Triumph Front Leg Frame Repair with Special '79


Ok, the time has come to make some progress on this Triumph build that’s been collecting dust in the shop corner for a while now.  Aside from some basic cutting and smoothing, I will be keeping the front frame section close to stock, only replacing the dented frame sections.


Upon disassembling the project Triumph, I noticed the nicely dented lower front frame legs coming off the single downtube during the visual assessment of the frame’s integrity. Would these frame sections hold up to the wear and tear I’ll be putting on the finished bike?  Probably.  Am I happy with probably?  Not in the slightest.  Time to come up with a repair plan that is pretty easy to wrap your brain around.


First thing on the list is to fabricate some sort of motor dummy to hold all the motor mounts and frame geometry where it belongs when we cut into it.   I’ll measure and turn down some tubing sections to bolt between the lower and front motor mounts and start to weld some metal pieces between those sections of tubing.   These sections will have multiple bracing welded to them to keep the frame from moving.  I made some “saddle” sections out of some 1.25” .120 wall tubing that would get tack welded to the lower stock frame rail that runs from the backbone to the frame headtube.  This ensured a nice sturdy support of the frame and bracing.

Next step would be to determine the amount of frame to cut out of the damaged area.  It’s good to place the cut lines on an area that has at least 1.5” to 2” of flat, un-curved sections on each side of the cut.  This will help with the sliding/placing of the interior slugs that will reinforce the splicing of the new bends to the original frame sections.

Once the cut lines are determined, I use an angle grinder with a cut off wheel or a sawzall with a metal cutting blade (duh) to remove the damaged bends. In the event that you don’t have enough of a flat area in the tubing so you can slide the slugs completely inside one side of the tubing you’re replacing, you can “clamshell” the tubing ends around the interior slug.  “Clamshelling” consists of cutting the tubing equally lengthwise on opposing sides so as to help remove a section of tubing equal to half it’s circumference (in whatever length is needed).  This will allow you to place a slug inside the tubing and close up the tubing around it for welding.

Now that I have the damaged sections removed, I take the burr left on the interior of the frame tubes to get an accurate read with my calipers.  This measurement will determine the diameter of the slugs I’ll turn down on the lathe to slide into the frame and new repair bends.

With the new sections of 1.125” tubing bent up, it’s time to mark them up, cut, and make a test fit.  Keep all your notes on the bends you’re making for future frame repair notation.  A couple minutes with a pen and paper will save you a chunk of time if you ever have to do this repair again.  Once I’m happy with the fit, I’ll chamfer all the edges of the tubing to ensure proper weld penetration. Next I’ll drill some staggered holes in the frame and new bends so I can plug weld the spliced sections to the interior slugs.  Once everything is cleaned up with acetone or isopropyl alcohol, I’ll assemble the sections and tack weld.  It’s a good idea to weld small sections at a time on each joint to keep distortion to a minimum. 

Now it’s time to make the repaired area blend into the stock frame.  There are many ways to take the welds down, but I’ll give you the rundown on how I handle it.  I’ll initially take the bulk of the weld bead down with an angle grinder (or die grinder) with a resin fiber sanding disk backed with the flexible rubber backing pad.  Once I get the weld area really close to the tubing surface, I break out the flat bastard cut files and make the weld seam disappear.  A little work with some emery cloth strips and the repaired area looks brandy new.  Now I just have to get to the motor and this build will really get moving!  

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Comment with Chopcult (4)

Commented on 5-23-2013 At 08:24 am

Nice job, solid repair, thanks for posting.

Commented on 5-23-2013 At 08:37 am

The best part of ChopCult are the Special 79 tech articles - hope someone is grabbing screen shots...
J. is a wizard

Commented on 5-23-2013 At 03:08 pm

Damn fine the kids say these days "I'm jelly."
The un-cool kids it seems...

Commented on 5-25-2013 At 06:15 am

Nice work and excellent pics!

The best part of ChopCult are the Special 79 tech articles - hope someone is grabbing screen shots...
I use Firefox and print any pages I want to save to .pdf.

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