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HELP Changing sprocket size on 2009 G650gs

P

patrickj14

New member
I keep having problems with chain tension and chain slapping and my sprockets getting chewed up . looking again to change both sprockets and chain, but thinking maybe changing the sprocket size from the stock 16/47. I do about 80% of riding on pavement at 50 to 80 miles per hour. I saw some interesting posts on another forum alluding to the sprocket sizes and going to a smaller gear ratio. Anybody that’s done this and can provide specifics....advice would be greatly appreciated. Also any advice on keeping the chain tensioner from slipping would be very helpful.
 
Welcome to the forum!
I guess I don’t understand the “slipping” problem.
Maybe you can post a picture of the adjustment point?
I don’t think I have ever had an adjuster slip.
Chains are pretty rugged and trouble free unless there is a bad environment or severe abuse.
Good luck.
Gary
 
Hi Patrick:

Have a look at the thread links in the "Similar Threads" box below.

Welcome, and good luck.
 
Omega Man said:
Welcome to the forum!
I guess I don’t understand the “slipping” problem.
Maybe you can post a picture of the adjustment point?
I don’t think I have ever had an adjuster slip.
Chains are pretty rugged and trouble free unless there is a bad environment or severe abuse.
Good luck.
Gary
Click to expand...

( bring
So, after riding 100 miles or so, the chain starts slapping. Put it on stand, loosen rear axle nut, pull tire to snug chain close to desired tension, re-tighten nut. then readjust the tension screw at the back of the swing arm to bring chain to spec measurement....everything fine for another 100 miles. I cannot get the rear axle nuts any tighter and it is tight when I put it on the stand. I do not know if source of the problem is something that is causing the sprockets to wear too fast or if there is tension issue with the tension screw in the swing arm. I do know that the sprockets did not last 5K miles....as I type this, it occurs to me that I trusted the chain/link count the last time I replaced all this (when the problem started) and did not count the number of links....I wonder
 
Last edited:
patrickj14 said:
So, after riding 100 miles or so, the chain starts slapping. Put it on stand, loosen rear axle nut, pull tire snug, re-tighten nut. then readjust the tension screw at the back of the swing arm....everything fine for another 100 miles. I cannot get the rear axle nuts any tighter and it is tight when I put it on the stand. I do not know if source of the problem is something that is causing the sprockets to wear too fast or if there is tension issue with the tension screw in the swing arm. I do know that the sprockets did not last 5K miles....as I type this, it occurs to me that I trusted the chain/link count the last time I replaced all this (when the problem started) and did not count the number of links....I wonder
Click to expand...

It sounds to me as if the suspension movement is pounding the chain loose. You need to adjust the chain so that on its wheels but unladen there is approximately one inch vertical play in the middle of the bottom run of the chain when the top run is pulled snug. (See the manual or the decal on the swingarm for the exact specification).

If you adjust the chain tighter than this as you described in the bold above then when the suspension moves up and/or down it is pulling the chain too tight. This accelerates chain damage and sprocket wear. BUT this is the least of the problem because it also will damage the transmission output shaft bearing and maybe the shaft itself. Once this happens then the work to repair is serious compared to a simple chain and sprocket swap.
 
PGlaves said:
It sounds to me as if the suspension movement is pounding the chain loose. You need to adjust the chain so that on its wheels but unladen there is approximately one inch vertical play in the middle of the bottom run of the chain when the top run is pulled snug. (See the manual or the decal on the swingarm for the exact specification).

If you adjust the chain tighter than this as you described in the bold above then when the suspension moves up and/or down it is pulling the chain too tight. This accelerates chain damage and sprocket wear. BUT this is the least of the problem because it also will damage the transmission output shaft bearing and maybe the shaft itself. Once this happens then the work to repair is serious compared to a simple chain and sprocket swap.
Click to expand...


yes, I use the specs in the manual and on the sticker on the arm to adjust the tension screw at the back. I just didn't give all details. thank you.
 
which sprockets to change ratio

I really need to get to ordering the replacements. Does anyone have knowledge of which sprockets/link count would be best for highway miles? I have seen references to using a 15 tooth front or a 49 tooth rear and various other combinations, but haven't seen much follow up to know what worked well.
 
