XR50 Big Bore Installation. Step by Step w/Pics

Here’s a quick overview with some pictures (not enough, I know) on how to install a big bore kit into an XR50. This kit is the Takegawa Hyper E Stage 81cc kit. Hopefully I can answer some common questions here. If I seem to miss anything, feel free to ask.

Here’s a shot of what you get with the kit:
Parts.

Drain the oil and get the motor onto the bench and remove the skidplate (if you have one). If you need help getting this far, then a big bore kit is going to be too much for you! Turn the flywheel so the “T” mark lines up with the notch on the case. This will be very obvious once you get the side cover off. The mark is at the 12 o’clock position-directly above the flywheel.
Ready to go

Remove the valve adjust covers and the cam cap. Loosen the screw on the right side of the head a few turns and tap into it to pop the large circular cap off the left side of the head. Next, take the small finned cover off the right side of the head (2 screws).
Cam cover removal

Take out the two screws holding the timing chain wheel onto the cam and remove the wheel. Note the timing marks on the wheel and on the opening in the head (9 o’clock position). Next, loosen the nuts on both the intake and exhaust valve adjusters. It takes a 9mm wrench. Back the adjusters all the way out until they are flush with their holders, and then-Important tip!-run the lock nut back down and snug it finger tight so the adjusters don’t inadvertently fall out and get lost. Now you can remove the cam. You’ll have to hold the rocker arms out of the way to get it out, but it is very easy. You’ll notice also that the lobes on the cam are pointing back toward the case, so there is no pressure on the rocker arms when at TDC. This makes it virtually impossible to put the cam back in 180 degrees out of position. There is just no way to turn it by hand to activate the valve springs.
Cam gear removal

Now, take the bolt out of the head on the timing chain side using an open-end wrench. It runs into the top of the cylinder. Then, take the four acorn nuts off the top (front) of the head and remove the head. Tap it outward with a small rubber mallet if it needs some prodding. Next, remove the bolt holding the timing chain idler wheel and remove the wheel. Take the bolt going from the cylinder to the case, and you’re ready to pull the cylinder.
Head removal

Here comes the section with the lack of pictures, but hopefully complete enough descriptions. Pop one of the circlips out of the piston and remove the wrist pin and piston.

It’s now time to start putting things back together!

First thing I did was to put one of the circlips into the new piston. Next come the rings. There is a 3-piece oil wiper, a middle ring, and a top ring. It’s hard to see, but the top ring has a chamfer on the inside diameter. This ring is also “two-tone” gray/copper in color, where the middle ring is a solid metallic gray color. The oil wiper is made up of three pieces-a gold-colored, sawtooth-looking ring and two thin, flat rings to capture it. The sawtoothed ring goes in first, in the bottom groove. Next, put the two thinner rings on the top and bottom of the lower groove, one on each side of the sawtoothed ring. Be sure to stagger the gaps by about 60 degrees for these three individual pieces. Next, put the middle and upper rings into their respective grooves. Again, be mindful of their alignment and stagger them.

Now, put the piston onto the rod using the new wrist pin-dip it in oil to prelube it-and install the second circlip. Using a provided gasket for the cylinder-to-case surfaces, and the provided o-ring for the oil return port, guide the timing chain through the slot in the new cylinder, and get the piston into the bore. Just work the rings in gently, being careful not to damage of break any of them. If you do, you’ll be done for the day. It’s not too difficult, just have some patience and maybe an extra set of hands to help you. If you’ve ever done a top end before, this should be no problem.

Put the cam chain idler wheel back into place using the stock bolt, and reinstall the bolt that runs through the tab in the cylinder into the cases (near the idler wheel bolt). Next comes the cylinder-to-head gasket and oil return o-ring. Again, guide the timing chain through the slot in the head as you feed the head onto the studs. Put the bolt from the head to the cylinder in place, and then you can reinstall and tighten the four acorn nuts that hold the head and cylinder to the cases. Torque accordingly-I went with one hand, choked up on my ¼” drive ratchet. Tighten in a criss-cross pattern, continue until applying the same force no longer turns the nuts. Be careful to not snap one of the rods! (this would be bad, and again, you would be done for the day!).

Prep the new cam by pouring some oil onto the roller bearings and spinning them to distribute the oil and avoid a dry startup. I also coated the entire shaft in oil to prelube it. To install the cam, just reverse the removal procedure-jockey the rocker arms and it will pop right in. Now, put the chainwheel up against the cam and work the chain onto it. By aligning the center hole in the wheel with the hole in the center of the cam, you can see if you have the mark on the chainwheel pointed to the notch at 9 o’clock in the opening. Adjust accordingly. Once you have the chainwheel in the correct spot on the timing chain (your flywheel is still aligned with the “T” mark, correct? :thumb: ), you can use a small screwdriver to rotate the cam so the two mounting holes line up with the mounting holes in the chainwheel. If the chainwheel won’t quite pull forward enough, use a good sized Phillips screwdriver to pull it forward into alignment, and install your mounting screws. You’ll have to hold the flywheel when you tighten these. After that, pop the finned cover back onto the right side of the head using the new gasket, then reinstall the camshaft cover using the long screw through the head.

