How can I check my frame is straight

[T. Cotten]

I agree 100%, Tom. Every motorcycle frame I have had, and had the awareness to check, has been mangled, bent, or just tweeked, but still out of spec. I agree that frames seem to have a memory, and are partial to returning to their original shape. However, both of my Hendersons had traumatic damage, and from my forensic research; they had been seriously hit in the right rear. It's remarkable how much stress is transferred to the (seemingly) undamaged areas.

So.... ..

Did you fix them?


....Cotten

[fillibuster]

This topic is a favorite of mine, and I've straightened (by my own definition) about a half dozen Chief frames and several Sport Scout frames. A few concepts can guide you through the inspection, and help explain the end result your after.
First concept, by my reasoning, is that the center planes of the wheels and the neck should all lie in a common plane. This apparently speaks for the parting lines of the engines too, although they are less critical to the handling of the bike. When working with a bare frame, of course, you have to know axle dimensions so you can transfer the center lines to the appropriate frame parts or references, i.e. the slippers in the rear, or the centers of the forks. The forks should be managed separately anyway so you can work with the neck.
Concept #2 is left-to-right symmetry. If you have a common center plane the slippers should be the same distance from that plane, and the centers top and bottom should show this. The neck can be referenced with a framing square if you have a table and a center-line, and the lower portion of the frame is in a fixture that centers it on the center-line. Finally, a shaft that projects through the neck's bearing centers should also project through the centerline on the table.
If the language of the involved geometry is confusing try to find a book with some diagrams. We are relying on definition of the plane, and the line, and symmetry. My work all happens on a 4' x 12' x 3/8" table slab, and I've used a variety of large "persuaders" to move things to where they belong. My fixtures secure the frame in the front motor mounts and the base of the lower casting on the seat post. ... and I've used 10' long steel tubing to move the slippers, so that requires some pretty firm fixtures. Slippers are easier than the neck, imo,.. I've only used heat when straightening collision bends, or to relieve stress to limit that "memory".

Wish I had pix.

[T. Cotten]

Filibuster!

I agree but.. the "parting lines" on a Milwaukee machine can lead you astray.

That's probably why they ignored them in the Service Manual.

....Cotten

[exeric]

So.... ..

Did you fix them?


....Cotten

I did fix the Henderson frames, but they were pre Deluxe and not as stout as the double down tube frames; hence easier to move. I have done a few H-D frames and there is more to be mindful of to achieve orthagonality, and dimensional correctness. I have not done an Indian slipper frame, but they look like they would be more difficult than an H-D frame. My Excelsior frame, and Merkel frame were the easiest to move as they are both very light, and minimalist. I think you can assume that any frame that uses the motor as a stressed member will be bent like a noodle. If I ever get a title for this mid-70s Honda that I have, I will be curious to see if the frame is bent. I'm betting it's not as I think Honda put a lot of engineering into making it strong; albeit, kind of ugly

[T. Cotten]

Big Twin H-D frames were almost fun, Eric!

Until the steel turned to mud by '84 or so.

But I never attempted a single-down-tube model, and I don't know how I would hold onto one. (Never a sportster either of course.)

My Chief frame experience, beyond weld repairs (couldn't find a pro..), was only to straighten bowed sections of frame members using the grate at the bottom of my framing tools photo.
As with Milwaukee machines, straightening individual members in the best, often intuitive, order brings the entire assembly back to harmony.

Missed my chance at a REAL table once, for a song.
But it would have been impossible for me to transport or handle, and no place to put it.. ... . *sigh*

.....Cotten

[Green Indian]

DSC01886.jpgDSC01889.jpg

Here's a Four frame at John's shop in LA, taken some time ago on a vist out west.

[T. Cotten]

Good pics, Green Indian!

I recognize the headstock rod straightedge, and a vertical reference rod within the left "plunger".

The rest is the necessary "immovable object".

Its awesome, but I would roll it outside, where you can back off far enough to actually 'eyeball'.

I had to stand in the alley.

....Cotten

[Green Indian]

I wish I had video of him straighten the frame. I was there once, sans camera, when he was straightening a Chief frame and it was quite a bit of work, some are more tweaked than others. A lot of heat, applied a crucial points, helps the frame "remember" its correct settings but some do require more radical surgery to fix.

[T. Cotten]

I wish I had video of him straighten the frame. I was there once, sans camera, when he was straightening a Chief frame and it was quite a bit of work, some are more tweaked than others. A lot of heat, applied a crucial points, helps the frame "remember" its correct settings but some do require more radical surgery to fix.

Heat can destroy "memory", Green Indian!

....Cotten

[ryan]

Heat can destroy "memory", Green Indian!

....Cotten

That it does, they are not made out of smart alloys.

[Green Indian]

Well then maybe it's not "memory" - I may have used the wrong word here, I'm no expert, but the application of heat on that frame worked wonders; as the frame fell back into alignment with careful application of a torch to select points. My poor choice of words in this case.

[T. Cotten]

Just what I was taught, Green Indian!

If it was bent cold, it is straightened cold.

Most 'speltered' or brazed frames were straightened after assembly, then treated in an oven to give them springy-ness, and its 'memory'.
Excessive heat turns that to mud. (But ya gotta do what ya gotta do, sometimes!)

I wish I could learn how Schwinn 'tempered' his frames.
(Not that I am entertaining any more through my shop... Retirement sounds like a dream.)

....Cotten

[Green Indian]

Thanks, Cotton. That does clarify things a bit. I'm just an observer in John's shop and I can not argue with his success at these things he's done hundreds of frames, I'd wager, and I'm sure there are other methods employed to bring errant frames back into correct alignment other than heat. It's just that particular day and that frame had heat applied to select sections which worked wonders for the one that was on the table to be straighten that particular day.

[ryan]

Just what I was taught, Green Indian!

If it was bent cold, it is straightened cold.

Most 'speltered' or brazed frames were straightened after assembly, then treated in an oven to give them springy-ness, and its 'memory'.
Excessive heat turns that to mud. (But ya gotta do what ya gotta do, sometimes!)

I wish I could learn how Schwinn 'tempered' his frames.
(Not that I am entertaining any more through my shop... Retirement sounds like a dream.)

....Cotten

I may be able to get you this information Cotten.

[T. Cotten]

Are you 'channelling' Ignaz, Ryan?

If so, set me up for a séance!... thanks.

....Cotten
PS: I guess "memory" should not only apply to making a frame straight again, but also to staying straight.