A bit difficult to explain, but here goes.
My chain diff cog is a bit close to the rear cross rails on my car, but there is a 10mm gap.
The rail is close to the bottom of the diff sprocket.
Does the chain go loose on the bottom as it goes tight on the top under power? because somehow the chain close to the rail has started to wear it away.
I know that I can tighten it but it already feels tight and I don't want to damage the output sprocket bearing.
I gather that under power the chain is slackening and 'pushing' off the bottom of the chain sprocket.
If the answer is just tighten away then I will, but I just wondered if the chains needs a tensioner along the bottom?

Or should I just let it cut a groove?

There is no wear on the chain


[Edited on 2/6/2009 by nitram38]

Chain will go slack underneath when under tension.
If you mount a piece of brass for the chain to run on, it will wear until the rollers of the chain make contact and then wear will cease. Bit like a chain tensioner.
HTH

Since this is "normal" for the chain to slacken underneath, I think that I will leave the chain as it is and reshape the rails so that it can't touch it.
The bike doesn't have a tensioner and my setup is a lot shorter than the bike, so it looks like it will be just some unnecessary work.
Apart from that no other problems to report!

most MX swingarms have chain sliders on. A plastic/rubber thick sacrificial cover to stop the chain eating the swingarm.

That is on the top of the swingarm, under the chain, when it is in tension there is some pressure eating at them, but they last for ages.

With it just being chain slack, why not try a similar idea? Plastic chopping boards are the perfect material, I'm sure you could knock something up for a few quid to protect the chassis rail without having to cut and weld anything.

If nothing else it might give you some peice of mind till winter, when you can do a full fix. I bet the last thing you want to be doing is fixing it when you could be driving!

[Edited on 3/6/09 by Dangle_kt]

30mm is the max movement l like on my crosser.

My road bikes would be nearer 20mil. Obviously I need that much more on the MX bike due to the massive jumps and suspension travel

Tricky cos too loose and it could slip off but too tight and it could pull out half the 'box

It is looking more like a tensioner is needed just to the support the slack (not much) as I daren't tighten it anymore.

I had another go today and it is just a slack chain and tightening it makes it ok, but I don't have any further adjustment.
I need to shorten the chain so I am after a new link. The crush type, not clip on link.
Anyone?

Although I bought a new link, I didn't need it. I reused a pin that I pushed out.
The chain is now shorter and I have a lot more adjustment.
Hardly any slack now, but I need to road test it after the F1 race!
Got it done due to the wet weather so no Newlands!