6.5 block cracks

[rlb]

I've heard a lot about 6.5 diesel blocks cracking. Was this a problem only in earlier model years or did they re-design the block at some point?

I'd like one but prefer my engine block to be crack-free.

 

[great white]

All of the GM castings are suspect for the cracking issue. Some worse than others.

The later years are actually worse than the early years.

Casting numbers are you best bet to find a good one.

599 castings are reported to be the best, but I've had one that cracked in the cap registers, so no guarantees.

506 castings are generally agreed to be the worst, a lot having to do with the tooling errors when making the piston oil cooling jets in the main webs.

GM castings seem to crack everywhere: main cap bolts, Cap registers, oil cooling jets, cylinders, heads, starter mounts, etc. Someone even posted up once where it had cracked around the head bolt holes.

Now if you do find one that is not "euchred" by now, it's probably a fine candidate for a stock power level rebuild. Generally, if it was going to suffer cracking it will show signs of it by the time is makes it to a "worn out" rebuild vice a catastrophic failure death. No guarantees though, it's still a comparatively weak GM casting.

You best bet to get a block that will be in good shape, drop in like OEM and likely to not suffer the cracking issue is a GEP Optimizer block. These were cast by IH for GEP (AMG subsidiary) to supply re-power engines in the HMMWV for the re-power/up-armor project. these have "506" cast in the block, but they also have the IH symbol cast in the valley. You can get these from surplus suppliers if you ask the right questions and shop smart. Ted's trucks are/were a popular supplier, but it seems his stock has been drying up lately.

The optimizer has different metallurgy, is a high quality casting by IH and has changes in it production process (like shot peening parts, etc).

This is what I have in my truck and it's getting on for 4 years and running strong. It has been "massaged" to 300HP and 500 Lbft crank (estimated), 271 hp 446 lbft at the wheels (rear wheel dyno) with no issues so far. Granted, I haven't pulled the oil pan off for a look, but I've had "eyes" in there a couple times in the form of a boroscope. Same one we use to inspect compressor blades deep in to the compressor section in jet engines. No cracks to date. My engine also gets the best of bits, Fluidampr is one of those, but not a forged crank. My 6.5 is pretty much at the end of it's development life for me. If/when it dies, it's coming out in favor of a 6BT or a Duramax.

The final word so far on a crack resistant 6.5 is the optimizer P400 casting. Major redesign of the block while retaining the "drop in" servicing for the heavy up-armored HMMWV's, but requires some oil pan work to fit in a gmt400 4x4 chassis. But you'll be in to it for $5-8,000 at this point as they are currently not available as surplus.

One day, it will be. But not today.

 

[great white]

Forgot to add that although I've listed a few (very few) reasons for block failures in the GM castings, there are other reasons.
Like composition (metallurgy if you prefer), core shift, machining process, etc....

 

[Will L.]

We had a lot of the 6.5's in a couple of fleets I worked on. All most all the cracked blocks and all the broken cranks had old harmonic dampers on it. A fluid damper is worth its cost if you are not going to start with an optimizer (the IH spoke bout above). Even if you decide to ditch the 6.5 world later, that balancer will resell no problem.

Also Great White is a freakin magician with the 6.5, so don't expect to just walk into his power numbers...

The 6.5 is a decent engine once you know the proper things to keep her happy.

 

[Burning oil]

FYI I can get the P400 for $6950 brand new.
Center mount or side mount turbo.
Some Features are:
Forged crank.
Forged rods.
Heaver duty pistons.
Main girdle.
Hardened valve seats.

I can get Optimizer for $5750
Center mount or side mount turbo.

I have the best price on a Fluid Damper also, but you have to email for a price [email protected]

 

[WarWagon]

"Someone even posted up once where it had cracked around the head bolt holes."

:grumble: That would have been the bored .10 over block that came out of my 93 truck. Mains looked good and in fact were crack free. After sending it up to Missy she found a crack near a head bolt on the side of the block that would/could continue till it hit coolant. The engine had lived 2 lifetimes. Unknown why it was rebuilt the first time and the second life had copper showing in the bearings. It was pulled because the crank seals were leaking bad and it had on-fire quantity blow by. Although the mains were good - it wasn't worth the cost of needed machining to take the risk with the crack.

I recall someone had a engine out of a bus with a crack running the length of a section of the oil pan gasket.

There was a spot on zombie survival CL ad featuring a 6.2 CCUV as the ultimate thing to have. And why not? After all there are lots of 6.2/6.5 walking dead engines with cracks that don't know it. :hihi:

Leory's prices aren't bad for a new improved longblock. Otherwise you are looking at used and with used you really don't want to know. Low mile used is a crack gamble and almost always need new rings.

 

[rlb]

Thanks for all of the replies. I don't have the time to do an engine swap really. What I was really looking for, is if I pick up a well maintained 6.5 suburban with 200,000 miles for a few grand, is it likely a walking dead 6.5 with cracks in the block? Sounds like it probably is, and there is no way to tell if the block is cracked in a pre-purchase inspection unless I dropped the oil pan, which is not practical.

 

[TurboTahoe]

Thanks for all of the replies. I don't have the time to do an engine swap really. What I was really looking for, is if I pick up a well maintained 6.5 suburban with 200,000 miles for a few grand, is it likely a walking dead 6.5 with cracks in the block? Sounds like it probably is, and there is no way to tell if the block is cracked in a pre-purchase inspection unless I dropped the oil pan, which is not practical.

I agree with the guys, especially Great White. It is an issue with the design and the metallurgy from the 90s. To get more power, especially if towing, you're going to want to look at a repower.

Most of us who stick with the 6.5 are suckers for low-cost maintenance, easy-to-understand and perform repairs, inexpensive parts, and a large network of people who use these engines... plus, moderate power.

You want big power? You need a modern powerplant like a Duramax, but now we're into a whole different design and such. That said, my experience is if you aren't towing anything (e.g. My Tahoe just carts people and luggage around), then the 6.5 works quite well. Some who tow and haul a lot have good results as well, but mine is "Nearly" stock, and it's fine for hauling the 4800 lbs around.

-Rob

 

[Sentinelist]

The 6.5 does a good job of hauling my truck camper around, even at 80mph on the highway if I want. I suspect it'll get there faster (soon) with a ATT, but the 'moderate' power is pretty impressive. Especially unloaded, this truck really scoots for what it is.

While I largely got mine over a Ford IDI because I found the 6.5 first, I'm here for the HMMVW connection and the mechanical injection. I plan to have the oil pan taken off on the next oil change interval to check for cracks- probably my greatest fear on this rig. If the engine goes, I plan to rebuild it to keep the rig mechanically injected. I love my analog brute.

 

[vegtech]

Here is my

506 block with a crack or 2

Sent from my ADR6350 using Tapatalk 2

 

[Will L.]

Hey that's the light weight model for higher rpm, right?

 

[vegtech]

definitely light weight not so much on the higher rpm

Sent from my ADR6350 using Tapatalk 2

 

[bowtiebutler956]

Here is my

506 block with a crack or 2

Sent from my ADR6350 using Tapatalk 2

OMG!!!!!

 

[NVW]

It can be welded up, nooo problem.

 

[WarWagon]

definitely light weight not so much on the higher rpm

Sent from my ADR6350 using Tapatalk 2

Still running or 2 part crank option? This should be in the carnage thread if not already.

 

[vegtech]

Well when it happen, it stopped running and I had to tow it home. It wouldn't turn over. The next day it started up and drove in the garage.

Sent from my ADR6350 using Tapatalk 2