First Attempt at a Build

Also, the guy who will be doing the welding, in my second hand conversations with him, has expressed concern about the frame "losing its temper" and said it may need some kind of treatment after welding? I'm not sure what exactly that means or if its something to even be concerned about as I haven't seen any mention on here about doing some kind of treatment after welding on a hardtail. He said he has zero experience with welding motorcycle frames so he isn't sure if that's concerning either. He was a union welder so he can weld, he just never did a motorcycle frame before. Any input here would be helpful too.
For something to "lose" it's temper, it needs to be heat treated and quenched to a specific "temper" in the first place.
If you think it through logically... anytime a frame gets damaged and needs welding... even welding up a small 1" crack... you'd have to disassemble the entire bike, strip the paint off, put it in an oven, heat it to cherry red then quench it to whatever "temper" the factory calls for. Then it's back to paint and reassembly.

That's a long way of saying no, frames aren't heat treated. They use normalized mild steel tubing. Call it "weld and forget." ;)
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Well, I got the frame stripped down to just the forks/wheel and engine. I cleaned up most of the nasty oil/dirt that was caked onto the frame and engine, and I'm ready to cut the frame. I want to run my plan by you guys and see if it sounds good.

I'm going leave the engine in the frame and follow the instructions from TC Bros with regard to where to make the cuts. Then, clean up the cuts and set the hardtail in the frame. I don't have a jig, so I was planning on using a bunch of ratchet straps and some creativity to pull/hold everything in place once I think I have it all squared up. I will also have a pipe between the axel plates with the axel running through it to prevent the plates from moving inward or outward. Then, my guy will weld what he can reach. Then, remove the engine so we can move the frame around to finish the welds. Does that sound about right?
1) As suggested before - remove all electronics from the bike - including the stator on the LH side.
2) I like to use 3/4" all-thread and nuts/washers to keep the axle plates aligned while welding - one nut on each side of each plate (4) tensioned at the correct spacing before welding.
3) The TC bros. kit should have slugs that slip-fit into the stock frame. Test fit, align, clamp and weld. I'd use clamps at the joints as the straps may allow movement. You need to fab up some kind of table to clamp it to.
I started cutting the frame and once I got to the point where I’m just cleaning up the cuts and working it back to the correct length I noticed a big difference in the distance between my frame tube and the engine. It’s a big enough difference that it can been seen with the naked eye.

I think I have a big problem here. What do you guys think? A rough measurement says it’s about a half inch difference.

You're ok there.....I just took a rough measurement and get 1.25" from center of right frame rail to starter motor and 1.5" from left frame rail to starter gear case
I've been working on my hardtail for a little bit now, and I think it looks pretty good but I'm afraid I'll get it welded up then find out down the road I messed up. I followed the advise of mrtwowheel and just followed the tcbros instructions of cutting the lower frame rails 3/4" behind the exhaust mounts.

But, when I put the hardtail into the lower frame rails then rock it forward, the upper frame rails don't squarely line up with the back bone. Specifically, the left side contacts the back bone and I need to apply a fair amount of pressure to get the top (open end) of the hardtail to straddle the backbone (wrap around reinforcement section).

I took measurements from the front axel to the axel plates on each side and they appear to be off by about 3/4". I took the side covers off both sides to try to get a more accurate measurement but it still seems off. Other than that, when I pull a string from the neck back to the axel it lands perfectly in the center.

So I guess I have two questions:
1) Are there better places to take measurements from other than from the front axel to the rear axel plate? The string does contact the engine a bit and this may not be the most accurate measurement.
2) If it is off, how to I go about adjusting it since both lower frame rails are cut to 3/4" of an inch from the exhaust mount? Since both frame rails are cut to the length specified by TC Bros, grinding one down further to align the hardtail would put it well below what TC Bros calls for.
Just as a further check - measure from the bottom center motor mount in each lower frame rail to the front of rear axle slot on both sides.

