I have a 4bt that Im rebuilding. The head gasket blew and the must have been driven for quite a while because it has a divot between the cylinders. My question is how much can be taken off the block and still use the stock head gasket?
One thing you need to check is whether your block has been decked previously. If Cummins decked it, they stamp an X or XX on the top of a pad on the exhaust side. X means it's been cut .25mm (.010") and XX is 50mm (.020"). What you have to keep an eye on is piston protrusion. Max limit for a stock gasket is in the .023-.028" range. Anything higher would require pistons to be cut or you can get a thicker gasket from Cummins. You can measure that as it currently stands to see where you're at. Any significant cut to the deck will require a thicker gasket or cut pistons or both. Also remember that this has an effect on compression ratio.
Thanks for the reply. The machine shop ended up taking .004 off. I didn't see any markings before he decked it. But should probably check anyways. Just out of curiosity, is there a formula for calculating how much the compression ratio increases per thousandth? Thanks