Driveshaft straightening 101

[Myself]

Quick and easy method to straighten out a bent driveshaft. You'll need a set of V-blocks, a dial indicator with holding fixture, and a press. BUT.....I've done this in the past using Lego's as V-blocks, dial indicator clamped to a block of wood, and a big brass hammer as the press. Hey, you work with what you've got.
Set the shaft in the V-blocks and use the dial indicator to check runout at BOTH ends, AND about every 2" a long the length. Use a sharpie to mark the highest point of runout. This one started well over .030" bent!! It was also crooked more in one direction.
Here is the shaft after I marked runout. Those numbers are thousandths of runout.

 

[Myself]

Here is the shaft getting pressure in the area with the MOST runout facing the press point. DO NOT overdo this. Just put enough pressure to see the shaft deflect, then tap (not smack) along the shaft with a small hammer. That helps relieve the stress in the metal and bring it back into shape. I had much more bend in this center section so I placed the wooden blocks closer together to help get this larger bend out first.

 

[Myself]

Now back into the V-blocks (or Lego fixture LOL) for measuring. Yep we're making progress. If you didn't make any progress, press to deflect the shaft a tiny bit more and try again. Just keep going like this a bit at a time. You can use a shot of carb cleaner on a rag to wipe the previous sharpie marks back off.

 

[Myself]

In this pic you can see 2 sets of marks. You can also see they are NOT on the same line anymore. The lower numbers were after I pressed it on the higher points. This commonly happens cause the shaft was rotating when it bent.....and it also got crooked off to one side. Not a big deal at all. Just chase the runout around the shaft and bend as necessary. Moving your support blocks to only bend the section you need to. Most of this session the blocks were out right to the splines except the first bend or 2.

 

[Myself]

Getting real close now, less than .003" runout along the whole thing. A lot of times when you get this close, you can just support the shaft on wooden blocks and tap down the shaft with a hammer. Without a press you can use this method to beat the whole thing back into straight........but the shaft will have hammer marks all over it. After a bit of tapping and measuring a few more times I have the whole thing running less than .0015" runout. The whole process took me about 1.5 hours.

 

[DAG]

What made it .030" to begin with? That's 3x spec at USL. Have you re-checked one after it sees load?

 

[WFO Speedracer]

What made it .030" to begin with? That's 3x spec at USL. Have you re-checked one after it sees load?

It would take just as much force to rebend it as it did to straighten it , we straightened motorcycle forks and ATV axles all the time, unless they were wrecked afterwards they never came back bent.

 

[Myself]

What made it .030" to begin with? That's 3x spec at USL. Have you re-checked one after it sees load?

On the couches people have a tendency to float over the tube rope. The pump of course sucks it right up. Sometimes, they float over it, then stab the throttle. The rope wads up around the driveshaft very quickly then BAM......stops and bends the shaft. Done this MANY times over the years, never had a problem with any I've straightened.............Oh ya,.......except one idiot who turned right around a week or two later and did THE EXACT SAME THING!!

 

[vcolf]

Cool write up, thank you. Have you guys ever seen bent shafts on standups assuming know rope mishaps? I’ve always wondered with the surf riding stuff, broken motor mounts, and all the abuse we do to them if it ends up bending the shaft. My assumption is if it’s bent that bad you’ll feel it and see it in the vibration of the motor.


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[bkspeedwerks]

i think alot of shafts are bent from people removing stubborn props with out supporting the pump and the driveshaft taking the brunt of the force.

 

[Myself]

If they're bent very bad at all....you'll feel the vibration. On the couches the vibration is in the handlebars and footwells. On a standup, you'll feel it in the tray.