DT1 flat track project

I welded up the exhaust and the front mounts for the gas tank.


For the rear tank mount I got a new reproduction from CSM Restoration Parts, the same place I got the mount for the CT1 tank on the '79 XS650.


The engine rebuild will be starting soon, and one problem with the DT2 engine in the bike is a broken case at the shift shaft. This was likely from a chain breaking, and likely the reason the bike was parked. It is possible to weld this, but I figured replacement would be better.


Looking at replacement cases on ebay, I found a DT3 bottom end for $64.99 with free shipping. That's a deal since I also get a spare transmission and crankshaft.


When the DT1 came out in '68 it quickly got a reputation as having nervous handling. One popular mod with the DT1 is lowering the engine cradle and swingarm pivot. It is supposed to lower the center of gravity and reduce the swingarm angle, so an option I looked at. It kinda makes sense, but since it reduces ground clearance anyway, it also sounds like a more complicated way of what could be achieved by just lowering the entire bike. I started comparing the '68 frame with my '73 DT3, and about the only frame geometry difference I noticed is a 1" longer swingarm on the '73. A later, longer round tube swingarm can be fit, but I wanted to keep the early square swingarm, so decided to stretch it.


The rear axle to lower shock mount distance is the same on the '68 and '73 swingarms, so the longer arm also moves the shock mount back, changing the shock angle, one of the reasons I decided to stretch the front rather than extending the axle plates.




I needed slugs for the square tubing, so started with angle stock.


After welding and grinding I have a piece of square tubing to cut the slugs from.


I did some mock-up, and a 1.5" stretch looked about right.


Here is how the slugs fit to the front part of the swingarm.


Since the swingarm tubing isn't square to each other I needed to cut slots to allow the slugs to slide in.


Here is how it all fits together. After welding in the slugs, it will then get skinned to look like it came from the factory.


The pieces fit tight enough to mock it up and see how it's looking before welding it up. It is a bit lower, longer, and with less swingarm droop and more shock angle than before. It'll be interesting to see how it handles. I'll also need a longer brake stay and brake rod. I'll finish the swingarm this weekend. I've got a '73 SC500 rear wheel on the way. I think it is the same wheel as a DT2MX, so it should fit right in.