Halden wrote:blammogarage wrote:Got some bad news today from the machine shop. They magnafluxed it and discovered my head has 2 cracks in it.
Where are the cracks in the head. These engines tend to crack between the valve seats, which I would not worry so much about, no coolant runs above them. Lots of these engines running around with cracks in that area.
If this engine has liners in it already it has been rebuilt once in it's life. These are parent bore engines, no sleeves from the factory. Unless maybe it is a gen 3 block? I don't know if those by any chance came sleeved. They were warranty replacements. To remove, weld a bead around them let it cool and they should come out much easier...
When putting in new sleeves DO NOT use sleeve retaining compound!
Halden & All - -
Actually, coolant passages do run under the valve seat cracks. Jerry says these cracks generally do not go through to the coolant passages, but they possibly can. Here is a photo (taken by a member that I cannot remember) of a head that has been cross sectioned right between the valves. You can see that the head is quite thick under the valve seats and hopefully a crack would not make it all the way through.
However, The AERA Technical Committee (an engine rebuilders association) has a bulletin that talks to this. Here it is as posted by Steve PT in 2009. Click images for larger, clearer view.
I have implemented this repair on two turbo heads that had significant cracks, although they were not known to leak there.
Here are some photos of some steps in the process. Not necessarily comprehensive but should give an idea of the job.