Over the many years attending various bike shows and racing motorcycles, it amazes me on how many bikes have bad chainlines. Chains should run straight and have no binding while on the drive sprockets. This should be the case not only on old motorcycles, but also on show bikes. I have seen some motorcycles that have chainlines so bad they could not actually be ridden without the chain popping off.
As you look down the chain backbone, it should be straight. When it rolls onto a sprocket, it should be smooth without any binding. Many times it is hard to see this and it may appear straight, but is it really?
I am in the process of installing a Buell XB engine into a frame the customer has had for some time. The frame was built for a hard mount Sportster engine and stock Sportster rear wheel and tire size. The XB, being a rubber mounted engine to the frame, was belt driven. The Buell XB was fitted with a 180mm wide tire size. This frame will use a Sportster wheel, but now fitted with a 160mm tire along with a Sprotor (sprocket/brake rotor combination). This bike will also now be converted from belt to chain drive, will need different wheel spacers made for the rear axle, and will require rear sprocket spacers because of the increase in tire width over a stock Sportster, including fabricating new engine mounts. As you can see, the engine placement for proper alignment with the chain and sprockets will make this a great example on how to check the chainline of any bike.
The first thing to check is the alignment of the rear sprocket and how it lines up with the front drive sprocket.
Using a piece of 1”x 1” x 1/8” thick aluminum angle, placing it on the rear sprocket and hold it firmly against it. This is showing the exact direction the rear sprocket is going.
The front part of the angle should align with the front drive sprocket. This is how you check the rear sprocket drive line.
Now using an aluminum piece of flat stock, hold it firmly against the front drive sprocket. This indicates the exact direction the front drive sprocket is facing.
The aluminum flat stock should align with the outside edge of the rear sprocket. This is how you check the front drive sprocket chainline.
So far we have checked that the front and rear drive sprockets are in proper alignment with each other. This will look straight, but is it really as straight as it should be?
The one thing most people forget about is, are the sprockets aligned vertically? Visually this is really hard to see and yet is so important. If they are not aligned, the chain and sprockets will not wear correctly or last as long as they should. It can also cause binding of the chain which will promote faster wear and excess heat on the chain.
To check this, we need 2 shorter pieces of the aluminum angle and a couple of small vice clamping pliers.
Clamp a piece of aluminum angle onto the rear drive sprocket using a vice clamp plier. Be sure the angle is straight up and down.
Do the same to the front drive sprocket. Again, check to be sure the angle is straight vertically.
After doing this, check that they are lining up to each other vertically. This will determine if your drive sprockets are aligned vertically.
Just being slightly off will cause premature wear and damage to your chain and sprockets.
So, after checking out your chainline, how good is it? A good chainline not only will make your parts last longer, but will also make the bike more dependable and prevent premature lailign of parts. Plus, you can walk around telling everybody “I’m really straight!”
Article by Brewdude / Facebook / @brewbikes