Re-ground crank or no?

Tom-D

Tom-D

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Tom-D
The crankshaft was removed from an TCM 0-300-A / C-145-A, it is a 8 bolt which is getting very difficult to find.
all journals measure Service limits.logs from day 1 shows no strike. the flange dials .001" and it is not rusty/pitted.

Would you re-grind it and fit it with .010" bearings, or let it go with standard?

Customer wants inputs
 
Send to a suitable facility to be IRAN'ed. Including NDT. Then you will have something better than "not rusty".
 
JAWS said:
Send to a suitable facility to be IRAN'ed. Including NDT. Then you will have something better than "not rusty".
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Where would you send it? cost?
 
Tom, no offense intended, but aren't we the folks supposed to ask you these kinda questions?
 
I've got a better one for ya,

Some bloke owns a lycoming 320 with 150 horse pistons

The crank is 52 years old, never been out of the engine. It is not subject to the corrosion AD as that is limited to 160 horse engines, if there is pitting in it and the crankshaft shop returns it yellow tagged would you soldier on and use or or sell and buy a new crankshaft for around $6k?

Given the terrible history with even new crankshafts I'm inclined to say just use the one you have. I found a heavy equipment dealer that mentioned similar results, a new crankshaft seemed more likely to break than a serviceable one.
 
steingar said:
Tom, no offense intended, but aren't we the folks supposed to ask you these kinda questions?
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I respect Tom for asking these questions. No doubt he already has a perspective. Difficult to ever fault someone seeking input to a decision.

Part of what's loaded into the question is market place perception, what would you rather own; Crank within service limits or clearances within new limits .010 over?

With that... as general practice... +1 for sending the crank to Aircraft Specialties for NDT, grind, polish, and re-balance. I'd also send them the connecting rods for balancing as well for total weight to each other and end to end per rod. Makes a very smooth engine.
 
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steingar said:
Tom, no offense intended, but aren't we the folks supposed to ask you these kinda questions?
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They have, and we are simply looking for opinions.
 
NordicDave said:
I respect Tom for asking these questions. No doubt he already has a perspective. Difficult to ever fault someone seeking input to a decision.

Part of what's loaded into the question is market place perception, what would you rather own; Crank within service limits or clearances within new limits .010 over?

With that... as general practice... +1 for sending the crank to Aircraft Specialties for NDT, grind, polish, and re-balance. I'd also send them the connecting rods for balancing as well for total weight to each other and end to end per rod. Makes a very smooth engine.
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Keep in mind, you can expect to run to TBO on a service limit crank. If you cut it to .010 under that is one TBO gone. and the last time you can run it without getting the STC to allows .020" under (?- $$$)

OBTW I always use NEW rods and NEW rod bolts.
 
Tom-D said:
Keep in mind, you can expect to run to TBO on a service limit crank. If you cut it to .010 under that is one TBO gone. and the last time you can run it without getting the STC to allows .020" under (?- $$$)

OBTW I always use NEW rods and NEW rod bolts.
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I flew in a buddy's plane with factory new Superior rods and pistons that were fully balanced along with the crank by Aircraft Accessories. Very surprising how much smoother the engine was. He also dynamically balanced prop to the engine. A lot less shake on start-up and after mixture cut-off.

Western Skyways had a great video on balancing. Fast forward to 5:35 mark.

The video compares engine manufacturers requirement to only balance rods for equal total weight, compared to also balancing big end to small end.

 
If it's within service limits now, what does a regrind buy you except less metal in the journals? I would rather have a crank that's soldiered on for thousands of hours remain as it is, all else being equal. New bearings and fly with it.
 
Get the darn thing cleaned and measured and NDT inspected. From there, decide what to do. It might be fine as is. It might be cracked.
 
JAWS said:
Get the darn thing cleaned and measured and NDT inspected. From there, decide what to do. It might be fine as is. It might be cracked.
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Just to be clear, this is not my crank, It belongs to a customer. He already knows my opinion.
What he does with it is his business, I am no longer in business.
My last engine is installed and running great.
 
Tom-D said:
The crankshaft was removed from an TCM 0-300-A / C-145-A, it is a 8 bolt which is getting very difficult to find.
all journals measure Service limits.logs from day 1 shows no strike. the flange dials .001" and it is not rusty/pitted.

Would you re-grind it and fit it with .010" bearings, or let it go with standard?

Customer wants inputs
Click to expand...

Here's my $.02. And, yes, it's a story with a Franklin engine, which isn't TCM.

I once bought a Franklin-powered helicopter. The engine had about 40 hours on it, after being recently overhauled by a reputable shop. The crankshaft had been ground, supposedly to proper specs, and oversized bearings were installed. In one of my first flights after acquiring the aircraft, I was flying along at about 1,500' when I started to feel an unusual vibration. Within a couple of seconds, BANG! The gauges go to zero and I'm headed for the ground. Obviously the autorotation was successful, because I'm here to tell the story.

