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Discussion Starter #1
Having two K3500 CC/LB trucks in the family ('89 & '91), and having recently been "gifted" with three 6.2L diesel engines ("660" block ID), by my friend who's moving to the lower-48, I've been trying to educate myself on the subject of crankshafts. We plan on keeping these trucks until they rust out from under us.

What I'm hoping I can do:

1) - Build two 6.2L engines with NEW crankshafts. (Reliable bottom ends that won't leave us stranded with broken cranks, hundreds of miles from the nearest help.)

2) - Build for fuel economy - NOT power.

Problems:

1) - Cannot find NEW cranks for use in the "660" blocks. (Forged steel or nodular cast iron.) These blocks utilize the two-piece rear main seal. All NEW cranks that are marketed are for the "599" and newer blocks, which utilize the one-piece seal.

2) - Used two-piece seal cranks (nodular iron) available all have 100k+ of miles on them. And living where I do (Fairbanks, Alaska) these cranks have likely seen the equivalent of MANY more miles, due to all the wintertime idling.

I've read so many horror stories about broken cranks, and on one of the engines I was given, the crank is broken outside the engine where the harmonic balancer (damper) mounts. I'm aware the blocks are weak. I'm also aware of the need to use a GOOD balancer, and to try to keep the POP pressures close on each cylinder, to minimize any damage to the crank.

Possible Solution:

I've read somewhere that one of the forum members (MaxPF) purchased a new-old-stock, one-piece seal GM crank, and machined the read end of it to work in a 6.2L two-piece seal block. Therefore, I know it's possible to make a NEW crank work in these old "660" blocks.

I was thinking of buying a NEW one-piece seal forged crank, and having it machined to fit. If I had this work done, I'm not sure how well the lack of a large-diameter oil slinger ring would work out.

Questions:

Does this solution have drawbacks? Durability issues? Too expensive?

What say you?

-Nacla
 

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If you want longevity out of those engines, use lower compression pistons. drop the compression down to 18:1 and if you can find a turbo for it go that route. The 22:1 in those is a beast on the bottom end. blocks and cranks. Actually I have read more about busted mains than cranks, or the mains go and take the cranks out later.
 

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I wouldn't get too worked up over the broken crank stories. Yes it can happen but generally only for very high mileage and hard use. My '90 has over 120k on it (I've owned it since 49k) and has been run hard that entire time I've owned it. I also personally know of several other very high mileage 6.2's, including one that spent about 10 years on the farm pulling stock trailers, and it never had an issue.
 

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my understanding is many of the broken cranks in 6.2 diesels can be traced to a harmonic balancer going bad. my balancer started to separate at less than 70K miles, so I bought a Fluiddamper to end that worry.
 

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Discussion Starter #5
MaxPF did it...did he regret it?

MaxPF machined a NOS 6.2L crank, making it fit into the older blocks. He also beefed up the bottom end with splayed main caps.

I wonder if he regretted going to all that effort? Obviously, he has skills. I'm wondering what it would cost for another competent machinist to do the same.

By the way, regarding the durability of their forged steel crank, Peninsular Diesel claims: "The fatigue factor more than doubles the engine cycle hours." Could be hype...or not.

Most all the diesel engines in Alaska get idled a lot. There aren't many low-time 6.2L engines in Alaska. Idling a diesel for hours on end sounds a lot like "fatigue factor" to me.
 

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It sounds like throwing thousands of dollars at fixing factory/engineering defects to get reliability out of it when that money could be better spent on going an alternative route. If you're really set on running a diesel then find a different diesel that doesn't suffer from so many inherent flaws. Otherwise, go gasser. A few mpg takes a LONG time to recoup when you're talking about thousands of dollars in rebuild costs.
 
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