Needed: A Master Frame Tru-er! - UPDATE - Success!

[dougfisk]

eI have a 1951 Murray built JC Higgins that is my best original paint bike. Unfortunately the frame is noticably un-straight. I believe the seat tube is not square with the bottom bracket and lays to one side an unacceptable amount. The result is the rear triangle and wheel point left while the front half of the frame points right. :shock:

I have theories about where it should be tweaked, but no fixture or methods to hold in place or levers to bend it. Is anybody out there accomplished at this?

 

[Walker]

Re: Needed: A Master Frame Tru-er!

Strip everything off the frame. clamp the bottom bracket in a large bench vise. Get a piece of string (carpenters chalk line is just about perfect) tie a 1" loop in one end and hook it to one rear drop out ear, run the string around the head tube and back to the other drop out, do some measuring and tie in a rubber band so you can tension the string and it will stay put. Now you have a rear triangle alighment tool.

Now you can measure from the string to the seat tube to see which way the rear triangle needs to go. I perfer a caliper to a tape measure. For example, (assuming riding position on the bike) if there is a 1/2" gap on the right side beyween the seat tube and the string and 1" on the left then the rear triangle needs to be pushed or pulled to the right to equal things up. keep an eye on your rear drop out spacing..

With the frame set up, you can now also visually eyeball the "plumbness" between the seat tube and the headtube. You may also want to insert a piece of tubing in each (seat tube & head tube) that extends ±18" or so out of the seat tube and out of he head tube so you can visually line them up by standing away and off the front or rear of the frame. this can help alot visually as it will enhance any issues.

If the seat tube and head tube are out of plumb, your frame is likely broken . In which case, you have nothing to loose by putting some torque on the headtube to see if you can get it plumb.

Once you can get it set up you should be able to see what needs to happen. it's steel, so cold setting is fine. start with the rear triangle.

Good luck.

 

[dougfisk]

Re: Needed: A Master Frame Tru-er!

Should I pay any heed to the outside edges of the bottom bracket tube as a point of reference to plumb and allign? Using a long straitedge, I already know that the seat tube is not plumb to these surfaces. The first thing I did was align the rear triangle with these surfaces. This may have accentuated the misalignent with the front half. :? I am left wondering: is taking a a measue from a straightedge off these surfaces inaccurate; as the edge isn't precise and the length of the straitedge is magnifying the imprecision. :?: Is a tilted, cocked, or poorly fit bottom bracket tube irrelevant to truing a frame?

 

[Walker]

Re: Needed: A Master Frame Tru-er!

A straight edge works instead of string, but string is hands free which can make the job a little easier.

ignore the side to side alignment of the bb shell, but it should be perpendicular to the seat tube.

you could put some dense wood blocks like Oak or mahogany or something between the bb shell and the vise.

if the head tube is out of plane with the seat tube I think your only option would be to try to twist the head tube back. I've never dont this and I would imagine a lot can go wrong.

Did this thing get run over?

 

[scrumblero]

Re: Needed: A Master Frame Tru-er!

you could always find a shop with one of these.. :lol:

 

[dougfisk]

Re: Needed: A Master Frame Tru-er!

Is that yours? I send it to you. :wink:

you could always find a shop with one of these.. :lol:

 

[deorman]

Re: Needed: A Master Frame Tru-er!

Bottom brackets are often displaced slightly to one side, even on undamaged decent bikes, for running gear alignment and balance issues. Getting the wheels and steering head in a single plane, and getting the seat and crank as closely as possible centered on that plane is what you're striving for. On some cheap coaster bikes, both new and old, this is going to mean the stays and/or the bottom of the seat tube are going to be off center. Some are impossible without bending or cutting and welding. Some are unworkable for adult road use, while others will turn out as good as a bike costing 5x the price. If it looks okay but the back wheel just can't be nudged into plane, filing the dropout can often solve the problem. Good luck, and happy cycling. :wink:

 

[user 135]

Re: Needed: A Master Frame Tru-er!

Walkers string trick is the easiest to tell at home about the condition of the frame. If you can find access to some tools at the local bike coop or friendly LBS, that is the ticket.

Using tools like this really helps bending the rear triangle back straight.
http://www.parktool.com/product/frame-a ... auge-...-2
http://www.parktool.com/product/frame-a ... -set-ffg-2

and here is a great article talking about frame alignment of the rear and front triangles. http://www.parktool.com/blog/repair-hel ... -alignment

 

[B607]

Re: Needed: A Master Frame Tru-er!

The Sheldon Brown website has a good tutorial on this. I don't have the link. Gary

 

[Walker]

Re: Needed: A Master Frame Tru-er!

Any progress?

 

[c.p.odom]

Re: Needed: A Master Frame Tru-er!

When I was doing full restorations I would fully align all frames, forks, and crank arms. Multi piece springer forks were the hardest and not many people realize how bent some one piece cranks can be after decades of use. I would rather not comment on all the bent parts I have seen with expensive paint and chrome jobs on them. It sure is a pleasure to get on an old bike that rides perfectly straight hands off and without the pedals swimming around under your feet.

 

[dougfisk]

Re: Needed: A Master Frame Tru-er!

Any progress?

I read everything to be found at the links mentioned and elsewhere, and then I attacked in earnest... sorry, I was too focused to take pics...

The seat tube was, in fact, not square to the bottom bracket. The head tube was not plumb, parrallel, with the seat tube. It would seem to me very difficult to bend the seat tube out of square with the bottom bracket so I wonder if this frame was just poorly fit together and should have been weeded out at the factory. Especially since there is NO damage to any of the sheetmetal on the bike, and paint is very very nice. The critical 3-point centerline - head tube, seat post, rear triangle, was out of line by at least 5/8 inch!

Over many years I have watched my father, a true old-world skilled craftsman, do miracles with junk he pulled out of the scrap pile, so, in his honor...

I bolted a bare hub in the rear triangle. Laying the frame on its side, I slipped the bottom bracket under something heavy and stationary, (think of a fully loaded shelving unit for example). I placed a block or 2 of scrap 2X4 under the rear axle, and under the top edge only of the head tube, as I wanted to induce some twist on the head tube. The frame was held off the floor, pivoting at the 2 ends and pinned down at the BB. Then I stepped, and stood, as necessary on the top end of the seat tube, hoping to address all the problems in one operation. I did this repeatedly, talking it out, re-measuring, repeating possibly 10 times, each time making a little process. I stopped when the alignment of the 3-point centerline was near perfect, within .030 or so. I checked the head tube; it was much, much closer to plumb with the seat tube, probably within factory specs.

I re-assembled enough parts to ride it, and I'll be damned, it rode fine, I felt no abnormalities, and it tracked as straight as anything I own! I suspect that the working edges of the BB are still not square with the seat tube, and maybe not with the rear triangle either, but it doesn't matter, I don't care, and I'm not going to check.

I call it a home run. My thanks to everyone.