GRV-2 Jet Bike Project 9/9/09

Posted on September 9, 2009

       Hello again folks! The front end of the GRV-2 is showing signs of progress. I had just finished building the disc hub and was poised to mount it to the Douglas wheel. The 1/4” holes that were pre-drilled into the disc hub will now serve as drill guides for the six 1/4-20 threaded holes to be made in the wheel hub. The disc hub has a hub collar cut into the back side which will greatly help center the disc hub on the wheel hub. This feature should make the alignment of the two as near as perfect as possible.
       I used a 1/4” bit to “mark” the centers of two opposing mounting holes in the disc hub and then used a smaller drill bit to make holes for the 1/4-20 tap. Once the two holes were tapped I installed two 1/4-20 x 1-1/2” alloy steel cap screws to hold the hub in place. I could now drill the centering holes in all of the remaining hub screw holes.          

       I removed the disc hub and tapped the remaining holes with a hand tap.

       After cleaning out the tapped holes with compressed air I was able to permanently mount the brake hub. I tested the hub for runnout or wobble with a dial indicator and was pleased to see that it was true. Not too shabby :0)

       It was now time to figure out how to mount the front end brake caliper set. The dual piston caliper that I had chosen for the build has a steel mounting bracket that was designed to mount on the fork shock of the “pit” bike it was intended for. I will need to fabricate my own bracket to hold the caliper to the Suzuki forks.

       I bolted the wheel to the forks to get an idea of how I was going to mount the caliper to the shock.

       To mount the caliper I fabricated a 1/4” steel mounting tab which will be welded to the shock as seen below. A 1/8” steel bar was used to shim the caliper bracket off of the brake disc to aid in the layout of the tab. This shim will allow clearance for the brake disc.

       I was now ready to tack weld on the caliper bracket. This will hold the alignment of the assembly in place until I can take it all apart and weld it permanently.

       I can now disassemble the front forks for welding and modification.

       The Suzuki K10 forks are oil filled for hydraulic dampening. I had to be careful not to blast myself in the face with oil by accidentally compressing the shocks without the end bolts in place :0P

       You will notice the coil springs used for the suspension. These stock springs will need to be upgraded due to the fact that the Suzuki K10 was a lighter bike than what I am building. This modification will be fairly easy as the K10 springs are easily accessible as opposed to an in-shock spring design.

       Once the shocks were removed from the “triple trees” I was able to weld on the caliper tab. I had to be careful not to use too much heat as it would blister the inside surface of the shock cylinder. This could damage the shock plunger and cause the shock to stick. I welded the tab in four sessions, cooling the shock with water in between sessions. This process helped keep the shock cool with no apparent damage to the cylinder wall.

       Now that I have the forks apart I can modify them as I see fit for this project. I decided to remove the fender mounting tabs on the bottom of the fork shocks as they will not be needed. Now is a good time as any for this task.

       Notice that the fork end holes are offset to one side of the shock. This offset is intended to improve the stock motorcycles geometry. I will be using this feature to improve on my cycle’s trailing geometry by reversing the offset (from stock) to the rear of the bike to compensate for my smaller wheel size (more on this subject later). The forks will actually be installed into the triple trees in reverse to accomplish this task.

       Another item I wanted to trim up was the steering lock bracket on the triple tree. This bracket will not be used so off it goes!!!

       I used a flap disc sanding wheel to clean up the band saw cut on the tree. Like it was never there........

       One last thing I wanted to “trim up” was the shock covers which are used to dress up the top of the shocks. The stock shock covers have integral mounting brackets welded to them to support the K10’s headlight assembly. I will not be using that style of headlight so off they go.

       I carefully ground off the spot welds for the headlight brackets and then gave the covers the old flap disc treatment.

       The next issue to address is the handlebar clamp of the top triple tree. The stock handlebar of the Suzuki K10 is about 20 mm in diameter. Unfortunately the drag style bars I want to use for my bike are the standard 7/8” diameter (about 2.2 mm too large for the clamp). I will need to bore out the clamp to accommodate the larger handlebars I wish to use.

       The proper tooling for the job would require an expensive 7/8” reamer but I found a cheap alternative. I used a 7/8” step drill or “Unibit” to carefully widen the clamp from either side. Surprisingly enough the bit did a very good job of keeping the holes axial. This is probably due to the step of the drill which helps to self center in the existing hole.

       Notice the spacer washers used to separate the clamp halves below. This space will allow the clamp room to clamp down on the new handlebars without bottoming out.

       The 7/8” handlebars fit like a dream :0))))

       The next step was to make a new set of springs for the forks. The stock suspension springs seemed a bit weak out of the box so a new set are in order. I am guessing that the jet bike will weigh in at about 275 pounds dry witch is way too heavy for the stock springs. I also have to take the rider (me) into consideration. When all is said and done the front end will have to support about 230 pounds.

       I was lucky enough to find a suitable spring replacement at McMaster-Carr (Cat# 9662K36). The new heavy coil spring came in a 36” long piece and required me to cut it down to size. My angle grinder handled the job nicely :0)

       I wanted to “close” the ends of the springs so they will sit evenly in the shock spring cover tubes. I did this by heating the spring ends red hot with a propane torch and then bending them together to make a “square” end. I then used the belt sander to grind them a bit flatter, finishing the springs.

       These new springs should do the trick nicely. If they end up being too weak later on I will make longer ones from the same 36” piece. I will have to wait and see how they hold the bike up when it is finished.

       I decided to primer paint the forks before reassembly. This will prevent any rust during the construction phase of the build. This is easier to take care of in the beginning than worry about later on...

       At this point I can bolt the forks back together. The new springs fit like a charm!!!

       Once assembled the forks were tested for suspension spring deflection. I was able to get a rough reading of about 240 pounds when the shocks were completely compressed which should be a good start for my bike.

       The front wheel was mounted along with the caliper assembly as seen below. The fit is perfect!!!!

       I now have a complete front end ready for mounting. This will be very convenient when I am ready to start framing up the front of the bike. I can now focus on the rear end assembly of the GRV-2. It wont be long before the bike will start looking like a bike :0)

       Please visit again for the continuation of the GRV-2 jet bike project!!!

Don Giandomenico


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