Correct chain tension

[pbear62]

Hi guys & girls, I've read on this very fine & informative forum a few comments about ensuring you have the chain tension correct to eliminate "chain snatch" on TRX's. Looking at the photo of Lars TRX (TOTM) it appears to me that the lower chain run is nearly straight meaning that the chain must be fairly tight. I reckon that when the rider sat on a bike when the chain is this tight (unladen) it would become as tight as a guitar string. I was always taught to adjust a chain with the rider sitting on the bike to ensure there was some slack when under riding conditions & to have approx 20/25mm of slack (measured half way between the sprockets on the lower chain run) to allow for extra suspension compression over rough surfaces. If the chain is too tight it will put extra load on wheel bearings & gearbox bearings - especially as it gets tighter over the aforementioned rough surfaces. This adjustment method is also advised in a number of workshop manuals I have. What does everyone else do re: setting theirs up? I would have thought a bit of chain snatch was preferable to replacing shagged gearbox bearings?
PS: I'm not in any way having a dig at you Lars - it's a gorgeous looking bike - same colour as the one I had (& loved) in '97!

[Mincehead]

Yep,I agree with you on this one.
I ALWAYS rotate the wheel with the bike unloaded first to check for tight spots(there are nearly always these),a dot of tippex gives a visual mark on a link
I then sit on the bike and roll it along with my weight on the seat.
At every say foot or so I hitch the lower run of chain with the heel of my boot to double check the tension and only when it`s done a complete revolution will I nip up the spindle etc.
My Skorpion is a bugger for snatch being a single but I`ve got very used to just how much movement it snatches least with,I must say it`s not within the movement/dimensions given in the riders handbook either.

[pbear62]

Come on guys - surely Mincehead & I can't be the only ones that adjust our own chains & have an opinion on this. Where is everyone who has previously mentioned chain snatch problems?

[slow codger]

I'm sure the majority adjust our own chains.
Lubrication of chain, and just get a feel for it being right, not too tight, and aligned straight, I dont allow a lot of play on the underside so that under load (me sitting on it) it has very little play, keeps it from rubbing away the swing arm protector.

Dave E

[Excalibre]

In my opinion the recommendation in the manual is spot on. ie. 20-30mm slack with no load.

I use a race stand to lift the rear wheel off the ground. Then rotate the tyre a few times while wriggling the chain up and down to find where it's the tightest.
While at it's tightest point, use a ruler and measure the distance the chain can move the chain up and down at the mid point. If it's outside of the 20-30mm tolerance it should be adjusted. Make sure both sides are adjusted evenly and then re-measure again after the axle nut has been tightened (sometimes the chain gets a bit tighter when the nut is done up).

For peace of mind, with the bike back on the ground and wheel rotated to it's tightest spot again, load up the rear of the bike (ie. lie across seat or get someone to sit on it) so that the front sprocket shaft, swing arm pivot and rear axle are all lined up. That's the situation where the chain will be at it's tightest.
Wriggle the chain in that configuration and there should be very little movement. If it feels like it's under tension then it's too tight.

It's better to have a chain that's a little too loose instead of a little too tight.
The best case scenario of a tight chain is that the chain will stretch until it's in tolerance. Other than that you could expect damaged output shaft bearings, damaged gearbox bearings, damaged wheel bearings or a broken chain (often with catastrophic results).

There endeth the lecture

[Wombat]

I'm with Excalibre here....... I do mine on a race stand as well. And yes a little loose is way better than too tight! Even if the chain is a little bit slack, when your weight is applied the chain will fall into the recommended tolerances. I also use a Profi LaserCAT chain alignment tool. Gets it accurate everytime.

Bob

[drix]

Bringing this topic back up as I'm having some challenges with the chain tension.

My chain was a little loose recently so had a look at it today... rear wheel on paddock stand, spindle freed up, pulled the wheel to tighten up the chain allowing for a little play, I setup each side bolts/markers to the same position and tightened the spindle. Put the bike on its wheels, sat on it/wheeled it, all looked fine. Went for a short ride of a few miles and came back only to find that the chain had loosened up to how it was previously.

Am I missing something? Chain and sprocket kit have circ 5K miles so can't be shot already. Would it the spindle or the tension bolts/spacers becoming lazy?

Any help or tips welcome for an occasional Sunday DIYer like myself.

[Stu99]

My 2 cents.
Always clean your chain prior to adjustment.
Inspect for any tight or damaged links.
Always adjust your slack on the chains tight spot.
Only loosen you axle nut enough to be able to move the adjusters freely.
( if you loosen too much, the chain tension can change as you retighten)
After adjustment, always re-check tension at various spots around the chain before hitting the road.

And remember, stated chain tolerance slack is for standard chain length and sprockets.

Oh, and as others mentioned a little loose is ALWAYS better than a little tight.

[cobbadiggabuddyblooo]

My 10c
Remember to warm the chain up with a short ride before oiling and if using lightweight wheels ,tighten the axles to 50% of the specified torque settings.
.