correct chain tension after gearing/sprocket change

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correct chain tension after gearing/sprocket change

Post by Dunk » Sun May 17, 2015 9:00 pm

Hi, I've just done a 16-42 gearing change with a new chain and I'm wondering if the chain adjustment figure of 7mm of clearance from the top of the chain to the bottom of the swingarm still stands.

I'm thinking that it shouldn't make difference but I'm not sure.

Thanks

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Re: correct chain tension after gearing/sprocket change

Post by Thirdway » Mon May 18, 2015 10:01 am

It will make a difference. The chain is now in a different place in relation to the swing arm.
No idea how critical it will be.

The key is that it shouldn't prevent movement of the swing arm at the point where the two sprockets are at the furthest point on their arc of movement. You can check it by removing the shock and jacking the wheel until the swing arm is horizontal ( that should be the tightest place ). I've no idea what chain tension should be at that point, but it should not be tight and likely not have too much play either. If it is too tight then you need to add slack. Bolt the shock back and then measure the new chain slack in the standard position if you have made any adjustments. That will be the new number from then on.

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Re: correct chain tension after gearing/sprocket change

Post by ogden » Tue May 19, 2015 12:01 pm

Thirdway wrote:You can check it by removing the shock and jacking the wheel until the swing arm is horizontal ( that should be the tightest place ).
ITYM "until the sprocket, swingarm pivot and rear spindle are aligned". That may or may not be when the swingarm is horizontal.

Personally, I wouldn't worry about it too much. 7mm is still probably fine, give or take a small margin of error.
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Re: correct chain tension after gearing/sprocket change

Post by Thirdway » Tue May 19, 2015 12:23 pm

ogden wrote:
Thirdway wrote:You can check it by removing the shock and jacking the wheel until the swing arm is horizontal ( that should be the tightest place ).
ITYM "until the sprocket, swingarm pivot and rear spindle are aligned". That may or may not be when the swingarm is horizontal.

Personally, I wouldn't worry about it too much. 7mm is still probably fine, give or take a small margin of error.
Agreed. I have no idea on the SMT. I don't think I would trust to luck. That figure of 7mm is awfully precise. It's not like somewhere between x and y. You know the Germans. If it says x it means x. Tolerance isn't a Germanic trait either in character or engineering.

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Re: correct chain tension after gearing/sprocket change

Post by ogden » Tue May 19, 2015 12:33 pm

Thirdway wrote:You know the Germans. If it says x it means x.
Yeah, but these are Austrians. "If it says x, have another schnapps and get back on the tractor."
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Re: correct chain tension after gearing/sprocket change

Post by Dunk » Tue May 19, 2015 7:42 pm

Here are 2 pics of the chain set up.

Does it look too slack?
Attachments
IMG_6340.JPG
7mm between top of chain and bottom of swingarm
IMG_6339.JPG
Bike in 1st gear with top of chain taut

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Re: correct chain tension after gearing/sprocket change

Post by Thirdway » Tue May 19, 2015 10:00 pm

Yes, but then that's what they always look like :D
7mm is right for the standard sprocket and that's all I can say.
Nice clean chain by the way.

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Re: correct chain tension after gearing/sprocket change

Post by ogden » Tue May 19, 2015 10:03 pm

Yeah, they always look ludicrously loose. I once made the mistake of doing the chain on my Duke so it looked "right", and then spent a morning sitting at a roundabout in Wandsworth waiting to be recovered after the chain snapped.

Lesson learnt.
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Re: correct chain tension after gearing/sprocket change

Post by Thirdway » Tue May 19, 2015 10:47 pm

ogden wrote:
Thirdway wrote:You know the Germans. If it says x it means x.
Yeah, but these are Austrians. "If it says x, have another schnapps and get back on the tractor."
Or Poland looks a nice Place for a quick blast :?

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Re: correct chain tension after gearing/sprocket change

Post by ogden » Tue May 19, 2015 10:51 pm

You annex one Sudetenland...

(In a Bridge Builder Joke stylee)
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Re: correct chain tension after gearing/sprocket change

Post by Dunk » Wed May 20, 2015 9:36 pm

The chain's only so clean because it's not been used yet.

Thanks for the replies.

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You're sure, 7mm is not too loose?

Post by ktm55guy » Sat Jun 20, 2015 3:00 am

Wow, 7mm sure seems way loose. But having a number of KTM bikes I know they like loose chains.

So 7mm sitting on the kick stand is what I will set it at. :?

