Is there any reason why

Dakman

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When the head is off you only mill the head and not it's opposite mating surface ?
 
When the head is off you only mill the head and not it's opposite mating surface ?

The cylinder is a better made surface. The head is the one you are concerned as it tends to be warped from the factory. I do both because I already have the cylinder off. You need to remove the cylinder to check for broken rings, re-tap the stud holes and install a better grade of studs, all at the same time before installing the engine.
 
well, in this case (these engines) Al is correct. You need to worry about the head more than the cylinder.
On a car engine you can "deck" the block, meaning mill down the top of it where the cylinder heads bolt on. You can also mill the heads, same as with these engines.
when you mill the heads on a car engine, it's adviseable to deck the block so that you have a 100% true mating surface for the heads. but you can deck the block just to get it true, not to remove so much matierial to raise the compression. Milling the heads is where you take off more material to bump up the compression.
The problem with decking a v-8 block more than enough to just get the mating surface trued up, is that taking too much off the block will lower the mating surface of the intake manifold. This requires thicker intake manifold gaskets to get the intake manifold back up to it's original position. The intake manifold will sit lower and the intake ports on the heads and intake manifold will not line up correctly.
but on these engines, there isn't as much involved, and milling the head is all you need to do really.
 
unless some dodgy asian at the factory happens to leave this dirty great gouge in the cylinder top that causes the head gasket to blow, but thats another story and not normal... :)
 
You took your head off, now you need a torque wrench to put it back on properly.

I torque all my 66cc engine heads to 20#, 5# at a time in an X pattern.
 
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