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Old 04-07-2009, 10:13 PM   #1
randy847
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CAT 3126 cracked block

Hi All, New to the forum and have lurked around before. Great site. I have a 3126 Cat 99 GMC 7500 on a boom truck and the right front top side of the block is cracking. Hair line crack about 2" long.Is this a common thing for this Cat. It has only 69,000 miles and is parked in the shop when we are not using it. At first we thought the water pump was leaking then we started to see the crack in the block. It starts to seep out when it is reved up to 1500 or so. Any thoughts on the best way to go besides telling Rover to go after the cat. Thanks
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Old 04-07-2009, 11:23 PM   #2
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3126's are throw away motors, if the block goes your in trouble, looking at a short block probally. But i was seen a cracked block welded before, got to use some stainless rod a belive on the cast, not sure a good welder could tell you for sure. then epoxy over it and it should stop the leak. This is what we did at work to our yard truck with a 3208 in it and it has held up so far, and its been a while since it has been done to.
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Old 04-08-2009, 12:32 AM   #3
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Quote:
Originally Posted by randy847 View Post
Hi All, New to the forum and have lurked around before. Great site. I have a 3126 Cat 99 GMC 7500 on a boom truck and the right front top side of the block is cracking. Hair line crack about 2" long.Is this a common thing for this Cat. It has only 69,000 miles and is parked in the shop when we are not using it. At first we thought the water pump was leaking then we started to see the crack in the block. It starts to seep out when it is reved up to 1500 or so. Any thoughts on the best way to go besides telling Rover to go after the cat. Thanks
If it for sure did not freeze, 800-call-cat, and freak out on em. No, not a common prob at all...

(and welding a cast block takes cast rod and an external heat source, not stainless)
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Old 04-08-2009, 12:51 AM   #4
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Has the engine been apart before? I have seen this twice in the same spot, It was the result of the head bolt hole not blowen out during a headgasket job. liquid left on the hole gets compressed by the head bolt and when the engine heats up it has to expand. One of the engines cracked the cylinder wall too.
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Old 04-08-2009, 01:23 AM   #5
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Positive that it never froze. The only work that I had done on it was an injector went bad and had it replaced by a Cat dealer. I'm going to call the Cat line. I was wondering how common it was. Thanks for the help
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Old 04-08-2009, 02:43 AM   #6
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Originally Posted by gregdav View Post
Has the engine been apart before? I have seen this twice in the same spot, It was the result of the head bolt hole not blowen out during a headgasket job. liquid left on the hole gets compressed by the head bolt and when the engine heats up it has to expand. One of the engines cracked the cylinder wall too.
^^^ Good one bud. That's a common problem with any engine, and I've seen it tons, even by some purdy descent wrenches. Kills the block, every time. I see alot of that stuff, and never once could I even fix one with a salvage sleeve. It's suprising how many people will take this wierd lookin grease gun sucky thing and suck out water jacket holes, oil dump holes, etc., and won't even touch a head bolt hole. Here's yur sign! Good job man!!


(BTW, I assumed it was a one piecer with 69K and he didn't say it'd been stripped before so I left it out. Good one to throw in for a search engine line for someone tho. Don't think I've ever seen it brought up here).
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Old 04-08-2009, 06:08 AM   #7
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Its junk. i will give you $7,500 for it depending on what boom is on it.


the above advice seems pretty sound.
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Old 04-08-2009, 12:39 PM   #8
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Originally Posted by ynot View Post
^^^ Good one bud. That's a common problem with any engine, and I've seen it tons, even by some purdy descent wrenches. Kills the block, every time. I see alot of that stuff, and never once could I even fix one with a salvage sleeve. It's suprising how many people will take this wierd lookin grease gun sucky thing and suck out water jacket holes, oil dump holes, etc., and won't even touch a head bolt hole. Here's yur sign! Good job man!!


(BTW, I assumed it was a one piecer with 69K and he didn't say it'd been stripped before so I left it out. Good one to throw in for a search engine line for someone tho. Don't think I've ever seen it brought up here).
Thanks, been following your posts, nice to hear from someone that knows whats up, read alot from guys who give false info.

Another thing to check on the one with the cracked block, has it been overheated? Cat did have a problem with cracked blocks but the crack was usually found about three inches from the rear cover on the right side, coming up from the oil pan bolt. Cat found it to be a result of oem driveline vibration. We would send out the drive shafts to check balance and check drive line angles. The ones I have seen were on box trucks with long chassis with a two or more hanger bearings. There is a Cat letter somewhere on proper diagnosis.
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Old 04-08-2009, 01:27 PM   #9
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I've seen a couple of failures from the water jacket into #1 cylinder due to poor coolant maintenance, but never a failure to the outside.
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Old 04-08-2009, 09:04 PM   #10
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Quote:
Originally Posted by gregdav View Post
Thanks, been following your posts, nice to hear from someone that knows whats up, read alot from guys who give false info.

Another thing to check on the one with the cracked block, has it been overheated? Cat did have a problem with cracked blocks but the crack was usually found about three inches from the rear cover on the right side, coming up from the oil pan bolt. Cat found it to be a result of oem driveline vibration. We would send out the drive shafts to check balance and check drive line angles. The ones I have seen were on box trucks with long chassis with a two or more hanger bearings. There is a Cat letter somewhere on proper diagnosis.
Now that you said somthing about that i remenber changing a 3126 for that reason. Did not get into the reason it broke because it was sold to my freind which got it for salvage price and he sent little money on it but it was a long wheel base box truck.
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