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Discussion Starter #1
I've been searching for about a couple of hours now, and was just curious.... how common are cracked blocks for 5.9 magnums? The reason I ask this is I have in my basement, a 5.9 short block that was pulled out of my friend's father's truck. It was pulled because the oil pressure took a shit and it JUST started to scrub the main bearings. If it were just a regular short block I'd turf it and start over. But, It has forged pistons, rods and what looks to be a aftermarket crank. The block has also been align-honed and zero decked. So again, how common is it that these blocks crack? any and all input on the topic is greatly appreciated. Oh and the truck was blown(SC'd) at one time, for what that's worth.
 

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If it is cracked it would be at the coolant passages on the upper part of the block. It is common. But I guess worth taking it to a machine shop to have it checked out.
 

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I've been searching for about a couple of hours now, and was just curious.... how common are cracked blocks for 5.9 magnums? The reason I ask this is I have in my basement, a 5.9 short block that was pulled out of my friend's father's truck. It was pulled because the oil pressure took a shit and it JUST started to scrub the main bearings. If it were just a regular short block I'd turf it and start over. But, It has forged pistons, rods and what looks to be a aftermarket crank. The block has also been align-honed and zero decked. So again, how common is it that these blocks crack? any and all input on the topic is greatly appreciated. Oh and the truck was blown(SC'd) at one time, for what that's worth.
I bought a cracked block from a dick suck weed named Buzz...You probably don't anything about that POS.

A guy named Sam Pranther came to my rescue....:mullet:
 

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Discussion Starter #4
If it is cracked it would be at the coolant passages on the upper part of the block. It is common. But I guess worth taking it to a machine shop to have it checked out.
I think his main concern was that it cracked by an oil galley, thusly allowing it to lose pressure and scrub the bearings. :anyone:
 

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A 360 block is a very strong block. If you lost oil pressure it could have been the oil pump. Don't give up on it yet.

If it looks to have had engine work done, it may be overbored. You are removing metal from the cylinder walls in this process and thus weakening the block a little. Not saying it can't handle it, but it is just the way it goes. But for the forged pistons and forged crank, I would have it looked over. Post pictures too. :)

Good news is if you have the block out right now I would take all the pistons out, visually inspect it, and if nothing looks bad take it to a good machine shop and have them look it over for you. They can pressure test it or magnaflux it for you and find cracks you can't see with the naked eye.
 

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Discussion Starter #7
So, I've learned that all the bearings are Clevite bearings...and are 0.020" over. The pistons are 0.030" over and I'm not sure of their make, but they have a small relief in the center of them...will post more pics soon. As you can see in the picture above, the front bearing and rear bearing have the least discoloration....It appears that the 3 in the middle got the worst of it. The top halves of the bearings (in the block) have little to no discoloration at all, as does the crankshaft. The low oil pressure light was flickering (which is what caused the motor to be pulled in the first place) but the motor itself was not labored when running. When I have more time, Im going to try and check the oil passage for blockage, which is the theory I'm going with right now. Don't get me wrong, it's still going to the machine shop to get checked...but I'm really intrigued to make a diagnosis before it goes in to be checked.
 

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Discussion Starter #9
Blah! I also took note of some permenant marker writing on the block, where the oil pan mates to (possibly from the machinist who was building the motor) that said to use straight 30 weight oil....could this have any effect on the scrubbed bearings?
 

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I've never heard of an engine builder saying to use straight 30 weight. Scrubbed bearings are going to be from a lack of oil pressure since the bearings should never have metal to metal contact under normal operation, either it lost a seal in the oiling system somewhere(maybe collapsed oil filter?) or he knew it had crap tolerances on it and thought 30 would be heavy enough to make up for bad machine work and it wasn't.

Who said it was cracked?
 

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"Old School" engine builders used to set the clearances pretty loose, use high volume oil pumps and want heavy oil in their high performance or race engines. That was before they started to figure out it took HP to spin it with thick oil and also power the oil pump.
 
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