The Vespa stayed parked for a while, because I couldn't decide whether to replace or rebuild the subframe. I didn't have a welder, so rebuilding wasn't an option at the time. I had gone ahead and made templates for plates and began to cut them out with my angle and die grinder (very time consuming). I built up an OA rig and was contemplating doing the project with O/A - I'm so glad I didn't do this because the welding would've taken forever. Unfortunately, my cutting torch parts still didn't get here in time so I had to mechanically remove material any way. This past weekend I picked up a miller promig 135 with gas shielding (and a bunch of HID stuff ;) and I decided to go for it since it was my fall break.
I did some work on Thursday when I got home, but it was mostly getting all the kinks out, setting up the welder and riding with nashville's vintage motorcycle group Pseudomoto. The CB100 rode great and got me in shape to work on the Vespa.
My plan consisted of using cold roll steel to inlay the cutout of the subframe. I used 1/8" for the major inlays. It's been over a year since I'd had any time on a welder, so my welds weren't pretty but they should hold just fine... I didn't lay anything that was so bad I had to cut it out, but it definitely could have been better. I made sure to put a bevel on the pieces that would be adjoining to thinner material - this along with torch angle is important to get a consistent heat and penetration when welding together materials of different thicknesses.
Here's some footage from me working... not as epic as I wanted it to be... cam kept dying :/
In my infinite wisdom, I did not do a fit check with the transmission components installed with everything tacked toegether, and I ended up having to remove metal from my main reinforcing plates after welding them in completely. This made it way uglier and take way longer... IF YOU REINFORCE A SUBFRAME THIS WAY, DON'T FORGET THE TRANS CUT OUTS!!!!! This was a HUGE disaster and I would've finished the bike Saturday instead of Sunday (because the paint took a whole day to dry) as I didn't have it in me to finish fabrication Saturday night after this mistake.
From there I did some cosmetic welding and sanded everything down and started prepping for paint (and of course did another fit check before paint lol). I decided to go with two coats of automotive primer and two coats of Rustoleum gloss enamel.
Re-assembly went fairly smooth except for the 4 bolts that go into the rear transmission housing were too short with the lock washers (I need to get new ones that are long enough for lock washers) and the main bolt up front that the subframe hinges on was too short. Everything else went smoothly and the bike was back together and running.
For Those Thinking About Doing This:
I would suggest including the trans cutouts in your design if you decide to go the plate overlay method.
Another thing I would suggest to those who would want to do this in the future is to consider using round stock instead of plate. The plate was incredibly thin in some spots and certainly could have been thicker. Round stock would allow you more flexibility and be way easier to manipulate.
Lastly, I suggest you just make another subframe entirely. After having done a reinforced subframe, I think that if I'd had an oxy-acetylene torch setup functioning or a plasma cutter, I wouldn've just gone this route. It would've been more effective and easier. I'm not sure I'd recommend doing it out of plate either - I really think that maybe next year I'll build a tube sub-frame. I'm not incredibly satisfied with the reinforced stock subframe.
Some how I picked up 5mph during the rebuild...
I took her for some speed runs and I guess she's loving the cold weather and not having a huge gaping crack in the exhaust :) I hit 52mph with stock vario notched with my aluminum weights, gates AX39 tri-power belt and a polini blue contra in the back with a 13mm carb and a DR65. The amount of vibration is still a bit disconcerting, so a mazi crank this winter (thanks for the suggestion Joe) and a homeade dynamic balancer for my stock vario (that'd be fun right??) or a polini vario are in order. I can probably build a ghetto balancing setup cheaper than I can buy a polini vario and weights, so I'm probably going to go that route... would be awesome to offer that as a service to all the stock class racers...
The subframe is fixed, but before next rally season ...
I set some parts on the bike to see how possible throwing a disk brake on the front would be and I think I'm going to go for it this winter since the forks are substantial enough, hyrdaulic and the fork lowers are steel. The setup would be a Z mag with china disk fitted and a honda caliper and master cylinder with a custom stainless line from the local hose manufacturer. With a disk brake, this would be the ultimate doubles bike for knoxville campus or rally bike period. I'm super stoked to bring this bike back up here next semester and rally on it next summer if/when I get out of school :P
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