Two Wheel Tuesday: How I screwed up a vintage frame, and how a lathe, a sledgehammer, and the Internet fixed it.

Early last summer, I picked up a derelict 1973 Harley/Aermacchi SX SS-350 frame for just the cost of shipping. It’s a back-burner project (even more back-burner than Bultakenstein), but I’m doing a bit here and there. Last week, while attempting to install new steering bearings, I stupidly bumped the frame, sending it flipping off the workbench. It smacked the concrete garage floor right on the end of the steering stem. I was heartbroken, wondering if my frame was trash.

I briefly tried heating it with my puny Bernzomatic propylene torch but, as expected, that wasn’t going to do much beyond haze the paint. So, I sought advice online. I posted a photo on the Aermacchi FB group, and a couple of forums. Most people said I should take it to a machine shop, but—free frame. I’m not even sure what will become of this project. It’s not worth spending a ton of money on it at this point. One of the guys on the Adventure Rider web forum suggested I try a cold repair. That surprised me, but a couple of other folks backed him up as being a viable approach. So I figured, why not?

I made up a big mandrel from a heavy chunk of scrap steel (which took a WHOLE LOT of metal hogging on the lathe!). It had a section that was the diameter of the center section of tube, then stepped out to the diameter of the bearing race.

I notched the back to index on the steering stop and keep it from rotating, then I judiciously filed down where the dented lip would be, making a gradual ramp instead of  catching the dent on the lip of the mandrel. Then I got out some all-thread and the impact driver.

It would ugga-dugga about three-fourths the way home, then stop cold. So, I did what anybody would do: I resorted to a bit of persuasion with a sledge hammer! Three carefully-aligned whacks seated it all the way. After I tapped the mandrel out, the inside lip of the steering tube was slightly grunched up, so I cleaned up the edge of the lip with a grinder for about 5-10 seconds. I was then able to seat the mandrel using just the impact wrench.

I decided to use the the mandrel to do double-duty as a bearing driver. When I was ready to install the outer tapered bearing race, I chucked up the mandrel again and turned the smaller diameter section even further, so that the bearing race just slipped over it. After loading the race into it, it slowly ugga-dugged into place. (I did give the bottom of the mandrel one good whack with the sledge to ensure it seated firmly and square.) I was slightly worried it would end up out-of-round. Measuring with a bore gauge showed the race was still circular, however. When the inner bearing is dropped in place, it rotates smoothly, with no rocking (as would happen if it were out-of-round), so we’re golden!

I don’t have much experience bending metal, and find it kind of scary. Not having a bunch of gearhead/machinist friends close by IRL to help me, I want to thank all those guys who took the time to discuss a solution with me, a stranger. No way would I have dared attempt this without the suggestions and encouragement I found online.

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9 responses to “Two Wheel Tuesday: How I screwed up a vintage frame, and how a lathe, a sledgehammer, and the Internet fixed it.”

  1. outback_ute Avatar

    Nice work!

    Can only relate to changing a press-fit water pump pulley without one “in the field” – a sledgehammer was part of the process there to knock the pulley off the old pump shaft.

  2. Zentropy Avatar

    Impressive! Usually my fixes aren’t nearly as innovative as my f**k-ups.

  3. Batshitbox Avatar

    You had some good advice; that’s just what I would have done and I’ve been metal fabricating for decades. Extra fancy style would be to add a chamfer to pilot the mandrel, and use some grease to chase away the ugga-duggas, but that wouldn’t get you much.

    Once again, a curated mix of asking advice and then proceeding with sheer bloody mindedness wins out over reading the instructions (and not only because there aren’t any.)

    1. Peter Tanshanomi Avatar

      I did file a small ramp where the dented section was, but yes, I sould have chamfered it all the way around.

  4. Fuhrman16 Avatar

    Nicely done Pete!

  5. SlowJoeCrow Avatar

    Excellent work, this inspires me to find a fix for the crunched chain guide tab on my son’s mountain bike. The cause was similar, moved the wrong thing while building up the frame and it fell out of the repair stand. I also really need to get my wife’s Honda CM250C back on the road too.

  6. theskitter Avatar

    Bottom left, that’s you.
    Top right, that’s what we want for Bultakenstein.

  7. wunno sev Avatar
    wunno sev

    i love this post! good story, great use of the phrase ugga dugga, which i will henceforth use often. steel is great because you can pretty much just beat the shit out of it and if it bolts back in place, it’s probably good. fixed a couple bike frames and lots of pieces of various machines just by giving them a few good whacks.

    smashing the outer race into it probably helps keep it beat any residual springback that the mandrel didn’t take up. because the entire race is being loaded in compression, it really wants to stay round, and that probably helps force the housing into its roundest shape.

  8. Trebuh Avatar

    Nice work! Impressive! Usually my fixes aren’t nearly as innovative as my f**k-ups. Regrads 🙂

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