XR100/RM80 Conversion Pit Bike Build On A Budget – Part 2

If you’ve seen other XR100 conversion builds, you know that this isn’t just an easy bolt-in process. It takes many hours (especially if you haven’t done it before) mocking things up, welding, making sure everything fits, and fixing anything that doesn’t work on the way. There’s some skill required (welding is the most important), but I believe most anyone that is mechanically inclined and motivated can do this conversion. You must have patience though, as there are a lot of little things that take time…

If you haven’t read Part 1 on the XR100/RM Conversion Build, click the link before you continue reading here.

Part 2 is the tear-down and engine mock-up process. In order to get an XR100 engine in an 80/85cc mini motocross bike, you have to take everything off so you can cut and re-make the frame cradle. Getting the frame and engine mounts right is probably the most important part of this build. Not only does it all have to fit, but if you make the cradle wrong, the shift lever, rear brake pedal, or kick-starter may hit the frame. More on this later, as it is more difficult to explain without pictures. Here’s the tear-down:

’97 RM80

Here’s the bike stripped and ready for mock-up.

In order to get the xr100 engine in a mini motocross bike frame, you want to place it as far down and back as possible. And to do that you have to cut off the lower mount on the engine cases. Below is a picture of what it should look like. You can cut it off, mill it off, grind it off (just remember that it’s aluminum), or any other way you can get rid of it. This is so you can set it back in the frame. In addition, it lowers the center of gravity on the bike (better handling), and there’s more room for the cross-brace above the cylinder head.

XR100 bottom engine mount cut off

Now it’s time to start making the engine mounts. Luckily I have a junk XR100 engine that I can use to make my mounts since I didn’t have an XR100 dirt bike at the time. Here’s the material for the rear engine mount:

Rear Engine Mount Materials

I used 3/4″ round stock and drilled it to the size of the bolt (didn’t have any tubing at the time). The steel plate is just some 3/8″ that we had laying around. I tried my best to center the pieces so everything bolts up straight. Other than the tools to take the bike apart, the next tool you will need is a welder. This is probably the most expensive part of your project, unless you have someone doing the welding for you. However, I highly recommend getting a just a MIG (wire-feed) welder if you plan on building more projects or repairing stuff yourself. I use a Lincoln 180 MIG welder because it’s simple, reliable, and relatively cheap. They are very useful and can save you a lot of time in the future. A MIG welder is fairly easy to use, but I suggest getting the basics taught to you by a local welder/friend. The goal on these engine mounts (and pretty much any welded part) is to get the best penetration so the weld is nice and strong. Remember to always clean the metal before welding, otherwise it will turn out looking like pooh and the weld will be more susceptible to breaking.

Rear Engine Mount Welded

Below is the tube pieces welded to the plate and mocked up on the swing-arm bolt. The smaller length tube (lower) has a dimension that allows it to just barely fit in between the swing-arm. The longer tube length is suppose to match the length of the bolt tube on the xr100 cases. That way I can make tabs on it with holes for the bolt to go through. You’ll see in the next picture.

As you can see, part of the mount on the right case broke off. Fortunately for me it didn’t make much difference because I could still get the full length out of it. You want to take your time with this mount, making sure everything is straight, lined up, and the engine is where you want it to be.

All welded up with the swing-arm.

Below is an estimate of what it should look like. My research found that you should have the counter-shaft sprocket aligned with the swing-arm bolt; both up and down, and side to side. This is so the chain is straight on the sprockets and rollers and won’t fall off.

Centerlines of the Sprocket and Swing-arm aligned

We’ll go over the front engine mount in the next article because that is when I’ll be making the frame cradle. So stay tuned, because this will be the biggest part in the conversion! Here’s the link for the next article: RX100 PART 3!

-Tom Stark

XR100/RM80 Conversion Pit Bike Build – Is It Possible? Pt. 1

No, this isn’t like one of those forum threads you see posted by some 12 year-old wondering how to make their xr100 fast enough for motocross racing. This is taking one of, if not the best, all-around and most reliable engines for adults and kids-alike, and placing it into a much more race-suited and agile chassis.

