Chain Tension really 40mm? - Honda CBR500R Forum : CB500F and CB500X Forums
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post #1 of 10 (permalink) Old 05-14-2019, 07:19 PM Thread Starter
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Chain Tension really 40mm?

I read the manual on the side of the swingarm and it says to have 40mm of slack in the chain, does this seem excessive? I recently had it serviced and they tightened the chain right up to about 20mm of slack. The bike is smoother in gear changes too. Am i breaking anything by leaving it tighter than the manual dictates?

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post #2 of 10 (permalink) Old 05-15-2019, 07:08 AM
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I read the manual on the side of the swingarm and it says to have 40mm of slack in the chain, does this seem excessive? I recently had it serviced and they tightened the chain right up to about 20mm of slack. The bike is smoother in gear changes too. Am i breaking anything by leaving it tighter than the manual dictates?
Tight chains lead to excessive friction and wear on the sprockets and counter shaft bearings. I believe it also affects the suspension travel. I had mine way too tight by the dealer and yes it allowed for a smoother shifting but I would have it readjusted for the aforementioned reasons.
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post #3 of 10 (permalink) Old 05-16-2019, 08:36 AM
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Adjust it to stated spec or suffer the consequences. Donít go tighter than 35mm.

Ride like your life depends on it.
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post #4 of 10 (permalink) Old 05-16-2019, 11:15 AM
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the trouble is that the pivot for the swing arm is not in the same place as the axle for the front sprocket, this means that as the swing arm goes up and down the chain is required to get shorter and longer to keep a constant slack!! Obviously the chain length cannot change as the suspension moves up and down, so they have you adjust the chain tension when the suspension is unloaded, but you have to have enough slack so that when the suspension is compressed during riding the chain has the correct slack (~20mm) at the tightest point. I don't know if that makes sense, but as you compress the rear suspension you will see that the chain becomes significantly tighter (until the rear wheel axle, swingarm pivot and front sprocket axle are all aligned) and then as the suspension continues to compress the chain will start to become slack again. by setting 40mm of slack with the suspension fully extended (no one on the motorcycle) you should have about 20mm of slack at the tightest point (when the rear wheel axle, swingarm pivot and front sprocket axle are all in a straight line).


If you run less than 40mm of slack then you risk to damage the bearings on the gearbox output due to an excessively tight chain and can even break the engine casting around the gearbox output shaft!! and you will cause the chain to wear more quickly due to excessive tension.. The best way to adjust the chain is to compress the suspension until the rear wheel axle, swingarm pivot and front sprocket axle are all aligned and then adjust the chain tension to 20mm, but it is very difficult to compress the suspension and hold it there so honda just state 40mm of slack with the bike on its centerstand or side stand (no load on the rear suspension).


Hope that makes sense.


Gary
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post #5 of 10 (permalink) Old 05-16-2019, 12:17 PM Thread Starter
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Thankyou so very much for your answers, I understood them 100%

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post #6 of 10 (permalink) Old 05-17-2019, 01:06 AM
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Originally Posted by Thrasherg View Post
the trouble is that the pivot for the swing arm is not in the same place as the axle for the front sprocket, this means that as the swing arm goes up and down the chain is required to get shorter and longer to keep a constant slack!! Obviously the chain length cannot change as the suspension moves up and down, so they have you adjust the chain tension when the suspension is unloaded, but you have to have enough slack so that when the suspension is compressed during riding the chain has the correct slack (~20mm) at the tightest point. I don't know if that makes sense, but as you compress the rear suspension you will see that the chain becomes significantly tighter (until the rear wheel axle, swingarm pivot and front sprocket axle are all aligned) and then as the suspension continues to compress the chain will start to become slack again. by setting 40mm of slack with the suspension fully extended (no one on the motorcycle) you should have about 20mm of slack at the tightest point (when the rear wheel axle, swingarm pivot and front sprocket axle are all in a straight line).


