Decking six cylinder block with recessed bores

[llessur]

My 2500 block is currently at the machine shop for a rebore, crank grind etc. They have asked about decking the block and want me to run the head gasket into them so that they can see how this will affect the recessed bores.

Before I do, what are the general thoughts on decking the recessed bore blocks? I'll go in and have a chat with them about whether or not it's really required but thought I'd ask here first. Is this likely to cause problems with sealing of the gasket? Does any block decking need to be accompanied by a corresponding shaving of the pistons to maintain compression ratio?

This is my first full rebuild so whilst I'd like to pretend I know what I'm talking about, I don't really :)

[Pete Lewis]

i think you need to ask why they feel the block needs decking 

if its a few thou to just get a clean surface or theres some distotion they have found 

if you drop the recess you may need to add a slight chamfer to the crown to avoid contact

[Nick Jones]

As Pete says..... Possibly it’s just “standard procedure” (habit) at the machine shop, who are used to flat blocks.

That said, it is possible to take a very light cut (say 3 thou or less) without needing to worry about the recesses. I had this done when I had my PI engine machined a few years back. Not sure what the number was now but the engine number was still clearly visible afterwards.

You certainly don’t need to worry about decking pistons. You have to machine the recess completely off before that comes into play!

Nick