HD spring fork straightening

[kurly]

Does anyone in the Milwaukee area straighten spring forks? My 1948 offset needs help. On the rigid fork the neck stem is slightly bent and is not centered in the handlebar hole by approximately 1/8". When I lay it front side down on my milling machine table, the left lower fork leg is off the table 3/16". Hope to have it done by the Badger Derby Ride in August. If no one is in Milwaukee area, who would be the best one to call. Should I attempt straightening it myself with a Tool & Die maker friend? Thanks, Curly

[exeric]

This is just my opinion; but you should do it with your die maker friend. I do my own work on frames and forks because I'm going to be the guy in the saddle. I feel like I'm going to make structural decisions based on safety, and not on profit. I'm not saying I'm an expert, and I am willing to bet an experienced frame guy is going to know better, how to do some things, but I think I know when I need to go to an expert, and when I can do something myself. There are things I will not do on a frame or fork, and that usually involves welding in a sensitive area like the fork stem. With a machine background, you and your friend are going to have a better feel for steel and it's limitations than many.

[T. Cotten]

I agree with Eric, Kurly!

H-D springers are very friendly, as they retain a lot of their "memory".
I have taken one that was S-shaped sideways and retrieved it so easily it surprised me; It was actually fun and rewarding.

But one warning: Stay away from heating it.

Good luck,

....Cotten

[sirhrmechanic]

I think there has been a fairly detailed thread on here about rebuilding/straightening springer forks... I recall it was rather well done!

And I agree with Cotton and Eric... The dimensional issues you describe should be something you can handle with a flat plate and careful measurement. Post some pictures as you go!

Cheers,

Sirhr

[motorpickle]

If you're interested, I have a straightening table I do forks on. Call me @262-886-2072 Ask for Don

[kurly]

Well Thank you, I know "no heating on spring forks". My friend being in tool & die is a perfectionist. We have tackled many other jobs with excellent and also rewarding results. His first thought was take it to a professional, but then called me the next morning after (sleeping) thinking about it and said we could do it.
I'll try to take pictures, everyone including me likes pictures.
Curly

[sirhrmechanic]

Trick with straightening 'mission critical' parts is to figure out what it takes to get them far enough beyond their elastic limit to get them back where they should be, without going 'back and forth' in a way that causes work hardening and embrittlement.

We occasionally have to straighten crankshafts at the shop. The RR/B shafts from the 1930's were nitrided. The nitriding process involved heating the cranks and then grinding the hardened surface, which went about .040" into the metal. Unfortunately, this also stored up stresses inside the cranks, so that when the crank journals are ground to clean off wear... they have a tendency to warp. Which just sucks because you end up with a crank that has .008" of wobble on number 4 journal... with .0015 - .002" bearing clearance. The result is a locked-solid crank in its 7 bearing saddles. And that just won't do.

The answer is to set the crank up in V-Blocks with 3 indicators... and put it under an arbor press. You then deflect the crank until you hear a tiny 'click' and then check your indicators. You usually take 3 - 4 of these little 'clicks' before the crank is straight. Last one we did had to be deflected .440" at its center journal before it passed its elastic limit enough to bring it into .001" of straightness, which would clear the bearings. That takes a 4 foot bar on our arbor press and all of my weight pressing down on it as we listen for the click.

It is a terrifying process with an irreplaceable crankshaft belonging to a customer who is trusting you with their very expensive car. But we've never failed. That said, that little crack/click is the loudest sound in the world when you hear it. Even though the slightest background noise will cover it up, it's so minute as to be almost inaudible. I'll see if I can find a photo. Crank straightening has taken on the aura of black art. It's not. It's about knowing your materials, measuring with indicators and being both aggressive and careful at the same time.

That also, shows the value of a forged crankshaft. Most modern cranks would crack in half at the first sign of deflection. Vintage cranks made on drop forges from virgin steel.... well, they are pretty impressive bits of kit.

The takeaway is to use indicators... get a feel for how much deflection results in how much straightening. Use screw jacks or arbor presses where you can control your pressure. And go for it. You will have no problems...

Cheers,

Sirhr

[T. Cotten]

Whew!

Springers are a LOT easier!

Indian girders are much more of a test.

.....Cotten