Chain Tension Issue

vtryorks · Post by **vtryorks** » Sat Sep 17, 2011 4:31 am

Hi gents,

Just got home at 4am after spending all night trying to figure out a bizarre problem.

I've fitted a new chain and sprockets, its a DID kit so should be decent quality. I think the spacers are correct, axel seems straight, rear caliper is in position, nuts are all torqued correctly, chain has been linked and they look properly mushroomed. The cush drive rubbers looked in perfect condition. Basically I've done everything as carefully as possible using a combination of Tatmans guide on here and a haynes.

The only thing I have noticed is that the rear disc appears to be very slightly warped. But only very slightly and I was careful not to rest the wheel on its side without proper support around the rim.

Anyway, I get down to the last little part, tensioning the chain prior to tightening the rear axel nut fully. I check the slack and its 20mm. I realise this is tight but that isnt really the issue I'm having (I can adjust that later)

After tensioning the chain, I rotated the rear wheel to check the sprocket alignment using the chain as a guide and all looked fine. Here is where the problem appeared.

After tightening the rear wheel to the specified torque as a test, I decided to do another check of the chain tension. It was much tighter this time, however, no adjustment had been made to chain tension. It is even on both sides and the chain does run straight.

I proceeded to check the tension at multiple points around the chain, as you'd do for a worn chain with stiff links or such. This is where it gets really weird, to me at least.....

There is no consistency to the point at which the tighter spot appears. I thought perhaps I'd overdone the pressing of the pins, so I positioned them at the center point, indeed, it was slack. Then I did one full rotation again, using the soft links as markers. This time it was tight at that point.

Does anyone have a suggestion for what might cause this, because I've been thinking on it all night and I just cant find the logic in it at all. Am I looking at something terminal like an ovalised sprocket? I really hope not as I will be gutted. The rear was quite tight fit on to the carrier, but not horribly so.

Could this whole thing be just because the chain is new?

I hope this is something simple and I'm just being thick..

As always, any advice will be gratefully received.

vtryorks · Post by **vtryorks** » Sat Sep 17, 2011 5:01 am

OK I solved part of the issue I suppose. The chain is rubbing the link pipe with 30mm of slack simply because there is no load on the suspension when its on a stand and therefore the wheelbase is shorter. Simples...(oops)

So I'm now thinking I will adjust the tension to 32-35mm and then place the bike on its sidestand to measure the slack. Does this sound ok?

However, this doesnt explain the issue of the varying chain tension.

I'm sorry for all the info, most of which is probably irrelevant but its hard to know what would be needed to identify this problem.

Kev L · Post by **Kev L** » Sat Sep 17, 2011 8:07 am

I check mine whilst sitting on the bike so the chain is fully loaded, and set the slack at .75" - 1" of travel. As for the tight spots, do you have a straight edge or laser level you can check the swingarm adjusters against? The marks put on at manufacture aren't always correct. Just confirm you have adjusted both sides correctly as looking at the time of posting tiredness may have caused you problems.
What's with the nocturnal maintenance regime anyway?

tony.mon · Post by **tony.mon** » Sat Sep 17, 2011 10:29 am

Best way to get the correct chain tension is to get someone to sit on the bike while you adjust tension.
Doesn't matter much if they're lighter or heavier than you, as long as the suspension is compressed.

I found that when the chain just intermittently touched the link pipes when wheeling it backwards, but cleared it when wheeling it forwards, was a rough and quick/easy way of getting tension correct, without someone sitting on it, if there's no-one around to give you a hand.

+1 on the adjuster marks, they aren't accurate.
If they're out, you could try taking off the chrome adjusters and swapping sides, they may be in better alignment that way round.

Check with the string against rear tyre edges, pull it straight towards the front wheel, there should be an equal gap at the front tyre.
Grandma egg-sucking, probably.

vtryorks · Post by **vtryorks** » Sat Sep 17, 2011 12:29 pm

Thanks for this guys. I'm heading over to try it shortly, just woke up.

Kev, I wanted to try and make the Workshop, if only to observe what was going on, so tried to get finished.

I'll definitely check the chain tensioner level. Is this because if the wheel is slightly out of alighment that the chain isnt sitting perfectly on the sprocket? The thing is, it looks perfect to the eye but I guess thats not good enough heh

What I'm not sure on here, is that if the wheel is out of alignment, wouldnt there be a consistently tight chain measurement instead of seemingly random tight spots?

I'll report back when done!

PS. Tony, I'm new at this, so definitely not grandma sucking eggs stuff

darkember · Post by **darkember** » Sat Sep 17, 2011 1:12 pm

tony.mon wrote:Best way to get the correct chain tension is to get someone to sit on the bike while you adjust tension.
Doesn't matter much if they're lighter or heavier than you, as long as the suspension is compressed.

I found that when the chain just intermittently touched the link pipes when wheeling it backwards, but cleared it when wheeling it forwards, was a rough and quick/easy way of getting tension correct, without someone sitting on it, if there's no-one around to give you a hand.

