Would anyone know if having a cylinderhead machined/plained raise or lower the compression?

TIY

 

Raises compression, but only a little. The amount usually needed in a rebuild will make maybe .1 or so increase.

 

This techniquie is called "milling". and in reality you can mill any amount within the service limit of the head.
There are different milling limits for different heads.

 

think about what youre doing, lowering the volume between piston and CC at TDC. since its the ratio of TDC volume to BDC volume then yes it raises comp. since theres a smaller numerator

 

Unless you're building a motor specifically for some purpose that requires milling, I'd recommend not doing it too much. Look into a thinner head gasket and higher compression pistons, they can always be undone, but milling can't.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Kendall &raquo;</TD></TR><TR><TD CLASS="quote">Unless you're building a motor specifically for some purpose that requires milling, I'd recommend not doing it too much. Look into a thinner head gasket and higher compression pistons, they can always be undone, but milling can't.</TD></TR></TABLE>
I agree with this.
Milling is usually done to clean up or repair a damaged mating surface on the face of the head. Like a last resort. It's not really a recomended technique for changing CR. There are a couple a couple of drawbacks to it, and there are better ways to change CR.

 

Very little is being machined. Dealer will be doing it cause the headgasket has to be replaced.

So, really there is no disadvantage for my head to be machined?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Darryl Musashi &raquo;</TD></TR><TR><TD CLASS="quote">Very little is being machined. Dealer will be doing it cause the headgasket has to be replaced.

So, really there is no disadvantage for my head to be machined?</TD></TR></TABLE>

In that case go with it. Milling the head for the purpose of sealing the head gasket is a good thing.

 

If the dealer's having a quality machine shop do it, I wouldn't worry too much about having your head milled. I had my head milled after a blown head gasket. No problems so far. Felt more torquey afterwards, though.

 

you also need cam gears if you gonna mill, since it changes cam timming