Thoughts on a cracked case

[mondtster]

Cases have been beefed up from the factory over time to reduce the number of cracks that occur, but they still happen. Nothing you can do besides replace the case.

I'm sure they have, but I've seen and have heard of more problems with wide deck Lycoming cases cracking than I have with the old narrow deck ones. Perhaps it is simply because there are more of them out there these days.

Both the new and old cases have their quirks but I'd honestly prefer the old narrow deck ones over new.

 

[Ted]

I'm sure they have, but I've seen and have heard of more problems with wide deck Lycoming cases cracking than I have with the old narrow deck ones. Perhaps it is simply because there are more of them out there these days.

Both the new and old cases have their quirks but I'd honestly prefer the old narrow deck ones over new.

I think some of that at this point has to do with the relative numbers out there since most of the older ones are gone at this point. I can tell you that when I was working at Lycoming, there was nobody there who thought the narrow deck cases were better and it was a mistake going to the wide deck. Eventually all cases are going to crack given enough hours, the question is when and how long. I've not kept up with any recent trends on cases leaving the factory today, but it seems like any of these parts end up getting bad batches at times so I won't deny that there may be some new cases that are having more issues currently.

In the Continental world I can say that I've never met anyone who's ever said anything good about the light cases. The Lycoming world, the biggest thing people seemed to like about the narrow deck cases was reduced weight. I will say my Aztec had narrow deck cases and I had no issues with them in the 1,000 hours I had the plane.

 

[Tom-D]

Eventually all cases are going to crack given enough hours, the question is when and how long.

Your probably right, but I've never seen a 0-200 case crack in service.
I just rebuilt a 0-200 with a case that has 16,700 hours.

 

[thomasdr72]

It's funny, but I just read an approved repair procedure on some engine cases that was literally a stop-drill and epoxy crack seal job. AFAIK, it was on Continental o-520 cases - but it had specific limits on crack locations and length.

Cheers!

 

[3393RP]

Only counts when you have the money to do it now.

I was suggesting the cost difference between removing the engine then disassembling it to effect repairs and a factory reman could be evaluated based on owning a very nice airplane as the used fleet shrinks.

It might make the pain more bearable.

 

[thomasdr72]

Make a mechanic friend, and see if you can find one that will supervise you to take it off and do it yourself. Your local EAA chapter might be a good place to start ;-)

 

[Dan Thomas]

i don't care for unlearned opinions, but I will listen to anybody that can quote me chapter and verse about the legalities (and even more the practicalities) of welding cases without removing them from the airframe.

That case has to be clean. REAL clean. When I welded aluminum and cast iron I often had to bake those parts after washing to make sure there was no oil hiding in any pores in the metal. Any oil present will cause serious porosity in the weld, and now you have a mess.

Cracking in a case under a cylinder tells me that the cylinder pressures did it. That cylinder is trying hard to pull itself off the case. At 2500 RPM it yanks on the case 1250 times a minute. An O-360 has a 5.125" bore, and when combustion pressures reach 800 psi, that 5250 pounds of force on the piston is reacted in the cylinder's attachment to the case. Do that often enough and hard enough and long enough and sometimes things break.

 

[mondtster]

That case has to be clean. REAL clean. When I welded aluminum and cast iron I often had to bake those parts after washing to make sure there was no oil hiding in any pores in the metal. Any oil present will cause serious porosity in the weld, and now you have a mess.

Yup. Even if it is theoretically possible to repair with the engine assembled and installed there is no way I’d even want to try to do it.

 

[Tom-D]

The only case I've seen welded the case was stripped by soaking in strip tank over night, then rinsed with freon, after that it was died with red dye, and the entire crack ground out until no trace of red dye could be found.
then the case was etched, rinsed again, then placed in a cabinet, that cabinet was purged with argon, after that the hole in the case was backed up with fire clay, (putty of some sort) and the cavity left from removing the crack was filled with the same alloy that the case was made from.
and allowed to cool in the cabinet, then smoothed over the weld.
After the weld procedure, the case was sent to the heat treatment oven to be stress relieved, and re-heat treated.
Then it was lapped and line bored, re-etched and alodined, inspected, and issued a Yellow tag.

 

[Ted]

Your probably right, but I've never seen a 0-200 case crack in service.
I just rebuilt a 0-200 with a case that has 16,700 hours.

True, I would expect an O-200 to last nearly forever. Most of my experience is with 6-cylinder engines. The O-200 may not make enough power to fatigue the case but your standard big bore cases will all eventually break.

 

[Kenny Phillips]

Ya just have ta know, it is the new cases that are cracking. Welding relieves the problem.

Well, technically, the cases are perhaps stress-relieved by the cracking!

 

[Tom-D]

Well, technically, the cases are perhaps stress-relieved by the cracking!

technically true, intolerable in reality.

 

[Tom-D]

True, I would expect an O-200 to last nearly forever. Most of my experience is with 6-cylinder engines. The O-200 may not make enough power to fatigue the case but your standard big bore cases will all eventually break.

No, the the 0-200s are just built way too heavy. 0-300 same thing.
Their problem is, the cylinder hold down studs pull out.

 

[PaulMillner]

they found a crack about 3 - 4 inches long on the right side of the case below the front cylinder.

Cessna issued a service bulletin to beef up the alternator bracket located in that location on the engine. The improved bracket has two pieces, the U shaped piece that came originally, and an F-shaped piece that attaches aft, spreading out the alternator load aft on the case, so it's not all concentrated in one spot under #1 cylinder. The original U-shaped piece comes in two thicknesses too... not so much for beefiness, but to change the resonant frequency. Sometimes the later, beefier bracket works better; sometimes the older, thinner bracket. Vibration analysis by your prop balancing friend, putting a sensor on the alternator, will show you if there's a problem or not. Bad vibration on the alternator can be 50 ips, inches per second, which is huge!

Paul