Pics may help
I just wanted to come on this thread to say I really like that Gold CB350 in the background of your first post! Thats my new obsession lately (besides my obvious XS-650 fixation). I now have a Gold 1970 CB350 and a Purple/Iris 1973 CB350 in my stable as well....theyre just fun little around town bikes that like to rev to the moon. Fun to tinker on too!
Yes, I’m still here!!! So here’s two pictures of what I was trying to explain. The first picture is the hardtail after the bottom has been put into the lower frame rails and I’m “rocking” it forward. As you can see, the hardtail doesn’t line up nice at all.

The lower picture is with a tiny bit of pressure I can push it into place. I don’t know if this really matters or not.

I took some measurements from the backbone below the lower motor mount where I cut the frame to the axel plates. They seem very close. And a string from the neck to the axel lands within about 1/8” of the center.

My gut is telling me to call it good and have my guy weld it. What are the tolerances for something like this? Obviously I’d prefer everything to be perfect, but if the measurements are off by 1/2” is that acceptable? 1/4? 1/8?
I just wanted to come on this thread to say I really like that Gold CB350 in the background of your first post! Thats my new obsession lately (besides my obvious XS-650 fixation). I now have a Gold 1970 CB350 and a Purple/Iris 1973 CB350 in my stable as well....theyre just fun little around town bikes that like to rev to the moon. Fun to tinker on too!
Yea it’s a cool little bike. I got a great deal on that. The PO sold it bc he said it stopped running right and didn’t want to mess with it. I tinkered with it for like 20 minutes and found the choke linkage wasn’t connected so one carbureted was always on choke even when he hit the switch to take it off. Runs good now.
To me, I'm not real concerned about the upper rails ATM - they could have (likely were) sprung, "cocked" during shipping. The current concern is alignment of the lower rails and the axle plates. Once those are aligned and tacked the upper rails can then be aligned and tacked.

Some vendors temporarily tape or tack bracing to prevent that, but.....:shrug:
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I've done the TC Bros. I wouldn't measure anything from the front of the bike. The area that you should be concerned about is from the front sprocket back. TIGHTEN THE FRONT SPROCKET, THEY LOOSEN.

Do your cuts per TC Bros measurements.

You have your 8" spacer between the axle plates.

Make that spacer from pipe and 3/8 threaded rod. You can use that threaded rod later to spread the axle plates before mounting the wheel. Yeah! You will have to spread them apart, don't worry about that.

Pull/Clamp the frame and hardtail together with the plugs in place, tack weld or not at this point.

Prop and shim the front of the frame until the tight front sprocket is plumb (vertical, up and down).

You've got your spacer in there pushed to the front of the axle plate and the pipe is perfectly parallel to the threaded rod (not sitting on burrs or cockeyed). Is the pipe level side to side?

Now, at the spacer, measure from the inside of the left axle plate and make a mark on the top of the pipe at 7/8". This mark represents the outside of the rear sprocket.

Tie off a string somewhere in front of the front sprocket, hook it through one of the teeth above the nut and washer, pull the string tight from the rear of the bike while passing over that mark that you made on the pipe. Starting with the string too far to the left, gradually move it to the right until it barely touches the rear part of the front sprocket. Do this a couple of times, you'll see how accurate it is. Where is the string in relation to the mark on the pipe? This is your chain/sprocket alignment. I'd say you should be within 1/8" of the mark to call it good.

Don't take any measurements from those tack welded crosspieces, they're just randomly slapped in there and not even square to the other parts. Next is axle spacing, you'll need four 1/8" thick washers so that your adjusters won't look like bent up hunks of metal and the castle nut and cotter pin will match up nicely.
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Ok, I’m new to this, so I’m going to repeat that back to you to make sure I got it right. Hope I'm not getting annoying, I just want to get this right. I really do appreciate all the help I'm getting here.

