Heads milled....er, maybe!?

How can I tell if the heads on my...well, any engine for that matter, have been milled before? Is there some kind of milling pattern visable that wouldn't be on factory fresh heads? Some way to measure head thickness (yea, long shot on that last one). Anything? Thanks.

Measure the cc's of the chambers maybe....and compare them to the advertised. If it's more than 5cc's less, it's likely been milled. Usually the tolerances are higher cc's than rated, but there's no hard fast rule.

Cris

There is also a micrometer that measures the thickness of the mating surface of the head. Most machine shops have them and they can tell you just how much has been milled off the surfaces of your head.
Bottom, intake and exhaust sides can all be milled - usually only the intake and bottoms are milled but I have seen the exhaust sides milled to fix burn scores.
Paul

Thanks Paul, interesting. I had wondered about a micrometer reading of some kind, but what point woulkd you reference it to? The valve cover rail? The bottom of the port openings? And I've never seen references to what is the stock measurement. Cris's idea sounds reasonable, although in experience I've found that chamber volume varies considerably from that advertized, even on chambers in the same head.
I heard somewhere that milled heads usually show a pattern on the milled surface different from the stock (unmilled) appearance, but I have no examples of what that would look like. I'll ask the local shops about the micrometer idea.

i heard the same about the surface looks diffrent from milling
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Here you go.

I work in a machine shop on a daily basis so I can get free machine work for myself... Anyhow, The top drawing represents 99% of the stock milled heads I've seen, and the lower drawing represents what a machinist's millwork looks like. The lines are much closer and shallower than stock milling.

I can elaborate on why if required but this should do... It's a good indication but not 100% accurate, some Foundry's where heads are made do not cook them out as fast as possible and therefore leave a nicer milled surface.


FE


[addsig]

Thanks FE, I thought there might be something like this out there. Thanks everyone! I have a set of heads that I want to mill for a compression increase, but I suspect they may have been milled before, and I don't want too much compression! I think all this will help.

lol... FE, i have never seen someone draw a picture, and then take a picture of it.

But it works! [img]/forums/images/smiles/icon_tup.gif[/img]

Hell yeah! [img]/forums/images/smiles/icon_tup.gif[/img]
[addsig]

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On 2006-11-11 14:51, polkat wrote:
Thanks FE, I thought there might be something like this out there. Thanks everyone! I have a set of heads that I want to mill for a compression increase, but I suspect they may have been milled before, and I don't want too much compression! I think all this will help.
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My advice here is pretty important I think. If you're planning on milling them, regardless of whether they have been milled before, you NEED to cc the chambers. This becomes MUCH more important if they'd already been milled, but either way you'll need the baseline cc's to know what has been taken off. Without that you'll never figure the compression correctly.

Cris