How to check head warpage on 95 3.1L

[gacowboy30]

Been searching the net for this answer, but am getting conflicting numbers. Using a straightedge and feeler gauge, whats the maximum tolerance for warpage on a 1995 3.1L head before they need to be resurfaced or replaced?

[gmtech1]

Originally Posted by gacowboy30

Been searching the net for this answer, but am getting conflicting numbers. Using a straightedge and feeler gauge, whats the maximum tolerance for warpage on a 1995 3.1L head before they need to be resurfaced or replaced?

.005" warpage requires milling, If more the .010" of material need to be removed, the head should be replaced.

[gacowboy30]

Thanks for the fast response. Fixing to go see if they are in spec or not. *crossing fingers*

[Tech II]

It's not a straight edge like a ruler, it's a special tool in a case....in other words, you don't "sword fight" with it.....

[gacowboy30]

I used a 1/4" piece of straight steel that I checked for trueness against a framing square. It checked out good so I checked the heads on all four sides, diagonally, and across the center both ways using a .005 feeler gauge. I only found one spot on the rear head right around one of the inner bolt holes that the .005 would just BARELY slide under. The area was MAYBE about the size of a nickel, if that. Would that small of a spot in that location warrant taking it to a shop to be milled or should it be ok?

[gmtech1]

Originally Posted by gacowboy30

I used a 1/4" piece of straight steel that I checked for trueness against a framing square. It checked out good so I checked the heads on all four sides, diagonally, and across the center both ways using a .005 feeler gauge. I only found one spot on the rear head right around one of the inner bolt holes that the .005 would just BARELY slide under. The area was MAYBE about the size of a nickel, if that. Would that small of a spot in that location warrant taking it to a shop to be milled or should it be ok?

Without using a true "straight edge", its tough to be sure. If the head really does have a spot that is questionable, for piece of mind, I would have it milled. Hate to have to do it twice...

[Schurkey]

Mill it. A localized low spot is worse than one spread over the entire surface of the head.

I had .015 shaved off the heads of my 3.4 Dual Cam. GM wants to sell replacement heads.

[maxwedge]

Should do both heads in this case.

[Schurkey]

Originally Posted by maxwedge

Should do both heads in this case.

I was pleased that I did have both heads machined. In my case, the head gasket had popped, right where the localized low spot was on the rear head. The front head gasket was wounded, but not actually leaking--at the exact same place.

Planing both heads made good sense, since they were both defective in the same way; and the only way to know is to yank them both and inspect.





HOWEVER

I don't trust GM to make the heads within .005 of each other to begin with. Taking some material off of one head, but not the other does not seem to me to be especially relevant on a grocery-getter. A performance engine might be another story. (This assumes that the second head is not actually warped, and that's probably far-fetched.)

[gacowboy30]

Gonna wait till Monday and call a local machine shop that a friend referred me to, and get both heads milled the same. Looking forward to getting it all back together, but want to do it right the first time. Thanks again for the replies, I'm always learning from everyone here!

[maxwedge]

Check whether the head bolts are TTY ( torque to yield) if so you must use new ones.

[Tech II]

Good advice Max.....

[gacowboy30]

I bought the 2nd generation gasket set that includes everything from the block up, new plugs, and new head bolts. Is there any special type of thread locker, permatex, or anything else I may not be thinking of?

[maxwedge]

Bottom tap the head bolt holes, check with the bolt MFG some recommend dry threads others lite oil, this affects the torque setting. If the bolt holes are blind ( not open at the bottom) no sealer is required.

[gacowboy30]

will do Max