transmission chain tensioning questions

[ghostdancing]

hi gentlemen, my bike is an XT250  dualshock converted (KLX250 swingarm\IT250 forks), to set the tension of the chain i first removed the shocks, then had the swingarm horizontal to get the max distance point front\rear sprockets.. i left some slack in this position and tighted the nuts.. when the swingarm is back in rest position i have (of course) too much slack.

i alredy fitted a chain guide (just back the swingarm pivot, where it was in the original setup), but i need a form of chain guide also in the rear section (just ahead the rear sprocket)

a firend of the forum pointed me to the protec style tensioners listed on ebay US, they are spring driven and looks a good solution

i also noticed that the contemporary bikes (i mean serious offroaders) do not have spring loaded systems, but just some form of static guide..so  i'm geting doubtful.. where is the benefit of a spring driven tensioner Vs a static guide?

any experience and knowledge are welcome

[mick25]

Go for a chain roller like modern bikes have fit one below the swingarm and one above this will take up chain slack right through the rear travel of the rear wheel , but both rollers need to be set up Spot on in the right location to do the job needed.

[HeavenVMX]

Also consider a universal type rear chain guide off a modern type machine at the rear sprocket which also satisfies the rear sprocket guard requirement. This will help a lot to stop chain derailing. There are several good cheap designs from China on eBay that work perfectly.

[TT5 Matt]

klx250' s came std with a pretty nice rear chain guide and easy to space out on the mounts if needed

[80-85 husky]

have a look at the twin shock husky chain tensioners

[ghostdancing]

tnx guys for the advices..

@matt: actually i do own one of the two plates from the original KLX device.. i'm making a copy of that device but roller equipped instead of slider (it's just for trying)

@husky: have you got picture\link where i can see it? i just googled but didnt found useful pictures

[evo550]

Because you have fitted a different rear end to the bike, automatically you have changed the way the chain tightens and loosens during the suspension stroke. The KLX arm is much longer than a standard xt, that combined with longer travel is what is causing you problems. I would fit one of the spring tensioners as well, a chain guide at the bottom of the sprocket only helps aligment as chain enters sprocket under power (as top of chain is tight) but when you back the throttle off or brake the top of chain becomes loose this can cause derailment on front sprocket (don't want that), a spring tensioner keeps equal tension on the chain in both instances.

[ghostdancing]

evo, so you say better i go with a spring loaded device, correct?

your point is just 100% exact: i got a so much longer chain now with the longer arm.. but.. contemporary bikes do have very long chain as well, and also much suspension travel, compared with mine XT.. why no manifacturer still uses spring loaded device to control the bottom chain tension?

[80-85 husky]

new bikes have the countershaft sprocket very close to the swingarm pivot to minimise tension issues as well as heavy rollers and nylon guides.

ol mate moons ago had a monty vb with an xl 350 donk dropped in. the swing arm / sprocket relationship was ugly and on landing off a jump, the chain would double up into the c/s sprocket and lock the works up . took some rollers and tensioners to sort that out.

check out café husky - vintage left kickers, lots of rebuild threads with picks of tensioners. also check out husqvarnaparts.com and look at the tensioners for sale. phil has a neat one with finger grips on so you can check the tension easily.

[evo550]

evo, so you say better i go with a spring loaded device, correct?

your point is just 100% exact: i got a so much longer chain now with the longer arm.. but.. contemporary bikes do have very long chain as well, and also much suspension travel, compared with mine XT.. why no manifacturer still uses spring loaded device to control the bottom chain tension?

It may help, Yamaha fitted them to the original xt swingarm, you might have had better luck fitting an IT swingarm and shock instead of the KLX unit with twin shocks.

[brent j]

I fitted a PE swingarm to my XT500. The XT has the sprocket a long way from the swingarm pivot so has major fluctuations in chain tension. Long suspension travel just adds to the problem.

I tried spring loaded tensioners but found they let the top run of the chain go loose during over run.

I eventually settled on rollers. As Mick25 mentioned, set the front sprocket, swingarm pivot and rear axle in line and set the chain tension with a little slack. This is the tightest it will ever get.
In this position mount a roller under the swingarm pivot with a few mm clearance from the chain and another above the pivot. This way the chain tension is nearly always even no matter where the wheel is in it’s total travel or whether the power is on or off

Also add a late model chain guide at the rear sprocket.

This worked well on my XT’s and I will be doing the same on my PE250B. I know it’s not original but it is safe and reliable

[HeavenVMX]

Have to agree with brent J and Mick25

Correctly fitted rollers and a good rear sprocket guide is a solution to the chain tension problem which is why all manufacturers have gone that way.

Adding a spring loaded chain tensioner is very much a Band-Aid to try and hide the problem.