Cracked Piston
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Laughing Gas
Joined: Mar 2006
Posts: 1,083
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From: Fitzpatrick Alabama
Cracked Piston
I bought an 86 F250 with a bad 6.9 Diesel. I put a used motor in it with the intentions on selling it, but I am planning on building the motor that was there to put in my 88 Ford. I pulled it apart today, in record time I might add, I think it took 2 1/2 hours from the time I put it on the engine stand to the time I pulled the last piston, but number 4 piston came out in 3 pieces. the rest of them look fine, even the rings look pretty good. I think 2 of them need rings, but it looks pretty decent. What would cause just one to crack that bad?
Post Fiend
Joined: Nov 2004
Posts: 5,638
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From: Manitoba
I think it took 2 1/2 hours from the time I put it on the engine stand to the time I pulled the last piston
Did you lay out all the parts for reassembly in the correct/same location they came from.
Laughing Gas
Joined: Jun 2007
Posts: 1,106
Likes: 35
From: Virginia
The cracked piston is probably a result of manufacturing and starting fluid. What does the cylinder wall look like for that cyl? Although, I've rebuilt engines before with up to 5 cracked pistons, and they were still running with no noise and the walls of the cylinders were fine. There are probably more cracked pistons out there than people know about, because other than a major failure/ compression test, people will continue to drive them without knowing it. And, usually when someone says that they have blow-by, they blame the rings.
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Laughing Gas
Joined: Mar 2006
Posts: 1,083
Likes: 1
From: Fitzpatrick Alabama
I didn't see any evidence of a glow plug tip, I will go look again. The cylinder walls look great, I don't see any problems there, I'm thinking too much ether as well, however I would think the rings wouldn't look as good as they do if that were the case, however it may be if it received a bad dose just one time. I have seen people tell me "I just spray a little dab", then spray for 6-8 seconds straight, and call that "a little dab"! I wish I knew more about this truck, but I sold a 454 chevy engine I had and the guy gave me this truck to take $200 off the bill, so I thought it was a great deal. The junkyard offered me 800 for the engine, this guy gave me 800, a truck, and a .44 Magnum Ruger, so I thought it was a good deal.
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Laughing Gas
Joined: Mar 2006
Posts: 1,083
Likes: 1
From: Fitzpatrick Alabama
By the way, i've rebuilt lots of engines before, but never one of these, and I've never heard of unbolting the heads a little at a time???? We always just put a pull handle on them and take them out.
Laughing Gas
Joined: Jun 2007
Posts: 1,106
Likes: 35
From: Virginia
This engine should be the same as any other internal combustion engine. If the walls of that cyl are fine, you are probably alright. I would check the rod for any distortion, check ring gaps, piston grooves, turn heads upside down with glow plugs/ injectors in them, and pour dry-gas on the valves- this will give you a VERY GOOD indicator of how the valves are sealing. slight leakage, hand-lap; major leakage, investigate seat/valve/stem, etc. But go ahead and replace valve stem seals anyway- look at the keepers as well. Keep your ring gaps placed properly, and slap that baby together. The best that I have ever done with starting and stopping new projects is 24 hours for a complete rebuild.
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