that it is a know fact that its a collection of parts constantly trying to self destruct themselves But Bruce, You Da Man How's the Harley and you getting along

Bryce wrote:...The engine has been stripped and inspected as the service bulletin ...

That's great, Bryce! Thank you for clarifying.

I agree with you that ANY runout is suspect and I would insist upon a replacement crankshaft. Your best bet will be to get the shop to agree with you. If they agree, then the insurance company will be less inclined to argue. Keep in mind that the insurance company has to please YOU. Don't let them get away with anything YOU don't approve, because YOU are the one who will be flying behind it.

In any case, if the runout is the result of the prop strike, then the damage must be corrected. It is incumbent upon the insurance adjuster to prove the runout existed BEFORE the strike. (Hint: I seriously doubt he can prove that, so your damage must be corrected by them.)

Bruce mentioned the 4 thou run out exceeded new limits.
What are the new limits ?
I am aware after talking to the engine shop that at the last engine rebuild in 2000 with the same engine shop the run out was recorded as 2 thou so it would appear the additional runout is as a result of the prop strike.
I have written to the insurers with these facts.
Thanks
Bryce

There may be some "assumeing" going on here, and you know what that means.

First we need to define what type of "run out" we are discussing.

Runout is a measurement which is taken to determine "wobble" if you will, from an aboslutely true condition. In other words, if you rotate the crank and all main journals are absolutely "true"... then NO runout will exist with regard to journals. New cranks will have a min/max runout at the main journals of .000/.015 at the CENTER journals...when the crank is supported at the front and rear journals. It just so happens that the max SERVICE limit for rounout at this location is also .015 .

The Prop flange has it's own, and seperate, runout limit, new min/max is .000/.005, and max service runout is also .005 .

The Table of Limits can be found in Section 13, page 39 of the TCM Overhaul Manual, Form X30013 .

I havent seen the inspection requirements from TCM but I'll guess the shaft needs several inspections, as in mag particle for obvious cracks and eddy current for deformation and failures not detectable by the naked eye in and around the counterweight flanges / bushings. Most shafts probably fail the later inspection. If these two NDT processes fail to find a defect then its probably good to go.

As well as the SB96-11 listed above here is an article that appeared on the Mattituck site:
http://www.mattituck.com/new/articles/ss.htm
As they mention, be sure you not only check for runout but also get it magnufluxed along with your gears. The cluster gear in these engines is very susceptible to cracking and are very expensive (up to $1000 used and $2000+ new).