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Old 02-05-2007, 09:27 PM   #1 (permalink)
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What causes cracked heads?

I see some dudes on the 7.3 forum talking about cracked heads. Is that something that occurs frequently in these motors and what causes it?
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Old 02-05-2007, 09:57 PM   #2 (permalink)
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Re: What causes cracked heads?

It DOES happen. Often? not really...They arent "known" to be terrible head cracking engines. It could be from many things including: poor metallurgy properties during the casting process. Not giving a proper warm up time. (Driving at higher RPM's under load will cause the combustion chamber area to heat up and expand but still have cold coolant surrounding the chamber in the water jacket which is acting against the heating process by trying to cool it, obviously, this causes stress in the cast. And it also plays hell on your head gaskets.) Too much load for too little truck, re: High EGT's.
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Old 02-05-2007, 11:00 PM   #3 (permalink)
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Re: What causes cracked heads?

I would also agree that the 6.9 heads are good solid heads, however we have had bad luck with the intake seats in them. We have had 16 different heads checked in the last few months and only had 2 that did not have cracked intake seats. These seats must be taken out with a step cutter, other wise the water jacktet will be hit. There are only a few shops that will even consider putting these seats in.
I does appear that the cracks are supperficial and will not cause problems, as they do not go to the water jacket and the valves were not burnt. We are about to put a pair on a rebuild and see how they do.
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Old 02-06-2007, 12:35 AM   #4 (permalink)
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Re: What causes cracked heads?

Most here will tell you the heads can crack if you take them off by just removing any head bolts. The proper way to remove heads is 1/8th to 1/4 turn on each bolt in the reverse torque pattern till the bolts are loose. I have done it that way all along without any problems. I'm not really going to experiment now because of the costs of heads.
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Old 02-17-2007, 11:35 AM   #5 (permalink)
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Re: What causes cracked heads?

[ QUOTE ]
Most here will tell you the heads can crack if you take them off by just removing any head bolts. The proper way to remove heads is 1/8th to 1/4 turn on each bolt in the reverse torque pattern till the bolts are loose. I have done it that way all along without any problems. I'm not really going to experiment now because of the costs of heads.

[/ QUOTE ]

That is true, Caterpiller figured that one out a bunch of years ago on the 1693 engine( the old D-9 dozer engine ). They had developed a reputation for all being cracked when removed, so they came up with the reverse untorque procedure and solved the problem. Any diesel can suffer the same fate if not removed properly.



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Old 02-17-2007, 04:13 PM   #6 (permalink)
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Re: What causes cracked heads?

Never heard of that one. We had a long time Cat mechanic transfer over to our shop to get a supplemental retirement in addition to his Operating Engineers and he zipped them off with an impact wrench after breaking them loose with a breaker bar (on Cat dozers too) just like the rest of us have done for years with no problems. Of course we always just instinctively more or less started with the center bolts and worked out. Since 99.9% of head cracks are between the seats, plus most all heads are stuck so tight to the block (except old Detroits, they don't use hd. gskts.)that mechanics have a collection of little wedges to drive between the two to break the head loose, it would be interesting to hear another mechanic's opinion on the slow untorqueing theory.
Did you work for Cat, or was this an "I heard"?

TwelveOsix, I agree, a lot of that plus overheating is the main cause. And ironically, like one poster above found for about the second time, when the slow untorquers get the heads off they find cracks up the wazhoo. [img]/ubbthreads/images/graemlins/biggrin.gif[/img]
But whatever floats your boat.
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Old 02-17-2007, 04:20 PM   #7 (permalink)
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Re: What causes cracked heads?

[ QUOTE ]
Never heard of that one. We had a long time Cat mechanic transfer over to our shop to get a supplemental retirement in addition to his Operating Engineers and he zipped them off with an impact wrench after breaking them loose with a breaker bar (on Cat dozers too) just like the rest of us have done for years with no problems. Of course we always just instinctively more or less started with the center bolts and worked out. Since 99.9% of head cracks are between the seats, plus most all heads are stuck so tight to the block (except old Detroits, they don't use hd. gskts.)that mechanics have a collection of little wedges to drive between the two to break the head loose, it would be interesting to hear another mechanic's opinion on the slowly untorqueing theory.
Did you work for Cat, or was this an "I heard"?

