reason for blown head gasket and ? about timing belt
 

hi. i have recently bought 1985.5 944 but the car smokes white smoke (previous owner stated blown head gasket).
the question is what are the reason for head gasket to blow in this typical vehicle. the engine has been rebuilt 40k miles ago.
also, how hard is it to change the head gasket on this car?
i have changed head gaskets of few car but mostly were japanese so not sure how hard porsches are.
also, how much do shops usually charge for this kind of repair?
can anything else go wrong because of this blown head gasket for this engine?

RE: reason for blown head gasket and ? about timing belt
 

Head gasket remove and replace at a shop will run probably 10 hours of labor (if i was at work, i could give you the exact book time), plus since you have to remove all the timing belt/balance shaft belt, etc to get to it, that stuff usually gets replaced as well while you are in there...Odd that the HG would go after a 40k mile rebuild, could be a defective gasket, warped head, etc. www.clarks-garage.com will walk you through the entire process (his garage shop manual) if you want to tackle it yourself.