Motosport

Rocky Mountain MC

I tightened up the sprocket bolts before the first days riding and everything else checked out fine. On the morning of day three of the trip I was eager to get out and do some laps as the rain had been on and of since we arrived and the weather had cleared for now. I quickly looked over the bike for visual signs of loose parts and didn’t see anything suspicious.

Dirt Bike Broken Sprocket

After cutting quite a few laps and landing on the down ramp of a table top the motor stopped suddenly and the bike felt weird. I new something was wrong as the motor seemed to just drop out without the usual drag from the engine when it stalls.

Sure enough, i looked at the rear wheel only to find my rear sprocket had broken into three separate pieces, torn the bolts and tabs clean off a couple of points on the hub, and jammed the chain into my now broken my chain guide. After pushing the bike back to the camp site and stripping the broken parts off the bike I noticed that it also took a gouge out of the inside of the swing arm and tore teeth off the front sprocket.

Dirt Bike Broken Hub

Now I’ve fitted a new Talon sprocket on a new set of rims and used medium strength loctite to make sure they stay tight. Also fitted a new chain, front sprocket and chain guide. I’ve had to learn an expensive lesson, so hopefully by reading this you won’t do the same.

Grab your spoke wrench and loosen the spokes on the opposite side of the rim from where the line is further away from the center, where its buckled. Put tension on the part where the buckle is after loosening the opposite side.

Only adjust the spokes by no more than half one full turn at a time and alternate in sets of 2 or 3 spokes leaving 4 to 8 spokes in between. In other words make small adjustments and spread them around on opposite sides of the rim.

With some patience and few quiet drinks you’ll have a nice circular rim again. Just remember to keep your spokes tight to prevent it from happening again.

Check out the diagram below, the port to the right and down is hidden by the cover. If the cover was orientated any other way one of the sleeves would be visible on the left side of the filter cover.

Prevention is better than cure
Your chain should be at the top of your maintenance list before you go for a ride. Looking over the sprockets will also reveal wear and problems waiting to unfold. You should ensure your chain is at the correct tension, is not stretched and in doing so you’ll get a lot more mileage out of your chain and sprockets.

If the teeth of a sprocket are chaffed on either side it can mean either, the rear wheel is misaligned or the chain is badly stretched and can sway left or right under load. A stretched chain will make a harsh chatter sound when accelerating in a tall gear.

Chain types
Unless you ride your dirt bike very little and don’t ride it very hard you should replace the standard chain with an O ring or X ring chain. Every link on a standard chain is exposed to the elements and there is no defence against sand or dirt grinding away at them. The links wear quickly which causes the chain to increase in length, often referred to as a stretched chain. This problem causes your sprockets to wear prematurely as the profile of the chain will no longer match the profile of the sprockets. So if you are replacing an old chain you should also replace the sprockets.

The X-ring chain is a low friction version of the O-ring chain, both prevent grit being embedded in the chain and grinding away at the pivoting links. These chains wear in sync with the sprockets and will take a serious amount of motocross, supercross or trail riding abuse before they need to be replaced. If you want reliability, on of the best things you can do is fit your bike with a heavyweight (520) O-ring chain and steel sprockets. To get the most out of your chain you should replace the front sprocket as soon as the profile of the teeth starts looking more worn than the rear. Low quality sprockets should be replace every few months even if the wear appears minimal. The teeth on the front sprocket contact the chain around three times more than the rear, therefore it will wear quicker and contribute more to the wear of the chain.

Chain tension
Dirt bikes have different dimensions when it comes to the length of the swing arm. Bikes with a longer swing arm will require less chain tension than those with a shorter swing arm. This allows the swing arms to move as the rear suspension compresses. If your chain is to tight, it will be stretched as the suspension compresses. The only way to accurately gauge what your chain tension should be is to compress the rear of the bike until countershaft sprocket, swing arm and rear axle are all on the same plane. At this point the chain is at its tightest so there must be at least 10-15mm of slack in the middle of the chain. You can compress the rear end of the dirt bike by attaching a tie down strap from the axle to the muffler.

