Milling small block heads
#1
Milling small block heads
In bill traVato's book he said he has ccut heads as much as .1, I think that was that was on big block heads. Wonderng if small block heads with take that much as well, not that I'm trying to go that far.
#2
Sure, but you will have to account for the valvetrain being slightly longer (change to shorter pushrods, use adjustable rockers, or shim rocker pivots if it's not a highly stressed engine) and for the loss of combustion chamber volume (depending on pistons, original chamber size, etc.).
- Eric
- Eric
#4
Why use the Felpro's? You can purchase Cometic head gaskets and avoid milling the heads (if that is the only reason you have to mill)? Cometic gaskets come in various thicknesses, most certainly less than the Felpro's. Seems like I recall Cometic making a .028 thick head gasket for Olds..
#5
Why use the Felpro's? You can purchase Cometic head gaskets and avoid milling the heads (if that is the only reason you have to mill)? Cometic gaskets come in various thicknesses, most certainly less than the Felpro's. Seems like I recall Cometic making a .028 thick head gasket for Olds..
I know you can go .060" on either big block or small block with no sealing issues. I have personally never went further than that, but I have heard of others doing .100" with success.
#6
If all you are doing is taking up for the change in gasket thickness, then you're not really changing anything.
Original gasket ~0.016", FelPro Gasket ~0.043", if you mill the heads 0.027" you're right where you started.
- Eric
Original gasket ~0.016", FelPro Gasket ~0.043", if you mill the heads 0.027" you're right where you started.
- Eric
#7
My question is if you go .028 gasket how much compression are you gaining over the .043 gaskets if you are using flat top pistons at zero deck? Is it really that much of a difference?
#8
Your profile shows a '68 Delta Custom, which should have a 455, and a couple of earlier F-85s, which should have either 330s or 215s (I don't recall the years you listed).
Figuring a 350, if you have a 1968 high compression (10.25:1) 350, it should have a 6cc dish and a 0.016" head gasket, with about a 0.020" deck height and an average 68cc combustion chamber, which would give you an actual static 9.78:1 compression ratio.
Changing the head gasket to a 0.045" FelPro will change the CR to 9.16:1, a change of about 0.6:1.
- Eric
#9
I'm trying to gain compression. I already have the felpros and I can get the heads milled for about the price of smitty's .011 gasket which won't give me as much as milling with the felpros.
#11
I do thanks you for your help, but I'm not asking for help building an engine I just want to know how far I can safely cut a pair of small block heads. But it is a 350, I have a cam but will only use it if I can get the intake I want, which will also be the deciding factor on pulling the heads to get them milled
#12
It's not that I don't need or like help, I just already know what I want and have most of the pieces. I just need to know what the safe limit is on cutting sbo heads so I know If I can get what I want out of what I have
Last edited by young olds; January 26th, 2015 at 08:34 PM. Reason: posted on my ipod
#13
Sure, cut 'em down.
There comes a point where you will also have to mlll the intake (or mill the intake side of the heads, up to a point), but if I recall, you can usually get away with 0.100".
Just be sure to re-measure and re-calculate valve train length, and be sure that you've got enough valve clearance if you're going high crown or high lift.
- Eric
There comes a point where you will also have to mlll the intake (or mill the intake side of the heads, up to a point), but if I recall, you can usually get away with 0.100".
Just be sure to re-measure and re-calculate valve train length, and be sure that you've got enough valve clearance if you're going high crown or high lift.
- Eric
#17
"Wow isn't .1 a LOT?! Makes me feel better about the.050"
can we please use thousanths of an inch to discuss such things? All three decimal places, even if they are zeros.
.050 [fifty thou]
0.100 [a hundred thou]
0.030 for pistons, etc. [thirty]
thanks
can we please use thousanths of an inch to discuss such things? All three decimal places, even if they are zeros.
.050 [fifty thou]
0.100 [a hundred thou]
0.030 for pistons, etc. [thirty]
thanks
#19
Why? A tenth is a tenth
#20
#22
#23
Ever work aircraft? .10 tenth also .100 hundred thousandths i don't care how you slice it dice it!! You guys need to quit being so condescending.
#26
Haha first search "proformance" was money.
I think I might be better off getting the thin gaskets, I just read some #4 heads are more towards 61cc than 64+ you'd expect w factory tolerances. If this is the case they may be worth more in the end uncut.
Plus with a thin gasket I'm still getting a compression bump.
Only question.... Will Smitty's gasket seal 100% on a used block w the fresh heads. Felpros will.
I think I might be better off getting the thin gaskets, I just read some #4 heads are more towards 61cc than 64+ you'd expect w factory tolerances. If this is the case they may be worth more in the end uncut.
Plus with a thin gasket I'm still getting a compression bump.
Only question.... Will Smitty's gasket seal 100% on a used block w the fresh heads. Felpros will.
#27
http://www.shopengineparts.com/parts...403+%26+455+V8
They come in .027, .030, .036, .040, .045, .051, .056 thicknesses to tailor your compression ratio.
Last edited by cdrod; March 6th, 2015 at 07:57 AM.
