I THINK I KILLED THE 340

spd691 said
Here is the deal. I bought a 73 Dart Sport 340 car. It has a 69 340 in it with X heads. I had a bent valve and other issues that needed addressing so I took it out. I decided to "freshen it up". I took it out and apart. Found bent intake valve and heads needed rebuilding. I decided I would put a set of closed chambered aluminums on and set the quench to .040 with gaskets and if needed crown machining. The deck didn't look so good, very grainy, so I sent it out for decking. Crank was .020 under on the mains and .030 under on the rods and looked nice. Home polished it miked it, good to go, pistons are .030 over and look great even the timing chain was tight. I had one odd ball rod so I bought a set of "H" beams in stock length. I was told the block was twisted and a special fixture was needed to deck it properly. I told him its the only block I have so make it right. When I picked it up I asked how much was removed. His reply was which end? I had a sinking feeling... Fast forward to today. I was doing my mock up to see where I stood to get the quench I was after. I measured the piston to deck before I disassembled it. It was +.018.

Now the problem. After carefully measuring the deck and triple checking it and inline with the wrist pin, checking the rock, I think I'm screwed. I am way out of the hole now (see pics). With a .040 gasket I would need to remove .040 off the top of the pistons. Seems like to much. Then I may have a problem with the valve pockets. I already own the heads so... Any ideas you motor heads could throw my way would be REALLY appreciated. I don't want to source a another block. But the car must live on. (I soda blast the top of one of the pistons)

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Couple things. As mentioned a thicker head gasket could be your answer.

As to your question how much was the block cut. It isn't really the right question.

Your machinist is right that the twisted block would require taking more off one end than the other to bring the deck in parallel to the crank. Likely needed more of one side of the deck than the other as well if twisted.

The real question is what is the new deck height? You need this measured from the crank centerline. I wouldn't assume the guy did anything wrong unless that measurement is off between ends of the same bank or from one bank to another.

I would also want to know why the positive deck height of the pistons was higher on some cylinders than others. Did your machinist assemble the short block or did you? Who measured the rod length and piston compression height? Was the crank indexed? I would suggest swapping a couple piston and rod assemblies from the same side IE the .040 proud one for a .034 proud one to see if that would bring the heights closer together. Entirely possible that tolerance stack of parts could be the difference and not anything that the machinist did wrong.

Another possible solution would be to run a set of the 340 edelbrock heads that have a chamber relief cut.

If you are going to have to cut pistons for valve clearance anyway you might want to shop for pistons instead at that point. Get a newer lighter piston with narrower rings rather than spending money on the old used TRW heavy pistons you have to cut deck height and valve clearance.