machine shop /decking block

how much can be removed before there is trouble with pistons

The block should tell you...piston top at TDC...mostly folks deck the head and not the block...

If you are going to raise compression by either method isn't it better to take it off the block and just true the head...

And take a close look at clearence (eyebrow) for the valves if you do the block!
RS

If it's a 67 engine, no eyebrows...

.010"-.015" is safe usually.....if you need to take more off the block...better measure the deck height with the pistons installed to be sure.

Eyebrows are a function of head used. My '67 block has eyebrows but I ground them in 'cause I'm using a later head (and a slightly higher lift cam).

If you want to be safe you can do one of two things.

Either do some considerable cypherin' with all of the dimensions of the crank, rods, bearings pistons, etc and compare them with the dimension of the block between the existing deck height to the center line of the crank....or....

Assemble the block/crank/rod and piston and physically measure what you have to begin with.

After that you can start planning how much you want to take off the deck.

If I recall correctly Burgess has notes about this in his book. I don't have mine at hand so youuo might want to check there.

BTW: Getting this sort of thing right is the difference between "sticking a road engine together" and doing up a full out motor such as what would come out of a shop like Hap's. It is also the difference between mildly expensive and really expensive.

Jack

This is a question that I hope no one comes up with a definitive answer for, because there isn't one. It depends on what parts you have currently installed in your block, and what parts you intend to keep in that block. Basically the full engine needs to be mocked up and measured as Jack said. Then and only then can you calculate an accurate compression ratio and figure out of the deck is true, measure piston heights, and go on to cut it. Lloyd's right that you can easily cut .015" with no issues, but if you're going for high compression, there's a LOT of meat to play with. I cut roughly .100" from mine, if I recall, but that's not anywhere near a typical build.

I have made the assumption that you just wanted a 'perfect' surface to work from. Why are you so concerned about doing this to raise the compression ratio...for the street? There are many ways to skin this cat....Huffaker used to mill the block to 'pop up' the pistons and then counter bore the head...but why for the street? Like I said .010-.015" is do able with stock components and you won't need a dry build. If your purpose is to raise the compression ratio for a race motor.......you need to think the whole package...gather more information. Anything over 9.5:1 is not going to be a fun motor to live with day in day out on the street (with SU carbs and distributor ignition...even if it is Jeff's). So with an over bore, a little off the block and a little off the head....you'll have your 9.5:1 and nice gasket surfaces as well.

my 2 cents........

Read my post about confessions of a rebuild.

There you'll see that a machine shop 'accidentally' decked the virgin block so much that I now have zero deck height. Accidents happen but living with it is a problem. Why take the chance. Best to listen to the people above and save the headache.

the shop just wants to clean it up thanks for the info there not goimng to take alot this is going to be a road car its only $$$ from here,,, new moto from the bottem up... on the road sooon,,thanks