RT3 MX project

I'm waiting on the weather to do the paint on the XS650 enduro project, so took some time to work on the RT3. I bought the '71 DT1 and '73 RT3 a few weeks ago, and since the '70 RT1 and '71 DT1 won't have any fabrication I thought I'd go a little wild with the RT3.


I stripped it down to the bare frame.


I'm wanting to do laydown shocks for more rear travel, so will be using an XT500 rear frame section.


The rear frame needed narrowed to fit the RT frame, and for the shock mount spacing of the swingarm I'll be using.


I cut off the rear frame from the RT3.


I'll be using a '77 RM250B swingarm, which is what I also used on the blue tanked '69 DT1. The early DT square swingarm frames use a 12mm bolt, but the RT3 frame uses a 16mm pivot bolt, and the RM swingarm uses 14mm. The RM swingarm does take a 28mm OD bearing or bushing, which is the same size as most Yamahas, so I'll be using XS650 bronze bushings. The machined area on the RM pivot isn't quite deep enough to fit the XS bushings, so I had to shave the last 5mm of the outside of the bushings to fit.


Here the bronze bushings are in. The RM pivot is narrower than the RT, so I trimmed down the center spacer of the three piece RT pivot tube leaving the the outside collars slightly proud of the bushings. I'll be using XS650 end caps, since they have a grease seal unlike the RT caps, and will use washers on the outside to make up the rest of the width difference.


Here is the RM swingarm fitted to the RT frame. I put a bare set of engine cases in the frame for reference.


I then made a simple jig in order to locate the shock mounts in the correct location.


Here the rear frame is beginning to be fitted. The jig makes this much easier.


Here is the rear frame nearly fitted and close to being ready to finish weld. I put a set of shocks on to see how it is looking so far, and I'm really liking it. I'll also be using an aluminum YZ125C tank that I'd bought at the swap meet last year. I think it will be perfect for this bike.