#29
#32
Yeah, between the very thin head gasket and manufacturing tolerances that tended to make the combustion chambers on the large side (higher-than-specified compression = detonation, early engine destruction, and warranty claims, while lower-than-specified compression = no problem at all), there is generally plenty of room to mill the heads, so long as you then adjust for the needed change in pushrod length.
- Eric
- Eric
#33
And pray tell, how does one do that? Is there a procedure I can look up to learn more about it?
W my pistons .028 deep and all things set I will be just right about at 8.9:1 w the mill job. Totally just what I was going for in the first place when I got the 64cc heads
W my pistons .028 deep and all things set I will be just right about at 8.9:1 w the mill job. Totally just what I was going for in the first place when I got the 64cc heads
#34
The simplest way would be to simply calculate the difference in the height of the heads considering the milling and the thickness of the new head gasket.
If you aren't changing other aspects of the valve train, this will probably work well enough.
The right way is to use an adjustable checking pushrod with weak testing valve springs to measure the right height, and, if you are using roller rockers, to get the center of the rollers' contact point in the center of the valve stem face.
There are instructions for this all over the internet, and recent discussion of it on this board.
- Eric
#37
If the stock head gasket was 0.016" and the new head gasket is 0.040", and you mill the heads 0.055", then you are adding 0.024" (0.040-0.016=0.024) in height, from which you are subtracting 0.055", so 0.055-0.024=0.031" lower, which, if you are using stock hydraulic lifters and valvetrain, may not require any adjustments...
... BUT, since you are installing a new cam and lifters, even though they are theoretically the same dimensions as the originals, you would be wise to check.
Since the dimensions should be close, you may be able to get away with just assembling it, running it to get the lifters properly pumped up, and then using the known thread pitch of the rocker pedestal screws (18 per inch or 0.556" per turn) to indirectly measure lifter preload. Considering the 1.6:1 rocker arm ratio, every ⅓ of a turn of the rocker screw will correspond to 0.029" of movement at the pushrod, and since the desired lifter preload is usually given as 0.030-0.060" (I've never seen any one "definitive" number), that means that:
If you place a cylinder at TDC compression and you loosen the rocker screws, then tighten until the pushrod is just making contact with the rocker, then tighten another half a turn or so until the screw bottoms, that valve is adjusted correctly.
If it takes over ¾ of a turn before it bottoms, your preload is a bit deep, indicating a need for a shorter pushrod (or, if you're not going to overstress the engine, shimming the rocker pedestal).
If it takes less than ⅓ of a turn, it's a bit shallow, and you need a longer pushrod (milling the rocker pedestals is possible, but doesn't make much sense unless you've got a milling machine).
- Eric
... BUT, since you are installing a new cam and lifters, even though they are theoretically the same dimensions as the originals, you would be wise to check.
Since the dimensions should be close, you may be able to get away with just assembling it, running it to get the lifters properly pumped up, and then using the known thread pitch of the rocker pedestal screws (18 per inch or 0.556" per turn) to indirectly measure lifter preload. Considering the 1.6:1 rocker arm ratio, every ⅓ of a turn of the rocker screw will correspond to 0.029" of movement at the pushrod, and since the desired lifter preload is usually given as 0.030-0.060" (I've never seen any one "definitive" number), that means that:
If you place a cylinder at TDC compression and you loosen the rocker screws, then tighten until the pushrod is just making contact with the rocker, then tighten another half a turn or so until the screw bottoms, that valve is adjusted correctly.
If it takes over ¾ of a turn before it bottoms, your preload is a bit deep, indicating a need for a shorter pushrod (or, if you're not going to overstress the engine, shimming the rocker pedestal).
If it takes less than ⅓ of a turn, it's a bit shallow, and you need a longer pushrod (milling the rocker pedestals is possible, but doesn't make much sense unless you've got a milling machine).
- Eric
#38
FWIW- I have a set of #6 W-31 heads. They were bare when I got them. I milled the heads 0.030" to clean up the head gasket surfaces. The combustion chambers were cc'd after all work (new valves, guides, welded center dividers, etc). My set measured 60 cc combustion chambers.
#39
OK Eric, roger on that. We did that on my dad's Starfire back in the day.
So if I put some petroleum jelly along the valves to seal em closed and I level the sealing surface of the head then if I fill the chamber w liquid from a 100cc syringe I should be able to measure the chamber volume, correct?
I've heard some 4 heads error on the side of being smaller, multiple sources (2) claiming 61cc stock production volume, the opposite of what you'd expect from a production tolerance. (64 stock)
I got .31 too guess I remember SOME maths though
So if I put some petroleum jelly along the valves to seal em closed and I level the sealing surface of the head then if I fill the chamber w liquid from a 100cc syringe I should be able to measure the chamber volume, correct?
I've heard some 4 heads error on the side of being smaller, multiple sources (2) claiming 61cc stock production volume, the opposite of what you'd expect from a production tolerance. (64 stock)
I got .31 too guess I remember SOME maths though
#40
Wait I was crossed up from too much reading. Scratch that last bit the heads are already 60cc huh. I need to take a break from this car thing my head is spinning.
Good thing tomorrow is a work day all this theory is buggin me out
2 sources did quote 61cc which makes perfect sense
Good thing tomorrow is a work day all this theory is buggin me out
2 sources did quote 61cc which makes perfect sense