How to check head warpage on 95 3.1L

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?

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.

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

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.....

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?

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...

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.

Should do both heads in this case.

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.

http://hbassociates.us/Lumina_Head_Gasket_02.jpg

http://hbassociates.us/Lumina_Head_Gasket_03.jpg

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.)

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!

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

Good advice Max.....

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?

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.

will do Max

Coming back with bad news, and hoping to figure out whats wrong and get it running. Have the motor completely finished, tried to start it, but it sounds as if it is out of time. It just turns over and every now and then puffs back thru the intake never once sounding close to cranking. Have already triple checked all the spark plug wires, sensor electrical connections, plugs have gas on them, and we have spark at the plugs, and all seems good there. What I am afraid of....and I am no mechanic so I hope I don't get proven dumb here, but could this happen IF by chance when setting the valves we didn't have the #1 and #4 cylinders at TDC on the compression stroke? This is the only anomaly in the entire rebuild where something was adjusted. Now, on to the description...when spinning the motor over it sounds what I describe as "tight" or "labored" because it isn't spinning over freely as it did when it was running good.

Long exhausting day. Dunno.

You got gas in the Gas tank? That is what happened to me after I fnished doing heads. All the gas evaporated out.

Did you double triple and otherwise verify that the pushrods were put in back in their original places? If im not mistaken, the 3.1 has the exhaust pushrods longer than intake. Long exhausting day for sure.

Long exhausting day. Dunno.

You got gas in the Gas tank? That is what happened to me after I fnished doing heads. All the gas evaporated out.

Did you double triple and otherwise verify that the pushrods were put in back in their original places? If im not mistaken, the 3.1 has the exhaust pushrods longer than intake. Long exhausting day for sure.

You are correct, different length pushrods. Yes the exhaust are longer than the intake...

I can totally relate to the long exhausting day. Yes, the tank is full of gas, and we made a special holder for the pushrods so we would be sure to get them back in the right place. there is no clacking, banging, just sounds like its off timing.

hmm.. Maybe perhaps take all the spark plugs out and turn the engine by hand and see if there is any tough spots.

I thought that the 3.1 liters were self adjusting with hydraulic lifters. You should not have to adjust anything once they are torqued. I dont know if the 95 is different.


Edit: I just looked it up, seems the 95 runs hydraulics lifters, and you should not have to adjust them. I would try to turn by hand, and maybe take valve covers off and just make sure nothing is jacked up. IE a pushrod not seated correctly, a rocker arm broken/stripped.

Ha, One last edit, hydraulic lifters love synthetic oil, so once you get it back up and running, run synthetic. I know all about synthetic blends and regular oils having seal conditioners, but you will definitely notice the engine running quieter if you run synthetic.

And another thing, make sure you get getting spark, once your verify that there is no binding by turning it by hand.

Do a compression check.....

Verify there is no binding first, by removing sparkplugs and turning engine by hand. You want to remove the sparkplugs so you don't have to force your way through the compression stroke. DO this first, before compression test as Tech Stated. That way, if there is a problem with binding you can correct that first, rather than have the engine eat itself even more.

Verify there is no binding first, by removing sparkplugs and turning engine by hand. You want to remove the sparkplugs so you don't have to force your way through the compression stroke. DO this first, before compression test as Tech Stated. That way, if there is a problem with binding you can correct that first, rather than have the engine eat itself even more.

Well, you guys wont believe this, but yesterday afternoon we turned over the motor by hand and all felt good. Just to verify that it wasnt anything attached to the motor bogging it down while cranking we took the belt off. Believe it or not the thing started right up! We only ran it a few seconds because we noticed the rocker arms were making a little noise. Took the valve covers off after cooling the motor with a fan for a couple hours and adjusted a couple loose rocker arms. After that we put the belt back on, fired her up and she purred like a kitten. Bled the cooling system, and my son went to take her for a test drive. made it about one mile from the house and she started messing up...again. Son said it didn't make any loud noises, it ran cool....no overheating, just went weak and started running really bad. As he drove back up it almost sounded like a spark plug had come out, but upon checking, all were in and tight. I know the guy had problems with one rocker arm nut staying tight but thought he had it fixed before he covered it up. IF it happens to be that the nut came loose on the rocker arm, how bad would or could that be to fix?

adjusted a couple loose rocker arms.
Are they adjustable? I thought they were non-adjustable, "net lash" system.

Yes, there is no "adjustment" per se.....it's a specific torque.....if rockers are coming loose, that is a problem......

Yes, there is no "adjustment" per se.....it's a specific torque.....if rockers are coming loose, that is a problem......


Agreed...I'm pretty sure all these had bolts and not stud/nuts to tighten the rockers. I have seen several that the tower where the rocker arm bolt threads into had broken, requiring the head to be replaced. Lets hope this is not the case with this one...

Sorry about the misunderstanding about the rocker arms. I am so exhausted from working long days and helping work on this motor till midnight some nights. Anyhow, he under torqued the rocker arms by mistake the first time by only going 3/4 of a turn instead of the required 1 1/2 turns past zero lash. If it turns out to be what gmtech1 says.....I don't know what my next course of action will be. I am already wishing that maybe I should have just invested in a good used motor and saved all this headache. I will let you guys know what I find the next chance he gets to come over and take it apart.

Sorry about the misunderstanding about the rocker arms. I am so exhausted from working long days and helping work on this motor till midnight some nights. Anyhow, he under torqued the rocker arms by mistake the first time by only going 3/4 of a turn instead of the required 1 1/2 turns past zero lash. If it turns out to be what gmtech1 says.....I don't know what my next course of action will be. I am already wishing that maybe I should have just invested in a good used motor and saved all this headache. I will let you guys know what I find the next chance he gets to come over and take it apart.


I may be way off base. With the year, this may have cast iron heads and studs. If that's the case, the breakage I was referring to is unlikely..

Anyhow, he under torqued the rocker arms by mistake the first time by only going 3/4 of a turn instead of the required 1 1/2 turns past zero lash.

Last time I remember doing that was on a 2.8, in an '88 Fiero, and that was when pistons where in a specific position.......That is not the torque spec for this engine......spec should be either a specific foot pound, or a lesser foot pound and the final turn is in degrees.....

Got the spec, GMTech1?

One thing you have to be careful with, especially rocker bolts, is removing them with a power tool before breaking them loose.....very easy to pull threads out of those heads.....

Anyhow, he under torqued the rocker arms by mistake the first time by only going 3/4 of a turn instead of the required 1 1/2 turns past zero lash.

Last time I remember doing that was on a 2.8, in an '88 Fiero, and that was when pistons where in a specific position.......That is not the torque spec for this engine......spec should be either a specific foot pound, or a lesser foot pound and the final turn is in degrees.....

Got the spec, GMTech1?

One thing you have to be careful with, especially rocker bolts, is removing them with a power tool before breaking them loose.....very easy to pull threads out of those heads.....

Rocker arm nut is 18 lbs.ft.

Thanks for the info gmtech1. That did the trick. Engine is running perfectly now! I'm attaching a screenshot of the info he was going by from a site called Mitchell1. Thats where he got the info to tighten 1 1/2 turns past zero lash.