Next, adjust the valve actuators down so they just touch the backside of the cam-Improtant! This is my own experience here, I adjusted them to .005 intake and .009 exhaust, ala my YZ426F manual (I don’t have a manual for the 50, so…) and the valvetrain was very noisy on startup. I went back and took them down to just barely touching and it quieted things right down. You can hold the actuators with needlenosed pliers while tightening the locknuts. Pop the covers back over the adjusters, and the motor is almost done!

Refill the case with oil, install the new plug (it’s different than the stock one, different heat range, etc.), and get the motor into the frame!

Next, install the intake, and then the carb and air filter. Note that I routed the throttle cable to the left of the frame spine and through the opening in the forward tank mount. I had to rearrange my wiring a bit, but mine was different from stock. I had to move all the wires off the left side to make way for the throttle cable.
Throttle cable routing

The only major issue I had was that the petcock clashed with the new air cleaner when I went to reinstall the tank.
Petcock clash

I solved this by spacing the tank up about ¼” with some rubber spacers I had, and got some longer bolts from the hardware store. While there, I happened to notice that they also had drawers of rubber spacers, too. A couple bucks will take care of this problem if you run into it.
Gas tank spacers

The new carb only has one drain line, and I routed it right through the stock metal loop on the motor. The air cleaner has one ¼” port on it, I ran the case vent to this one, with the air cleaner port on the top side (which positions the “Takegawa” logo so it can be read). This low number of hoses really cleans the overall look of the bike up.


Well, that’s pretty much it! You may have to do some tuning for optimum throttle response, etc., but it should start right up. Took me a while since I was playing with Phillips B35 fuel, but I got it fired. I haven't ridden it proper yet, but I will say this: I popped it in gear to ride it to the front of the garage and nearly looped it out! :aj: Keep in mind, it's no 426, but the difference is about double the HP and torque, with a much steeper torque curve off the bottom. This is gonna be fun...

Below is a link to the finished project, motor running. Right click this link and then click “Save Target As” and download it to your hard drive.

Mpeg movie of finished product

Bud Lite, two. Leinenkuegel, one! btw-This took me about 6 hours total, from start to finish. But, I am slow and thorough when I work (<---there's an understatement!). Other things I should mention: Bang for the buck, this is the best kit out there, IMO. $395 retail, includes the cam, the carb, everything, and the Takegawa quality is every bit as good as OEM Honda. According to the guys at Classic Honda, this is about as big as you can go without having to add a manual clutch.

Try her now. Man, that Yahoo! site is giving me hell lately about linking to video there. I try to copy the url, but it comes out as gibberish, so I have to look at how it used to link, and rename the url accordingly. Giant PITA. Good point about putting the piston in before mounting it to the connecting rod. Only took me about 2 minutes to get the piston in the bore with it attached, but your way still sounds easier. Also, with the motor laid flat, I didn't really have any trouble with the cam chain running away on me.

One more important tip-Don't forget to take the two guide pins out of the old cylinder to put into the new one to align the head.

Originally posted by Rich Rohrich
...I think there might be some additional horsepower still hiding in there :aj:

Click to expand...

Yes, Doctor. Yes there is. And we shall find it. Then, and only then, will I know the sweet taste of success that only a very large man riding a very small bike can know.
Aha-aha-aha-hahahahaha! (<---evil laugh) :laugh:

I'd have to look at the 88cc kits. There are definitely bigger kits to be had, but for four bills you get the 82cc and the carb, which is ~ a $200 option in itself. It's a very complete kit and a great bargain, relatively speaking. Also, it does include a 16-tooth front sprocket in the kit.

As for suspension, it has the fat-boy springs in the forks, and a Fox shock with resevoir in the back. Both were on it when I bought it, and the shock is a prototype unit. This bike originally belonged to DRN member "michman" (also known as "napper") and he was at one time a factory mechanic for the Volvo-Cannondale MTB team, hence the prototype shock.

Yeah, the guys at CH say that 88cc is the max without going to a manual clutch. I've seen some stiffer clutch springs for sale, too. Can't remember exactly where, maybe at CH. I was under the assumption they were for the stock auto-clutch, could be mistaken about that.

FYI-There is an 02 xr50 for sale in the For Sale Forum for $750. Pretty good price from all that I've seen.

I have some footage from this past weekend riding around Mr.Luckey and GSR's back yard in St. Louis. I'll try to get off my arse and get it hacked together here shortly and I'll post a link!

Try this: Click!

Right click, then "Save Target As". Approx 1.2meg.

Sorry, you have to be signed in to Yahoo! to view it. It wouldn't even let me view it until I signed in.

Yep. I'm running Amoco Premium in mine. However, I'm getting ready to "try" the switch to race fuel again. (issues with the bigger, bluer bike last time...) The cool thing about the "fiddys" is that they run forever on a tank of gas! Probably ride for 6 hours nonstop on one tank.

Also, I have a two-stage UNI "pod" foam filter if you want it. Paid $16 for it, send/PayPal me $10 and it's yours shipped. Fits the stock carb opening. Ran it about an hour total!