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Re: You're sure, 7mm is not too loose?

Post by ogden » Sat Jun 20, 2015 7:00 pm

ktm55guy wrote:Wow, 7mm sure seems way loose
Long travel suspension. Best to go with the manufacturer recommendation, unless you want to do what I did and spend a whole morning sitting waiting for recovery after the chain snaps.
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Re: correct chain tension after gearing/sprocket change

Post by Rangoonruns » Tue Jun 23, 2015 6:58 pm

Damn that's clean Dunk
Image

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Re: correct chain tension after gearing/sprocket change

Post by Magic Wand » Sat Aug 08, 2015 8:19 pm

Could anyone please explain WHY the chain has to be that loose?! I want to understand it and want technical details about it.

As I know from motocross bikes and also my previous road bikes, I have always put weight to the rear suspension until the swing arm is at a straight level/line from center of front sprocket, through center of swing arm axle to the rear wheel axle. In this position the chain is put into its longest distance it can ever be at.
Then measured the chain tension/slack, and adjusted it to be about 10 mm (0,393 inch). Then the chain has "perfect" tension/slack.

/M
Last edited by Magic Wand on Wed Jun 08, 2016 8:31 pm, edited 1 time in total.

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Re: correct chain tension after gearing/sprocket change

Post by retardonamotard » Fri May 13, 2016 4:31 pm

Ive only ever seen one thing that's looked as slack as that chain ...my gonads after turning 50!

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Re: correct chain tension after gearing/sprocket change

Post by ogden » Sat May 21, 2016 2:39 pm

Magic Wand wrote:As I know from motocross bikes and also my previous road bikes, I have always put weight to the rear suspension until the swing arm is at a straight level/line from center of front sprocket, through center of swing arm axle to the rear wheel axle. In this position the chain is put into its longest distance it can ever be at.
Then measured the chain tension/slack, and adjusted it to be about 10 mm (0,393 inch). Then the chain has "perfect" tension/slack.
That'll also work. The standard instructions are just a way of measuring the slack to be near enough correct without having to load up the back of the bike so the sprockets and spindles are in a straight line.

There are bigger things in life to worry about than perfect chain tension.
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Re: correct chain tension after gearing/sprocket change

Post by Magic Wand » Wed Jun 08, 2016 8:30 pm

ogden wrote:
Magic Wand wrote:As I know from motocross bikes and also my previous road bikes, I have always put weight to the rear suspension until the swing arm is at a straight level/line from center of front sprocket, through center of swing arm axle to the rear wheel axle. In this position the chain is put into its longest distance it can ever be at.
Then measured the chain tension/slack, and adjusted it to be about 10 mm (0,393 inch). Then the chain has "perfect" tension/slack.
That'll also work. The standard instructions are just a way of measuring the slack to be near enough correct without having to load up the back of the bike so the sprockets and spindles are in a straight line.

There are bigger things in life to worry about than perfect chain tension.
-

Yes, you are right "ogden". Both ways will work properly.

When I replaced the old rear sprocket to a new 38 t and also replaced the front sprocket to original 17 t and put a new drive chain on (smaller plate hight than original one), the "chain clatter" dissappeared. Veeery nice!
When going back to the 41 t rear, the clatter directly came back... :/

Maybe there are bigger things in life to wory about - but if I can have my SMT working in the best of ways, I will have more time to think about more important things to worry about ;-)

/M

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Re: correct chain tension after gearing/sprocket change

Post by MadMoose » Fri Jul 01, 2016 9:38 am

Does anyone else have the problem where the chain actually starts to eat into the tire?

There is so much slack on the chain if set to the 7mm that if I move it side to side it hits the tire.

Also, when I lube my chain, I just place the bike on its side to be able to turn the rear wheel to quickly apply the lube to the chain. Naughty I know, but then we ride KTM!

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Re: correct chain tension after gearing/sprocket change

Post by akuma » Mon Jul 04, 2016 4:44 pm

MadMoose wrote:Does anyone else have the problem where the chain actually starts to eat into the tire?

There is so much slack on the chain if set to the 7mm that if I move it side to side it hits the tire.

Also, when I lube my chain, I just place the bike on its side to be able to turn the rear wheel to quickly apply the lube to the chain. Naughty I know, but then we ride KTM!
if the chain is eating into the tyre you are probably looking at the chain having stretched rather than having the incorrect slack- when i had my 950smr i took the chain off after this had happened and you could bend the chain sideways until it was almost a semi circle- time for a replacement i'm afraid.

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