If you run less than 40mm of slack then you risk to damage the bearings on the gearbox output due to an excessively tight chain and can even break the engine casting around the gearbox output shaft!! and you will cause the chain to wear more quickly due to excessive tension.. The best way to adjust the chain is to compress the suspension until the rear wheel axle, swingarm pivot and front sprocket axle are all aligned and then adjust the chain tension to 20mm, but it is very difficult to compress the suspension and hold it there so honda just state 40mm of slack with the bike on its centerstand or side stand (no load on the rear suspension).
This was a much appreciated explanation. I never thought of it in terms of suspension. I had assumed the slack was constant while riding around, but it makes sense that it would fluctuate.

I also notice that when I check my slack day-by-day it goes up and down on its own. Is this some other force at work, or am I somehow getting a change in at rest suspension status (on relatively flat, paved ground)?

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post #7 of 10 (permalink) Old 05-17-2019, 03:24 AM
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Originally Posted by Luke Shreddar View Post
I read the manual on the side of the swingarm and it says to have 40mm of slack in the chain, does this seem excessive? I recently had it serviced and they tightened the chain right up to about 20mm of slack. The bike is smoother in gear changes too. Am i breaking anything by leaving it tighter than the manual dictates?
I think most shop mechanics set chain slack at about 25mm. I have had two bikes serviced which required 40mm play (600 mile services) and the mechanics did set them at 25mm. It seems that they are incapable of reading the label on the swinging arm.
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post #8 of 10 (permalink) Old 05-20-2019, 04:06 PM
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I also notice that when I check my slack day-by-day it goes up and down on its own. Is this some other force at work, or am I somehow getting a change in at rest suspension status (on relatively flat, paved ground)?



This is usually a sign of an unevenly wearing chain, usually referred to as tight spots. You will probably find that as you rotate the back wheel the amount of chain slack will vary, it usually means some links in the chain have worn or seized more than others and causes the tension to vary, a little variation is normal but if you are seeing a significant variation it probably means your chain is worn out and needs to be changed!! Sorry for the bad news, this often happens if the bike is left un-ridden for a long period of time, water gets in the chain and rust starts to form and then that area wear more quickly or seizes up.. If you get a new chain, the best thing you can do for it, is to set the correct tension and every few hundred miles rub some gearbox oil on the chain, you don't need an expensive chain lube (they cost a lot and cause dirt and dust to stick to the chain) just applying small amounts of gear oil to the chain will keep it nicely lubricated and will prevent wear and rust..


Gary
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post #9 of 10 (permalink) Old 05-22-2019, 09:14 PM
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Mechanics (bike, auto) often think they know more than to MFG's Engineers.

Sometimes they do, but best to go with MFG recommendation.
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post #10 of 10 (permalink) Old 05-26-2019, 04:56 AM
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Quote:
Originally Posted by Thrasherg View Post
I also notice that when I check my slack day-by-day it goes up and down on its own. Is this some other force at work, or am I somehow getting a change in at rest suspension status (on relatively flat, paved ground)?



This is usually a sign of an unevenly wearing chain, usually referred to as tight spots. You will probably find that as you rotate the back wheel the amount of chain slack will vary, it usually means some links in the chain have worn or seized more than others and causes the tension to vary, a little variation is normal but if you are seeing a significant variation it probably means your chain is worn out and needs to be changed!! Sorry for the bad news, this often happens if the bike is left un-ridden for a long period of time, water gets in the chain and rust starts to form and then that area wear more quickly or seizes up.. If you get a new chain, the best thing you can do for it, is to set the correct tension and every few hundred miles rub some gearbox oil on the chain, you don't need an expensive chain lube (they cost a lot and cause dirt and dust to stick to the chain) just applying small amounts of gear oil to the chain will keep it nicely lubricated and will prevent wear and rust..


Gary
Worn sprockets can give the same symptoms as they often wear to the point that they are very slightly oval. Correct chain tensioning and regular chain lubrication is a must to prolong chain and sprocket life.
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