Reassembly of the swing arm has been on hold for a while.  A few others indicated that they'd like to know more about this, so I'm sharing an update on my progress and problems.

There was a lot of corrosion in the tube so I used a brake cylinder hone to clean it out.

 

As I cleared away the rust, I discovered there's a groove machined into the ends of the tube where the bushings reside.

 

The hone can't clean the rust out of that groove, so I took a chance and shot a little glass bead into the tube.  I inserted the blast gun nozzle into each end of the tube and was careful to maintain a shallow angle while rotating the tube.  Both ends came out relatively clean.  I ran the hone a second time to make sure I had clean, smooth surfaces to seat a new set of bronze (aftermarket) bushings.  With all that working, I was concerned that I may have removed too much steel from the tube.  That turned out not to be an issue.

When everything was finally cleaned up, I was able to take a closer look at the machining in the bushing ends of the tube:

 

I was surprised to find a spiral groove.  Here's a closer look at the machining:

 

None of that is terribly important, but I found it interesting that Yamaha did such intricate machining on the swing arm tube.

Now it was time to get on with the task of inserting the new bronze bushings.  I followed the recommendations of other posters and put the bushings in the freezer for a couple of hours.  Before I pulled them out, they were at 4 degrees Fahrenheit.  While the bushings remained in the freezer, I heated one end of the swing arm tube to 500 degrees Fahrenheit.  No one mentioned a target temperature, but I figured (estimated, assumed, guessed) that 500 degrees had to be hot enough to get the required expansion.

 

As soon as the tube was at 500 degrees, I reached over and pulled a bushing out of the freezer and dropped it into the hot tube.  I expected it to slide right in, but it did not.  It didn't go in at all.  I'd been warned not to pound on the bushing, so I gave it a couple of taps with a plastic mallet.  No go.  The bushing went in about an eighth of an inch and jammed.  I quickly turned the swing arm over and used a wood block to tap the bushing out before it seized inside the tube.

Now I'm stuck.  Both literally and figuratively.  I'm considering taking the bushings down a little with emery cloth, but that's just guess work.  Remove too much and the bushing will rotate in the tube.  Remove too little and the bushing will be jammed part way in as the temperatures equalize.

Can can anyone suggest a solution?  Do I need to use a torch on the tube to get it above 500 deg???

Thanks for your time.

*I wore gloves because, on a trial run, the cold bronze bushing (4 deg F) stuck to my hand and I couldn't release it.  Not fun.



 

I've done 2 swingarms with the bronze bushings. Didn't have much trouble removing the plastic ones. Spent less than 2 minutes removing the rust with coarse sandpaper. The new bushings push in with almost no resistance. And they will slide right out.

 

 
 

I suspect the challenge is with the bushings, not your technique.

Years ago I bought a kit for an RD350 (I think it uses the same bushings as your DT) and had to press them in.  Then the bushings needed to be reamed to size, even though they were a perfect fit on the sleeve before they were pressed in.  If you do get the bushings installed, as tight as they are you'll likely find they will need machining. This is technically the "best" as with the proper reamer you'll insure the bushings are in perfect alignment. 

But WAY too much work and hassle...  and my adjustable reamer wasn't quite long enough to use the alignment sleeve on the other bushing.  Eventually I got it to work.  Never again.

On another RD I worked on, the bushings were shot so I helped a friend replace them.  He bought a different kit and the bushings were a light press fit into the arm.  We used some loctite on the OD to help make sure they spun on the sleeve and not inside the arm.  No reaming needed.  The whole process was super easy and probably came out better than the "tight" set I had installed.



 

As others have shared here... Go with the upgraded Bushings from MikesXS...

Works so much better and you will never have to mess with it agin.

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The bushings are finally in and all is well.  I hope this update will be helpful to anyone contemplating this project.

 
       (You can still see some discoloration on the tube from the heating process I tried earlier.)

I went back and reviewed the information on the web page I ordered the bushings from.  Two things stood out:

   }  We sized the inside diameter to allow perfect clearance between the bronze and the steel bushing after the bushing is pressed into the swing arm.

   }  CAUTION!  The bushings must be pressed into the swing arm.  If the bushings are struck with a hammer or pounded in, the bushings will be damaged.

There are lots of variables in a project like this and, while the heating and freezing method seems to work well for some, it did not work for me.  I decided to take the swing arm and bushings to a local machine shop.  The guys there were great - a family business since 1923.  I explained what I'd done with regard to the prior heating and they were careful to inspect and measure everything.  The side that I'd heated (500 deg F) was slightly out of round.  The machinist said it was minor, but probably due to the heat I'd applied.  He said heating with a torch would have been a big mistake and might have ruined the swing arm.  He also measured the bushings and said that the bushings' external diameter oversize was a perfect match for the steel tube diameter.

When he was satisfied that everything was in order, he took the swing arm and bushings to a press.  It took less than two minutes to press both bushings.

When the machinist returned the swing arm to me he cautioned that the bushings' internal diameters would be slightly smaller after the pressing process.  He explained that bronze is a relatively ductile alloy and that pressed bushings frequently require reaming.  He said he'd be happy to do that for me if required.  I remembered the supplier's comment about sizing and crossed my fingers.  I can't offer any information regarding machine shop pricing because the machinist refused to accept payment for his services.  He said that he was glad to hear that I was restoring the bike and he was happy to help with the project.  Go figure.

I purchased stainless steel internal bushings from the same supplier.  When I got home and checked, they were a perfect fit.

 

Now I have just one more thing to figure out and I'm hoping someone can offer their advice . . .

For all the years I've owned this bike, I never noticed the openings at both sides and both ends of the welded stampings between the two arms.  Bead blasting really made the gaps obvious:

 

 
         (Underside of the swing arm)

The openings are important because they allow drainage, but the inside of that steel structure has been open to the elements for the past 48 years.  I'm concerned about hidden corrosion.  At an earlier point in this process I decided to have the swing arm powder coated.  I'm rethinking that now.

I'm considering sealing the bushing ends and spraying a liberal amount of brake cleaner into the cavity to flush it out. Then, when dry, submerging that end of the swing arm in a tank of rust converter to completely flood the interior of the assembly.  After draining and allowing time for curing, the third step would be to repeat that process with Rustoleum paint.  The last step would be to sand all of the paint runs smooth and then apply several finish coats of gloss black Rustoleum.

Does anyone have any experience with this?  Can anyone offer recommendations, . . . or is this just a really bad idea?

I've had this bike for forty-eight years and I'm planning to pass it along to my son.  I'm hoping he'll have it for another forty-eight years.  That's why I'm being so meticulous . . .  I'm thinking long term.  With any luck, very long term.        : )

Thanks again for everyone's suggestions, recommendations, and advice.