Final drive chain tension

robs ss

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I have been wondering about final drive tension - at what point in swingarm movement is the chain tightest?
I know what the manual says - but Norton didn't get everything right - did they?
Well, it's obviously when the swingarm aligns with the gearbox output shaft - but where is that?
So... I pulled both shocks off and, using a tape measure from the floor, adjusted the rear wheel height until the swingarm pointed at the C/L of the final drive sprocket. That equates to 315mm, eye-to-eye, on rear shocks. For me that is 15mm compression - probably what it is when I'm sitting on it.
Problem is, unless you're some kind of contortionist, you can't sit on the bike and measure chain deflection.
Anyway, now I know that the position of the swingarm on the centre-stand is not far from the tightest point.
Peace of mind for anally retentive me (and maybe others?)
Cheers
 

Mart UK

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Is it possible to get an assistant to sit on the bike. Get it adjusted, then put it on the centre stand. Now measure the deflection. Use this measurement for adjusting on the centre stand going forward. IIRC, for mine, it adds 6mm /1/4" approx, so I check adjustment to 1 1/4" - 1 1/2" on the stand.
 

robs ss

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Is it possible to get an assistant to sit on the bike. Get it adjusted, then put it on the centre stand. Now measure the deflection. Use this measurement for adjusting on the centre stand going forward. IIRC, for mine, it adds 6mm /1/4" approx, so I check adjustment to 1 1/4" - 1 1/2" on the stand.
Yep - I was just looking for a "solo" method where I was confident I was not over-tensioning the chain (and hence the primary!)
 

BERT

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Yep - I was just looking for a "solo" method where I was confident I was not over-tensioning the chain (and hence the primary!)
I use a length of straight heavy gage fence wire with a hook on one end to catch the chain and a loop on the other for my finger while seated on the bike to check the chain slack.
 

concours

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Eyeball for all my bikes. Too loose & you can feel the snatch going from light throttle to coast & back. Too tight... well, anyone can see when it's too tight. Pretty wide window of acceptability. The dimensions published are for those who need a starting point of reference.
 
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You guys are far too fussy. Loose is better than tight. I never tighten mine up as close as the book says. Remember the saying. "Too tight is broken". I also remember I remember one rider asked his mechanic to tighten his chain before a race. The mechanic said it was too tight. Couldn't argue with the rider though. The chain jumped off during the next race. Go figure.
 

SteveA

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You guys are far too fussy. Loose is better than tight. I never tighten mine up as close as the book says. Remember the saying. "Too tight is broken". I also remember I remember one rider asked his mechanic to tighten his chain before a race. The mechanic said it was too tight. Couldn't argue with the rider though. The chain jumped off during the next race. Go figure.
No...you don't argue with the rider...same as you don't argue with pilots...you just rattle spanners, mumble and curse, say 'jobs done' and give it back as you got it!
 
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The chain is at it's tightest when the gearbox mainshaft, swinging-arm spindle and rear wheel spindle axes are all in line with each other. Not easy to check unless the inner chaincase is off the bike. However I have done this some time ago and with approx 1/2" free play with the axes lined up and then with the bike on the centre stand (zero rear suspension compression) this equates to 1" freeplay mid-point of the chain. So no need to use compression straps or have someone sit on the bike, just set to 1". The manual states 3/4" to 1" rider seated but tension is dependent on rider and luggage weight. Last time I adjusted the chain was 2,500 miles ago lubing with chain spray every 200 miles and occasionally gear oil. Chain will probably go another 2,500 miles before requiring adjustment. Iwis non o-ring fitted. The manual recommendation is too loose in my experience.
 
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Dommie Nator

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The PDI sheet states 3/4 to 1 inch on the centre stand. I'd always thought, rightly or wrongly, that would be too tight and aimed for around 1&1/4 inch at the tightest point.

20220112_085339.jpg
 

Mart UK

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That is PDI. I wonder if it is stated tighter than the service manual because the chain has never been used at PDI and so is ready to stretch a little, to bring it to service manual spec. 3/4" (<20mm)seems to tight to me, compared to any other bike I've had?
 

Dommie Nator

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That is PDI. I wonder if it is stated tighter than the service manual because the chain has never been used at PDI and so is ready to stretch a little, to bring it to service manual spec. 3/4" (<20mm)seems to tight to me, compared to any other bike I've had?

I did think that, but do they stretch or wear? If it's the latter then surely they don't wear quick when new.
 

L.A.B.

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Edit: "3/4 to 1 inch" is what it says in manuals and handbooks (pre-Mk3 and Mk3) but "with the rider seated" so not sure why the PDI says "on centre stand" or exactly how much difference that makes?
 
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robs ss

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Edit: "3/4 to 1 inch" is what it says in manuals and handbooks (pre-Mk3 and Mk3) but "with the rider seated" so not sure why the PDI says "on centre stand" or exactly how much difference that makes?
I set mine to 1" seated - then checked on centre-stand, it was 1 1/4" - so... plus 6mm (1/4")
At least I know now.
Cheers
 
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The most important consideration is that the chain is not too tight. Also, remember that chain tension varies as the sprockets rotate so find the rotation point with the least play and adjust at that point. Adjusting for minimum play at random might turn out to be the loosest point and produce NO play at the tightest point.
 
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