This little XR100 started out as a school project for my son Trent. The original plan was to find a used bike we could get cheap, fix it up cheap, and use it for play riding on our track. Well, we got a little carried away and this project turned into a lot more than we planned. For $160 we came up with a 1997 XR100 in pieces. The bike itself was in good condition with no rust and nothing bent. The cylinder and piston was scored pretty bad but we planned on boring it and installing a new piston anyway so this wasn't a problem. We loaded up the bike and took it home thinking we would have it cleaned up and running in a week or two. Once we had all the parts layed out in the shop we started to realize this would take more than we had panned to get it back together. Turns out the cylinder head on the XR80/100 bikes are easily damaged if it is run with low oil. The bike we bought had definitely been run low on oil and the head was destroyed. After searching for over a month we finally found another used bike with a ton of spare parts including 2 good cylinder heads. $250 later we were back at the shop with everything we needed to get this project together including a spare bike.

As you can see the frame is in good condition. The paint is not so great but we'll take care of that. The main thing is we've got a good, straight frame to work with that's not all rusted up.
At first glance the engine looked ok although it was really dirty. The exhaust was good too with only 1 small dent. We tore into the engine to check everything out and get it cleaned up. This is when we found the damage to the cylinder head. We split the cases to inspect the transmission and get the cases cleaned up. The bottom end was reassembled and we found a good head.
The frame was completely disassembled, sanded, and painted. We did find a small crack on one of the rear engine mounts which got a little welding job making it better than new. Yes, we did use spray cans to paint it but the way we figure it the frame is going to get scratched from normal use anyway. No reason to spend big bucks on powder coat just to mess it up on the first ride.. Trent did all of the sanding and painting which turned out really good.
With the frame, swingarm, and all the bolt on pieces painted we began putting it back together. There were a couple of the swingarm bearings that were rusted a little so we replaced everything with the All Balls bearing kits to make sure the suspension works properly. We also did a little work on the forks to stiffen them up for a larger rider. Unfortunately the shock can't be disassembled so we left it alone. With the frame back together it's time to get the engine going.
The seat was in really bad shape. The cover was torn and chunks of the foam were missing. We turned it over to Anita Connell who worked her magic. Now we would have been happy with a solid black seat cover but she went all out and made a two tone seat cover. She also fixed the foam. The seat looks awesome and the foam now has a good, firm feel to it. This really made the bike look complete.
Here is where we went a little wild. We went up 1 tooth over stock on the front sprocket as the stock gearing is too low. We also installed a BBR ignition unit which changes the ignition mapping to make more power and increases the rev limiter. We also installed heavier clutch spring to handle the extra power the engine is going to put out. An FMF exhaust system was installed to increase the power as well and make the most of the port work that was done on the head. A Hot Cams camshaft was installed to increase mid range and top end power.
Since the cylinder was scored pretty bad we went with a Wiseco piston that is 1.5mm over on the bore bringing it up to 105 cc's. This isn't a huge increase but will make a little difference. The carburetor was opened up to allow the engine to breath better and to work with the porting that was done.
We put a lot of time and work into the engine. The cases were worked over to remove years of use and abuse. The cylinder and head were cleaned up to look better than new. Once finished it's hard to believe this engine is 15 years old. At this point we have the engine back in the frame and we're ready to start it up for the first time.
Here's the finished bike. We replaced the old worn out tires with a fresh set of Michelin Starcross tires to help put the power to the ground. All plastics were replaced and the bike looks like new. We have tweaked the stock jetting to dial it in for all of the changes we made and the bike runs and sounds really good. The changes we made gave a slight bottom end increase with huge gains in the mid range and top end. Overall it turned into an awesome little old school pit bike. The power is great and it handles pretty good. I still think we can do a little fine tuning and make the handling even better if we can get it to sit still long enough.

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