212cc Gas Pit Bike

Over a year ago when I started to get into two wheeled machines I had picked up a little 50cc 4 speed semi automatic pit bike. I got it running and used it a ton but eventually it started running worse and worse, losing compression along the way, till one day it didn't start. So I decided I should swap the engine out for more reliable 212cc utility sort of engine which I would pare with CVT (Like the clutch that is in a snowmobile). I had used them before together and they worked great, lots of torque and lots of speed. The timeline of this build worked out great, since I am currently in high school I would document this for one of the projects.

Ignore how it says Step, it should be Day.

Welder

Grinder

Scrap Metal

Miter Saw

Drill

Sockets and Wrenchs

Scissors

Fabric

Wood

Stapler

Parts Bike

I started off by taking off the pieces that I knew that I would need for the front end of the new bike that included forks, handlebars, front wheel, brakes and plastics. The front end had to pivot of course, so I removed the bearing races from the old frame and went ahead and cut off the tube that held the bearings. I made sure to mark the top and bottom on it since once it was sanded there would be no way to tell.

Next I took the rear swingarm off and cut off the pivot for it too. Then I picked out the engine I was going to use. I had a 212cc PowerFist engine sitting around and decided that it would work perfectly for this bike. The only issue with it was it didn’t run. It had no spark and the carburetor was all rusty oh and the cooling fins on the flywheel were almost all shredded! But I was still going to use it! It turned out it had a great spark, just the plug was fouled so I took the torch and wire brush to it, and soon enough I had a good plug again. Since I had another carb I managed to make one good clean one out of the two. For the flywheel, well I probably made that sound like a devastating situation but it was just a plastic cover that got shredded and what-do-you know we’ve got an extra one laying around. So soon enough I had a well working engine perfect for my new bike!This is possibly my favorite part of any build, mockuping it up! Even though it is so far from completion you can get a good idea of what it is going to look like when it is done. With the use of magnets, bungee cords, wire, wood, and whatever else I can find to support the different parts of the bike. I could finally see where things needed to be located.

Now that I had a rough idea where I wanted stuff to be it was time to think about where they actually could be and at what angle. I decided to start at the front since I had not totally figured out how I was going to do the rear. I knew that the angle at which the forks sat would greatly affect the steering. For example if it was parallel with the top of the frame I would have no steering at all. And if the forks sat vertical the front wheel would act like a wheel on a shopping cart. So I went and measured the fork angles on some other bikes to see what they were. The number averaged out to be about 70-75 degrees, as you can see in the photo I set mine at 60°. My thinking behind this was, I might be a little cramped on the bike so the less twitchy the better, the saw that I used only went to 63°, and I thought that when I put my top tube on doing 60 and 30 would be the easiest way to get it to sit at 90°. Finding these angles and cutting them was not as easy said than done. I only had one shot at the cut so it was crucial to get it right, to help with this I cut the angle I thought I would need out of wood and did this till I got it right. Then I made the cut and tacked it to the frame with the MIG welder. The other part of the frame that you can see, which is outlined in blue, was a piece I had from another project. As you can see they were each cut at 45° for maximum strength.

Next came the engine and swingarm. The engine already had mounts bolted to it so I set it in the frame as far to the right as I could to try to get the sprocket on the secondary to line up with the one on the wheel. The goal was to have the rear and the and the front wheel in a line, so the farther I could have the engine and swing arm over the better. Once I got it where I wanted them to be I pulled out the welder and tacked them in place. As you can see in the photo on the left the chain line is very straight. Mind you this was not not all the consideration that went into the swingarm placement. And you can probably see circled in red the chain is resting on the top of the swingarm. This was to help keep the chain from hitting when the swing arm moved up the chain would want to hit the bottom of the swingarm. This happened due to the fact that the distance from A to B changed as the swingarm moved. So in other words the closer it sat to the top chain in full droop the farther it would be from the bottom chain in full compression.

Now came the subframe this would support my seat, rear shocks, and help to stiffen the frame. Again I took the majority of it off of the original frame since I liked how it looked and it seemed to be very strong. Then using more wood blocks I got it positioned where I wanted it. After that, I cut a piece of tubing to fill the gap, and a top tube remembering to cut the front of it at 30°. Then I welded them in place. Now that I had everything major welded in place it was time to unbolt the swingarm, engine and front forks and get to fully welding the thing. Once welded I put it back together, hooked some brakes up, put a very temporary exhaust on, and took it for a spin!

There were still many things that needed to be buttoned up before it was done including; rear suspension, gas tank mounts, seat, foot pegs, exhaust, brakes… I decided to start with the foot pegs since it rode fine with everything else jimmy rigged, but I thought it would be really nice to have some place to rest my feet. I decided that the easiest thing to do would be using the footpeg and kickstand assembly from the old bike. So I made a nice plate that would get welded to the frame and then the foot peg assembly would be bolted to the bottom of it. I went back and forth from adding that in here but fabrication is all about trial and error so I thought I would. Mounting them that way I realized that the wheel would hit them so I was forced to think of a different idea. I had used rebar for foot pegs before and it held up fine so I decided to use it again. I found a random piece of it and bent it in a vice to clear the wheel and chain.