My mechanic came to the landing site and immediately diagnosed the problem as a broken crankshaft. His first clue? A chunk of the crankshaft sticking out of the side of the engine. When we finally pulled the engine after getting it back to the hangar, we discovered the crankshaft was in three pieces. WTF? The engine only had 40-ish hours. We decided to send the crankshaft out for metallurgy. The report came back that it had not been "hardened" properly after it had been turned/ground (I don't remember the exact terminology...this was 25 years ago).

So, why am I telling this story? Simple. Never. And I mean NEVER, would I want to fly behind an engine that has a ground/turned crankshaft. It's just not worth the risk. My advice, Tom, is to scrounge, dig, and do whatever you need to do to find either a serviceable used or NOS crank.

YMMV.
 
SoCal 182 Driver said:
Here's my $.02. And, yes, it's a story with a Franklin engine, which isn't TCM.

I once bought a Franklin-powered helicopter. The engine had about 40 hours on it, after being recently overhauled by a reputable shop. The crankshaft had been ground, supposedly to proper specs, and oversized bearings were installed. In one of my first flights after acquiring the aircraft, I was flying along at about 1,500' when I started to feel an unusual vibration. Within a couple of seconds, BANG! The gauges go to zero and I'm headed for the ground. Obviously the autorotation was successful, because I'm here to tell the story.

My mechanic came to the landing site and immediately diagnosed the problem as a broken crankshaft. His first clue? A chunk of the crankshaft sticking out of the side of the engine. When we finally pulled the engine after getting it back to the hangar, we discovered the crankshaft was in three pieces. WTF? The engine only had 40-ish hours. We decided to send the crankshaft out for metallurgy. The report came back that it had not been "hardened" properly after it had been turned/ground (I don't remember the exact terminology...this was 25 years ago).

So, why am I telling this story? Simple. Never. And I mean NEVER, would I want to fly behind an engine that has a ground/turned crankshaft. It's just not worth the risk. My advice, Tom, is to scrounge, dig, and do whatever you need to do to find either a serviceable used or NOS crank.

YMMV.
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It is standard practice to grind aircraft crankshafts, but it's also easy to screw up. If the fillet radii aren't right, cracks can form there. If the crank was originally nitrided, it needs to be nitrided again. Most aircraft cranks are nitrided for hardness and strength, and if that "reputable" shop had farmed out the grinding to an automotive shop that didn't know about re-nitriding, there's a big mistake right there. They ground off the nitrided layer and left it like that.

Some years ago there were two ADs that came out against cranks that had been reworked by two different outfits. They hadn't been sticking to the specifications. One of them:
https://rgl.faa.gov/Regulatory_and_...ED3F1B9AF861486E8625684A004EE501?OpenDocument
 
Dan Thomas said:
IIf the crank was originally nitrided, it needs to be nitrided again.
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That's the word I couldn't remember - nitrided. Metallurgy tests determined the crank had not been properly nitrided after it was ground. I have no doubt grinding is a common practice but if, as you say, it's easy to screw up, then that confirms my decision to never fly behind a ground crankshaft again!
 
If a crank is a Standard (never cut) and within limits why would it need a another nitrided coating ?

This customer will have the crank cleaned and inspected, and go for a new re-build with all new parts. Rods & bearings, cam kit, case (lapped & line bored), new gears, and 6 new cylinders, baffle kit, mounts, and exhaust.
 
SoCal 182 Driver said:
That's the word I couldn't remember - nitrided. Metallurgy tests determined the crank had not been properly nitrided after it was ground. I have no doubt grinding is a common practice but if, as you say, it's easy to screw up, then that confirms my decision to never fly behind a ground crankshaft again!
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shops that do this work, are required to adhere to FAA procedures.

When the crank is below limits there is nothing to but re-grind, except new, and the 0-300-A has not seen a new crank in years. (1954 I think)
 
Dan Thomas said:
Nobody said it would.
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no argument there .
Then what are trying to say in post #25

The cranks that were worked on buy the shop mentioned were all accounted for. (no issue)
 
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JAWS said:
Send to a suitable facility to be IRAN'ed. Including NDT. Then you will have something better than "not rusty".
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"not rusty" probably wasn't the correct wording.. this crank looks new :)

many old cranks of the old 0-300-A/C145 have rusty crankshaft flanges, this requires a grind to see how thin they can be. and the primary reason to condemn them.
 
New cam kit, yummy.
 

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Tom-D said:
add new gears, spendy
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This has been on backorder for almost two months. I have kicked the idea of a new crankshaft gear but think I'll hold off on that till I see what old one looks like.

(Lycoming 320 parts)
 
Tom-D said:
Then what are trying to say in post #25

The cranks that were worked on buy the shop mentioned were all accounted for. (no issue)
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I was using that as an example of how some shops can mess up cranks when they don't follow the manuals.
 
Dan Thomas said:
I was using that as an example of how some shops can mess up cranks when they don't follow the manuals.
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Show me a crankshaft that was messed up by a certified machine shop.
 
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