How can i know fore sure if head has been milled

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Wrencher

Wrencher

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Greetings,

I am toying around with the idea of pulling the head off my engine to fix some broken intake studs and while it's down ill probably put a timing chain in, go ahead and drop the electronic ignition and hei setup in, and give the engine a good once over to make sure it stays mechanically sound. I'm not having any problems other than leaky exhaust and a little oil consumption. My grandfather told me he had the engine rebuilt years ago, and i dont know if the builder had the head machined at that time.

Is there any way to know for sure that the head has indeed been milled at some point in its history?
As a follow up question, while the head is off would it be wise to have the head milled on an otherwise stock engine with a Holley 2300 2-barrel? I'm leaning toward doing it at the moment as i see no real downside. Thank you.
 
..............If its been milled u will be able to see the circular pattern on it........I presume u have adjustable rocker arms, u may need shorter pushrods depending on how much u take off.........kim....
 
I wouldn't even worry about it being milled, before. While the head is off, cc the combustion chambers, measure the deck hight, and new head gasket thickness. Then figure out what cc's you need to get about 9.0-1 compression ratio. Subtract the required cc's from what the head has now, multiply that cc by .0066. That will tell you how much to mill the head. There is no downside to milling the head to achive a CR between 8.5 and 9.0 -1. I like closer to 9-1 on a street car. If installing a hotter cam, and willing to modify the distributer curve, you can go higher.

PS: I have measured several stock heads, and they measure between 3.595 to 3.606 from valve cover surface, and head surface.
 
Milling would be a good thing. The procedure above is the way to go. Make sure to include the head gasket thickness; the newer thicker head gaskets these days will require you to mill about .020" just to keep the same old CR. (It would be hard to say what head gasket was put in there at the prior rebuild.) Milling/lowering the head .050" or even more form its original height will be easily adjusted out by the adjusters with no pushrod changes; not sure how much more you can go with the original push rods but it is some more.

The only downside would be if the rings are old and tired and the higher compression pushed more blowby into the crankcase. Hard to say if your oil use is due to oil rings or valve seals. With the head off, makes sure you have the guides and vlave stems checked and renewed if needed. And check the block surface whiel you are at it just to make sure it is not too far out of straight.

9:1 CR (or even apporaching that) will really make a difference for you. If the timing chain is stretched enough, you will see an improvement just putting a new one in and getting the cam back in time.
 
I just saw an interesting youtube video where the guy (SoCal homeboy) levels an aluminum head to 1 mil using sandpaper on a glass backing. Not so easy on cast iron. Anyway, he points to the depressed spots on head with a rough casting surface and says as long as you don't remove past that, you haven't over-milled the surface. I always wondered what those spots were for. I can't recall if I saw them on an old Mopar cast-iron head. Somebody here may know.
 
I was given a head that had been shaved 0.120 (not a typo) and according to the Mopar Performance book, this raises compression by about 2 points. I put it on a stock slant six in a 65 Belvedere with about 60,000 miles. I shimmed the rocker shaft to give me more room to adjust the valve clearance. It pings a little with 89 octane gas, but there was a noticeable difference. I am going to put a super six intake setup on it and just goof around with it. I have nothing to lose as the engine is being replaced this spring with a big block.
 
I think my machinist bud told me that theres flat spots that are measurement pads around the outside. So a machinist could tell if they have been milled.
 
Back to the OP...
Generally, machine shops will only mill just enough to make things flat, unless otherwise specified. Slant six heads aren't generally known for warpage, so I would be surprised if they took more than 0.010 off it.
 
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