Next came the rear suspension since having a hunk of metal wedged between the frame and the swingarm is not a permanent solution. There was not enough room to fit just one shock in the middle so two shocks it had to be. The only problem was I didn’t have two of the same so I found some cheap ones on amazon and they came in a few days. Next I made some mounts out of some rectangular box which took longer than expected and then started to set them up where I wanted them. I then welded them on and then took the bike off the stand to try them out. I thought that it made the ride smoother but I think that it was just the placebo effect because I checked later on and they did not move! So I took the coils off to make sure that the shock body could go though the range and they could. Then I measured the range and it was only 2 ½ inches. I wasn’t happy with that especially since I just bought new shocks, so back to the drawing board I went. I started to think back about why I didn't use just one shock. The issue was that the top of the shock would sit like 3 inches higher than where I was supposed to sit. But looking at it again I could just raise my seat height. So I made some more mounts and welded them in place now I had almost 4 inches of travel using an old shock. Again more trial and error. Yet I do think that it looked cooler with two shocks rather than one

Next came brakes this probably should have been first but they don’t make you go faster, right? For the first test ride I did hook up the front brakes with the original lever and cable, but having only front brakes was dangerous. Luckily the cable on the front was long enough to reach to the back so all I had to do was make a bracket to hold it since it originally had a foot brake. I took a small piece of flat bar drilled a ¼ inch hole in it and a slot to fit it past the cable the welded it on. They worked fine, I might go back to a foot brake though to get more leverage. Well now being like two weeks later, I am going to go back to a foot brake so that I can have all around brakes I will put the cable and lever back on the front and make a custom brake pedal. I started by cutting of the rear brake mount that i had made earlier since I would not need it anymore and it was in the way. Since it was mounted to the old shock mounts and I didn’t like how they looked being there plus I had no use for them so out came the grinder and off came the mounts. Now that the bracket was out of the way I could start on the brake pedal. Luckily I would most likely be able to use the original pivot, return spring, rod, and pedal I would just have to shorten it.

Now I needed to make a seat. The seat pan couldn’t be flat because otherwise there would be no room for the top of the shock. So I took some cardboard and cut out the shape that the bottom of it would be then traced it on some ¾ plywood and cut it out. Next I found a 2x4 and cut one piece at roughly 2 inches and the other at around 3 each having the same slope as the shock then I screwed them on with 2 #8 screws each. Now it was time for the padding/foam. I had a bunch of sheets of 1 inch soft closed cell foam that happened to be the right width so I used it. The first three were all about the same size and I connected them to the seat pan and each other with 3M Spray Adhesive. For the little front piece I just taped it on. Then using knives, saws, sanders, and a collection of other tools I shaped the foam so that it would have few abrupt edges or corners and be comfortable. Now it was time for the seat to be covered. We have a roll of faux leather that is meant for upholstery but I have used it on other bike seats before and it has worked well. I cut a piece out that would fit and started to stretch it over and staple it in place. I always find the corners the hardest to do but I feel like this seat turned out looking pretty good. All that was left to do was make a simple bracket out of a flat bar with two holes for screws weld it on then connect my seat. Next I will make some plastics and rear fender.

I started off by searching for tubing that I would make the pipe and muffler out of. I found some tubing that was about 2 1/2 inches in diameter which I would use for the muffler and an old set of old 1 inch handlebars which I would cut down for the pipe. Since I was going for the more vintage style on this pit bike I decided to search the web to get an Idea of how they looked on the older bikes. I liked how the oval mufflers looked better so I went ahead and put that 2 1/2 piece of pipe in the vice. Then I started on the tip. I cut some pie shaped pieces to make it taper, from the same piece of tubing, then started to weld them in place, I also found a short chunk of 1 inch pipe for the end which I also welded in place. After a lot of welding and sanding I came out with the result that I was looking for. Next I worked on the back. I could have just welded a plate on the back but I thought that I might want insulation in it if it was still too loud. so I cut another piece out of the same chunk of tube about 3/4 of an inch long and split it open enough to fit on the outside of the muffler then laid it on a piece of flat bar and traced it out then took it to the bandsaw and cut it out. Next I welded them together and fit it onto the muffler. All that was left to do was drill a 1/4 inch hole through both pieces and a bolt. Next came the pipe. I found a piece of 1 inch handlebar, and if I cut it down it would be exactly the right size to go from the muffler to the little piece of pipe in the engine. So I cut it, welded it to the back plate on the muffler and and welded it to the little piece on the engine. And now I have a muffler. Later on I welded on a 1 inch piece of angle iron with a hole in it to bolt to the frame.

Unfortunately I was unable to get photos of The steps of making the side panels, muffler hanger, rear fender, and rear fender reflector mount. But I will do my best to explain with words. The side panels and rear fender took the same process starting by cutting out the shape from cardboard then laying it over the plastic and cutting it out. For the plastic I used old tool cases and melted them with a heat gun though as you can see after very little ride time the left one melted completely in half!(do to being to close to the exhaust) My next idea for this would be to make this side panel out of sheet metal so like before I laid the cardboard template on the sheet metal and cut it out. This time though I left a 1 inch flange all the way around that I bent over in order to make all the edges smooth. Since raw cut thin sheet metal, like the stuff I had, had a tendency to be sharp. Now fingers crossed it wouldn’t melt this time! Then for the tail reflecto I don’t know what it came from but it was the right size so I used it. I made a simple mount bent out of ½ inch flat bar. And welded it on all the dimensions were estimated I used #10 machine screws to hold the reflector on. The muffler hanger was just a 1 inch long piece of 1x1x⅛ angle iron that had a ⅜ hole on one side.

Super happy with how it turned out and such a fun bike to ride as well!