Obviuosly it depends on how much has been skimmed off, but I just wondered how much difference it actually makes?
If say you take an average head skim thats been done not because of damage to the face but just a routine skim as you would do when building up a new engine, and the same for the block is it actually enough to measurably effect your CR?
Will it for example increase 7.5:1 to 7.6:1 or 8.0:1 or is it nothing really measurable?

Cheers!

 

Not that this really helps, but my dad took -60 thou off a head when he was in his teens working for his aprenticeship. he bolted it onto his pre x-flow cortina and it kept poppnig spark plugs out aparently

so for reference.... - 60 thou is too much

 

Lol thats roughly 1.5mm (i think) so quite a lot!

To be honest Karlos, i would be surprised if your block actually needed decking.... i guess if you wanted to do your head you could, but i would put it on an engineers surface first to see if it actually needs doing...... never remove material that you dont have to!

however a few thou off of each shouldn't cause any nasty problems with cr.....

Rob,

 

his CR is a little too low for what he wants, so decking the block a bit won't do any harm.
i'd get the bottom end built up with a piston and then fit the head with a headgasket loosely.
fill with parafin and check the CR, then adjust as necessary.

 

true... but decking the block too much will mean slight machining to pistons as well......

 

or get the faces lapped properly
same as decking but takes next to nothing off

 

I would think it would change the cr but that would depend on how much you get took off. I had the head and block skimmed when i build my new engine.
I would get the block and head skimmed then when you work out what cr you want then get the pistons done
here is my engine
nov09092.jpg?t=1262722765
nov09095.jpg?t=1262723482

 

Yeah i've already had my block decked, and my head has been skimmed twice in it's life I was just wondering how much that would effect the CR my pistons are 7.5:1 so there is plenty of overhead?
They were only skimmed ready for rebuilding so I would guess around 2/3 thou was taken off each time totalling 6/9 thou (0.15/0.23mm).