Honda CB125

Replacing the Drive Chain on a Honda CB125E

A stretched drive chain

It was probably around the 3500km mark when I noticed that when the drive chain became dry on my Honda CB125 there were five links in a row that would become stiff. Keeping the chain well lubricated would resolve this issue at first but the problem steadily worsened and by the time the bike was approaching the 15000km mark it was obvious that the chain had to go. It didnt matter how well lubricated they were or if I took the chain off and cleaned it those links were on the point of seizing up.

Having a chain that kinks and binds causes vibrations that can be felt through the whole motorcycle at any speed. When I replaced the chain I was amazed at how much smoother the bike became, which indicates to me that the drive chain was probably defective to some degree from new. A chain that binds will also cause the sprockets to wear prematurely and I was fortunate that they were still in very good condition. You should never use a new chain with worn sprockets or an old chain with new sprockets but replace them as a set. Mixing and matching old and new parts will cause the new parts to rapidly wear. If the sprockets were even slightly worn I would not have hesitated to replace them.

I take the opportunity whenever it presents itself to speak to other CB125E owners and a percentage of them have the same problems I was having with the factory chain binding. This section on replacing the chain is provided for those people who have elected to replace the chain early rather than put up with it. Replacing the chain and sprockets as a set will be covered seperately.

At the time I chose to replace the chain the motorbike was still under factory warranty however I did not pursue this as I did not want a standard chain. The O-ring chain I selected for my Honda will provide thousands of kilometres of service beyond a standard chain (of any brand) and require less maintainance.

The image at the top of this page shows the old chain removed from the bike lying on a sheet of cardboard next to the new chain which is waiting to be cut down to size. I wanted the image to be clear but I didnt want to include all four feet plus of chains so this is basically two pictures, one of each end that I have joined together. The new O-ring chain is at the top and the factory chain is the one at the bottom.

The reason I have made some effort to include this image is to illustrate how much a chain will stretch with normal use. If you look on the right side of the image you can see that the links on the chain line up perfectly but on the left side of the image they are about one third out. The chain on my Honda is 60 links including the split link so over that length it has stretched a good 10mm (3/8 inch). Wow! No wonder we have to keep adjusting the tension. When you buy a new chain it will probably be longer than you need, especially after market chains. Dont lay them side by side and cut the new chain to the length of the old one, count the links of the old one and cut the new one so that it has the same number of links. And bear in mind if you cut the chain too short it will be much harder to correct than if it is too long. Consider all of this carefully before proceeding.

Replacing the Chain

Chain Replacement Step by Step

When I replaced my factory chain with a new O-ring chain I had a new rear tyre fitted at the same time. Which of course meant that I removed the rear wheel. The order I took things apart was a little different as a result but here is a good break down of how simply replacing the chain is performed.

Lets start by removing the cover from the front sprocket. This is held on by two bolts circled in red in the first image on the left. Be warned, it will be very very dirty in there, a wonderful mixture of road dirt and whatever you lubricated the chain with. Theres no point in polishing it till it shines but it would be wise to clean up under there with a rag if only to reduce the build up.

Loosen the axle nut on the rear wheel and back the chain tensioners off on both sides so that the wheel can move freely in its slot on the swing arm and the tension drops off on the chain. The section on Adjusting the Chain will probably be useful to you if you are not familiar with the drive chain tensioners. In this instance you want to loosen them rather than tighten them as described in that section so that the chain will go slack.

Rotate the wheel until the split link or joining link is located on the chain and is in a position that you are comfortable working in. Remove the split link and put it in a safe place. They are handy things to keep around sometimes.

Lay the old chain out on a clean surface that will allow you to stretch if out flat. It will be greasy so the wifes ironing board is a poor choice. I used a big piece of cardboard. Lay the new chain next to it. Count the links in the old chain and cut the new chain so that it has the same number of links. If you are changing the sprockets and they are not the standard ratio you will need to add or subtract links. Remember, if you have a doubt make the chain too long rather than too short. If you make the chain too short you will need to buy an additional split link so that you can add more links to the chain.

Thread the new chain over the rear wheel sprocket first and then run it over the top of the front sprocket, pulling it through so that the ends of the chain will join at the bottom of its run between the two sprockets. Make sure you pull it the correct way around the swing arm. Fit the new split link that should have been supplied with the new chain making sure that the rounded end of the clip on the split link points in the direction of rotation. It is less likely to come off that way. Tension the chain as described in the Adjusting the Drive Chain section, lubricate it and you are ready to go.

Shortening Chains and Fitting Split Links

Shortening the chain and fitting the split link is easy but can take a little practice. When I was just starting to learn about repairing my own motorcycles I spent a few hours looking for the clips of various split links that had flown across the garage while I got the knack of installing them.

Shortening the chain is very easy indeed, pick the link where you need to shorten the chain. The link you remove must be a full outer link, look at the images if you dont know what I mean. Grind the pins down on this link until they are level with the rest of the link (the link plate) and then seperate it with a screwdriver or similar tool. You might have to hit it with a hammer. Its that easy!

To install a split link (or joining link as they are sometimes called) is also easy. You must bear in mind that the split link replaces an outer link. The split link comprises of one link plate with grooved pins, another link plate without pins and a clip that is installed into the grooves on the pins to make sure that the split link stays together. Joining the ends of the chain together and installing the split link is performed by pushing the ends of the chain onto the pins of the joining link. The link plate is then pushed onto the pins so that the inner links of the end of the chain are sandwiched between the two link plates of the split link. The retaining clip is then installed into the grooves on the pins of the split link to prevent the whole lot from seperating. The rounded end of the clip (not the split end) should face in the direction of rotation. Incidentally, removing the split link is the exact opposite of assembly.

Shortening the Chain