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4Strokes.com Technical: Basic Dirt Bike Overhaul by New Old Stuff
Page Jump Links: Disassembly & Inspection | Rear Wheel Assembly | Rear Suspension | Reassembly | Intake & Carb | Electrical | Front-End & Controls
Do these things to your bike and you'll be happy all year long. I charge pro racers big bucks for this service and they keep coming back! All this work should only take a weekend or two to complete. The following is really just common sense and what I think is important to do to a bike. It also comes from years of being around dirt bikes.
If you want to install grease fittings in the suspension linkages during your overhaul, mark with a Sharpie where you want them to go BEFORE you take off the shock and swing-arm. Mark the locations for the grease fittings so that they don't interfere with anything. Remember that you have to be able to get to them with a grease gun too.
Disassembly & Inspection
Take of the swing-arm, linkage, pipe, sub-frame, rear wheel assembly, seat, air-box, etc. In other words, strip the entire rear half of the bike down, from the carburetor on back.
Once your bike is taken apart, we'll put it back together piece by piece with modifications that cost next-to-nothing.
Take a look at ALL of the welds on the frame. Check for flaking paint at the welds. This may indicate a crack. If it has been cracked a while, you may see a small rust trail. If you find a crack, get it fixed! These frames are mild steel, so almost any welding method will work.
This is a good time to tighten EVERY bolt on the main frame too, as they're easy to get to while the rear is out of the way. Important: Check the engine mount bolts and make sure they're tight.
Rear Wheel Assembly
The rear wheel assembly is next. Pull the axle spacers out of the seals on both sides (mark them R and L) so ya can see the outside of the bearings. Stick your finger in to the inner race of the bearing and turn it. Feel for smooth turning with some resistance. If it turns real easy, there's not enough grease in the bearing, and if it's a little rough, it's junk. It should not be a bit loose!
Replacing Wheel Bearings
If you have a bad bearing, find a punch that is long enough and thin enough to go clear through the hub like the axle does. There are two sealed bearings, one on each side of the hub, and between them on the inside of the hub is a steel "spreader" tube. Stick the punch in the opposite side from the bearing you want to knock out and kind of pry the spreader tube sideways a little so the punch can get a bite on the inner race of the bad bearing. Hit it gently then move the spreader 90 degrees and tap some more. Work the bearing out as straight as you can.
If you take the bad bearing to a bearing/belt/chain dealer, there's a great chance you will be able to purchase a replacement bearing for one-third to half the cost of what someone will sell you an OEM part for. When you get the new one, just tap it into the hub until it bottoms-out.
After the bearings have been installed, put the spacers back in on the proper sides and that's done. Don't forget to put the spreader back in BEFORE you seat the last bearing.
Check the spokes for tightness. If you find some that don't seem as tight as the others, tighten them up.
Replace the brake shoes or pads at this time if needed.
This is the time to install a new tire and tube if needed.
Check the sprockets for wear and tightness.
Inspect the swing-arm for cracks or damage and get it fixed if needed.
Now we're going to install the grease fittings in the links.
Installing Grease Fittings
Go to an auto parts store and buy three grease fittings. They come straight, 45° and 90°. Get the ones you need with a 1/4-28 thread. Don't forget to get a 1/4-28 tap (bottoming tap preferred) and two drill bits in the size of #3 and 1/8".
Take the needle-bearings out of the link and clean the grease out of it. Find the spot you marked at the beginning and determine the best angle to drill that will go into the space where the needle-bearings were located. Find the THICKEST part of the casting that will put the grease fitting close to where you marked. Drill the first hole with the 1/8" bit through the casting AND the wall of the outer race. Now take the #3 drill bit and drill through the same hole again BUT stop drilling when you hit the steel bearing race.
Do NOT drill this big hole through the race as you did with the little one. Screw the tap into the casting and work it in-and-out a little at a time un til you have threads. Once the tap hits the race it wont go any further be cause it wont fit through the 1/8" hole in the bearing race.
Important Note: Go gently be cause if you break the tap off in the hole you're going to have another job on your hands! The tap is harder than a drill bit and real hard to get out if it breaks.