[/ QUOTE ]

Well, while we did mostly gassers, we did do the occasional diesel. Keep in mind that most of the work we did in the machine shop was already torn down, I would guess 75% or so, but we also used an impact to remove them and I can't remember seeing any big difference between those coming in and the ones we tore down as far as cracks. I know quick cooling will crack them, like taking them out of a 500 oil drying bake oven then having an accidental fire sprinkler go off (hint: you let them cool before opening the oven, unless you are the new guy that tries to pull 1000lbs of cast iron out into the workshop on the trolley!) I can say that will crack them, but haven't seen the slow loosening process used anywhere other than mentioned here. I was ASE master certified and spent my youthful days working as a mechanic.

That being said, when/if I ever do the heads on my 6.9, I will probably remove them slowly! [img]/ubbthreads/images/graemlins/eek.gif[/img] [img]/ubbthreads/images/graemlins/wink.gif[/img]
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Old 02-17-2007, 04:29 PM   #8 (permalink)
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Re: What causes cracked heads?

Actually, the service manager at the Cat dealer informed me about it when I went in for parts about 25 years ago for my 1693 that I had in my '72 Kenworth, he broke out the service bullitin book and showed it to me, then he copied it off for me along with the proper procedure.

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Old 02-17-2007, 04:33 PM   #9 (permalink)
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Re: What causes cracked heads?

[ QUOTE ]
I know quick cooling will crack them, like taking them out of a 500 oil drying bake oven then having an accidental fire sprinkler go off (hint: you let them cool before opening the oven, unless you are the new guy that tries to pull 1000lbs of cast iron out into the workshop on the trolley!) I can say that will crack them

[/ QUOTE ]
I agree, once in a while we had to do some really off the wall welding or brazing of cast iron that absolutely shouldn't work but due to part unavailability we had no choice and had to go for it. We had a general machinist who had my undying respect, pure genius, metal expert, etc, and he'd make sure we kept that baby warm as long as possible. Odd as it sounds, he didn't weld or braze but there wasn't much else he couldn't do and very little he didn't know. One day I went over to him and said, "Holy Crap, you're actually making a helical gear", and he had to blow my drawers in with his favorite statement, "Machine work's easy, it's just gett'in rid of steel where you don't want it".
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Old 02-17-2007, 09:57 PM   #10 (permalink)
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Re: What causes cracked heads?

[ QUOTE ]
I agree, once in a while we had to do some really off the wall welding or brazing of cast iron that absolutely shouldn't work but due to part unavailability we had no choice and had to go for it. We had a general machinist who had my undying respect, pure genius, metal expert, etc, and he'd make sure we kept that baby warm as long as possible. Odd as it sounds, he didn't weld or braze but there wasn't much else he couldn't do and very little he didn't know. One day I went over to him and said, "Holy Crap, you're actually making a helical gear", and he had to blow my drawers in with his favorite statement, "Machine work's easy, it's just gett'in rid of steel where you don't want it".

[/ QUOTE ]

We welded aluminum heads. They generally went in the oven in the morning (stripped of course) and were gradually brought up to 350 to 400 degrees, then taken out hot, welded for short periods, then put back in and the temp brought down overnight. We rarely repaired a cast iron one, too many variables, but when we did, he process was the same. Our oven, which was used mainly to dry grease on cast iron or aluminum parts, had a step up/down timer, so we could cool/heat them slow. At any rate, I truly believe that was why are repairs held so well and the company is still in business after about 35 years. It was owned by an old man that taught me a lot about welding, he was 88 when I left in 1998 or so and had welded on oil rigs and ships most of his life when not in a war somewhere! He is still kicking today, and I would put his welding against any I have seen, even though he is in his 90's! His sight isn't so good, he sometimes welded things to the iron tables etc. and it was a REAL pain to get off!!! [img]/ubbthreads/images/graemlins/smile.gif[/img]
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