You mean "heads" and ".008", right?

I heard this and read this from several different sources. All I can do is hope there is a reason other than the amount "milled" (like the machinist).

Again, I believe the machinist is the key and hope the machinist that milled my heads knew his trade.

 

Wow, thanks for the great replies, never expected this much!

This sounds like good advise.

My local machinist is an old timer that's been doing this for a long time, in the back of the local NAPA store. He was also recommended by the local diesel shop & Ford dealer whom I've been consulting with. I have as much trust in him as one could.

In my line of work, doing precision measurements (micron level at a tier 1 automotive supplier) and gage calibration, it makes me wonder how he obtained his number of .008". At this point I'm assuming that from the point in which his cutter made contact with the head, he had to dial it down .008" until it cleaned up the surface, so how accurate is his milling machine?
In precision measurements there is a thing called "Uncertainty of Measurement" which basically states a range that the true value could be within. So when the machinist says .008" and the uncertainty is unknown, the true value could be between .007 & .009" (or worse). This is why it would be nice to be able to take other measurements to verify this, say from the head gasket surface to the riser surface or whatever there is a spec for. I watched the machinist use a depth indicator from the head gasket surface to the valves and he pronounced them good. I do not know what the value was that he was getting.
Maybe I'm getting too wrapped up in the actual number, since everyone here, my local diesel mechanic, RCD saleman and the machinist have all pronounced it good. I probably just need to quit sweatin' it.

Thanks again to everyone for making me more at ease with this!!

 

^^ True and very important point. Monty may be just fine with his .014 heads, your neighbor down the street may cut his .020 with no problems and yours may fail at .012. Any machine work on a head (no matter how skilled the machinist) can change internal stresses and create stress risers that weren't there in in the original casting. I suspect the .008 figure is an effort to have a safe figure for everybody. I wouldn't be surprised for someone to post their heads were cut .005 and cracked.

Another point is 99% of machinists aren't going to take the time to set-up and measure the entire surface of the head before and remeasure after. They know how much they dropped the cutter on each pass, add it up and pass that number on to the customer. Usually they'll find the high spot drop a couple of thou and make a pass. The first pass is a cut. How much? Depends on where you measure unless the head was flat to start with and your set up was perfect.

If I recall correctly the original limit for head surfacing was 0.000 wasn't it? And if it was warped more than 0.003 Ford Replaced it? I think that says something about their assessment of the quality/design of these castings.

With a compression ratio of 18:1 the squish area is pretty small, surfacing the head will raise c/r quickly. I don't know but I suspect that could raise emissions and that may have been a consideration when coming up with a "max" number.

The shorter pushrods change the dimension between the plunger inside the lifter in relation to the oil hole on the body. More time for oil to enter the lifter, plunger hits oil sooner and effective lift/duration is INCREASED (well, more correctly stated Maximized). I know that sounds backwards but consider when using PolyLocks on a drag racing engine with hydraulic lifters, preload is set to a minimum. Just barely get it to quit clacking and lock it down.

 

Rusty you are right in line with my thinking,my friend Kenny has a machine shop,with that I get to play with all the toys there.He showed me how to to these heads the right way,thats why I said what I said,also if the head is cut more than 8 thou the valves should be cut in the shoulder and the stem that will stop alot of the valve to piston issues. but like I said it's just cast iron and each pour is different,including the mix of metals

 

Well, I took a drive to a reputable machine shop here. I was told they do 6.0 heads. The max they take off to get them flat is .008". They also pressure check, and check for cracks. $350 a pair.

One thing caught my attention is they cut them if they are not flat, or within .002". So if they are within .002" then they don't need resurfaced. I thought a clean surface would help it seal.


.

 

Wow a ton of stuff flying around in this thread!

The right way would be to measure the deck thickness of the head before and after milling. That ELIMINATES the uncertainty that was brought up. The way we use to do this was take a DEPTH Micrometer and a 1-2-3 block and measure the thickness of the head. The depth micrometer goes on the head gasket surface and the 1-2-3 block on the rocker box surface. Take the measurement, dust the head lightly, remeasure. Repeat until the head cleans up with in the allowable spec. Micron is a measurement of finish and not a thickness. The micron measurement only matters for surface finish.

So if the heads are warped .002" or less the heads are not surfaced. Is that correct?

Someone said the valves should be cut in the shoulder and the stem...That is the most confusing thing I have ever heard! Are you implying that you need sink the valves in the seat to allow for clearance? That will cause other issues with the installed height.

One thing to keep in mind folks.....there are many views on this....The right way(safe) is to follow what is in the factory specs. All others are like holding a hand grenade without a pin and hoping that you don't drop it!

I know plenty of folks, myself included that have pushed the limits and gotten away with it. But I also know the consequences if something goes wrong.

 

Most shops would touch the heads on a belt sander at that point to clean the surface.

That being said .002" should pull back into flatness when torqued.

The surface should be fine with .002" warp as long as it has not been hit with a wire wheel or gouged in any way.

 

As a metrologist working in the automotive industry, I would like to clear up a few misstatements.