Clean all the chips and burrs out and take the burrs out of the race where the bearings ride with a Dremel Moto tool and/or emery paper. Screw the grease fitting in and your done. Do this to all locations where you want grease fittings.
Once all the above is done, it's time to put it back together. Lightly grease all bolts, axle, etc. and install the swing-arm, links, wheel, subframe, etc. on the bike.
Rear Wheel Alignment
When you put the rear wheel assembly on and get ready to adjust the chain, find the center of the swing-arm shaft and mark it with a center punch (dimple) on each end. This is for measuring to the rear axle for wheel alignment. You will find out how close the snail adjusters really are. Sometimes they're rite on and sometimes they're not. Put a punch mark in the center of the rear axle on each end also. I made an adjustable caliper for this but you can use a tape measure or steel rule.
Adjust the chain as normal and snug the axle nut. Now measure the distance from the center of the swing-arm shaft to the rear wheel axle on both sides. This measurement MUST be exactly the same, whether or not the snail adjuster notches fit. If the snail adjuster notches don't fit when you know the swing-arm shaft and axle are parallel, you can modify the snail adjuster so it does fit. It's the little things combined together that make a world of difference over-all! This is just one of them and well worth the effort. I didn't tell you to clean and lube the chain as you already knew that anyway.
Once you have the back half of the bike done, we'll work our way forward.
Intake & Carburetor
Don't put the air-box on just yet. Take the filter out and service it as normal. Clean the air-box inside and out real good. Where the boot attaches to the box, on the INSIDE of the box, smear some clear silicone around the joint and smooth with a wet finger. Remove the excess silicone, as all you want is a final barrier to keep dust and water from getting sucked in between the joint of the box and the boot. (Some guys don't use silicone as I described, but they do use grease. The choice is yours.)
This next step is really important, as a lot of engines get "dusted" from this source. (Some leak, some don't) Grease the sealing lip of the air filter where it mates up to the air-box and install the air filter. Now, in the end of the boot that connects to the carburetor, smear a thin coat of grease around the inside of the boot and coat the inside as far up as you can reach with your finger. THIN coat! Real THIN! This will catch the dust inside the boot before it gets sucked into the carburetor if any gets past the air filter. Now install the air-box with a thin coat of grease between the boot and the bell of the carburetor. You are now done with the air-box, except where the side-panel mates to the air-box - use grease there as well.
Next little "ditty" is sealing out dust and water from the carburetor itself. After your done with this mod, the bike will idle submerged in water clear up to the top of the air-box near the bottom of the seat, so it's worth the effort!
Yank ALL the black rubber vent lines off the carburetor and go to a store that sells R/C model airplanes and cars and buy 6' of silicone (you can also use neoprene) fuel line made for gas R/C engines. Install the new hoses on the carb. and rout them up somewhere high on the frame and secure them. At least as high as the top of the air-box. Now take some silicone and seal where the throttle cable goes into the top of the carb. A little grease on the threads of the slide cap is good too. Install a fuel filter and you're rockin' as far as the fuel system goes.
Next on the agenda is the crankcase breather tube. The large (1/2") tube coming from the top of the lower engine cases has to go. It's the one with a cute little "T" fitting with one tube going up and one tube going down. Remove it and throw all this away! Buy a 3' piece of neoprene tubing and a small hose clamp. Connect one end to the nipple on the engine with the clamp and route it up to the air-box opening at the top. Install a filter (available at an auto parts store) on the end and just stick it into the top of the air-box. Let it dangle as long as its not near the air filter. It could wear a hole in the air filter and that would NOT be good. You may have to trim some the foam off the air-box where the seat seals against it (if your bike has foam) to allow the tube to fit between them without collapsing. The filter on the end of this breather tube is important because the air is being drawn into this tube, as well as being forced out.
An alternate to the mod above might be to install a bulkhead fitting into the airbox so the breather tube just connects to it as opposed to going all the way up to the top of the air-box. Obviously the other end of the bulkhead fitting needs to either have a short section of hose with a filter or perhaps you can find a filter that attaches directly to the bulkhead fitting.
