Have just removed head on my 03 wrx wagon to replace head gasket and have noticed both heads have cracks around spark plugs ,
Has any one else had this problem and will they be ok to use again or should I find some new ones ?

 

I read that these cracks are quite common. However i couldn't possibly say if they are ok to still use. Might be worth looking for another set.

 

It's toasted the valves as well

 

Valves seemed ok to me , had good compression (crack doesn't go into valve seat)

 

mine was a lot more cracked, but i only found out at rebuild time, and i didn't rebuild due to a failure, car was still running good. I have been told that these are common. I got another set though

Wrong torque setting on plugs can cause this and too much heat - but if you ask me it is the material itself which is not the best.

 

Think I'm going to reuse them again then , as it was running fine (apart from head gasket issue) ,
Thanks

 

unless its just how the pic looks you can see chunks out of the edges

 

These cracks are very common, but that crack looks very close to the valve seat, although it could just be the camera angle.
If the crack goes more than 5 or 6 threads deep into the plug hole it will be getting close to the water jacket.

 

The cracks are caused by the spark plug being 'shy' of approx 3 to 4 threads when tight - the open threads are then exposed to the flame front and eventually crack.

Provided the cracks dont go under the valve seat,then they are generally ok to reuse.
If you have a good set of heads without cracks, then its wise to have the spark plug seats on the heads machined so the spark plugs have full engagement in the threads.

Mick

 

How is that done? The unused threaded part drilled to make a slightly larger smooth bore hole? Do you chamfer the edge? I have a used set and would like to stop them cracking in the future.

 

No, not machined on the combustion chamber side - it's done on the opposite side where the spark plug tightens onto the head.
Material is machined off that face to allow the spark plug thread to come through flush and engage/use the open threads on the combustion chamber side.

Standard practice on the GRP N engines.

Hope this helps.

Mick