Is it true that the older the head, the thicker it is.  I'm on propane,
always cracking my heads.  Other trucks in the fleet were also on
propane, different years, different makes, different models, but never
seemed to have a problem with the heads.  I've always been a fanatic
about maintaining my vehicle, changing my oil every 4000 miles, tune ups
every 6 months etc.  Finally a friend told me about his theory about the
older heads might be better, so I threw on a set of heads from a 1980,
and sure enough, "no cracked head".  My rings finally went after 200,000
kilometres, but since I got my full core exchange back, I would assume
that my 1980 heads still weren't cracked.  But guess what, my new motor,
after about 70,000 km's now have a cracked head.  Is this just a
coincidence, or do you think my friend has a point.  Any input would be
appreciated....thanx in advance...