Milling Heads, What Surface Finish, Ra or RMS - Ford Powerstroke Diesel Forum
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Old 11-25-2011, 03:40 PM
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Milling Heads, What Surface Finish, Ra or RMS

I am in the middle of the proverbial Headstud, BPD, overhaul on my 6.0 and I am lucky enough to have a machine shop in the plant I work at.

The machinist is capable and willing to mill and/or grind my heads if needed after checking the flatness on a FARO CMM.

He suggested we could surface grind them to get them as flat as possible, but I remember reading on the SWAMPS website that they recommend a Ra 50 Surface Finish to allow the gasket to "hold".

Can anyone confirm this or even better provide an RMS number?

I tried to convert Ra to RMS but after much reading they are measuring two different ways and although you can convert them somewhat successfully, there is about a 11%-25% margin of error!

Any machinists in the house?
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Old 11-26-2011, 05:14 PM
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I don't say this to brag, or beat my chest, just to qualify this statement...I machine a few hundred sets of 6.0 heads a year. Typically ours are smoother than the factory, because of the coarse manufacturing tolerances and volume of the OEM's. Often you'll see the older graphite gaskets that require a "rougher" surface to grip, newer MLS gaksets require a very smooth RA, according to the OEM's, and nearly all gasket manufactureres. To answer your question, the ra on our heads and blocks ends up being roughly 10-20. We've seen lots and lots of heads come in that have been machined before, and 50 is waaaaaay too coarse IMO, that holds true on older graphite gaskets, but again, the MLS gaskets require very very smooth RA to allow them to do their job. The reason most heads are milled, and blocks, isn't to make them flatter... but rather to remove marks/impressions in the surface left from the head gasket. If your block hasn't been milled before (or even worse, wire wheeled, or someone used burnishing pads in the middle of a dealership head gasket job) you need to address that too...even if the head gasket surface is perfect, it means nothing without a good block surface too. Good luck

Last edited by Gearhead2012; 05-01-2014 at 08:18 AM.
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Old 11-27-2011, 10:00 AM
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So I measure one head last night, confirmed the 3.74 minimum, decided to go old school on the measuring, used the granite table, made three posts out of 1-2-3 blocks, with steel balls, shimmed them all to height, and used a surface gauge to measure the head surface which was now paralleled to the granite table. Got one set of readings, then switched the three points opposite, and confirmed the repeatability.

The head shows an arc with the center two cylinders .0025" less than the outer two, so looking at the head, fire surface up, it is dipped down at the two inner cylinders.

We will use the FARO to confirm these readings at lunch time.

I haven't checked the other head yet. If it is way out, the decision is easy,replace it, if it is "flat" or at .0025" again, risk it and run it?
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Old 11-27-2011, 10:29 AM
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They say not to mill much off of them, but we've milled as much as .008 off those, no problems, as long as your valve recession is right. Specs are .013-.027 intake and exhaust. I normally set the recession to roughly .030. Going over won't hurt at all, as long as the valve height is right. The valve height is 2.225-2.230. After they've been milled, and counting in for the block being milled, I set the valve height right around 2.220". This will provide for proper lifter preload. I'd definitely mill them while you got it off, until all the gaskets marks clean up - normally around .002-.004". Do both sides even, and make sure your valve recession is towards the high side of the specs. (.026-.030) and then set valve height to compensate, and you're good. (.2.220-2.225). New seals and freeze plugs and you're good. Trust me, the surface finish, or even .001 or even .002 warped isn't what will blow the head gaskets, only if its way way off. Also, I'd recommend using copper coat on hg's
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Old 11-27-2011, 12:02 PM
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What I am trying to avoid is all that extended machine work, I can handle the decking here at work, and even cutting down the stems is no big deal, but the seat grinding, and re installation is just something I don't want to make time for.

I set some pretty lofty goals for some mods and this overhaul to be done in one-week, I work 7 on and and then have 7 off, and this weeks on, and I had planned on having all the machine work done here, and re-install when I get back home.

So I am in limbo till I measure that other head.

How do you use the copper coat? Where does it go?

So by your last statement, .0025" would be allowable in your shop?
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Old 11-27-2011, 12:07 PM
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gearhead, have you ever seperated the layers and individually copper coated each layer?

would there be any benefit to that or have you ever heard of it?
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Old 11-27-2011, 01:06 PM
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Great info. Keeping my eye on this one.
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Old 11-27-2011, 01:27 PM
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This is some gravy info. I get to see alot of machining at my rig fab shop, and admire such precision work machinists can do. Never to late to pick up a new trade!
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Old 11-28-2011, 05:00 AM
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Quote:
Originally Posted by sinner6.0L View Post
gearhead, have you ever seperated the layers and individually copper coated each layer?

would there be any benefit to that or have you ever heard of it?
No, I never have...as I under stand it, those layers are 'supposed' to slide on one another, and i think maybe the copper coat would interfere, if you're looking for more sealing power I'd just look into o-ringed heads, but thats not really necessary unless you're talking way way high boost numbers. And advance auto sells it, you just need one can...shake well, and read directions. Basically spray evenly to both sides of gaskets right before you lay them onto a cleaned block deck surface. Then put heads on and torque as normal.

And .0025 would get milled, but we mill them all anyway. There might be one or two heads out of 100 that don't have gasket marks. While you have the heads off, I'd call around and have a valve job done, it'll cost more than a typical valve job on a set of 302 or 350 heads. I will say the guides wear out pretty bad sometimes too, and it would at least be worth taking the valves out and checking. All the most sophisticated surface finishing techniques mean nothing without the rest of the parts being top notch as well. You might also ask about putting hardened seats in the exhaust...I gaurantee you'll have at least several cracked seats. Not enough to hurt anything, or enough to go into water jackets, but probably cracked none the less.

Bottom line is if your heads are warped .002 you probably should mill them, as much for that as for the marks left by the fire ring. Your valve recession is probably .018-.020 right now, unless they've been milled before (which is another reason to check valve recession...we do lots of work for q couple local dealerships that are performing warrenty work). If you mill .003 off, you'll be .015-.018, which is right at the low side of the specs (.013-.027). There have been reports by Ford techs of valve to piston clearance problems even though the valve recession was still within range, like .017. We set ours .028-.030 and have never had problems. Good luck.
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Old 11-28-2011, 07:00 AM
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What is the advantage of using copper coat? I have a can in the garage and I've used it plenty on water pump gaskets, water neck gaskets and various other "non-critical" gaskets to prevent fluid leaks. But I consider the job of a head gasket to be much more "physical" than a typical seal gasket.

Aren't head gaskets supposed to do their job as-is? Don't you want the head and block (and gasket) perfectly free of any foreign substances? Just curious as I'm sure many install head gaskets without using any sort of coating aid.
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