is there some kind of formula to set chain tension on motorbikes (dirtbikes in particular)?

Question

and what is too tight and too loose also what will happen if either of these occur

Answer 1

The rule of thumb is this; adjust the chain so that while the bike is at rest and with out the rider aboard there is enough slack in the chain so that you can slide 2 ~ 3 fingers between the chain and swingarm at the rear of the chain slider. Roughly 1.5 ~ 2.0 inches of slack.

The chain will be at it's tightest when the swing arm is straight out, paralell with the ground. At that point you should be looking for about an inch of slack. When weight or compression comes off the bike and it's sitting normally there will be more slack as the distance between the axle center line and the countershaft center line is now shorter.

Too much tension on the chain will cause premature chain and sprocket wear, and in extreme cases, countershaft seal and bearing failure.

Too little and you can get increased chain and sprocket wear, and in extreme cases, wear to the swingarm and chain guide. Not to mention the chain could slip off.

Don't use motor oil or WD40 as a chain lube either. Invest in some quality motorcycle chain lube.

Chain and sprockets are truely one of those situations where you get what you pay for. Cheap chains stretch wildly and won't last. Cheap spockets hook and wear quickly. I've had the best luck with Tsubaki's Alpha Gold chain and Renthal sprockets. YMMV.

NEVER put on old chain on new sprockets, or vise versa. There "wear pattern" in the old pieces will prematurely wear out the new one(s) in short order.

Good luck!

Answer 2

The reason dirt bikes have such loose chain tension, is because of the long travel suspension.
--Look at it this way - if you unbolted the rear shock and linkage, then swing the rear wheel down (or up), the center of the rear sprocket will get closer to the center of the front sprocket. Making the chain tension looser and looser.
--The chain tension is the tightest on any bike when you can draw a straight line from the center of the front sprocket, through the swing arm pivot bolt, to the center of the rear sprocket.
--When those three points are lined up, a comfortable chain tension is about 20mm. To loose, and the chain can jump off the sprocket. To tight, and the chain wiil be trying to pull the F&R sprockets together and bind against the sprockets (making everything hard to turn).
--When you get the chain slack specs from the manual, the slack should be adjusted when the bike is standing upright with no weight on the seat.
--Dirt bikes are so loose, so when the rear wheel goes
up (by landing from a jump or hitting a bump) the F sprocket, swing arm pivot and R sprocket are close to lined up. Which is the tightest the chain will get.
--The only correct way to adjust the chain on any bike, is to get the
proper "chain slack" specs from the manual for that paticular bike.
http://www.motocom.com/motorcycles/

Answer 3

Gaurdrails answer is the closest to correct.
With the rear suspension bottomed (or shockless) the chain should be taught, but not tight or stretched.
If too tight a chain will stretch, break or wear sprockets, if too loose,it may derail, and wear sprockets.
A chain tensioner is a good idea, that way if the chain is a bit loose the tensioner will take up the slack.

Answer 4

changing the type of tooth on the sprockets differences the popular gearing of the motorbike. count extensive type the tooth on the previous ones to make particular the replacements are the your best option ones. Sprockets want replaced whilst the tooth look "hooked" and not U formed. it extremely is extremely useful to alter sprockets once you place on a sparkling chain otherwise worn sprockets can smash the hot chain incredibly today.

Answer 5

Buy a Clymer manual for your make and year of bike. They cost about $30, but it will tell you everything you need to know about the bike.