cylinder head cracked?!?!?!?! - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-24-2005, 12:08 PM
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cylinder head cracked?!?!?!?!

background: 406 sbc, world products sportsman II heads

two weeks ago I was helping my friend finish up his upgrades to his sbc (solid cam, vic jr intake, port polish heads, new springs and rockers) So after everything was installed we primed it dropped the distributor and she fired right to life.

We broke in the cam for about 30 min holding the revs above 1500 to 2000. The car sounded mean, everything seemed to be fine. So our plan was to change the oil, which he did, and re-torque the head bolts last weekend. after he changed the oil he fired it up and it seemed to run ok, stumbled a little a died but he thought nothing of it since it was below zero outside.

So saterday we were removing the rockers and headers to gain access to the head bolts to retorque them. he had noticed a little drip of coolent and figured one of the small head bolts was probibly leaking. The passenger side came apart fine, but on the driver side, #7 inner header bolt was removed and a stream of coolent came out, not a drip or two but a stream.

We talked to some local gear heads who figured a cooling jacket could have worn through or a crack into a coolent jacket. They suggested runing a stud really hard into the hole to try and seal it up, and maybe some RTV or jb weld. They said it should run ok unless the possible crack gets bigger.

So we thought back to when we were assembling the head on the block, everything was clean and new so a lump intbetween the surfaces was ruled out. But looking back we both remembered that when the head was just sitting on the block, at just the right angle you could see light from the other side. we moved the head a little to make sur it was laying flush and it seemed ok, so we torques it down.

I guess what I am getting at is for an opinion, for sure something is wrong with the head. We dont want to take it off just yet if we only need to stud the hole. btw the heads were never decked before install, only had 1500 miles on them.
Any suggestions would be great!

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Old 01-24-2005, 01:31 PM
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Some exhaust bolts run right through into the water jackets. It's normal for the coolant to come out when you remove it. Put some thread sealer on it so it won't leak.
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Old 01-24-2005, 01:42 PM
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The previous owner may have run too long a bolt into the hole and broken the back side of the hole. If that is the only place you are getting water. I would seal it with silicone sealer on a stud, as previously mentioned. Breaks like those rarely get into the port or cause major problems. It is common on some aluminum heads.
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Old 01-24-2005, 05:18 PM
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This is my engine he's talking about.

Addressing the header bolt hole: I know for a fact that these holes should not have water coming out of them (I even have pictures lol). I also know that the bolts used are not too long and are actually able to be driven all the way in.

He didn't mention that there is also a pool of water around the mid-sized head bolt that is located on the outer edge of the head (around the same cylinder). Looks like some has leaked into the crankcase.

When we put this head back on we both noticed that there was a gap between the surface of the head and the deck of the block in some spots. We could see light through these gaps, but didn't think much of it. Then we promptly forgot about this. Our current theory is that the head warped when we took it off, bent when we torqued it back on, cracked during the break-in, and expanded enough to leak coolant from the header bolt when I ran it the next day. Does this sound feasible?
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Old 01-24-2005, 06:12 PM
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The gap you saw was probably just the recessed parts of the gasket. If a head is warped bad enuff to see between the gasket and block. No way could you draw it down to even close to seal the gasket.

Did you even check the head for warp? If you can see it the head is JUNK! anything over .003 is considered bad and the worst heads are usually aluminum and at about .012 they leak like an open faucet.

Heads usually crack in combustion chambers and the center head bolt holes.
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