We see many dirt bikes come into the shop every year.
It is amazing how many of the have bad fly wheels.
The number one thing we see that is causing the damage is the owners trying to remove them with screw drivers, hammers, and air guns.
DON'T DO IT!!!
Here is the problem.
We have a 2001 RM250 and as you can see the fly wheel exposed and ready for removal.
First off you will need to remove the nut that is on the end of the crank shaft
Keep in mind that some fly wheels are on the opposite side of the engine which means that the threads will be left handed not right handed:
The next thing we do is clean the internal threads in the fly wheel with a small wire brush.
A Dremel tool with a small wire wheel works wonders
Once the threads are cleaned we apply a liberal amount of lubricant.
In this case we used some WD-40. (Yes, that is a WWII Machine gun oil can)
Next, you need a fly wheel puller such as this one below:
We have used this puller for several years and hundreds of Motorcycles.
You can see from the threads that it has been well used.
The biggest secrets to using this tool is lubricating the threads and backing off the Jacking bolt before you insert the puller into the fly wheel:
If you do not use lubricant this tool will not last very long.
Before screwing the puller into the fly wheel, make sure that the jacking bolt is backed off all the way.
If you do not back the Jacking bolt out first it may prevent you from screwing the puller in deep enough.
If the puller is not in deep enough you will most likely pull the threads out of the tool or your fly wheel.
If the top end is off the bike, you will need to hold the piston to keep the crank assembly from rotating.
If you are having a hard time you can get a broom stick and insert it under the piston to keep it from moving.
However, if your piston is going to be re-used you need to be careful on where you place the wood otherwise you could damage your piston skirt.
Note: The puller has fine left handed threads while the jacking bolt has coarse right handed threads.
So, to install the puller into the fly wheel you will need to turn it to the left, not the right.
Once the puller has been correctly threaded into the fly wheel you will need two wrenches.
One to hold the tool and one to turn the jacking screw:
Sometimes it requires a little elbow grease to get these loose.
Once the tool breaks the fly wheels contact with the crank shaft the fly wheel should pull straight off.
You might feel a little resistance from the magnets as you are pulling the fly wheel away from the engine.
With the fly wheel removed you are standing there with a smile on your face until you realize that the tool is stuck in the puller
What now???
Whatever you do, DO NOT stick your fly wheel in a vice, or attempt to grab the edges with vice grips or any thing like this.
Note that the inside of the fly wheel has a key way.
It is hard to see the key way from this picture but rest assured it is there.
Slip the fly wheel back on the shaft.
You should feel the magnetic force pulling the fly wheel back onto the shaft.
Be sure to align the key way so that the fly wheel slips all the way on.
Do not install the nut.
It just needs to be on there and not move around.
Now, turn the puller clock wise.
Remember, if the top end is off you may need to hold the piston from moving.
Perfect!
Once the puller is free of the fly wheel, pull the fly wheel straight out.
So there you have it.
Remember, always consult your manual for tips and tricks that may not be covered in this article.
Feel free to post your comments or ask additional questions.
SB