cracking upper 3100/3400 intake

[talon2swords]

http://60degreev6.com/forum/showthread.php/46154-large-port-3100-upper-intake

I know this is an old thread (above), but I recently attempted to put 2000+ upper and lower intake on my 99 lumina 3100, and I got the same result as above (pictures). I had a couple intake parts I had collected, so I probably over-tightened on the first intake. But I noticed a few things about these latter model upper intakes. They seemed to be warped, at least used ones are. I now have three of these upper intakes, and two lower intakes. One of the lowers is now on my car, so I put all three of the uppers on the other intake (not installed on a car) to test them and they all wobble. In other words, something is not flat. And it doesn't seem to be a fluke with one of them, this seems to be an issue with all these intakes (at least when placed on both of my lower intakes). I ordered another latter model upper intake on ebay for 30 bucks, and babied it with a 1/4" socket drive wrench while tightening so I would not over torque it. I think it still may have cracked in the same place as above, because I heard a popping noise and I think I see a small stress fracture.

If it did crack, I'm going to take this latter model intake system off the car and re-install my sturdier older intake. I have replaced a couple LIMs with the older intake system (that had extra bolts with the upper) and I never had an issue with cracking in the older upper. I think the latter design sucks, or either the aluminum warps with heat and age. Also, I have searched the internet and can not find the torque specs for the latter model upper intake. All I can locate is 13 ft-lbs. (if I remember correctly). If I used anywhere near that, it would pop and crack.

Only solution is probably to take used intakes to machine shop and have it milled. Otherwise used 2000+ intakes, in my experience (remember, experiences may vary), should not be used unless obsolutely flat.

[talon2swords]

Great. Seems I should have done my homework before I started this project. In addition to possible warpage, the torque specs may be wrong. Wasted a few intakes on this. I'll be buying a Tig one day I hope, maybe I can fix stuff like this.

http://www.gmforum.com/general-gm-chat-88/gm-v6-site-204891/

"Now get this, I was following GM's data for replacement of the gasket and they have revised many "wrong torque specs" for this particular motor from the rocker arm bolts to the lower intake to the upper intake. They have updated all of these specs but made a mistake on the upper intake manifold bolts. They claim 18 ft lbs for torque specs. That is dead wrong. When I was torquing them as per "GM's" published data what I thought was the torque wrench clicking when reaching 18ft lbs of torque was really the upper intake manifold cracking due to excessive torque being applied. "

[3400-95-Modified]

I've never seen one wobble before and I've messed with my fair share of 3400's and 3100's... Are you sure there isn't something in its way of sitting flat somewhere else which is causing your wobble.

The wiring harness path is different for the 99 vs 2000 intake too so if you get that wrong you could be lifting the intake due to the wire bundle for the injectors.

[talon2swords]

I've never seen one wobble before and I've messed with my fair share of 3400's and 3100's... Are you sure there isn't something in its way of sitting flat somewhere else which is causing your wobble.

The wiring harness path is different for the 99 vs 2000 intake too so if you get that wrong you could be lifting the intake due to the wire bundle for the injectors.

I tested a 2000+ upper(s) on a UNinstalled 2000+ lower. No wiring harness,etc. was present, it was naked. It wobbled. I then installed the upper gasket, and the wobble was gone.

I then tested a 2000+ upper on a different, installed 2000+ lower (w/o gasket). It wobbled too.

When I tried torqueing (to specs) during my first installation, I got the crack(s) and messed up my first intake.

The last time I tried with another upper I ordered from ebay. I did not torque it to the specs I was given, but snugged it up until it tightened, and I may have cracked that one, but it is hard to tell right now (visually).

The car is not showing any engine lean misfire code this time and it's running ok for now (given that it may have a few other idle issues). I'm letting the computer calibrate itself around town to see if it will be reliable.

Not very accurate, but I guess I need to do some checking on a flat surface and see what is actually warped on my UNinstalled parts.

However, I do know, from my debacle, that the 2000+ uppers will crack easily if too much torque is applied. Or either I was sold warped garbage everytime I ordered the uppers and I should have checked for flatness beforehand. Or something may be wrong with the lower on my car or I screwed it up. Who knows?

[3400-95-Modified]

I'm leaning towards lower, as I said I've been through a large amount of uppers on and off and different styles on different engines and in conjunction with 3500 lowers and 3400 lowers and NEVER once broke or cracked an upper intake. I also never torque them, I simply tighten them by hand.

[x-thumpr-x]

I've cracked 4 upper intakes for a 3400 motor. The third swap we did, the upper plenum was poweder coated, week after the install I noticed the crack on two corners. Went to the junkyard and pulled two more 3400 uppers (2000+) cleaned one up and installed it with only 18lbs of torque and it also cracked. At that point I decided to pull mine off (2001) to inspect it and it was also cracked. I didn't even notice it & the car ran fine. after a last attempt on my friends swap it cracked by using hand tight, but left it on since the car seemed to be running fine. I sent the other three to a guy who tig'd up the cracks. I cleaned one up and it's running on my car right now with no issues. The other two spares are sitting in a box waiting to be used one day. I'll be doing the 3500 upper plenum soon, so I'll have three repaired & strengthed uppers.

[ForcedFirebird]

No issues with welding them up. I have TIG'd a few. We actually thought about offering an upper with gussets on it, but not sure it's worth the expense.

[talon2swords]

I know some disagree, but I think over time the aluminum gets hard and brittle from the constant heating and cooling, and also may warp. I think one should use caution and gently tighten used 2000+ intakes, or check them for flatness and have them machined first if needed. And I think the existing torque specs are wrong (too high). I "gently" tightened my last one and it seems to not leak, or so I hope.