Topic: Bent frame - how to tell?

[Magpie]

Hey!
I have acquired a K0 that has been severely abused and crashed. There's a good dent in the steering head so I want to be sure it's straight before pouring more time and money into it. It has fewer correct parts on it than the $275 one currently on ebay, although it is the correct motor. Is there a quick way to check the frame without stripping it to a bare frame? The bike's close to that now but....
Thanks,
Cliff.

[bryanj]

With teh trees removed ged a couple of wooden cones turned that will fit into the headstock and whist being turned a 6mm hole through the middle.
use a long length of 6mm studding and clamp the cones top and bottom of the headstock.

This will give you a rough reference that needs to be upright when the frame is (by that I mean not angled off to one side or the other) and the point approximately in the middle of the rear tyre when viewed straight from the front.

Hope that makes sense as its a lot easier to do than describe

[754]

Use a thicker rod & metal cones if you use that method.

 For a quick check, eyeball the swingarm with axle in and try to check to the pivot part. If that looks ok then get the rear axle sitting level or close to it. Then hold the forks straight with axle in, no wheel. Use a small level like from a combination set or anything that fits.....the axles should be parrallel to each other..

[Magpie]

Thanks guys!
Cliff.

[HondaMan]

This sounds like a job for my lathe. 
Maybe I should make a set up for use by SOHC4 members?

Another method: requires straight forks...this is the "shade tree mechanic's" method...
Put the bike on the sidestand, but with shims under the stand until the bike is nearly vertical (or, find another way to make it stand vertical on its tires, like a rope to the rafters). Then, using two heavy, 2" tick (or so) wood blocks with a long nail in each one, and a long string, set the blocks-and-strings so the string touches both the front and rear of the rear ties, as high as possible, and also passes close to the front tire, similarly. The front is narrower than the rear, so a small gap between the string and the front tire should appear, on both sides. Now, align the rear wheel to get this relationship equal on both sides of the front wheel (or, add a second string and wood block set for the opposite side to speed things along). When the string(s) touch both sies of the rear tire, neither side of the front tire, and the gaps on both sides of the front tire are equal, check the rear axle's alignment marks. If the left-to-right difference is more than 1/8 of one mark, the frame is twisted between the swingarm pivot and the steering head.

Production tolerance was 1/8 of one mark for a "straight" frame. Very few were truly straight. (My K2 is 1/3 mark off, due to a wreck in 1972).
Following BryanJ's advice: it is possible to "untwist" these frames by inserting a large, strong, hollow tube (hollow is stronger than solid rod) into the steering head and clamping the frame thru the swingarm pivot mounting bolts, then twisting with a hydraulic ram. It's been done to racing frames I've seen: just not observed on CB750 (by me, anyway). It's often done on chopper frames (this part is missing on Orange County Chopper shows...) to ensure the final result is straight.

[754]

My Amen frame that I ordered direct was tweaked. I got it straight, but ended up using heat. That is one stiff frame at the neck..

 You can use 2 8ft flourescent tubes to do what Honda man described, but w/o 2 people you may break them.. However , its tough to make sure the back whel is straight on a bike that you suspect is damaged..

[Patrick]

If you use heat and pressure to untwist the frame, make sure to twist past the point where the frame would be straight. As untwisted steel cools it will tend to recoil back to its original orientation. You might have to do it two or three times before you actually have it straight.

We used to untwist the hitch mount on freight cars that had been derailed with very large torches back when I worked on the railroad during my misspent youth. For those we would put huge clamps on the mount, heat the neck until it was red hot and then jack up the side of the clamp allowing the weight of the 50,000 pound car to apply the pressure. The idea is the same, but obviously the tools must be different.

Patrick

[bryanj]

I am told that you are better cold straightening a frame but i have not delved into the theary. I do know that it is recommended to "jig" and straighten damaged cars BEFORE removing any damaged parts

[troppo]

When you heat steel it will shrink when it cools. Dont know about cold bending beyond the fact that it will lead to stress fractures. Ever bend a wire over and over?, it breaks.
One bend may not do too much, but the heat would probably be a better way to go, just got to careful about shrinkage, it will pull a lot of things out of line

[754]

I was not recommending heat be used. Just stating that is what I used at the time, it was back in 79, had the frame lashed to a heavy beam in the back yard. The Amen frame has no upper front motor mounts, stretched up to the neck, which is heavily gusseted, and thicker tubing.


Today  I would certainly try it cold first, and probably frame laid on a table, shimmed and clamped, then use a bar thru the neck..