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1975 Silver Fox Motocross
Well folks, I went to a vintage bicycle swap meet in Salinas CA. I was almost ready to leave when I asked a guy with a load of bikes in the back of his truck if I could see what he had. In the center of the pile I spotted something that caught my eye. could it be ? A 1975 Silver Fox Motocross BMX. Cool!! as soon as I saw it I knew what it wanted to become! He dug it out of his pickup and in my jeep it went.. I started by building a motor for it that tweaked a bit. I used a older style case from dax I had bought to replace a blown up bottom end. when I received it the crank was the older 5 piece crank and was really wobbly. I searched and found a new crank from BGF that had the newer style 3 piece crank. very straight! ok so I had a bastard bottom end that I had no idea if it would work, but the crank was true! a Good start. so I wanted to use the can that had the larger 40mm intake. I had to use the whole top end, head, piston, cylinder. the piston pin on the newer type has the piston pin in a lower position. I port matched the calendar to the case and had to remove material from the exhaust port. It was half way blocked! so I opened it up a bit. to use the head I had to drill the stud holes to 8mm to match the older case studs. seems all newer engines use the 6mm studs with 8mm cylinders and put 6mm heads on them. the 6mm studs seem kind of weak and stretchy, had 2 stock engines blow a head gasket due to factory stripped studs. they only thread them in about 1/4 inch and then torque the heak out of them! I put a cns carb on it that I re-jetted larger. Got the engine finished and running.
OK on to the frame!
So I felt pretty bad about turning this bike into a MB. But the frame had such perfect lines I could not resist! Got the bike all stripped down and reluctantly sanded and painted the frame. At this point my neighbor told me about a 2-stroke show in Orange co. at cooks corner. I knew I wanted to enter my newest creation and I had a week to finish the build and was feeling the pressure.
I mounted the gas tank to a plate of steel I cut. Due to time restrictions I had to raise the rear of the tank to get the petcock to clear the frame. Not the original way I wanted to do it but in the end it looked perfect. Tank was on, mounting tabs welded and the seat pan tank combo was almost finished. struggled with the tail section concept. I was originally going to cut a gas tank and use it for the seat bubble but I wanted to try a different rout before I hacked a good tank up. My buddy brought over a 1920 ford t tail light and I knew what needed to happen.. older style tail with a large round light! Looks great! Got the seat pan finished 3.15 am the day before the show!!
With the frame mostly finished I moved on to the exhaust. I had a cr80 expansion chamber I was thinking of using but almost seemed too big! I grabbed a few pipes I had around but none seemed to fit the attitude of the bike. On went the giant chamber! Seemed like a good choice for the show.. I had 2 stock mb silencers I had cut for other projects and they worked great. I used my handle bar remnants for tube and grinded a hole in the tube to create a 1 into 2 pipe that functions. Exhaust sounds real good!! (ill try to post a youtube vid of her running)
The bike was almost finished. I scavenged parts from my other bmx bikes, maxis freaky x tires, rebuilt the rear hub, used a small bmx sprocket in front.
First run was the day of the show and she ran real nice!! Was able to fire up for the 12;00 smoke out!! Fun show !! I went with my buddy that is chasing a 50cc land speed record of 86mph!! ok ill save the boring chatter now and show some pics.
Let me know what you all think please!
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