checking cyl head flatness

[blacksnapon]

CAUTION: Do not use metal scrapers, wire brushes, power abrasive discs or other abrasive means to clean the sealing surfaces. These tools cause scratches and gouges that make leak paths. Use a plastic scraping tool to remove all traces of the head gasket and other foreign material.

Following the directions on the packaging, use silicone gasket remover and metal surface prep to clean the cylinder head of all gasket foreign material, RTV, oil and coolant.
NOTE: Use a straight edge that is calibrated by the manufacturer to be flat within 0.005 mm (0.0002 in) per running foot of length, such as Snap-On® GA438A or equivalent. For example, if the straight edge is 61 cm (24 in) long, the machined edge must be flat within 0.010 mm (0.0004 in) from end to end.

Measure cylinder head flatness to make sure that there are no depressions of 0.0508 mm (0.002 in) or greater in the cylinder head.
Place a 0.0508 mm (0.002 in) feeler gauge on one of the measuring points.
Place the straight edge on top of the feeler gauge with the straight edge transverse to the cylinder head.
Gently pull on the feeler gauge.
If the feeler gauge is loose or slides out from under the straight edge, install a new cylinder head.

 

[bobf100]

Vince - this is good information. I know you were talking about 6.0 powerstroke but your points would also apply to any engine. Over the winter I'm going to be tearing into my project truck's engine which is an inline 6 (bowtie 235). Because of their length these heads tend to warp so most times they need to be machine flat again. This particular motor has never been opened so I've got 50 years of crud built up and my first reaction would be to scrape / wire brush / pick at the old gasket material of which I know now to not do that. Thanks of the tips.

 

[surewhynot]

Good Info Vince. I also didn't realize that you shouldn't clean the head with anything abrasive. I had always used one of those scotch brite pads that fit in an electric drill. Now I know not to. Does this info go for all engines?

 

[blacksnapon]

Good Info Vince. I also didn't realize that you shouldn't clean the head with anything abrasive. I had always used one of those scotch brite pads that fit in an electric drill. Now I know not to. Does this info go for all engines?

A lot depends on the tolerances for the cyl head and block deck. Newer engines have much closer tolerances than the older ones. Some of the older engines, you could build with a claw hammer and a file. The modular 4.6 and 5.4, .001 is all thats allowed (scratches or gouges are more than that).

 

[Jthe6ltek]

Heh,ive always used a brown roloc abrasive disc on sander/cutter.. havnt had any problems so far knock on wood. we've even had a 6.0 head machined .002 of an inch and still didnt cause any problems...could have just been lucky,but ive gone on to make a point on a cracked head and used 2 discs in 1 spot,and it still didnt fail the straight edge test...i dont think unless you have some ungodly hard disc that it will hurt it...but thats just my opinion

 

[blackhat620]

Heh,ive always used a brown roloc abrasive disc on sander/cutter.. havnt had any problems so far knock on wood. we've even had a 6.0 head machined .002 of an inch and still didnt cause any problems...could have just been lucky,but ive gone on to make a point on a cracked head and used 2 discs in 1 spot,and it still didnt fail the straight edge test...i dont think unless you have some ungodly hard disc that it will hurt it...but thats just my opinion

I would pay close attention when using a "roloc" Scotchbrite pad as we sand with them for paint prep. As far as milling 6.0 heads, several engine bulilders do it, the limit is 1.366 head thickness when finished, so generally max you can mill is .008.

 

[6L PWR]

Ok, stupid question, maybe. Does milling the head down up the compression and if so, what effect does that have on a diesel?

 

[blackhat620]

Ok, stupid question, maybe. Does milling the head down up the compression and if so, what effect does that have on a diesel?

Yes milling the head will up the compression ratio since there is less cylinder volume when finished. The effect on any engine depends on how much the compression ratio is raised, what it was before you started and the shape of the cylinder head bowl. On the 6.0 CR = 18 (6.4 = 17.5) a diesel engine likes compression and the higher the better it performs up to a CR = 25, minimum CR for a diesel is 16.

With the new EPA rules the CR in a diesel engine is being reduced to lower combustion temps which will lower NOx output, BUT the lower CR & Temps results in lower efficiency so the fuel mileage goes down. Yep burn more fuel to go the same distance but hey the NOx output is lower when it is tested.

 

[6L PWR]

So, if you mill of only .002 or .003, how much approximately would that raise it? I got a spare set of heads and I've been thinking of having them decked and ported and polished for the next engine.

 

[blackhat620]

So, if you mill of only .002 or .003, how much approximately would that raise it? I got a spare set of heads and I've been thinking of having them decked and ported and polished for the next engine.

Here is a calculator there are many values that must be known and input.
www.csgnetwork.com/compcalc.html

 

[6L PWR]

Kewel! Thanks. I'm calling my buddy to ask for all these values or if he knows where to find the stock ones.

 

[sdtheclub]

No milling a 6.0 head does not change compression ratio, There is no combustion camber like a gasoline engine. The head is already flat so milling it does not change the combustion ratio but it does make your valve to piston clearance closer. Ford does not recommend milling any of there diesel heads because the clearances are already so tight. If it could be done without any problems Ford would do it because it would save them millions.