Rotisserie question

[jkgts1]

Hey guys is it okay to place the car on the rotisserie when the frame rails are removed, will it be strong enough to stay straight?

 

Thanks

[JMortensen]

If you mean under the floorpan, yes. If you're talking about the engine compartment, I wouldn't.

[jkgts1]

Yes, I ment under the floor pan.

[Jeff]

I did the same thing with very bad results. I replaced the front frame rails with the car on the ground being very careful to check measurements and even hung all of the sheet metal back on the car to check the gaps. It was perfect.

 

I put the car back on the rotisserie to do the floor pans and sub frame connectors. The sub frame connectors went on first, then the floor pans one side at a time and then finished welding the sub frame connectors to the new floor pans. Everything looked great so off to the body shop it went. They hung all of the sheet metal back on the car to start working the gaps and getting everything flat. I got a call from my body shop guy telling me I needed to come see him and it wasn't good. We had managed to twist the frame rails by 1 1/2" when it was on the rotisserie.

 

The body shell had to be put on a frame machine and be pulled back to square. This resulted in the firewall and floor pans buckling a bit because something had to give to get her back in shape. That stuff was cut loose, reworked and the car is square within a few mm's now but it cost me big time.

 

In short, no I would not hang the car on a rotisserie with the under floor rails gone. But that's just my very expensive opinion.

[palosfv3]

The rotisserie should not be used for any repair that involves the structural integrity of the unibody. Jeff's story about his difficulty is testament to this. An auto body is not designed to be hung between its outermost points. To get an idea of what stresses go through a body mounted in this fashion , get a 12' 2x4 and place each end on a chair. You'll see it bow in the middle almost as soon as it contacts the chair. The body structure is affected the same way but it is not as obvious as in the example. Since the floor is used as a stressed component of the unistructure, removing and replacing it on the rotisserie is equivalent to cutting out a section from the center of the spanning 2x4 and glueing it back under load.

Floor pan and frame rail replacements should be done on a level surface with the body also level, preferably with the suspension under load. Its not a bad idea to brace the door openings when doing this procedure.

The amount of structural weakness from the rust damage will vary and has a major influence on the way the repair should be approached.

 

Larry

 

http://www.wgmauto.com

[JMortensen]

The Z chassis's main structure that connects the front to back is NOT the frame rails. It is the rocker panels. In early Z's the "frame rails" don't even connect the front of the car to the back. I'm not sure what happened in Jeff's case, but I have a hard time believing that it was putting frame rails on the floorpan that caused the problem.

[geezer]

I had no problems, the structure did not twist, but I did take a few simple precautions. Before beginning the project, preferably before the fenders & doors are removed or any cutting is done take several measurements from several different reference points and record them. Refer back to these measurements before permanently welding components into place. Use spreader bars between the A post & B post. Another bar tying both spreader bars together to prevent lateral twist could be implemented if you still have concerns. Only work on one side at a time, to retain as much ridgity as possible. The inner rockers are sufficent alone to prevent misalignment as long as you watch out for that lateral twist. Use a string or a laser, whatever you have to check for the "2X4" bow effect. The rottiserie itself, if not tied properly with a spreader bar, end to end could also cause problems. It's all just common sense with a measure of caution thrown in.

[jkgts1]

Cool thanks for all the replies. I was worried about the middle sagging, that is why I asked. So, would it be safer to just have the car on jack stands and weld in the new rails in upside down? That is what I was trying to avoid, don't like hot metal falling on me, lol. I don't need to do my floor pans just the rails, thank goodness.