davemosstuning

ADJUSTING A CHAIN

There are several benefits of doing this on a regular basis:
- chains can last up to 20,000 miles or more with street use
- rear suspension action is constant and not impeded
- ride quality is improved in all facets of the transmission shifting
- the countershaft bearing is never stressed in the engine case

The most serious of these issues is the countershaft bearing. If a chain is too tight, the only thing that isn’t steel in the entire engine assembly are the engine cases in that area. Therefore a tight chain will seek out the weak spot and start pulling the steel output shaft bearing back into the case which results in destroyed engine cases and a used engine purchase (much cheaper than a full rebuild and new cases).

NOTE:
Now that the chain has been cleaned check it for overall condition:-
- do the bushings rattle
- are the links binding causing them so sit at odd angles to each other?
- can you pull the chain away from the rear sprocket?
- Is there a lot of side to side play in the chain under the swing arm?
- is the clip link on the master link?

If there are problems that are immediately obvious, is it better to replace the chain or leave it as is? Would you prefer the chain to break and suffer the consequences of that from being stranded to having a large hole in the engine crank cases? Chains in the grand scheme of amortized expenditure don’t cost a lot compared to tires and oil – so why wouldn’t you replace it?


At this juncture it is also very important to check the chain to see if there is a tight spot in it. This must be found before you start any chain adjustment. Why? The tight spot of the chain sets the chain tension, so you must use that point for the adjustment. Obviously if the chain is far too loose to compensate for the tight spot, you need to replace the chain. Keep the person on the bike and roll the rear wheel around half a turn at a time and check the entire chain starting at the master link to identify the tight spot and go from there.

In terms of adjustment, some are easy to assess. On most bikes you can lift the chain just behind the left rear set and you should be able to just touch the underside of the plastic guide that protects the swing arm without having to force the chain up against it. Not sure if you are forcing the chain? Sit someone on the bike the same weight as you (feet on the ground, hands off the bars) and check again. If the chain touches the guide easily, the chain is too loose. If not, then it needs to be adjusted.

Other bikes such as the Daytona 675 and Yamaha R6 don’t allow this test as the chain is a long way down below the swing arm, so you have to measure from the chains natural resting spot whether it will rise above and below by ¾ of an inch and that requires a tape measure and some accurate measuring. Tedious yes, but worth the effort!

If you need to adjust your chain tension, this does requires a great deal of time, observation and attention to detail – but you only need to make that level of commitment once. I NEVER trust the marks on any OEM swing arm so I make a point with every bike that is new to me to make sure I know that the rear wheel is perfectly straight and mark the swing arm to reflect that with a punch mark (nail polish etc will chip off over time). There are 3 ways to get this accomplished:

- use a rod type tool that fits in the hollow swing arm pivot and hollow rear axle. Set one side and then go to the other side of the bike and check the alignment. There are a few variables in terms of positioning, angle and view point but it should be close.
- Use Vernier calipers to measure the position of the front side of the axle blocks to the beginning of the cast swing arm slot. That measures the total distance of the adjusting bolts very accurately to make sure they are the same length.
- Personally I prefer to use the string line method so that I can get it perfect, but that is very time consuming.

Once completed you should mark the swing arm so you know that at that point the rear wheel is perfectly straight. Then you can adjust fore and aft with Vernier calipers knowing the rear wheel is perfectly aligned, or count the number of turns or faces of the adjusting bolt.

On single sided swing arms chain adjustment is in one way very simple with the concentric drum to reduce or increase chain tension. There are very specialized tools made for these drums so make sure you acquire the correct one and don’t forget to tighten the pinch bolt(s) once you are done to lock the drum in place! Make sure you also know which way to turn the drum to get the end result you need for tension or free play.

There’s no really easy way to assess the chain slack on a single sided swing arm is it runs almost immediately adjacent to the underside guide on the swing arm. I will always check the free play ABOVE the swing arm close to the frame as the chain can be lifted easily at that point. Again, sit someone on the bike and see if there is any free play in the chain. If it looks like a dirt bike chain, add some tension. If you can’t pull the chain up very easily, back it off a little.

One other note:- these drums have a high and a low spot so you need to know where you are in the arc. Take it to the lowest spot, detach the chain and move the drum to its highest spot. Mark the drum at for high and low ends of rotation so you can see where you are in the range. This is critical in regards to swing arm angle.

Be patient with this task – your engine cases will thank you, not to mention your tires, rear shock and your spine.

Video links
http://www.youtube.com/watch?v=2ljRtU-pjTk
http://www.youtube.com/watch?v=vGCmpHLdxB4



The Author:
Dave Moss is the Founder of Catalyst Reaction and Host of OnTheThrottle video programming specializing in technical analysis and how too segments. He has been working with street, track and race riders and motorcycle suspension and chassis geometry since 1995 and has become an internationally recognized authority in his field through his work with regard to testing and tuning. Dave is an avid rider and races with AFM in Northern California and is the 2011 & 2012 450 Superbike Class Champion. For further information go to www.feelthetrack.com and Facebook: davemosstuning