Is your block cracked?

[fbronson]

So I pulled my engine to do a rebuild. For the most part it was in reasonably good shape. One little problem, though, was that the block is cracked. The cracks are coming from the part of the block into which the outer bolts from the main bearing caps for the crankshaft are threaded into. Apparently what can happen is that if the cracks propogate far enough up, the whole section that the bearing cap attaches to will separate from the block, and your crankshaft will either fall into the oil pan, or break since it is no longer supported in the middle. Not good! Anyhow, I've looked at about 3 other blocks, and they all have the same problem. Has anybody else seen this? Is it common? Should I throw it away and start over? Do I risk rebuilding it? I cringe at the thought of putting a gasoline engine in there. A little help please!!

 

[odee1]

What size engine are you working with? I have played with these engines some since I bought a diesel sub a few years ago. I too have seen the blocks with cracks in them. I have had about 5 6.2 and 2 6.5 blocks with the cracks in them. I kept them around for a while then my judgement took over, I took the good parts out keep the main caps and tossed them. I would try to find a red colored engine or miltary bottom end. I have a line on a miltary one right now. I have a red engine in my sub right now. Those engines are supposed have more nickel in the blocks. Might also think about the 599 engine block also. I would like to here from someone that built a block with cracks to see how well it held up.

 

[tRustyK5]

DSP makes a stud girdle kit that should keep the block together.

I've also 'heard' the AMG block is quite a bit stronger than the standard 6.2 block. Can't recall specifics or even where I read that though.

Rene

 

[joez]

Ive heard that numerous times as well. The AMG blocks are also what they are using for the marine motors, and they are pulling over 500 hp with a supercharger out of those blocks, reliably.

 

[BlueBlazer]

and they are pulling over 500 hp with a supercharger out of those blocks, reliably.

Where did you hear this? Link? I seriously doubt a 6.2 or 6.5 making 500 hp, unless it is turning well over 4000 rpm.

 

[imiceman44]

So I pulled my engine to do a rebuild. For the most part it was in reasonably good shape. One little problem, though, was that the block is cracked. The cracks are coming from the part of the block into which the outer bolts from the main bearing caps for the crankshaft are threaded into. Apparently what can happen is that if the cracks propogate far enough up, the whole section that the bearing cap attaches to will separate from the block, and your crankshaft will either fall into the oil pan, or break since it is no longer supported in the middle. Not good! Anyhow, I've looked at about 3 other blocks, and they all have the same problem. Has anybody else seen this? Is it common? Should I throw it away and start over? Do I risk rebuilding it? I cringe at the thought of putting a gasoline engine in there. A little help please!!

It is a common problem, I haven't checked any of mine but if I want to rebuild I will.

 

[joez]

Marine Diesel USA puts out everything from 170hp all the way to 400hp from their factory, all mechanical and supercharged, and they are governed at 4000 RPM. Its the individual boaters pulling more from them, ill try and dig up an older link for you on people modifying them further. Heres one to the MarineDiesel USA

 

[BlueBlazer]

According to their site, their products share little in common with our 6.2/6.5s. Fuel system, displacement, and v8 layout seem to be all thats common. I would like to know the duty cycle of these engines to see how much abuse they can actually take at full power.

 

[jarheadk5]

I would like to know the duty cycle of these engines to see how much abuse they can actually take at full power.

Well, if they're marketed as marine engines, that generally means theyre expected to be flogged at high power settings for extended periods. I know gas marine engines are spec'd a little differently than automotive gassers, especially in the high-performance realm. Probably slightly different build techniques, too.
Plus, there's the whole issue of reliability. A marine engine (gas, diesel, whatever) is only good when it's running. Engine failure in certain situations on the water can mean a capsized or destroyed boat, and a very unhappy owner. If these folks were building unreliable crap engines, I think they'd be out of business PDQ.

 

[BlueBlazer]

Well, if they're marketed as marine engines, that generally means theyre expected to be flogged at high power settings for extended periods.

This is not true. For example, a Cat 3126 marine engine can only be run at full load for 8% of the time. It can run at full load for 1/2 hour out of every 6. A 3126 is much more HD than what marine diesel USA produces, so I wondered what their duty cycle was in comparison.

 

[BlueBlazer]

Sorry for going off topic. In my opinion, rebuilding any engine that has known cracks in it would be a waste of money.

 

[jarheadk5]

Sorry for going off topic. In my opinion, rebuilding any engine that has known cracks in it would be a waste of money.

Agreed... unless it was some super-rare antique that only needs a running engine to impress the show judges and get in & out of the trailer.

 

[fbronson]

Well, I did some digging around and I actually found a block that doesn't have those cracks I talked about. It took me a while though. I had to have it shipped up from pueblo. I've never heard of the bottom end falling out of a 6.2 either, but just visually inspecting those cracks makes me believe it could happen. The shop that is doing the work on my block showed me a small block gasser in which the portion of the block that holds the main bearings had broken off. They said that one came out of a drag car, so I could understand it happening there. Good discussion on all of this though. AMG builds the 6.2's and 6.5's for the HMVEE's don't they? They would have to beef up those motors somehow for them to run reliably in those things. Those HMVEE's are heavy, and you know that the military uses them hard. Heck, if I got to drive around in a hummer that I didn't pay for I'd run over everything that I could see!

 

[arveetek]

Unfortunately, it's not that uncommon for the GM diesels to have cracked blocks. As I'm sure you've noticed, there's not much meat there in the center three main bearing webs, so there's an awful lot of strain on that part of the block every time the engine fires. I've only actually seen one busted block in person, and it was a 6.5L, where the entire main center section of the block had busted loose from the rest. But I have read and heard of a lot of cracked blocks and broken cranks. There's a debate about whether the crank breaks first and pulls the block away with it, or if the block breaks away first, snapping the crank.

Anyway, I have two crack-free blocks, and they're both 82 models. I have read and have been told that the 82 engines had a different alloy in them, but I'm not positive about that. That's why the suggestion of looking for a red engine was made. Oonly 82 models were painted red. Both of my blocks have a casting number of 14022660, but I don't know if that really means anything or not.

Hope this info helps.

Casey

 

[fbronson]

Casey,

I just posted a reply in a thread you started about your rebuild. My rebuild is done, and it probably cost me over $2500! But, I basically have a brand new engine. Nice, eh.

Fred