head problems on 1999 GMC Safari

Has a 4.3 liter with steel heads and block,I replaced the head gaskets and had the heads machined,it ran fine for an hour and a half then it overheated,a shop said it either had warped heads or a cracked block.I think that possibly the torque wrench i used may be bad ,if i over torqued the head bolts could this have made the head or block crack?I didnt put a whole lot of force when i tightened them down.

Asked by for the 1999 GMC Safari
the heads are cast iron. they requiring exact torque and in a specific sequence. you may have done damage by the overheating. a leak down test will tell the story. after all is fixed, you still need to find out why it overheated.

I did do it in sequence,but im not sure of the it possible for it to run for an hour and a half before this showed up?It ran perfect.Thanks for the speedy reply
the torque is very critical.
my guess is there is another issue causing the overheating. this overheating may have put you back to square 1. get it checked.

1 more answer , 1 more comment
The first thing I believe is your problem is that you don't have the right info to do this job. The torquing procedure for this engine is as follows.
You do not use the orginal head bolts. They are torque to yield head bolts. That means the final torquing is done by angle torque.

First pass, tighten all bolts in sequence shown; - 22 ft./lbs.
Final Pass using sequence shown, bolt 1; - turn 75 degrees
Bolts 2 and 3; - turn 55 degrees
Bolts 4 and 5; - turn 75 degrees
Bolts 6 and 7; - turn 55 degrees
Bolts 8 and 9; - turn 75 degrees
Bolts 10 and 11; - turn 55 degrees
Bolts 12 and 13; - turn 65 degrees

Go to and spend the $26.95 to get any factory info on your vehicle for a whole year. This is the same info that professional repair shops use.
If you had the heads done by a reputable machine shop you should be able to install new head bolts and tighten them according to the specs I gave you.
Really, $26.95 is money well worth spent. Good luck, Jim
Thanks, i might have to re do this with a good torque wrench.