#3 main bearing crack

[Forrest Walton]

Russ and I found this on a C145 we disassembled today. I thought you might enjoy seeing it. The engine was recently removed from a members airplane. He told Russ that it ran normally except for a vibration at 2000 rpm. There was no other apparent damage. Quite a tough little engine.

Forrest

c145 008 (2).jpg

c145 009 (2).jpg

[c170b53]

Thanks Forrest, that photo says it all and I've shared it with others.

[mike roe]

I have a extra set of C145 cases with log books if he is interested.

[c170b53]

Forrest do you have any pics of the bearing at that position? What was its condition and also curious as to the condition of the counterweight's bushings and pins (if installed).

[GAHorn]

Forrest do you have any pics of the bearing at that position? What was its condition and also curious as to the condition of the counterweight's bushings and pins (if installed).

...as well as any record of cylinder changouts near that area..??? (Re-torque of thru-bolts.)

[Forrest Walton]

Jim,

The bearing and journal looked great so we didn't take any pictures. The piece was wedged so that it can't be removed. That probably saved further damage. The crank is dampened and all looked normal.

Mike thanks for the case offer but he has already replaced this engine. We are just looking for a good crank.

George, Russ has the logs, I will ask him to look for those entries.

Forrest

[jrenwick]

I have a junk C-145 case with a similar crack. I was told the crack occurred because a main bearing half wasn't properly seated in the journal during the last overhaul, and it applied pressure to the journal after the through-bolts were tightened. It ran a long time that way, until someone pulled a cylinder and saw the crack.

[c170b53]

Could you carefully examine with a 10X the counterweight bushings and the pins to see if they are worn. I'm curious to the cause of the vibration as I've seen these worn to the point that the weight wears and I believe it may have a role in vibration especially when pulling off the power ( don't ask me why I've just have had the experience).

[Forrest Walton]

Unfortunately, the crank has already been sent out for inspection. I will let you know what they say about the counterweights.

I went back to the hangar today and reexamined the bearing. Here are pictures. The shape of the broken saddle is obvious in on the back of the bearing.

c145 001 crop.jpg

c145 003last.jpg

Forrest

[russfarris]

Forrest do you have any pics of the bearing at that position? What was its condition and also curious as to the condition of the counterweight's bushings and pins (if installed).

...as well as any record of cylinder changouts near that area..??? (Re-torque of thru-bolts.)

Russ here. The logbook shows number three cylinder was removed and repaired March 19, 2010. It then flew 16 hours until removal.

George, are you suggesting an over or under-torque of a thru-bolt?

Yes, one of the rear hold-downs for number three cylinder is near the crack
in the crankcase. Russ Farris

[GAHorn]

Forrest do you have any pics of the bearing at that position? What was its condition and also curious as to the condition of the counterweight's bushings and pins (if installed).

...as well as any record of cylinder changouts near that area..??? (Re-torque of thru-bolts.)

Russ here. The logbook shows number three cylinder was removed and repaired March 19, 2010. It then flew 16 hours until removal.

George, are you suggesting an over or under-torque of a thru-bolt?

Yes, one of the rear hold-downs for number three cylinder is near the crack
in the crankcase. Russ Farris

One of the hazards of changing-out a cylinder is inadvertently contributing to a main-bearing change in torque, which can lead to a shifted bearing (too little torque, or a bearing which shifted during disassembly...sometimes due to prop/crankshaft rotation while the case pre-load is relieved) or a cracked/broken bearing saddle broken such as this illustrated, (sometimes caused by inadvertent over-torque or shifted crank, or use of un-calibrated tools or improper use of tools...i.e. not "choking" up on the wrench while toque applied/radially twisting of wrench, etc..)

[wingnut]

Forrest do you have any pics of the bearing at that position? What was its condition and also curious as to the condition of the counterweight's bushings and pins (if installed).

...as well as any record of cylinder changouts near that area..??? (Re-torque of thru-bolts.)

Russ here. The logbook shows number three cylinder was removed and repaired March 19, 2010. It then flew 16 hours until removal.

George, are you suggesting an over or under-torque of a thru-bolt?

Yes, one of the rear hold-downs for number three cylinder is near the crack
in the crankcase. Russ Farris

Everything George said, but let me add emphasis to one of his ideas that the crank could have been rotated while the cylinder was off.
YES, the bearing can spin with the crank while a cylinder is removed IF the thru bolts have NOT been temporarily retorqued while the cylinder is out for repair/overhaul. ALWAYS and IMMEDIATELY put a stack of flat washers (to account for the thickness of the removed cylinder base flange) and the nut back on, and torque it to spec BEFORE rotating the crank for any reason.
Failure to do this can (probably the most likely cause) cause bearing failure, crank binding, excessive heat, etc.

[jrenwick]

Here's another case, left side, main bearing seat cracked between cylinders 2 and 4. It looks very similar to Forrest's.

IMG_2975.JPG

Do they all crack in the same spot? Has anybody got a cracked main bearing seat that isn't this one?