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Cracked O-320 Case - Best way to proceed?

Gordon Misch

Gordon Misch

MEMBER
Toledo, Wa (KTDO)
O-320 A2B narrow deck with about 500 hours since major.

I've been chasing a mysterious oil leak for a few months, unable to find it. Today I cleaned and sprayed dye penetrant developer all over, ground ran it for about an hour, and finally found this crack. It was invisible through the paint, without the developer powder. Also, I changed oil yesterday, and for the first time there were a few small non-magnetic particles in the screen.

Obviously it's grounded pending resolution, and obviously a teardown will happen.

I'd like to hear suggestions as to the best way to proceed. Possibilities that have crossed my mind:

  • send it out for welding; if that' a good idea, where would I send it?
  • best sources for an exchange case?
  • would it be a good time to convert it to 160 HP, or is that simply not a good idea for narrow deck?
  • Other thoughts?

I'd sure be grateful for good advice from those of you who have been there done that!

Thanks - -



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Check eBay for a replacement case...saw hold down plates there as well for 160 up grade if that’s what you want.
 
DIVCO in Tulsa can do amazing things with cases. It will be like new when they are done.
They should be able to install the longer studs as well if you want to convert it.
 
Divco also repaired a crack in the nose of a TCM IO360 for me. No issues after and seemed reasonably priced. Check in, however, on occasion with Divco. My case had been done for several weeks before I had finally decided to holler at them.
 
Gordon is this the same engine which was in the wreck? Sudden stoppage weakened the case perhaps? If so do you really want to spend any more on this light case?
 
Divco worked my O-200 case. When assembling the engine, the last stud on the last cylinder pulled out of the case coming up to final torque. Sent the case back and they helicoiled all the studs at no additional cost.
 
Divco rebuilt my current case including welding in a new center bearing support. I recommend them - but that is a strange crack! Is it in an important structural spot - that is, if it propagates, can you see a catastrophic engine failure, or not?
 
Gordon Misch said:
O-320 A2B narrow deck with about 500 hours since major.

I've been chasing a mysterious oil leak for a few months, unable to find it. Today I cleaned and sprayed dye penetrant developer all over, ground ran it for about an hour, and finally found this crack. It was invisible through the paint, without the developer powder. Also, I changed oil yesterday, and for the first time there were a few small non-magnetic particles in the screen.

Obviously it's grounded pending resolution, and obviously a teardown will happen.

I'd like to hear suggestions as to the best way to proceed. Possibilities that have crossed my mind:

  • send it out for welding; if that' a good idea, where would I send it?
  • best sources for an exchange case?
  • would it be a good time to convert it to 160 HP, or is that simply not a good idea for narrow deck?
  • Other thoughts?

I'd sure be grateful for good advice from those of you who have been there done that!

Thanks - -



View attachment 35793
Click to expand...

interesting technique for finding that!! thanks, going to have to remember that.... and as others have said, Divco was great
 
Thanks everybody, please keep good ideas coming. ;-)

p.s. the crack isn't nearly as large as the photo suggests - it's hairline, invisible to my eye without the developer. What's visible here is oil spreading into the developer powder.
 
skywagon8a said:
Gordon is this the same engine which was in the wreck? Sudden stoppage weakened the case perhaps? If so do you really want to spend any more on this light case?
Click to expand...
Yes Pete, it's the same one. I was thinking the same thing, though after the wreck it was majored. The firm that did the overhaul said they'd be dye penetrant checking the case, but - - -

Certainly if I send it out for welding I'll inform the company of the wreck.

Thanks - -
 
bob turner said:
Divco rebuilt my current case including welding in a new center bearing support. I recommend them - but that is a strange crack! Is it in an important structural spot - that is, if it propagates, can you see a catastrophic engine failure, or not?
Click to expand...
Not sure structurally, Bob. Without looking in the overhaul manual I don't remember what, if anything, important is inside right there. But I certainly agree with you that it's an important question. Thanks.
 
mam90 said:
Divco worked my O-200 case. When assembling the engine, the last stud on the last cylinder pulled out of the case coming up to final torque. Sent the case back and they helicoiled all the studs at no additional cost.
Click to expand...