The "Uncertainty of Measurement" that I was referring in a previous post is that any measuring instrument has this, whether you know the value or not. If one would have a depth mic calibrated at an ISO 17025 accredited lab, the calibration certificate would state the estimated Uncertainty of Measurement value. These labs create this estimated value by traceability to NIST. No measurement is exact, if you think it is, you are not using an accurate enough instrument. For example, if a depth mic would have an Uncertainty of Measurement value of 0.002" and you took a measurement of 2.456", then the true value lies somewhere within 2.454" - 2.458". When my machinist tells me he took off .008", what is the true value? I don't really know since I don't know his Uncertainty of Measurement value. No measuring instrument is truly accurate, micrometer, coordinate measuring machine or whatever. They all have a level of uncertainty to them, whether a known value or not.

While a micron is a measurement of surface finish, it is also a measurement of size or distance (or thickness as stated above). It's a value, how you use that value depends on what you are measuring. You often hear of a filter have "X" microns of filtration, my understanding is that is the size of the "holes" in the filtering media or what it will allow to pass through. A micron is 0.001mm or 1/1000000th (millionth) of a meter also known as a micrometer. A micron and a micro inch are NOT the same thing. A micron converted to micro inches is .0000393" A micro inch is 0.000001"

My point in the earlier post is that since I don't know my machinist's Unceratainty of Measurement" value, what is the true value when he tells me he shaved off .008", did he shave off .006" or .010"? I don't truly know. If I had some spec to check, say from deck surface to riser surface or wherever. I could put the head on my coordinate measuring machine at work and measure distances to within 0.001mm (micron level) accuracy, far more accurate than his depth mic or milling machine scales. This discussion is probably pointless since each casting is different. I was just wondering since at .008" I"m approaching the limit, what is the true value.

Restlesswildman - please don't take this the wrong way, I don't mean to get on your case. This is my profession and just wanted to clear it up. Sorry if I offended you. Also sorry to everyone here for getting off track of the original thread but as the OP, I would hope I can hijack my own thread.

 

Post #75 is a machinist's perspective on the subject:

::For Everyone Running “Black Diamond Titanium” Head gaskets:: - Page 2 - Ford Powerstroke Diesel Forum

"Metal does funny things when it gets hot...or sometimes more importantly, when it cools back down from being hot. It distorts and shifts. I would tend to say that it's maybe the block a lot of times that actually is responsible for warping the head...obviously not all the time...but think about it, you've got 20 main bolts with a tremendous about of torque on them holding the bedplate/main caps on the bottom, then 20 more holding the heads on, around what is essentially a hollow piece of iron, holes in the water jackets, holes for the cylinders and holes in the oil galley's and all. Surely tick for tack the block is more rigid than the head, but even bolted together, it's the heat cycles that really warp things...and especially as many cooling system issues as these motors have (cracked egr cooler, blown head gasket, clogged oil cooler) can cause temps to be way way way over the "norm" perhaps more so than other engines. It's not uncommon for the blocks to be warped...I'd say about 60% of the blocks and heads clean up with less than .004" milled off, and another 20-30% clean up with less than .006-7" milled off, any much more than that and you begin to mess with piston protrusion and injector tip protrusion, and compression ratio, and a myriad of other factors too much, plus if it was run hot enough to warp it .015" or whatever, it's usually cracked anyway."

 

If you have to go further just buy one extra head gasket and use an extra layer from it.

 

I don't think we can get away with that old trick. And no one that I
have heard of is making shim gaskets.

Sean

 

No offense taken! Just a few exceptions.

I miss stated microns it should have been micro when referring to finish.. I understand that as I work in a machine shop that manufactures safety devices for the nuclear industry. The variation in measuring devices is a moot point in my opinion being a machinist for 20 years. A machinist will know the variation and will be able to take into account. If I measure something 10 times and get the same measurement 8 of the 10 times and it is verified by someone else, I would say the variation is moot. If you are worried about a micrometer/measuring variation on a head resurfacing on a stock engine then...well....I think your over thinking it. As long as the head is flat and has a correct finish and still is above the minimum thickness called out in the shop manual, then that is all that matters.

The only shops I know that use CMMs on engine work are shops that the average JOE can not afford. Also CMMs are only as good as the people using them. My current employer bought one a few years ago. The guy that was hired to bring their QA up to speed didn't understand how to set it up and failed every single part for 3 weeks.

I can see the variation argument in parts for NASA, Lockheed Martin, L1 Communications, but not in engine work. Most NORMAL engine machining is not going to require tolerances of .0001".

BTW would love to hear how a Meteorologist ended up in the automotive industry doing precision measuring.

 

Lol. I was wondering the same thing. Oh by the way, Snowseeker, were you serious about putting extra hg for space?

 

My machine shop showed me in a catalog he got that there are 6.0 shims available. Not saying that cause I'd be willing to use them,, But I saw that they are out there. Who knows how they would react.

 

I not saying it works on the 6.0 but with other motors and metal head gaskets people have been removing and adding layers for years to increase or decrease compression and/or piston clearance because of head work, etc. Personally I see no reason why it wouldn't work on the 6.0.