Quadrajet- How much warp is warped?
 

Time to rebuild my 1968 Quadrajet (7028212) before bolting it on my rebuilt 327. After getting it all cleaned up, I thought I better check for warpage since the QJ are well known for this problem. I’m just not sure how much out of perfectly flat is acceptable.

I checked the pieces using a metal straight edge and a feeler gauge with the following results:

*The air horn (top) had a dip in the middle when I checked it side to side near the front part of the carb. It was about .015 low which I didn’t think was too bad. It indicated no warpage front to back in the center of the piece.

*I set the air horn on to the main body without a gasket and found a gap on the passenger side of the carb at .015 while the driver side was tight.

*The top of the body (float bowl) was almost perfect near the back of the carb while checking side to side, but .020 low in the front when checking front to back.

*The bottom throttle plate (throttle body) was very flat and in good shape.

I got the new primary shaft bushings installed today and used J-B Weld TankWeld High Strength Automotive Epoxy on the well plugs.

The new air horn gasket is .050 thick so I’m thinking since the variation from flat is well less than the gasket I’ll be OK moving forward with the rebuild. I’ve heard that if the warpage is less than half of the gasket thickness, there shouldn’t be a problem. FYI, very nice kit available from Quadrajet Power online.

Any comments or experiences regarding warpage on your QJ would be appreciated. Also, has anyone had any luck spraying the gaskets with silicon lubricant to soften them up before assembly?

Re: Quadrajet- How much warp is warped?
 

I've never used silicone lube on gaskets. Since you bought the kit from Mark, I'd highly recommend that any questions you may have about the assembly and adjustments of your carburetor be asked directly of him. He knows his product...and his stuff.

Re: Quadrajet- How much warp is warped?
 

I’ve rebuilt a few q-jets. They’ve all had flatness issues as you describe. I’ve always used the “thick” top plate gasket which is 1/16” nominal so it sounds like your close at 50 thou. I’m my experience, once it’s put into service and fuel gets in contact with the gasket, it’ll soften a bit. Also, if I recall correctly, there are some raised portions in the castings in key areas that seat into the gasket and help mitigate issues from flatness.

Re: Quadrajet- How much warp is warped?
 

hi,i do alot of Quadrajets here and you're right,It's not uncommon to see the air horn bent.it's always from folks overtightening the 2 5/16 bolts on the front corners.i always use small flat washers on those bolts and the 2 rear and leave the power bar in the tool box.i could look up what the correct torque is but i know it's not much.i did an Oldsmobile carb a few years ago for a fella,the airhorn was bent so badly,could've used a yard stick to measure the bend,never mind a feeler gauge,so i thought i had to try something,nothing to lose.i put the airhorn on the edge of my steel table and gave it a couple of bumps with a dead blow hammer.i didn't know if it would break the casting but it didn't.i was able to get it close,finished the carb.i did show the pieces to the customer while it was apart,told him i didn't have much hope that it would work.he said put it together,so i did,sent him on his way and no idea how he made out,he never came back but i have done the same thing with airhorn's just out a little and have had good success.probably isn't right or recommended in the grand scheme of things but sometimes a fella has to do what a fella has to do.

Re: Quadrajet- How much warp is warped?
 

Welcome aboard!
As others have said that amount of warpage should be ok.
I can't speak about using a product to soften the gasket, but I do know that the gasket material will swell a certain amount when exposed to gasoline. This seems help seal a small amount of warping.
Trying to soften the gasket may cause the gasket to split in the tightest areas. Just a theory no real proof on my part.