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onthegas

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About onthegas

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  • Bike
    Sherpina-TL125-TY80

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  • Location
    Pacific Northwest USA
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    Male

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  1. Thank you for correcting that mistake. Congress did enact other regulations, mostly import taxes, to protect H-D. These were primarily aimed at the Japanese manufacturers after it was discovered that Yamaha was selling motorcycles at a loss to capture the US market. Also the first US Bultaco importer on the east coast, John Taylor, originally sold the bikes out of Spitzies Harley-Davidson before forming Cemoto East.
  2. The original rear brake light was powered off the ignition coil and used a resistor in case the filament burned out. Without the resistor the brake switch became a kill switch every time you stepped on the rear brake.
  3. Two best things I did to my M98 Sherpina was swap over to a Mikuni and dump the points for electronic ignition.
  4. You don’t say what model of Bultaco you have. This is key. I have an M98 Alpina that I turned into a trials bike for vintage trials. I used the trans gears and heavier primary flywheel from an M91 Sherpa T to compliment all the other modifications.
  5. Did some testing going over logs and rocks yesterday. My son was racing his ‘79 YZ250 and between motos I gave the skidplate a good thrashing. It may have just a bit less ground clearance now (another reason for me to lose weight), but I didn’t really notice it. This material is certainly more slippery than the bare frame rails. This might be more of an issue with large, angled log crossings, but hitting them straight on it just glides right over. Same with rocks, but the area I was testing it in only had a couple good sized rocks buried in the ground. A better test will be in a rock garden with loose boulders.
  6. As for the shape, I drew it out based on the template from an old article I found where someone removed the frame rails and perforated bash plate from an M92 and replaced it with 3/8” thick aluminum. I’m not too thrilled about the shape, but I’m going to give it a go in some rocky sections tomorrow. If I were to do this again, I’d start out with making a cardboard pattern in the shape I want then trace it onto the material before doing and bending.
  7. Pic from the other side.
  8. For all the trouble I had bending this material, you’d think cutting would be the easy part. Nope! Even on the slowest speed with my jig saw and feeding it slowly by hand the material would melt and fuse back together after cutting. A good whack with the hammer would break off the cut piece. Trying to trim the cut edges was another lesson. One method only resulted in creating more balled-up melted material. The sanding drum on my Dremel used at half-speed worked best.
  9. The material, called a polygranite, as it’s imbedded with small pieces of granite, is under a lot of tension. Even bolting it at all four spots, using the clamps with flat stock and heating it with the torch still left about a 1-inch gap. UHMW is a much easier material to work with. Since there was little change from using the heat gun and bending it the rest of the way did not over stress the material, I decided to go with what I had.
  10. After the initial bend I marked the skid plate for downtube clearance, removed it and notched it. Then I attached it back onto the bike with the clamps and a strip of flat stock before more heat cycles with the heat gun. After sitting all night I removed the clamps and it sprung back about an inch. I realized then that shear size of the surface area make it difficult to get the material hot enough with the heat gun. So time for a new plan. I drilled the holes for the front mounting bolts and wrestled it back onto the bike. I replaced the speed clamps with a pair of C-clamps, using the strip of flat stock. Next I heated the entire underside with a propane torch. Unlike the heat gun, you can’t leave the torch sitting in one spot too long, but even moving it around quickly gets the surface much hotter than the heat gun can. By being able to heat the whole surface I’m hoping it will finally form to the curve of the lower frame rails. This is the first of three bends, but the other two are not as large as this one. Going to leave it clamped and bolted up overnight again.
  11. First attempt at bending the cutting board material. Used a couple of clamps and heated the underside with the heat gun. Took about 10-minutes to get it this far. Once it cools back to ambient temperature I’ll remove the clamps. The board will need to be notch for the down tube before I do any more bending. Once get the curve fitting tight I’ll draw out the basic shape and trim off the excess. This skidplate will be easily removable. Some of the areas we ride at don’t have rock gardens to contend with.
  12. Last fall I cracked the primary cover on my M98 Sherpina when I hit a rock at a trial. Luckily I was able to repair the cover, but ever since I’ve been a bit nervous about going through rocky sections. The standard skidplate, or bash plate, on the M98 is just some a perforated sheet between the frame rails. It’s made contact with a few objects over the years, but it offers zero protection for the primary and flywheel covers. I’ve seen a few homemade skidplates, so I decided to try and make my own. The material I selected was a 17” x 14” x 5/16” (432mm x 356mm x 8mm) cutting board purchased from Target for $15. Originally I wanted to use 1/4” (6mm) UHMW and may still build one from UHMW, but my local supplier did not have any available. Looking online, I saw a few people had previously used cutting boards and the end result looked better than one made from a manure shovel. So far I’ve notched the back corners the match the width of the lower frame rails. I drilled two holes to temporarily mount it. Next I’ll be trimming the width and then use a heat gun to form it into the final shape. Attached are a few pics of my progress.
  13. I would call Hugh’s Bultaco directly. (518) 851-7184
  14. On Monday I went back to a practice spot I hadn’t ridden at since before repacking the mid-box. This place has several long, steep hills with switchbacks. Normally I’d have to wrap out the engine just to make it to the top, but now the bike kept pulling with very little throttle. I was very surprised. It seems a properly packed mid-box does provide some low-end power to the 250. Now I’m going to build some sort of a skid plate that will protect both the clutch and flywheel covers from damage.
  15. Thanks, I wanted to be able to fully remove the core to clean it, pack it properly and be able to clean and re-pack it in the future. The motor is definitely noisier than my old M206 Pursang, but at least the exhaust note is more acceptable for some of the places we ride.
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