Put an 8” piece of pipe between the axel plates, with a 3/8 threaded rod through it and washers/nuts on each side. (I'm guessing so I have something to represent the axel and something to measure to, with the rod/nuts holding it tightly in place)

Put the hardtail in place with the plug (plug being the piece that inserts into the vertical tube and rests on the cross member of the hardtail?) and clamp in place (not sure how to clamp it since the c clamps keep slipping off but I'll figure something out)

Shim the frame so the sprocket is plumb (a bubble level on the face of the sprocket should be sufficient?)

Now ensure the pipe between the axel plates is level. (I can foresee this not being level, that’d be my luck but I'll cross that bridge later)

Measure from inside of left axel plate out 7/8” onto the pipe and mark that.

Now here’s where I really want to clarify this: I’m going to tie off a string somewhere in front of the sprocket, I’m guessing to anything heavy like a cinder block and weave it through one of the teeth on the sprocket (to keep it tight to the sprocket?) then pull it back to my pipe between the axels. Starting from the left while keeping the string taut, gradually move the string toward my mark on the pipe until it barely touches the sprocket. Once it touches the sprocket see where the string lands in relation to the mark previously put on the pipe, and keep my fingers crossed that its within 1/8” of the mark. If it does, then weld that sucker up?

You mention axel spacing, is that something to worry about after the hardtail is on?
The axle slots in the hardtail should be 19-20mm, that's why I use 3/4'' all-thread and nuts to space and fix the axle plates (post 22 above).

The bottom center motor mounts on the stock frame remain and dictate where the motor sits and its squareness - why not use that as the reference point for measurement? (post 27)

The original factory lower frame rails has a curve to it - what you want is for the hardtail lower rails to be in-line with the section from center motor mount, past the exhaust mounts to where you cut. (string)

The alignment of the sprocket comes later when you space your R. wheel.

You should have a level flat table to do this on and, once the above is achieved, check that the axle slots are equal height from the table (should be if aligned and squared, motor mount to axle slot). Your welder will (should) have such a table and clamps.

After lower rails are tacked and seat post slug tacked, then worry about upper rails.

You don't want to mess with the, more important, axle and lower rail alignment trying to get the uppers positioned now. You've shown that they can be easily sprung into place by hand


  • TC Weld-On Hardtail Installation Instructions.pdf
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John, that was the right order of checks that you listed. If all of those check out then I am trusting TC Bros to have welded the axle plates square. If the chain/sprocket alignment checks out then the four 1/8" spacer/washers will work for spacing just as the Bros designed the thing. Any different spacing..........your stock chain adjusters will not work, your castle nut/cotter pin has to be right too. A shame it would be to not take advantage of using the features designed into that hardtail. Stock axle, spacing that allows you to use the stock chain adjusters, easy find hardware. Check the sprocket alignment now.
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Really don't see the need for all of that wrestling with it. Shove the whole thing in place, hold it there by clamp/bungie/cable/tack weld, whatever, then check it, bet you'll be surprised.
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I've been adding this question to my decision making process lately. " If I don't like it, or it doesn't work, can I re-do it?". Seems to just make most things go a hell of a lot smoother. Haven't redone anything that I can think of lately.:umm::umm::). If it's really wacky you'll figure out why. Call the guys and tell them you might have a whacked out tail. They answer the phone. They even answer the door, surprised and happy that you found them.
Its been a while since I posted anything. Finally, got the time to get the hardtail welded on. I found a local welder who normally does custom hand railings. It was a bit of a pain getting the half a frame with the engine still in it loaded onto a trailer but a friend and I made it work (back is a little sore).

Once I got it there, he tacked it and then left me to take the engine out by myself. He’s an old timer so he was more just watching me. He seemed as interested in the bike as I was in watching him weld. Thankfully he had a hoist which made getting the engine out really easy. He had some cloth straps we wrapped around it then lifted the engine just enough so that it was supported and wiggled it out of the frame.

He gave me a helmet so I could watch him do the welds. He made TIG welding look deceptively easy.

I had to leave it there for him and once I pick up the frame I’ll post some pictures. I guess next would be to get the rear wheel on and sprocket aligned?