The International Cessna^® 170 Association

Hi ! Have a chance to buy a C-145 eng. ('51 I think ) . It has had a prop strike but the crank dials good. What else has to be done to satisfy myself and the FAA that everything is good to go on reusing this eng. in my '51 170A ? thx, the ButchPilot !

Butchpilot, you will need to tear it down. Often times the bearings are compromised. Parts replacement as necessary. Could be a good deal for the right price but not often. The cranks are harder to find should you have other damage maybe not necessarily from the sudden stoppage. just have to open it up to see.

Okay thx Canav8 ! Tearing down the eng . by my IA sounds expensive. Like you mentioned who knows what will be found good or bad ! He wants 4000 for this 0-145 and is complete with all accessories . Sure sounded tempting ! later, the ButchPilot !

Take a look at Teledyne Continental SB96-11B.
It prescribes magnetic particle inspection of the crankshaft, and new counterweight bushings and pins (counterweight bushings have gotten fairly expensive for this crankshaft). Also, fluorescent dye penetrant inspection of the crankcase. magnetic particle inspection of gears and all other steel engine parts, and overhaul of the magnetos.

Now you can argue that Service Bulletins are not required for Part 91 operations. But as a point of reference, I am going thru this currently after what seemed like a minor incident (and the crank flange ran true), but my crankshaft did indeed have a crack thru one of the counterweight blades.

I would not recommend ignoring the Service Bulletin.

fly it and watch it.

Sudden stoppage can affect a lot of parts over time. Dialing the crank may show that it's fine but that doesn't mean other things haven't been set up to fail early.

Gears in your mags are likely nylon. Cracks can develop and fail prematurely.

The counter weights on the crank float on pins and bushings. Prop strike slams those pins and bushings into the crank slots and possibly deforms them. The counter weights don't float as normal which can set up harmful vibrations that you don't notice but can fracture a crank over time. (This is the same reason only specific props of specific lengths are permitting on specific engines...to avoid those harmonics. A prop strike can put a motor enough out of balance to do the same thing)

Your first outward indication of this would probably come when the crank fractures - which may be a lot of hours later when you least expect it.

It can't be good for the steel gears in the accessory case either.

If the hit was bad enough to warrant repair or replacing the propeller, the motor is suspect and should be torn.

I don't think Part 91 REQUIRES any action on a prop strike - let alone a tear down. But I think it's a very good idea.

Butch, dialing the crank will NEVER tell you the engine is fine. It may only tell you the crank is bent in the WORST case of a prop strike.
There are too many other things which are damaged in a prop strike for a dial-indicator to be a valid diagnostic tool.
The TCM service bulletin mentioned is good guidance, and if a mechanic has any sense of liability and responsibility (IMO) he will insist upon a complete teardown if the prop was injured sufficiently to require it's removal for repair. (On the other hand, if it's merely a "ding" which can be dressed-out in accordance with the prop mfr's recommendations, then a tear-down is likely unnecessary.)
In every instance, flying it and watching it is bad advice. (Sorry, MIT, but unless that was a humor-sarcasm, I'll bet you know better.)

While on this subject, ... keep in mind that a prop-strike while doing an engine run-up or taxying not for purposes of flight.... is a non-moving event. Your insurance policy might treat this very much in your favor! Check your policy. (However, my most recent insurance quoted used very different wording in their definitions-section. "For purposes of flight" in FAA/NTSB parlance would mean what it says...and is considered an "in motion" event. But taxying from one hangar to another, or for warming up the engine for oil change, etc.....is not an "in motion" event (and may carry a zero deductible, etc.)

Just FYI.

George, Butch didn't have the prop strike, he's considering buying a engine that had a prop strike.

Personally I would never knowingly fly behind an engine that had experienced a prop strike engine stoppage.

Yes the engine can be rebuilt and run just fine. But it suffered the "shock" of stoppage.

Engine still has great value and is in demand for some one building a new airboat or replacement engine for Air boat..

Always check around the back side of prop flange on engine crank shaft. Some continentals have developed a partial crack and never had a prop strike incident.

AIRBOAT operator installs engine and uses many years without incident.

Your opinion, but my present engine had two prop strikes before I owned it, has 700 hrs on it after the last prop strike, dinged it good again and will fly behind it again after tear down.
If you're thinking you should always keep an eye out for a landing spot when flying behind an unreliable prop strike engine that might be a good thing as any engine can fail at any time.

Bruce Fenstermacher wrote:George, Butch didn't have the prop strike, he's considering buying a engine that had a prop strike.

I understand that, but don't quite get the point you're making, Bruce.

gahorn wrote:

Bruce Fenstermacher wrote:George, Butch didn't have the prop strike, he's considering buying a engine that had a prop strike.

I understand that, but don't quite get the point you're making, Bruce.

Reading this part of your previous post:

gahorn wrote: While on this subject, ... keep in mind that a prop-strike while doing an engine run-up or taxying not for purposes of flight.... is a non-moving event. Your insurance policy might treat this very much in your favor! Check your policy.

I thought you did not realize he did not have the prop strike. Butch can't get his insurance do to do anything, it was not his accident. That was my point. If I misread then, as Gilda Radner said, "never mind" https://www.youtube.com/watch?v=V3FnpaWQJO0

Thanks, ... that comment was placed just for general-knowledge, not directed to anyone in particular.

I have a friend who got two new engines due to prop strikes. The first was while performing a run-up purely to check a new ammeter. ( Non in-motion, no deductible =Free engine and prop/spinner/governor)
The second was due to a landing incident that collapsed a nose-wheel. He had to pay the deductible for "in motion". He still "lucked out" however as none of his damaged nose gear was available due to an AD, so they upgraded him at no addt'l cost to a newer style on his Beech product. (worth about $15K).

MoonlightVFR wrote:Personally I would never knowingly fly behind an engine that had experienced a prop strike engine stoppage.

Yes the engine can be rebuilt and run just fine. But it suffered the "shock" of stoppage.

Engine still has great value and is in demand for some one building a new airboat or replacement engine for Air boat..

Always check around the back side of prop flange on engine crank shaft. Some continentals have developed a partial crack and never had a prop strike incident.

AIRBOAT operator installs engine and uses many years without incident.

I don't post this to change your mind, but consider this; We send between 25 and 35 engines out each year to various engine shops for prop strike inspection, including some back to OEM. About 15% of crankshafts will reject and need replaced. About 30% of crankcases will reject and need repair or replaced.
We've been doing this since 1995, some years more, some less, but assume 25 engines per year for 20 years. So, 500 engines with a 15% crankshaft reject. If any of the remaining 85% (425 crankshafts) had failed after we returned the aircraft to service, I'm certain I would have received a phone call. I haven't, and we are just one company, a small company. There are tens of thousands of prop strike cranks flying today.
Another interesting observation is most reject cranks happen at low or idle power rather than full power. I have a theory on this and I'm sure the engineers among us can explain this better than I can.

wingnut wrote:Another interesting observation is most reject cranks happen at low or idle power rather than full power. I have a theory on this and I'm sure the engineers among us can explain this better than I can.

I'd love to hear the explanation for that. I would have guessed it to be the other way around.