My frame is narrower at the front than the back

[Reno Speedster]

I am getting ready to reassemble my 26 speedster and thought I would take a good look at the frame. It has about 1/4 inch sag in the middle, not a big deal and placing a long straight edge on the frame rails shows that they are both straight side to side. However, the frame in front of the rear crossmember is about 3/8 inch wider than frame behind the front crossmember. Measuring corner to corner, it’s about 1/8 inch out of square, which is pretty good. Not really a problem since the spring mounts are in the middle of the frame, but it’s got me wondering how common this is.

[Mike Silbert]

I have found that it is next to impossible to find an original frame that is not bent unless it has been straightened recently.
Life has been hard on them and one of the frequent issues is that the curved front and rear crossmembers flatten out spreading the rails.
They need to be flat, straight, parallel, square, and tight if you care about things lining up.
The rails need to be 23" outside all the way front to back.

See the following for proper frame dimensions
https://www.mtfca.com/discus/messages/5 ... 1431319132

https://www.mtfca.com/discus/messages/4 ... 1399931647

https://www.mtfca.com/discus/messages/5 ... 1431319132

https://www.mtfca.com/discus/messages/7 ... 1494003548

https://www.mtfca.com/discus/messages/3 ... 1366444998

http://www.mtfca.com/discus/messages/33 ... 1366397274

https://www.mtfca.com/discus/messages/3 ... 1376439772

Straightening a frame is a brain challenge to figure out where the problem is and where to apply the force to bend it.
Just needs an irresistable force and it bends

[TXGOAT2]

I'd want to get the sag out of the rails.

[Allan]

T frame rails are tough old biddies.To get a sag out of the rails I have had to press them until the lower edge is almost straight before they would hold the desired shape. Pressing that far means there is a risk to the rails bellying sideways. I have two short lengths of hardwood cut to fit inside the rails. These are clamped in place with proper sash clamps, not those loopy things that go on lengths of pipe. That ties the rails together!. It may take a number of presses before the rails will hold the correct line.

Allan from down under.

[Reno Speedster]

Honestly, it’s less trouble to just shim the mounts. It’s not that much distortion. I have thought about trussing the frame, but that would place some odd stresses on the frame and require special bracing. Placing a 4 ft straight edge on the top of the rails shows shows no real sag.

[Allan]

Forget the short straight edge. A taut string line will give a better over-all indication of any sag in the frame. Takes only a few minutes to do, and can be quite revealing! There is no better time to make corrections than when the frame is bare.

Allan from down under.