6.9L - Fatal Crack

[FrozenMerc]

So, long story short, I installed a CCD turbo kit on my '85 F350 last winter, spent most of the spring just driving the truck, and getting it tuned in how I was hoping. Everything was working well until August when it started puffing white smoke when I started it after a hot restart after unloading some stuff at work. I parked it right away, and came out to go home after work and it would not restart. It was acting like it hydro-locked. In fact, it kicked back so hard, it snapped the nose of the starter off. I ended up towing it home, and quickly discovered that the oil pan was full of coolant.

At that point, I figured the best thing to do was to pull the motor, tear it down and hope that there was nothing major wrong. Pulling the top end off revealed that the valley pan gasket had let go by the rear coolant passage (under the turbo) and the coolant was free to run down into the oil pan. I breathed a sigh of relief, as that was easy to deal with. When I put the head studs in two summers ago, 2 of the studs on the passenger side were weak and wouldn't pull torque. So I figured, I would completely disassemble it, fix the head studs, and hopefully get away with just a re-ring and gasket job. Turned out the rod bearings were toast from running with coolant rather than oil, but the crank was in excellent shape, so one less thing to worry about.

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Motor on the stand.

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Cleaned up and ready for work.

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After getting the block all cleaned up, I finished the decks, honed the cylinders, and flipped it over to run taps through all the bottom side bolts holes. That was when I discovered the cracks in main web #4. I don't think this is repairable. Anyone have a good 6.9 block near SW Missouri for sale?

The offending crack.

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Guess I am off to the junkyard to see what I can find...

 

[chris142]

That's common on the GM ones. At least you found it now and not 2 weeks after rebuilding it

 

[FrozenMerc]

True, it just sucks having the rebuild kit sitting here knowing that I will likely have to exchange pistons at a minimum. The block was in great shape otherwise. Only 130,000 on it, I would not have expected to see that failure mode given everything else. I may have to separate the crack entirely, I would not be surprised to see a casting flaw that initiated the crack.

 

[IDIBRONCO]

I haven't seen that happen without spinning a bearing(s). I may have a block, but would have to dig it out and look at it. I'm also not very close to SW Missouri. It's about 5 hours to drive to Kansas City from here.

 

[FrozenMerc]

Update: I found a block. Griffin Auto Sales and Salvage (Grovespring, MO) had a block and they were even nice enough to deliver it to my shop. They claimed it was a 6.9, turned out to be a 7.3. Not a big deal, I will exchange the pistons, and build the 7.3. Overall the new block seems to be in good shape, and should take minimal machining to make it work.

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[IDIBRONCO]

The cylinder that you have the piston at the bottom of does look pretty good. From what I can see, it looks like a quick hone and it should be good to go.

 

[FrozenMerc]

That one still has some very minor pitting in it, but I would run it if it was the worst of the bunch. Downside was that a couple of bores on the other bank were rusted and had a pretty good ring groove. It should all clean up at 0.020" over, so not the end of the world. Now if I can just find some pistons....

 

[TNBrett]

Try this

These are the guys I just bought a set of pistons from for my IDIT build.

 

[FrozenMerc]

Found pistons, 2 sets actually. One set will go back. Next we seem to have a national shortage of ARP head stud kits, so my search will continue. Worst case, I will buy a head bolt kit and re-stud it at a later date. Block goes to the machinist on Friday, so progress is being made.

 

[FrozenMerc]

The 7.3 is fully assembled and back in the truck. Fired it up over the weekend and took the first test drive last night. So far, I am very happy with the extra power and smoothness of this motor. It will go in for final timing check and tune at a local diesel shop next week. Hopefully there is another 200,000 miles in this motor.

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[rhkcommander]

Glad to hear it, great job saving another idi!

Crazy to see that much damage to the old block