GRV-2 Jet Bike Project 8/30/09

Posted on August 30, 2009

       Hello again folks! I have been busy gathering up all of the parts I have collected over the past couple years for my jet bike project. Now that I have most of what I need to start the project I can begin to figure out how I am going to put this thing together ;0)

       The GRV-2 jet bike was an idea I had way back when I first thought of the GR-7 turbojet engine. The basic idea was to build a large turbocharger based engine and then build a small lightweight motorcycle around the existing engine configuration. This is the reason that the GR-7’s engine frame is built with a truss design as it was intended to be a structural member of the future jet bike frame. By incorporating the engine frame into the bike design I will be able to save weight and keep the bike’s size reasonable.
       The jet bike’s overall design will be based loosely on a drag bike / chopper configuration. I going to try to build the bike as low as possible to reduce wind drag but also add a “chopper” look to keep the project unique. For this reason I am going to nickname the bike as the GRV-2 “Turbochopper” ;0) Yes, yes I know that there is a food processor called the “Turbo Chopper” but mine is one word so I am sticking with it ;0) Besides, my project really has a turbo involved!!!

       So far I have got a lot of really good parts for this build including DOT rated wheels and tires, hydraulic dampened forks, front and rear brake assemblies, a three gallon fuel cell and a full set of Auto Meter gauges. This isn’t everything I need but a good start.

       The hydraulic brake assemblies I will be using were acquired on eBay. They are from a Chinese made motorcycle line called “Coolster” and are sold as compete OEM replacement sets. I was lucky enough to find a seller in California (eBay) that imports these sets in bulk. For a very reasonable price I was able to buy front and rear brakes for the bike. Actually I bought a few different sets of brakes and pieced together a set to suit my needs.

       The front forks I will be using are from a 1965 Suzuki K10 motorcycle. They are special in that they have hydraulic dampers inside the forks but use external coil springs for suspension. This feature will be helpful in tuning the suspension for the additional weight of the jet bike. I bought the “new old-stock” forks back in 2005 from an eBay seller that had quite a few of them. They were probably surplus units that never made it to production. I also purchased from the same seller a weldable machined neck with bearings that fits perfectly into the triple tree.

       To get the GRV-2 started in the right direction I decided to work on the front end first. I wanted to complete as much of the front end as I could before moving on to the framework of the bike. It will be very helpful to have the front forks and wheel complete to aid in the overall layout of the bike later on.

       The front wheel I selected for the GRV-2 is a Douglas aluminum jr. dragster type wheel fitted with a Kenda 3.00-10 DOT rated tire. The solid-side wheel design not only looks cool but is very strong.

       The Douglas wheel has 5/8” bore sealed bearings for which a custom axle must be made. The axle is a very important part of the assembly so I need to get this part right. To build the axle I started with a piece of 5/8” OD aircraft grade 4130 steel alloy.   

       To make the axle work with the Suzuki forks I will need to bore a 3/8” hole in the middle of the axle. This hole will allow me to install a 3/8-24 x 7” grade 8 bolt securing the axle to the forks. Needless to say the bolt is as important as the axle. 

       I used my 7 x 10” lathe to bore a hole through the axle as seen below. The lathe does a good job of keeping the hole perfectly axial.

       The axle is complete and ready for fitting!!!

       To keep the wheel centered on the axle I will need some axle spacers. To make a set of spacers I used some 3003-H14 aluminum alloy tubing. I had to open up the ID a little with the lathe to fit over the 5/8” axle.

       The next step is a tricky one. I needed to add a brake disc to the Douglas wheel for the front brakes. The stock wheel has no provisions for a braking system so I will need to fabricate one. Luckily for me the Douglas wheel has a wide enough hub to allow me to bolt a disc hub to the wheel. The hub will hold the disk to the wheel and allow me to add a hydraulic brake caliper to the forks.

       The plan was to machine a disc hub out of a 5” diameter 2024 aluminum alloy disc. This disc hub will bolt directly to the Douglas wheel with six 1/4-20 alloy steel cap screws. The brake disc (from a Coolster “pit bike”) will in turn bolt to the disc hub completing the assembly.

       To get started on the hub I located the center of the disc so I could bore a 1-1/8” hole. This hole will allow me to hold the disc on the lathe chuck.

       I used a hole saw to cut a crude hole in the disc for the lathe chuck. Note: Cutting oil is always a good idea. I use Rapid Tap which works very well, especially on stainless.

       Once the disc was mounted to the lathe I finished the bore on the front side of the disc so it can be mounted on the same center from the opposite side (make sense - sort of ???).

       I proceeded to shape the disc to the size needed for the brake disc. The 2024 alloy is a dream to machine!!!! It is also expensive :0P

       I machined a shoulder into the face of the disc which will center the brake disc on the hub regardless of the hardware geometry.

       The next step is to machine a collar “lip” that will center the hub onto the protruding hub of the Douglas wheel. This collar will set over the raised wheel hub and keep the hub from shifting off center.

       Finally I removed the excess bulk from the disc by thinning the outer flange a bit. 

       It was now time to move the disc over to the milling machine. I centered the disc onto the rotary/indexing table with a dial indicator.

       I drilled four 5/16” holes 90* apart from each other to match the existing holes in the brake disc.

       I drilled six more 1/4” holes 60* apart inside the wheel hub collar.

       The finished product looks pretty sweet!!!

       To attach the brake disc to the hub I used four 5/16” x 1” flat head Allen bolts.

       Flat head bolts were necessary to provide the clearance needed by the brake calipers. The bolts were countersunk into the disc rotor with a countersink bit.

       Well, so far so good!!! I am getting more excited about finally putting the GR-7 to work. It has been a long dream of mine to “rocket” by on a turbojet powered bike. I am now a little closer to that dream :0)

       Please join me again when I put the rest of the front end assembly together on the next episode of the GRV-2 project!!!!

Till then be safe my friends!!!

Don R. Giandomenico


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