Checking a head for flatness

[fastback4]

How can a self proclaimed gear-head (me) check my v-6 aluminum heads for flatness?
How do the machine shops check an aluminum head for flatness?

[ForcedFirebird]

Really, you can't without some specialty tools. Some people say they can tell with a straight edge, but I don't see how that can be accurate when you are talking about thousands of an inch.

In the shop, there's a few ways. You can use a surface table, pad the head up so the four corners are the same height off the table, then use a height guage. You can do the same on a mill and use an indicator (touch the 4 corners level and check the rest of the head), and finally you can lay the head on the surface table and insert feeler guages under it.

For a quick check I will use an indicator stand and have the pad ~6" away from the indicator, move it around the head and that will give you a quick idea if it's warped or not.

[86FieroSEv6]

I use a true straight edge (they are relatively inexpensive) and position it across the center of the head. Then I take a feeler gauge of the max allowable value and try to push it under the straightedge with very gentle effort. Also check it with the straightedge placed across the head surface from corner to corner along the edge of the head as well as across the center. For my engines I don't want to see any more than .0015 anywhere along the surface. Depending on the warp and it's location, you can elect to have the head straightened as opposed to machining which preserves your compression ratio and valve clearance to the piston.

[Superdave]

I use a good straight edge and a set of feeler gauges, for a quick check i use the straight edge and a flashlight.

[SappySE107]

We used a straight edge on a set and found them to be about .003" warped. Took .004" to clean them up, so the straight edge and feeler gauge/flash light does work. You go corner to corner, then the othe 2 corners, then down the middle. I have all the heads that leave here milled, but that set was for the achieva so if it was .001", it would have been good. .004" is spec limit , but I didn't want to take chances with .003".

[fastback4]

I use a true straight edge (they are relatively inexpensive) and position it across the center of the head. Then I take a feeler gauge of the max allowable value and try to push it under the straightedge with very gentle effort. Also check it with the straightedge placed across the head surface from corner to corner along the edge of the head as well as across the center. For my engines I don't want to see any more than .0015 anywhere along the surface. Depending on the warp and it's location, you can elect to have the head straightened as opposed to machining which preserves your compression ratio and valve clearance to the piston.

How do they straighten a head. Heat it and bolt it down? .....Tom

[86FieroSEv6]

That's the basic idea. Of course it takes some special equipment and not everybody has it. However, when you are trying to retain a special setup or uniquely modified heads it's the only way to go.

[ForcedFirebird]

How do they straighten a head. Heat it and bolt it down? .....Tom

It's put in a mill, or head shaving machine and a little bit of material is removed to make it flat again.

[fastback4]

Thanks to all........Tom

[60dgrzbelow0]

Although this is for a boat motor... it still nicely serves as a visual echo of Ben's procedures...

http://forums.iboats.com/showthread.php?t=364237

... and this video echoes John's comments,,,

http://www.youtube.com/watch?v=m1I_ds3ow5s