This is exactly what happened with a friend of mine's IO-470 case.
Yes, Divco fixed the pulled-out studs (two) at no extra charge.
But the mechanic wasted quite a bit of time assembling the engine before the stud failed,
then spent extra time tearing it back down.
Dunno if the mechanic ate it (doubt it) or if the customer was charged,
but in either case somebody lost some money.
Apparently this stud pulling out business is not uncommon, so
IMHO it seems like those studs should have been tested,
or just helicoiled right off as a precautionary measure.
 
Hotrod, I agree and had to deal with the whole disassemble/re-assemble thing. They said they test all the studs on every case, and I believe them. Based on what I’ve learned there’s a limited life on number of times you can torque these studs. I would just request new helicoils on the next one. Probably would be people complaining if they were charged for new helicoils when they felt they weren’t necessary. In the end I was happy with the way they handled it.. Oh, and when I said it was the last stud on the last cylinder, I wasn’t kidding. Talk about a major let down...........
 
Only so many hours of daylight left for many of us. If you have the change to spare sell it to a airboat guy and build the motor you have always wanted. Divco would be a excellent choice and cost less!! No real right or wrong just something to think about.
DENNY
 
This from page 88: https://www.lycoming.com/sites/default/files/MM-IO-360-N1A - 3-31-2016.pdf

"3. Crankcase Inspection A. The external crankcase inspection is done to: Identify any oil leaks, cracks, and mechanical damage on the crankcase. Make sure that hardware fasteners are torqued correctly.REPLACE A CRACKED CRANKCASE. DO NOT TRY TO WELD OR REPAIR A CRACKED CRANKCASE. IF A CRACKED CRANKCASE IS NOT REPLACED, OIL CAN LEAK OUT OF THE CRANKCASE AND CAUSE ENGINE DAMAGE.(1) Examine the exterior surface of the crankcase for cracks and damage. Replace a crankcase with one or more cracks."

Somewhere I've seen a diagram of where cracks are and are not acceptable. This may have been on big bore Continentals??? Come to think of it, it may have been on that old AD note on light crankcase IO-520s. Perhaps there is a similar publication on Lycomings?
 
A thought Gordon,
Mark the ends of the crack with a magic marker. Cover the crack with some high temperature silicone to stop the leak. Or just let it leak and wipe it down regularly. It is not a pressure leak. Keep an eye on it as part of every preflight. Watch for any changes. What is the length of it now?

It is my opinion that this is in a low stress area of the case. There are no oil pressure passages in that area. Nothing is going to suddenly happen.

This will give you time to make an intelligent decision and find a solution which meets your pocketbook. If it were me, I would just exchange it for a factory reman or new and be done with it. As Denny says we only have so much daylight left in our lives which is something we retired folks understand. If I was still a youngster I would overhaul it myself and move on.
 
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I would send a picture to Divco. There are some areas they cannot weld. They and other case shops like Crankcase services have case in stock. Beware of places like Aircraft Engine and Accessory who charge the same amount as Divco and CCS but only strip, dye pentrant inspect and dimensionally inspect. Divco and CCS will mill the parting surfaces and line bore crank and cam. Less likely to fret and leak at the crankcase parting line late in it's life if mating surfaces are milled. AEA missed a crack in an O-470 case I sent them year ago. I found it when installing the prop after rebuilding the engine. Very frustrating.
 
I found a larger crack than that on a C172, other side and was better part of 4" long. No damage history on the plane. I was stunned how long the crack was before being seen at that years inspection. I had not worked on that plane before finding the crack that year. Personally I think the narrow cases lack a bit of strength in areas and do not need external forces to break. Case went to Divco. I have not been around that plane in the past decade but it had no problems after that repair I am aware of.
 
Steve Pierce said:
Are narrow deck cases built lighter than wide deck cases?
Click to expand...
I believe they are. The narrow cases and overall engine are a few pounds lighter. I had not paid attention to the differences back when I was actively working on them though to study this.
 
Keep in mind that the cylinder studs are not on the mandatory replacement list. You may want to consider replacing them if it is a high time engine.

Tim
 
skywagon8a said:
.
Somewhere I've seen a diagram of where cracks are and are not acceptable. This may have been on big bore Continentals??? Come to think of it, it may have been on that old AD note on light crankcase IO-520s. Perhaps there is a similar publication on Lycomings?
Click to expand...

yes, it was an AD on the continentals, something about "chevron" markings to tell which cases it applied to... you could stop drill the cracks and epoxy over them??? decades ago.....don't remember exactly
 
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