Front Fork Replacement Procedure

We had a customer crash his older pocket bike and send it in for a repair. I’ve taken the opportunity to document the front fork repair procedure so that you can replace your bent fork tubes as quickly and easily as possible. Please note that different pocket bike manufacturers may use bolts and nuts with differently sized or shaped heads. The directions are written for the most common sizes used on two-stroke pocket bikes, and while your bolts and nuts may use a different tool, most likely all parts are interchangeable and the directions will still work for you.

We’re going to be replacing the front forks with a stronger variety that use a separate CNC machined fork bracket so that the axle bolt goes through the fork tube instead of through a welded-on bracket on top of the tube. So let’s begin.

The Problem:

One or two bent front fork tubes on a two-stroke 40cc, 43cc, or 47cc pocket bike (no lights or electric start, pull start located on the right side of the bike). These instructions will work for almost all 2-foot-tall pocketbikes (mini motos) including the Daytona Cagllari, MX3, Blade, Raptor, RSR, MT-A2, A3, ATG-47A, ATG-47B, etc.

The Mission:

Remove damaged fork tubes and replace with new ones with minimal disassembly, fist banging, and expletives.

Parts Needed:

  • Two new fork tubes. It is always a good idea to replace both even if only one is damaged so that they match.
  • (Optional) If your existing forks don’t have the rectangular machined aluminum tips on the bottom (that the axle goes through) with a chrome brake caliper bracket on the left side, you will also need two metal fork caps and a front caliper bracket.
  • (Optional) During the repair procedure, it is possible that you will break one or both of your triple trees. It is also possible that they are already broken. As with the fork tubes, these should be replaced as a pair.

Tools Needed:

  • 4mm allen key
  • 5mm allen key
  • 8mm wrench
  • 10mm wrench
  • 14mm wrench
  • Two 17mm wrenches
  • Common sense

The Procedure:

  1. Put the bike on a table or other elevated, sturdy surface. I am going to work on the floor. Take off the entire front body kit. Tip: loosen the bolt that connects the front fairing assembly to the metal frame brackets (one of the left, one on the right, and one in the front). Then, peel off the entire cowling through the front forks. No disassembly of individual pieces required.
  2.  Your front cowling should now be off. Take off the front fender (mud flap, bumper…). Engage the kick stand if your bike is equipped with one so that it is standing on its own.
  3. Use a 10mm wrench or socket to loosen the front brake caliper’s nut that holds the brake cable in place. Pull out the brake cable.
  4. Remove the two bolts that hold the brake caliper to the caliper bracket. Save those bolts as you will be re-using them.                                                        
  5. Unscrew the main bolt and locking nut that holds the front fork assembly to the frame. Use two 17mm wrenches or socket wrenches. DON’T PULL OUT THE BOLT. Leave the bolt in place for now, and do not actually remove the front fork assembly off the bike. Put the nut aside.
  6. Loosen the four bolts on the side of the triple tree clamps that hold the fork tubes in place. There are two on the left, and two on the right. Loosen them but don’t take them out completely, because then the retaining nuts they go into will fall out. Take out the rubber fork caps too. You can pry them out with your fingernails.    
  7. Slide the fork tubes down out of the top triple tree only. The fork tubes will slide if you grab one with each hand below the bottom triple tree and push/pull against it with your thumbs.
  8. Since your brake levers and throttle cable are probably still wired up, we want to leave them with the bike while we comfortably work on the forks. Use an 8mm wrench to loosen (no need to remove) the bolt that compresses the handle bar against the fork tube. Do both. Then, pull the handlebars complete with the levers and throttle up and off of the fork tubes.
  9. By lifting the bike by its body, the front forks will now come off. Leave the main bolt and upper triple tree in the bike. If you take it out, the inner bushing may move, and it will be difficult having to fish for it inside the frame assembly. Watch out for the washer between the bottom triple tree and the frame. Save it.
  10. You should now have the front wheel with the two tubes, and the lower triple tree, all as a separate piece. There should be no wires attached to it. In a separate pile, you should have the beheaded pocket bike remains.
      