+1 on the adjuster marks, they aren't accurate.
If they're out, you could try taking off the chrome adjusters and swapping sides, they may be in better alignment that way round.

Check with the string against rear tyre edges, pull it straight towards the front wheel, there should be an equal gap at the front tyre.
Grandma egg-sucking, probably.

Spot on Tony running the wheel backwards I also dink the link pipe but running forwards not a single hit.

tony.mon · Post by **tony.mon** » Sat Sep 17, 2011 1:58 pm

vtryorks wrote:
What I'm not sure on here, is that if the wheel is out of alignment, wouldnt there be a consistently tight chain measurement instead of seemingly random tight spots?

If out of line far enough (not very likely) the chain can "ride up" on the sprocket sometimes, randomly.

Have you also checked the front sprocket?

Sounds like a daft question, but I've heard of people joining the chains together and just pulling the new one through, and fitting just a rear sprocket.

By sight is generally good enough, for me , anyway, but some people use lasers-- which has just got me thinking, you could easily adapt one of the little laser levels you sometimes see for just a few pounds in garages, taped to a piece of wood long enough to go across the forward and rearward edges of the rear tyre it would give a very accurate result, out of direct sunlight, anyway....
Must give that a try.

vtryorks · Post by **vtryorks** » Sat Sep 17, 2011 2:12 pm

Hi Tony,

I changed both sprockets for new (DID). I stripped everything, cleaned it all.

I'm quite concerned about the chain tension being apparently different all the way around. Is there anything else I should look for?

Could I perhaps have tightened the soft link too much, but again, if that was true, the tight spot would be in the same place each time.

Hmm

darkember · Post by **darkember** » Sat Sep 17, 2011 3:27 pm

What you are describing seems very odd ie: tight spots changing position on each rotation. Even with the wheel out of alignment you would still get the tight spot at the same place. My plan would be to lub it well the old fashioned way with heavy gear oil take it for a gentle ride to let the chain bed in then check it & re adjust. At the same time you will be able to get a feel of the rear brake.

tinysmall · Post by **tinysmall** » Sat Sep 17, 2011 3:35 pm

Not a bad idea as long as it is a gentle ride. If the chain has sat on the shelf for a while it could potentially go a bit stiff I suppose. Might sound daft but did you clean the chain before fitting it? That horrible white gunk they cover them in is very thick and sticky and could be causing a problem as you rotate the wheel.

Sent from my brain using my hands with that Tapatalk thingemybob.

stormingjoe · Post by **stormingjoe** » Sat Sep 17, 2011 3:44 pm

Check output shaft on gearbox, where the front sprocket is, make sure no play there, the bearing maybe in early stage of failure. Check chain is sitting in the sprockets, also make sure they are the correct size etc for your chain and that they are running true. Might be faulty chain, measure between sections of links, say 20 at a time see if you get similar measurements, if miles out get another one. Make sure swing arm mounting nuts are tight same with engine mount bolts etc.

Fatty on a motorbike ;0D

vtryorks · Post by **vtryorks** » Sat Sep 17, 2011 5:14 pm

Narrowed it down now. I was wrong, there is consistency but it took a bit of finding.

The whole wheel is moving backwards and forwards which could mean a problem with either worn bearings or the axel.

The wheel moves 2mm backwards at the same point the chain becomes tight. I have to do more checks but looks like this was pre existing.

Total chain slack difference is 5mm. I must have been riding it like that for a while.

Cant be buckled wheel because there is no side movement at all and bearings seem tight. So im going for a slightly ovalised axel. Like, a minicule amount out.

Does this sound plausible?

Thank you for all the help so far.

Miztaziggy · Post by **Miztaziggy** » Sat Sep 17, 2011 6:50 pm

I wouldnt think it would be the axle because it is just a steel bar, and you would easily be able to see 2mm bend in it.

If anything, you have your wheel misaligned or your wheel bearing has gone.

Count the number of threads on each side of the adjusting screws, are they the same? Are you getting any chain noise as you rotate the back wheel on the paddock stand? Louder than normal means your wheel isnt aligned.

I had mine way out of alignment once, and you couldnt tell by spinning it and looking for movement though.

Take off the back wheel, and the sprocket carrier, and then try to move the inner race of the wheel bearing, does it move at all? It shouldnt move, it should feel solid on both sides.

tony.mon · Post by **tony.mon** » Sat Sep 17, 2011 7:07 pm

And while you're there check all rear bearings, swingarm as well as linkage.

AMCQ46 · Post by **AMCQ46** » Sat Sep 17, 2011 7:39 pm

Could be the spindle is worn under the bearings, was there any witness marks?

Take spindle out and roll it on the most flat surface you can find (like a glass coffee table) and see if it is either bent or if there are wear grooves in it.

Also after thinking about it, a bent spindle won't make the wheel wobble each rev, as the spindle is stationary it will no produce a 1 per rev effect. You are looking for something in the rotating parts that has either got clearance or runout.

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