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Old 09-23-2009, 11:04 PM   #1 (permalink)
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6.2 Cracked Precup

So, Im in the process of rebuilding a 6.2 to replace my current 480,000km 6.2. Im trying to keep it basic, I dont want to send my block away to get bored because its a fairly low mileage motor (60,000 Miles), just honing, rings, injectors, glow plugs and seals. Anyways, I popped the heads off, dropped the crank, measured the cylinders and bearing surfaces, so far so good. I took the valves out and they looked ok, the only problem i found was every precup for every cylinder has hairline stress cracks around the opening. so now Im looking for options, Ive heard horror stories of precups breaking off and making a mess. Does anyone know if swapping out my 6.2 heads for 6.5 heads would be an improvement? or should I just just replace them with OEM precups and hope I can get 500,000 out of this 6.2 without it chewing itself up? Theres gotta be some diesel pros on here, Thanks.
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Old 09-24-2009, 04:16 AM   #2 (permalink)
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I've used the diamond style precups on a few rebuilds with good results. Have you checked the lower end of the block for main cracks? I've have fairly good luck with these engines.
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Old 09-24-2009, 12:35 PM   #3 (permalink)
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I have the block all cleaned up and inspected, its in beautiful shape, I might get away with just hitting it with the ridge reamer, and honing. Also got the seals/gaskets motor mounts on the way, still looking for a supplier for the precups. Diamond cups were the style on the 6.5s were they not? And speaking of having good luck with these engines, you cant argue with 480,000 kms and no failures (knock on wood) Im planning on keeping this 6.2 in my truck as long as I can. Maybe Ill break 500,000 befor i drop the new one in. Any more diesel guys out there? Id like you hear your 2 cents.
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Old 09-24-2009, 05:02 PM   #4 (permalink)
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Im kinda new to the GM diesel game, but...
in the 3 of mine that i have taken apart most of the precups had a little cracking going on. I figured it was kinda standard because of the kind of life they have and never really gave it much thought. They are little flamethrowers, literally.

the non turbo 6.5 i picked up was transplanted into the truck shortly before i bought it, has maybe 5-10k miles on the motor and little cracks on the precups. this is a GM crate motor that was purchased in 2006, installed in mid 2007 and i bought it Aug 07
I am rebuilding it to be a high mileage reliable expedition type vehicle and i had no problem putting them back in. ARP studs, timing gears, girdle...

All 3 had similar amount of cracking:
6.5 non turbo, low miles
6.2 K5 with 120k miles on the clock. I think its 620k based on the trucks condition and driveline wear.
6.2 former PGE service K30 flatbed with 280K miles

New ones are not too expensive if you are really worried about it. If it were me... id run em with confidence.
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Old 09-26-2009, 06:05 PM   #5 (permalink)
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I talked to my parts guy in Vancouver, he cant get me precups. The guy at napa didnt even know what a precup was.... and the local diesel shop says they have to do some hunting because there more into tractor trailers and heavyer diesels. Ive also tried ebay, no good. Whats a guy to do living up here in the boonies?
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