With the tank off, clip each wire connector out of the circuit one at a time and solder the wires back together using heat-shrink tubing to seal the joint. Do not solder wires that have spade-lug connectors on the points where they plug into the coil, CDI box, etc. These are good connections normally and can be tightened up easily. A dab of silicone will seal them from moisture and vibration. Once all the loose ends are taken care of, bundle the wires back together with electrical tape and secure them to the frame. NOTHING should be allowed to vibrate.
Next, remove the kill switch and take it apart. Make sure the insulation on the wires going into the switch are not able to short against the handlebar. Silicone works good for this.
Remove the timing/points cover and seal around the gasket with grease. Install a new spark plug and use hi-temp silicone to seal around the porcelain off the spark plug and the plug wire boot. Seal where the stator wires come out of the stator as well.
While were on the engine, remove the useless counter-shaft sprocket foot guard, if equipped. This makes it easier to change gearing and remove crap that gets stuck in the chain and sprocket.
Front-End & Controls
Block the bike up like you would if you were going to remove the forks. Take the front wheel off and do the bearing thing as you did on the rear wheel assembly. Again, check the spokes and tighten, replace the brake shoes or pads, etc. just as you did on the rear. Check EVERYTHING on the front wheel assembly. When you put the wheel back on, take note of the axle clamps. Some clamps have a direction indicator cast into the part. Lightly grease the axle and install the front wheel and axle on the forks. Insert the axle into the fork leg snug but not tight. Now install the clamps with nuts and screw them by hand until the clamp is a little closer at the bottom than it is at the top. Adjust the nuts until everything is seated and all have the same finger-torque. Now tighten the top nuts with a wrench. This will pull the clamp parallel and the bottom nuts will be tight as well. The reason for this tightening procedure is to keep the axle from tightening itself into the fork leg so tight that you cant get it loose on the trail with smaller tools.
Now we will grease the steering head bearings. Remove the master cylinder, clutch perch, kill switch, etc. as you would if you were changing the bars. Just let them dangle. Loosen the top triple-tree clamp bolts, remove the nut that holds the top tree on the steering stem, and tap the top tree off of the fork tubes and stem with a plastic hammer or piece of wood. Now you're looking at two large nuts that kind of look like the ones on your shock that set the spring tension. If ya have the right tool, then use it. If you don't, then use a punch and hammer to loosen and remove these nuts. The whole front-end will fall out of the steering head until the tire hits the floor. The top bearing will be sitting in its race along with a seal. You can just pick them out. The bottom bearing and seal will be on the steering stem and don't usually get removed because they require a press.
Note: The stem doesn't have to come clear out of the head in order to grease the lower bearing. Just leave it where its at and pack the bearing with grease. "Packing" means forcing the grease into the bearing, not just smearing it on.
Repack the top bearing too. Lift the front-end back up into the head enough to get the top bearing, seal, and one nut on the stem. Use a special tool or a large pair of pliers to tighten the top nut. Make sure nothing is binding as you snug the nut down. Turn the forks lock-to-lock a few times as you snug up the nut. Now put the front wheel back on the ground with the bikes weight on it. Loosen the nut. Now just snug the nut back down. Not tight. No torque, just snug. Thread the second nut on and as you hold the first nut with something so it doesn't turn, tighten the second nut down against the first. This is a jam nut and must be tight.
Now you can put the top tree back on and tighten the last nut and fork leg pinch-bolts.
There is also a right way to put on handlebars. You're going install the bar clamps just as you installed the axle clamps. The reason for this is SAFETY. What were after is bars that will rotate forward with a big hit, but at the same time, not rotate backwards when you land heavy on them with your hands. Mount the bars and snug the bolts down with your fingers as you did with the axle clamps. Make sure the bolt hole with the dimple is facing forward. Now adjust the bolts so that the clamp gap is a little closer at the rear than it is at the front. Now, holding the bars where you want them, tighten the two front bolts. The rear bolts will be tight, but not as tight as the front bolts.
When you put the perch, master cylinder, etc. back on, snug them up finger tight and adjust them to suit you. Then tighten them up but not real tight, as need to rotate in a fall. This will help keep you from braking levers in a fall.
Get a cable luber and use it!
Ride the bike and check EVERYTHING. Don't forget to pump up the brakes before you ride.
Credits: Article written by New Old Stuff and edited by 4Strokes.com
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