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2000 K3500 Gone Mechanical Build

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So tell us about it. The block in the first couple pics appears to have regular pistons, but the block in the last pic has the 18:1 pistons. Which one are you using, what casting number? Crack free? I know its alot of questions, but I like details. :)

Matt
 
18.1 Kennedy pistons. Should all be pictures of the same engine unless I accidentally put a wrong engine picture in there... I know some of the pictures are a little crappy too, I'll try to eventually get some better ones up. The block is an aftermarket block that is supposed to be designed the same as the Optimizer block. Has somewhere in the 50000 mile range on it. Appears to be crack free. Still has the cross hatches on the cylinders as well. Will clean it up and check it over more closely once I get some more time to work on it.


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It's one we built a long time ago, been so long I couldn't tell you the place we actually bought it from. The truck was sold last year and the guy decided to put a Cummins in it so I was able to buy the engine back.

I was just going to put the engine in as is, but it has the crank in it from the original truck with who knows how many miles on it now so I figured I should upgrade that while it was out. Also plan to do some head work and add some other upgrades so I just decided to disassemble it and start over. Figure it was better to do it all now so I didn't have to pull the engine again later on down the road to upgrade or end up breaking the crank and possibly damaging other things.


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With it already having the the 18:1 pistons, and a good block, it should make for an awesome foundation! I've often wondered about those blocks on ebay that are advertised as being updated. If it has 50k on it, and is still crack free, and in good shape, they must be decent. Are you thinking about a Scat crank?

Matt
 
Not sure yet. I was going to go forged, but they keep getting more and more expensive. Have debated on just going with a new stock one. The one in my truck has 243xxx miles on it and hasn't broke and has been used almost strictly for hauling by me and the previous owner. The crank in this engine still held up after putting power to it and have who knows how many total miles on it. I've never really seen anywhere as far as factual information as to what makes a scat crank stronger other than that's what everybody says, so I'm not even sure if it's worth the extra money over a stock crank to be honest. So in all honesty, I'm still up in the air on it. I'm a firm believer that the harmonic balancer is the reason for broken cranks...and cracked blocks that come apart, but that is less likely than the failed balancer...so going by that theory, a stock crank should be fine if it's taken care of.


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I agree with the balancer being the problem not the crank. I have seen a half a dozen broken cranks in 6.5s. all of them had bad or very questionable hbs. all of them had blocks cracked( some with complete broken blocks). I have never seen a lost crank and had someone say they just replaced the hb a while ago or ever replaced it. I say keep the crank and spend the money on fluid damper or a AC Delco balancer.

If anyone here has broke a crank with a less than 100k mile balancer - speak up, start a thread, I would like to understand that story.
 
Scat and the old GM are both "cheap" cast cranks. The new AMG cranks are forged and expensive. Peninsular diesel sells the forged ones. The are cast for cost and the improved design doesn't use them because they did not hold up overall. The original non-turbo 6.2 design was forged before the GM bean counters got to it...

Seriously the balancer is the only thing walking the thin line of not breaking a cast crank? That IS really weak and pushing the limits.
 
Well got to really test the truck out today. I hauled a 4500lb trailer with a Bobcat in it one way and the same trailer back home full of mostly dirt, brick and shingles. I hauled the bobcat in OD, had not issues. Roads were mostly flat and top speeds were 55. It was another hot and humid day, low 80s and 80+ humidity. Engine temps were normal, no problems with egts or anything.

The haul back was slightly heavier... Would guess in the 12,000lb range. Trailer has a GVW of 14,000lbs and I had it loaded down enough that it was awefully creeky... Figured I would try 3rd gear again with this load. And it worked great! The converter did lock up this time and ran 55 all the way with no issues. Was running 2500 rpm, 4-6 psi of boost on average, 190 +\- intake temps, 190 tranny temps and max engine temp was 210. Egts held between 850-950, with occasional drops as low as 700. Max I saw was 1050, but I was fairly easy on the throttle. Overall was a 100% better experience than the last haul and was close to double the weight (only guessing, could be wrong). I think the cover on the intake definitely made a huge difference and run in 3rd really helped with keeping the turbo in its sweet spot. Still has issues burning the fuel at low rpms and I was easy on it, but it pulled the load with no issues and pulled it very we'll, especially once up to speed. So thanks for the advice and input everyone, helped out a lot!

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I've had multiple 6.5 that I've put a ton of strain on to back the comment... Experienced one broken crank. It was on my dads 84 Silverado with a 6.2. Had over 160000 miles and found to have a bad balancer... Between me, my dad and brother over the last 15 years we have had 11 various 6.5s and 6.2s and have had one break a crank. Not saying they are the greatest cranks in the world and that forged isn't better, but there are a lot of other GM vehicles that come or came with cast cranks that have just as much rotating mass as a 6.5 and put out a lot more hp and torque and they survive. I was actually just looking at cast 454 cranks a few nights ago and they were rated up to 650 hp. Forged were 1200+ hp.

With all that said though....
I still always do have the worried thought in the back of my mind that the stock crank will give out on me right in the middle of a long hill with a load behind me. Just hasn't happened yet. Knock on wood.


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WW, what years had the forged crank?
WarWagon said:
Scat and the old GM are both "cheap" cast cranks. The new AMG cranks are forged and expensive. Peninsular diesel sells the forged ones. The are cast for cost and the improved design doesn't use them because they did not hold up overall. The original non-turbo 6.2 design was forged before the GM bean counters got to it...

Seriously the balancer is the only thing walking the thin line of not breaking a cast crank? That IS really weak and pushing the limits.
Click to expand...
 
FWIW I can get the AMG forged crank, but they are very pricey at $1300 IIRCC.
Also I can get the Fluid Damper for less than anyone, have to contact me for a price though.
 
Figured up the weight last night. Supposedly dirt weighs between 75-125 lbs per cubic ft depending on contents and density. I figured it at 80 lbs and came up with roughly 16,000 lbs total trailer weight. Not too bad if that is remotely accurate....

On a side note, I went out this morning and I now have a blown out tire on the trailer, still loaded. Yay.


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Burning oil said:
FWIW I can get the AMG forged crank, but they are very pricey at $1300 IIRCC.
Also I can get the Fluid Damper for less than anyone, have to contact me for a price though.
Click to expand...

Will be contacting you for sure when I get to that point. Thanks!


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As I understand it the original 6.2 Detroit Diesel design called for forged. I don't know if any prototypes were made with it and doubt it was in GM production. Later, when the 6.5 was redesigned to correct issues seen in the HUMMER they went with forged.

It's not about the HP. It's about 21:1 compression load, the rattle of diesel ignition, and high torque causing vibration. Thus you have fatigue failure. After all 1200 HP gas engines don't commonly bust alternator brackets or impressively rip the alternator clean in half due to a missing rear support like the 200 HP 400 Ft LB 6.5 diesel does. Even the 5.7 Olds diesel busted alternator brackets and we know how it's power was vs. a 455. The mains being cracked clean out of the block has also busted some cranks. Cracking the mains out of the block over time is the same issue after all because the same known technology holds up just fine in gas engines.

Fatigue failure is what GM never understood with their diesels. (And that lack of understanding is why the bean counters went with cheaper parts.) It's why alternator brackets are a common broken item. As well as extreme stress causing short life on the crank HB, cracked mains, and busted cranks. Gas engines tend to run after the HB completely fails and the noise of it rubbing on something causes it to be replaced.
 
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