Head Decking

[junglgoast]

how much can i have taken off my heads? i am rebuilding a 91 3.4 dohc. (olds cutlass supreme int.) looking for any help i can find on this.

thanks
steve

[Anonymous]

I do not know how much the shop took off mine, but he decked them, and combined with the new psitons gave me 9.75:1 C/R, and I do notice it. It is definately faster and has soooo much low end. It will smoke them if I punch it from 2k rpm.

[sd_iconoclast]

I need to know the same thing. I also wanted to know how much I can take off the block. I am taking a an automotive machining class and we must have this info somewhere. I will try to find out and get back.
I also wonder if we can correct for head/block milling with a thicker gasket between the heads and the cam carriers. Does anyone know if this is possible or even necessary?

[GPXSS]

Unless you are in a racing environment and can pay for rebuilds and new heads every so often, Id suggest not decking your heads any more than whats required to get them completely flat. The more material you remove, the more chances you have of them warping.

With the block however, you can go as far as you'd like really, but you start needing to machine the intake manifold to get proper sealing. You also end up with the pistons prodruding from the block, and you will absolutley have to check piston to valve clearance. You can get "head shims" to raise the had back up, but they aren't the best when it comes to sealing.

[Streetrodder83]

Usually you can go up to .020" on the block or heads before, you need to start, machining off the intake manifold. If you're just looking to take off any warpage you usually don't need to go much more than .005". Like GPXSS said, if you get too radical on machining piston to valve clearance becomes a real issue. First thing to do is find out what the clearance is to begin with, if you are looking for alittle more compression. Zero decking the block would be the way to go, meaning the piston comes flush with the block deck at TDC, being that there is sufficient clearance.

[sd_iconoclast]

You can get "head shims" to raise the had back up, but they aren't the best when it comes to sealing.

I do not know what you mean by "head shims". I am suggesting placing a shim between the head and the cam carrier to restore the correct height of the cams after milling the head or deck. It seems to me that sealing would not be much of an issue here as this area is not exposed to combustion chamber pressure. Do just mean sealing against oil leaks?

I am also unfamiliar with how the relationship between each cam gear and cam is set. I have heard that this relationship is infinitely variable. If so, shimming might not even be necessary.

[3.4Z24]

why would milling the head affect cam height? and what does that have to do with the adjustable cam gears?

on a pushrod engine, pushrod length or valve stem height need to be changed unless it has adjustable rocker arms(within limits) when an excessive amount of decking is done to either the head or block.


the only thing i see needing done(besides checking piston and valve clearances) is watching the tensioner pulley travel and machining the intake to mate correctly to the heads.

[Anonymous]

I thought Caviliers were Z24s not Z34s

[GPXSS]

I do not know what you mean by "head shims". I am suggesting placing a shim between the head and the cam carrier to restore the correct height of the cams after milling the head or deck.

My bad, thought you meant between the head and block. If you shim the cam carrier above the head, you will be losing valve lift.. since the cams push down direclty onto the valves, and you will also throw off the preload (bad idea..) I don't think it would be too much of a big deal as far as timing is concerned, if you bring the cams closer to the block, timing will be retarded just a bit, but you can compensate by timing the cams.

[sd_iconoclast]

Just to make sure we are all on the same page:

Milling the block or heads will make the distance from the center of the crank to the center of the cams (on the milled side) shorter. This will mean that the cam belt tensioner will take up a little more belt tension, thus changinging the relationship of the crank gear and the cam gears.
I guess my question coms down to how finely one can adjust the cam timing, presumably by setting the relationship between the cams and their associated cam gears. If this relationship is infinitely adjustable, you can correct for any error introduced by retiming the cams. If you can only adjust the relationship in (for instance) 10 degree increments, then you probably cannot correct for the error.
How is the relationship between the cam and cam gear set?

[GPXSS]

it is infinitly adjustable since there is no locating tooth or groove on the cams or gears. You just have to somehow figure out how far to turn them before you tighten the cam gear nut.

[sd_iconoclast]

That's a relief. It sounds to me like cam timing is not an issue in milling heads or block.

[jeremy96gase]

I thought Caviliers were Z24s not Z34s

He's got a 3.4DOHC in his cavi.

[SappySE107]

If you are worried about making the engine interference, you can take off .012" from one source, and according the machine shop near me, 4 times that.

[junglgoast]

compression ratio

thanks for all the comments..
are there any specifics on the compression ratio advantage to removed material? i bought the 91 olds for $500. it has 124k on it and has all maintainance records with it. it has been very well maintained. i am rebuilding the bottom end just so i do not have to do it later. i am looking for ways to get a few more ponies out of it, just to 250-275. it has a new 4t60e, new injectors and timing gear. i am selling my 94 z24 conv after i get this one complete. "gotta love 60degrees"

thanks
steve