  11. Use a 14mm wrench to take off both of the axle bolts on each side of the axle. Be sure to leave the axle bolt in the wheel at all times. As with the main triple tree bolt, if you pull it out, you will loose the bushing inside the wheel and have a frustrating time trying to put the axle bolt back in.
  12. Make sure your new forks are assembled like the ones in the pictures. You may be re-using the fork tube caps, or you may have a complete new kit. Either way, put all appropriate nuts on the bolts on with your fingers, but do not tighten down with a tool just yet. They will require some slack so that you can properly position the caliper bracket once you’ve put the fork assembly together.                    
  13. Remove and replace the fork one side at a time. This way you can keep track of your bushings. Pull out the axle just far enough so that it comes out of the tube but not out of the wheel.
  14. Pull the loosened tube out of the triple tree. The left tube will have an additional bracket for the brake caliper that the right one doesn’t have. Insert the new tube it into the bottom triple tree. Put the axle bolt back through the new fork tube and put the axle nut back on. Flip your project around and repeat on the opposite side. Notice that the bushings that go between the wheel and the forks may be different in size. Usually, the larger one will be on the brake side.
  15. Once you’ve replaced both tubes, hand-tighten the axle bolt. Make sure the lower triple tree is connected, and tighten the side bolts on it (4mm allen key). Try to lign up the forks so they are straight. At this point simply estimate the lower triple tree’s location, you are going to loosen and re-tighten it in the next steps. The picture is a good guideline.
  16. Lift up the bike. Put the washer you took off in step 4 on the main bolt and attach the fixed front fork assembly. With the kick-stand engaged, the bike will be able to stand on its own again. You can put the underside bolt back on, but don’t tighten it down all the way just yet.
  17. Checkpoint. Your bike should stand on its own again at this point. Don’t put the fork tubes into the upper triple tree just yet.
  18. Put the left and right handlebars back on the fork tubes. Mind the location of the cables – use common sense to make sure they’re not tangled up more than necessary. Tighen the handlebars with an 8mm wrench so that they don’t swivel around. Tighten the handlebars so that they poke out at a 90 degree angle to the bike. You don’t need to tighten them down permanently yet, just enough so they don’t move. Position the handlebars below the top of the tube so that there is room for the upper triple tree to go back on the tube.
  19. Now loosen the lower triple tree’s bolts so that you can move the fork tubes again. Gently push the forks up from the bottom and lign up the top triple tree so that they enter it. Allow the tube to protrude from the upper triple tree a small amount. Make sure the left and right tube are at the same height.
  20. Once you have both triple trees connected to the tubes, look at your work from the top down. By holding the tire with one hand and the upper triple tree with the other, you can twist the assembly left and right. Twist it so that it is straight. You don’t need to be precise yet, as you will repeat this step shortly.              
  21. Put the bottom nut back on the main bolt (if you haven’t already) and tighten it down. Use two wrences. Tighten it all the way. Then, check if your steering column still turns. If it is hard to turn, back out the bolt a little at a time until the steering columns moves freely again.
  22. After tightening the main bolt, check if the forks are still even vertically. If one pokes out of the top of the triple tree more than the other, you can gently hammer it down to match.
  23. Repeat step 20 to align your front forks one last time. Looking from the top down is the best way to level them.
  24. Your front fork assembly should be perfectly aligned but not tightened down at this point. Tighten the four triple tree bolts using a 4mm allen key (two on each side). Be careful not to disrupt your alignment when you tighten them. Do not over-tighten as sometimes the triple-trees have a tendency to snap. Sad, but true.
  25. Re-insert the rubber fork caps.
  26. Re-insert the front brake caliper behind its mounting bracket and put the two bolts back in. Tighten securely with a 5mm allen key.                           
  27. You need to check if the caliper is rubbing against the disc too much. The sliver bracket that the caliper is attached to should be attached but loose at this point. You may need to pull it towards you so that the caliper isn’t rubbing against the disc when not engaged. Once you find the appropriate position, tighten down the bracket bolts that connect the tube, tube bracket, and caliper bracket together using an 8mm wrench. You may need to hold the nut down on the other side with a 10mm.
  28. Proceed with tightening the same bolts on the other tube. Make sure they’re tight but don’t over-tighten. Do not use power tools.
  29. Tighten down the axle bolt. If you’re observant, you will make sure that the left and right nuts are equidistant from the axle bolt’s tips. Make sure the nuts are tight but don’t over-tighten because it will damage your bearings and prevent the wheel from spinning. Do not use power tools.
  30. Check if your front wheel rolls easily by lifting the front of the bike off the ground and giving the front wheel a spin. You may need to repeat step #27 and/or rotate the adjustment knob on the brake caliper for minor adjustments.
  31. Re-insert the front brake cable into the caliper. You must fish it through the hole on the caliper’s body  and into the second hole in the bolt/nut retainer on the moving caliper arm. Before tightening, pull on the cable tip to make sure there is no slack. Then, push the caliper arm all the way up, pull the cable end all the way down, and tighten down the retainer nut while holding the caliper arm in the up (brake engaged) position. This will provide the necessary tension on the cable for the front brake to have full stopping power.
  32. Put the rubber fork caps back in and re-attach the front fender. Adjust your handlebars and controls to your preferred position and tighten them down. You can now take the bike for a test drive before putting the front shell back on to make sure everything works.

You made it! Now please post a comment with the problems you had, and what we can do to improve on these instructions.

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