How much can I machine my head surface?

Sep 17, 2018
QLD, Australia
Hi all, this forum has been a great resource for me but I've now reached unfamiliar territory with my rig so here is my first post. I've just pulled the head off my 1HDT to do the head gasket (was pressurising the cooling system) and when I had the head machined the shop took 0.43mm (0.017") off to get it flat. In my mind this is a LOT and would bring the valves dangerously close to contacting the pistons.

So I am wondering, what is the most people have machined off their head without running into issues with valve contact? I measured piston protrusion at about 0.55mm (0.022") which is the upper limit according to the FSM and doesn't leave me much room to play with, even using the thickest 5 notch gasket.

Also, even if the head has been machined flat, is it worth using if it has been so badly warped? I was told that the cam tunnel looks ok but in my opinion the cam bearing shell has signs of wear on one side (will try to get some pics), could this be a consequence of warpage?

The shop has charged ~500AUD for the work which will be frustrating if I have to turf the head. Would I be correct in thinking that most places would at least put a straight edge on the head before spending $$$ on machining and crack testing? I'd like to get my facts straight before I go in and see them next.

I hope this all makes sense, when I bought this car I had no mechanical experience so I searched for something in good shape with low k's and had it looked at by a mechanic to avoid this kind of thing, yet here I am!
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