Cracked Head

no164ford

Registered User
What is some of the causes for a SC head to crack between the intake and exhuast valves? Mine is cracked on all 3 cyl's drivers side head. Pass. side seems fine.
 
I had a right side head crack from sparkplug hole to sparkplug hole to sparkplug hole. Not sure why mine cracked either. Ruined a nicely ported head.
 
Look at the exhaust ports. Are they sooty black or gray aluminum? Perhaps it's running too lean. I wondered if mine had been milled too thin.
 
The likely 'crack-prone' areas in the head are typically areas surrounding valve seats...between the intake and exhaust seats.

Get them stitched up and you should be good to go.
 
Look at the exhaust ports. Are they sooty black or gray aluminum? Perhaps it's running too lean. I wondered if mine had been milled too thin.

They have a nice dark gray color to them, I was also thinking mabe it was milled to much? The only thing that happened on that side of the motor different from the outher is I lost a bolt out of my header flange on the 40 mile trip to the track that night and had a bad exhust leak for a few miles then the car started to surge at idle when I got to the track so I reset the computer and it seemed to run fine till the third run I heard a rattle sound that seemed to come from the rear of the car than bam!!! she blew! but all night my trap speeds were down about 5mph from normal but I just changed the gears in my rear from 3:27's to 3:73's
 
The likely 'crack-prone' areas in the head are typically areas surrounding valve seats...between the intake and exhaust seats.

Get them stitched up and you should be good to go.

I know what you are saying, But I am woundering if this is a result of heat, detonation, junk head, ect.
 
>But I am wondering if this is a result of heat, detonation, junk head, etc.

Anythings' possible...

If you are looking for a specific reason, they range from common issues such as the use of dissimilar metals used in different engine components, which can't be avoided, to the simple mistake of pouring cold water into an already hot cooling system in an effort to cool it down. Unless you know the complete history of a particular engine, this could have easily occurred in the past.

Cracked cyl. heads can also be traced to localized hot spots in an engine, which typically point to a failure of one or more cooling system components. Try to make sure that all hot spots are addressed, especially if a head gasket failed and was recently replaced. It pays to study head gaskets in an effort to pinpoint why they failed. 'Hot spots' are frequently caused by uneven expansion of engine parts, leaking/plugged/mis-routed hoses, and of course cylinder pre-ignition. I find the spark plugs to be a great source of information when these things happen as well.

If a cyl. head has warped even a small amount, it can cause cracking. Best way to avoid issues, as you may know, is to have the heads checked and decked if needed.
 
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There are many reasons that a head can crack.

The first one is with a new head that has contaminated aluminum.
This happins during the casting process. The
molten aluminum during the first part of a head casting
pour can have to high of a temp. And during the very
end of a pour, the temps of the aluminum can be to
low for the perfect head casting. Both temps during
a pour be it to high or to low , can cause the aluminum
to be contaminated.

One way to see if a head is a good or bad casting.
Is by looking at all the machined surfaces. If you
see any pitting, this is a sign of a contaminated
casting pour. Caused by the temps being high during
the first part of the pour. And then the molten aluminum
cools before the pour is completed.

Randy
 
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I know what you are saying, But I am woundering if this is a result of heat, detonation, junk head, ect.

Cracking between the seats is caused by heat. I've seen many do this and it can be repaired by pinning or welding. Pinning is less invasive and can be done without removing the seats.

Cracking by the spark plug holes is caused by detonation. The heat treat in late model (94+) heads is more susceptible to cracking.

All SC heads are "junk" in that the castings are very porous and contaminated, some worse than others.

I have effectively repaired many heads cracked both ways. You do not have to junk an otherwise good head because of a crack although I would not use a cracked head to start out with. Repairing the cracks by the spark plugs is a delicate process and must be handled correctly or the head will be totally ruined. Repairing cracks between the valve seats is much easier. I've also seen some cracks behind the seats on the outside wall. This requires welding to fix and is generally only ever found by pressure testing the heads.
 
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