I’ve seen many of these builds from people in their small garages or workshops, and wanted one so bad that I just decided to do my own build to see what I could come up with. This is my first XR100 conversion bike, so it may not look factory in the beginning. I am doing this to show that with some basic and relatively inexpensive shop tools, someone can do this in their own garage on a budget, as it will be one of the funnest pit bikes to ride for us adults.

To get this project started, I happened to come across a rolling ’97 Suzuki RM80 that someone had started doing the conversion on. Luckily they didn’t go too far, so it was the perfect candidate since I picked it up for pennies. Most of these conversions are done with a Honda CR80/85R chassis, but I happened to find this Suzuki first. If I like it enough, I plan on building more of these conversion bikes. And that is when I will fix any issues I come across with this first build and take the time to make things look a little nicer. In addition, I’d like to try different bike combinations, such as a CR85 or YZ85 for the chassis, and possibly a TTR125 or DRZ/KLX125 for the transplant engine.

Here is how I got the roller…. I know, not much to look at, but when it’s finished, it will be more than worth the work. As you can see, the cradle has already been cut, and the previous owner started the build but gave up. Fortunately, I got a junk XR100 engine that I can use to mock up all the mounts (very useful because I didn’t have an XR100 yet).

’97 Suzuki RM80 (Click On Pics To Enlarge)
Since this is such large project with so much information and lots of pictures (I know how everyone likes pics), I’m going to separate this into a few different parts. Next part will be tear down and engine mock-up, so stay tuned if you want to see how one of these is built in a garage…
-Tom Stark

How To Fix A Dented Four-Stroke Head Pipe For FREE

Does your pretty new pipe have a dent in it? You can either buy a new one, pay someone to get it fixed, OR…… you can fix it yourself. You don’t even need tools or equipment. In fact, this repair can be so cheap that it’s Free. UVVRPEKQ57ZN

Dented Stock Head Pipe

Step 1:

Take the head pipe (header) off the bike and clean it up so there’s no dirt or grime stuck to it. (Usually just a few bolts to take pull it off)

Step 2:

Take the pipe and fill it with water. You should only have to put in enough to cover the dent, plus a little bit more.

Step 3:

Put the head pipe in the freezer standing up so that the water is still covering the dent and won’t run out. There’s no need to cover either end of the pipe.

It will take several hours to complete, so if you throw in the freezer before you go to bed it will be done when you wake up!

WARNING!!!

Do not, I repeat, DO NOT attempt to do this on a two-stroke or stepped head pipe (powerbomb/megabomb type header). Your risk of cracking the pipe is much higher, and it will NOT be my fault. I also am not responsible for what happens to your straight head pipe if it breaks. You are doing this at your own risk, as this is not the best way to do repair a pipe. I only suggest this if you’re in a jam, or don’t absolutely need the pipe…

With that said, if you have a rather large dent in your non-stepped four-stroke head-pipe, I suggest starting out with smaller amounts of water instead of trying to pop it out all at once. It will reduce the chances of your pipe cracking. Good luck, and have fun riding!

-Tom Stark

How To Clean Boot Marks Off of An Aluminum Frame

Whether you’re going to sell your bike, or you just want to make it a look a year newer, getting rid of the black marks on your bike’s aluminum frame will help accomplish either.

First thing to do is wash your bike. Any dirt or mud stuck on it will make the process more difficult. Now grab some steel wool that is more on the fine side. You can either spray a little water or WD40 on the frame; both work about the same. After spraying the area of the frame you want to clean the boot marks off of, scrub it with the steel wool. I usually take a few passes, spraying it with the hose every time, just to keep it clean and see where the black marks still are.

YZ125 Frame With Boot Marks

After I get done with one side I spray it down with the hose again and move on to the other side. Once all said and done I wash the bike with soap and water so that there’s no residual metal/WD40/boot material left on the bike.

There you have it… a pretty much new looking bike again! Well, it may just be the frame, but it definitely gives the bike a “newer feel.”

"Fresh" Aluminum Frame

Now when you Haul Your Bike to the track you can impress your friends with your fresh aluminum frame. They may be so envious that you could make a couple bucks from doing it to their bikes too!

If you don’t want to have to clean the marks off every few rides, I would suggest you look into getting some Frame Guards. They’re pretty cheap, and protect your frame from boots. Good luck, and stay safe riding!

-Tom Stark