Lubrication
There are many different types of chain lube you can use on your chain. Avoid cheap, low quality lubes as they will not give adequate protection and will most likely splatter and make a mess at speed.

Tacky lubes have a thick consistency like honey and are designed to cling to the chain and not fling off at speed. The problem with this type of lubricant is that dirt and roost from the rear wheel will end up coating the chain, forming a grinding paste that will seriously wear your chain. You should only use this type of lubricant in extremely good conditions.

Silicone lubes are the only lubricant you should use in sandy or dry, dusty conditions. Coat the chain up to three times, letting each coat dry and wiping the excess off the links. The silicone will give your chain rollers a slippery finish which will repeal dirt.

Chain wax repeals water and dirt and is best suited to wet conditions. After you’ve washed your bike it also doubles as a good anti-rust lubricant.

Checking over your bike can be time consuming, so to make the process quicker for the next time, after you’ve properly torqued a nut and/or bolt, mark the surface beside the bolt or over the nut and bolt with a permanent marker as reference point. Then, the next time you ride, unless the mark on the nut and/or bolt isn’t lined up, you won’t need to retighten it. Most new motocross bikes come with marks in place. Make sure you use a marker which won’t fade or wear off but will be easily cleaned off when necessary.

Place your wheel on the work stand or bucket and remove the valve core to release all the air.

Loosen the nut on the rim lock until it is at the very end of the threads. If it has one, remove the nut from the valve stem.

You need to “break the bead” from one side of the rim. Using your tire lever between the rim and the tire, push down on the tire and work your way around the entire wheel.

You can spray some soapy water between the tire and rim but be careful, it will make things slippery. You can also use a bead breaker tool

If you have rim protectors place them on now. With your tire lever work the bead off the rim starting at one side and working your way around the rim.

Flip the wheel over and repeat this process.

Push the rim into the center of the tire and pivot the rim out of the old tire.

Remove the inner tube from the old tire and inspect for damage – usually around the valve stem. If you find damage replace with a new one. If there is no damage, insert valve core and add a small amount of air to give it body.

Grab hold of your new warm tire and squirt some talcum powder inside. Roll it around to cover well. The talc allows the inner tube to rotate into its natural shape during inflation. Insert the semi inflated tube in the tire.
Once you have tube in the tire, push the valve stem through the hole in the rim and screw the lock nut on to hold it in place.

Place the wheel onto your stand and push the tire onto the rim. Using a tire lever, work the bead onto the rim so you have half the tire on.

Slide two tire levers under the bead to catch the corner of the tire, push the rim lock into place.

Well if this is true then it would cost me at least $60 an hour to ride my new thumper. This is not something I can afford to do so I asked around for some advice and if this was the norm. I was firstly directed to check my owners manual to see what it said. The manual states that the engine oil and filter should be changed and the valve clearances checked after every 15 hours. I have been sent a supplement to the owners manual that states the oil should be changed after every 7 hours of riding under race conditions.

The general advice I was given was that unless you are a pro rider wringing every last ounce of power out of your 450 and spending a lot of time in the upper rev range then your valves are going to need adjustment a lot less frequently than even 15 hours. Some had the valves checked after every 3 to 6 months it was also suggested that adjusting the valve clearances was only essential once the bike is hard to start or backfiring a lot. Do make sure you clean your air filter after every ride.

The majority of riders recommended doing the oil and filter changes yourself, make sure you have a torque wrench to re tighten anything you remove with the correct tension. Don’t be afraid to load your bike on the trailer and take it to your mechanic if you get stuck. Read your owners manual for instructions and don’t try anything you aren’t comfortable doing yourself. If you can, find someone who has experience doing the basic maintenance tasks you need to do to walk you through it the first time so you know what to look out for. My brother had the unpleasant experience of somebody at the service center putting an oil filter in back to front which resulted in a rebuild of the engine.

The are videos on youtube which show maintenance tasks, like changing the oil and filter. like the one below…

When it comes to adjusting the valve clearances shop around for the best price but make sure the mechanic you choose has some credibility.