Tuesday, January 8, 2013

Tech Tuesday

More Chain, Less Belt

Final drive belts on motorcycles are designed to propel the bike, but keep down the noise. They can be expensive. They need to be changed every now and then due to dry-rot and wear. Ever have a belt break on the road? It is impossible to fix without removing the primary. This is something very hard to accomplish without different specialized tools. There are different reasons people prefer belts over chains and vice versa. Regardless, changing a belt to chain drive is still very easy. Lets take an Evolution equipped Harley-Davidson Sportster as our example. The chain conversion can easily be reversed if it did not suit your bike.

Doing a chain conversion on a Sportster requires limited mechanical knowledge. Please note that a chain can be very dangerous if installed incorrectly, DO NOT attempt this if you are not certain it can be done correctly. A couple of basic socket wrenches, Allen keys and screwdrivers are needed. Secure the front wheel either down or against something. The rear wheel will need to be raised into the air so that it may come off. The belt has two pulleys. One is attached to the main shaft of the transmission and the other to the rear wheel hub. The rear wheel axle can be loosened as well as the belt adjusters. This will make slack in the belt. The main shaft pulley has a cover that is usually held on by two bolts. This is removed to gain access to the main shaft pulley. Depending on the motorcycle’s exhaust, it may have to be removed in order to gain access to the main shaft pulley. The belt guard will need to be removed as well. Pull the belt off of the rear wheel sprocket and let it hang. Remove the axle and remove the rear wheel. Make sure to keep in mind how many spacers if any were on the axle. The belt can either be cut or a shock may be temporarily disconnected to remove it.

To attack the conversion, both pulleys need to be replaced with chain sprockets. The belt pulley on the rear wheel is held in place with perimeter bolts on the wheel’s hub flange. Remove the bolts and pulley. A new chain sprocket can be bolted in place now. The same bolts or new hardware can be used, but don’t forget to put thread locker on the bolts. Torque the bolts as per the manufacturer’s service manual. The size and tooth count of the rear chain sprocket depends on rider preference. The size of the sprocket effects either low end off-the-line power or highway cruising. Mount the rear wheel with its spacers and axle. Just snug it up, to make sure everything is in alignment.

The main shaft pulley is a little more detailed. It is held by a large nut around 1-7/8 inches in diameter. It is easiest to remove with an impact wrench. Once the main shaft nut is off, two small bolts hold a locking plate to the main shaft pulley. Once they are removed the pulley will come off the main shaft. Behind the pulley is a spacer that will need to be replaced. Inside the spacer is a quad-seal. It looks like an O-ring. That will also be replaced. The main shaft seal should also be replaced, so that it does not leak in the future; it is worn to the old spacer. The seal comes off by drilling a screw ever so slightly into it. Once it has some grip the seal can be pulled from its place. A new seal is installed by lightly tapping it with a hammer. The spacer in the chain conversion is larger than the belt spacer. This is due to the chain having much less thickness than the belt. The main shaft seal and splines are lubricated, and the new quad-seal and spacer are installed by sliding them down the shaft. The spacer has a taper which is placed towards the transmission. A new sprocket is installed with a lock plate and bolts. The large main shaft nut is then torqued back in to place. Remember again to use a thread locker on all bolts and nuts.
Using a straight edge make sure the main shaft sprocket and wheel sprocket are in perfect alignment. Spacers can be used to make the alignment perfect. Make sure the wheel is at its forward most position in the axle plates. The belt tension adjusters should be completely unadjusted. An O-ring chain can be used for durability. The pitch of the chain determines how light or heavy it will be. This again depends on how the bike is driven. Lay the chain along the sprockets to determine where it needs to be cut. Find the link where the chain would fit the best and subtract one link. Use a chain breaker to cut the chain. Then use a master-link to put the chain together around both sprockets. The chain should be slightly loose, that is when the adjusters come in. Adjust the rear axle to tighten the chain. It should have a deflection recommended in the service manual, but a good rule of thumb is about ½ of an inch. Tighten the axle nuts to their recommended torque. Re-install the belt guard and transmission pulley covers. Just like that, it is all done. Chain conversion kits can be costly. All the parts can be basically sourced individually, but the kits are a great way to save that person the hassle. An issue on the road can be fixed simply with a new chain and master-link. The only maintenance is chain lube every now and then. Safe riding!

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