I fired my blazer up for the first time in a week or so yesterday and as it was cold I noticed a lot of greyish white smoke on startup which eventually cleared. She's always popped and banged through the exhaust on overrun and now despite me having done a full tune-up (plugs, leads, cap, rotor fuel and air filters and an oil change) I'm beginning to wonder if the head gasket has gone, she's always felt a little sluggish to me but then I also thik the rear brakes are sticking a little and dragging. She does use some coolant too. As she runs on both petrol (gas) and Gas (propane) that also complicates matters a little.

I guess a compression test/leakdown test will tell me for sure if the head gasket has gone or if its something more serious. How hard is it to change head gaskets on these engines? I've done em before on four cylinders but not on a six or eight although I've had the intake manifold off the small block in my pickup and I guess heads are just a few bolts away from there.

Would it be good practise to do both head gaskets or can I just do the one thats leaking? How hard is it to remove all the injection gubbins off the top of the engine as I've only really worked with carbs before. Do I need any specialist tools other than a decent torque wrench? Do the head bolts need replacing as a matter of course?

Are the heads on these engines prone to warping if they've been cooked (overheated) its never overheated on me but I don't know about the previous owner.

Can this be done in a weekend by an amateur?

 

A compression & leak-down test will definitely tell you if you have a problem with the head gasket.

If it were me, I would do both while in there. It isn't that much more work to pull the other head while you have the intake off.

As far as specialized tooling, you will need two different torque wrenches; one that is reads in in-lb and another that is capable of 75ft-lbs at a minimum. Some stubby wrenches come in handy to get the fuel lines disconnected from the back of the engine (do not try to just flex the lines away from the intake manifold, disconnect them at the firewall). Mark your distributor rotor position both fully installed and directly after lifting it ~1".

As with almost any cylinder head, if they got really hot, they can warp. It really isn't something that is very common with these heads, but it can happen. You can check them with a long machinist parallel block and a feeler gauge.

As far as how long it takes to complete the repair... That depends greatly on your level of experience and the tools you have available. It can easily be done in a day if you know what you are doing.