patrickj14 said:
So, after riding 100 miles or so, the chain starts slapping. Put it on stand, loosen rear axle nut, pull tire snug, re-tighten nut. then readjust the tension screw at the back of the swing arm....everything fine for another 100 miles. I cannot get the rear axle nuts any tighter and it is tight when I put it on the stand. I do not know if source of the problem is something that is causing the sprockets to wear too fast or if there is tension issue with the tension screw in the swing arm. I do know that the sprockets did not last 5K miles....as I type this, it occurs to me that I trusted the chain/link count the last time I replaced all this (when the problem started) and did not count the number of links....I wonder
Click to expand...
:scratch
Hate to say it, this sounds like the way I used to adjust a fan, water, alternator belt- back in the day.
PGlaves said:
It sounds to me as if the suspension movement is pounding the chain loose. You need to adjust the chain so that on its wheels but unladen there is approximately one inch vertical play in the middle of the bottom run of the chain when the top run is pulled snug. (See the manual or the decal on the swingarm for the exact specification).

If you adjust the chain tighter than this as you described in the bold above then when the suspension moves up and/or down it is pulling the chain too tight. This accelerates chain damage and sprocket wear. BUT this is the least of the problem because it also will damage the transmission output shaft bearing and maybe the shaft itself. Once this happens then the work to repair is serious compared to a simple chain and sprocket swap.
Click to expand...
I think this is pretty much spot-on. As the suspension compresses, the chain needs to have some slack in it as the distance between sprockets gets longer (slightly).
drneo66 said:
Albe has a very nice video showing us how to adjust:
Click to expand...
Not a bad video but....... Before I adjust a chain ( to about the specs Paul mentioned), I like to check for chain stretch within the length of the chain. This is done with the bike on the center stand and rotating the wheel to 4 or 5 different locations and seeing how much “sag” is in the chain at each location.
Chains or sections of chain chain can stretch within the loop itself. A hole-shot or coming down off a jump at the wrong engine speed can cause a stretch within the loop.
If you are actually Hearing a slap of the chain, you should see wear marks on something .
I actually remember in the mini-bike days, the #35 chain would get too hot to touch when it was too tight.
Pulling it snug, I think I would pass on that concept.
OM
 
patrickj14 said:
I really need to get to ordering the replacements. Does anyone have knowledge of which sprockets/link count would be best for highway miles? I have seen references to using a 15 tooth front or a 49 tooth rear and various other combinations, but haven't seen much follow up to know what worked well.
Click to expand...

It sounds like you want higher gearing for more relaxed highway riding, no?

If your stock gearing is 16/47, then using a smaller 15 tooth front sprocket will lower your gearing, as will using a larger 49 tooth rear sprocket. That is opposite of what you are trying to achieve, if I understand you correctly.

My son has the same bike as you and finds the gearing a bit low out on the highway. So I understand where you’re coming from. If you want to make a small adjustment, decreasing the size of the rear sprocket by one or two teeth would be a starting point. If you feel you need to make a bigger adjustment, then increasing the size of the front sprocket by one tooth might be better (assuming you have adequate clearance.)
 
vark said:
It sounds like you want higher gearing for more relaxed highway riding, no?

If your stock gearing is 16/47, then using a smaller 15 tooth front sprocket will lower your gearing, as will using a larger 49 tooth rear sprocket. That is opposite of what you are trying to achieve, if I understand you correctly.

My son has the same bike as you and finds the gearing a bit low out on the highway. So I understand where you’re coming from. If you want to make a small adjustment, decreasing the size of the rear sprocket by one or two teeth would be a starting point. If you feel you need to make a bigger adjustment, then increasing the size of the front sprocket by one tooth might be better (assuming you have adequate clearance.)
Click to expand...

Thanks yes, this is where I was headed....just hoping that someone with actual experience on the resulting effects would weigh in since...not sure if I am going to get desired results. I found this youtube which had a great explanation (not bmw} https://www.youtube.com/watch?v=C6_FtVTjKng
 
Take a look at https://www.gearingcommander.com/ - that will give you estimations based on the ratios you're looking for.



I'm going to agree with OM - it sounds like one area of your chain has stretched more than another area, so even when you set the correct chain slack, you're having binding/slap.

As a side note, I assume you're using a torque wrench to set the torque of the axel?
 
Add one tooth on the front sprocket, or drop two teeth on the rear and will make a noticeable difference. You could try both and if you don't like it put a stock front sprocket back on.

Try keep your sprockets a mix of odd and even teeth, odd on the rear is probably most important. Some people claim if you have a tooth count that divides evenly it is not good, like 15/45 for example. I am not convinced, but costs nothing to consider it.

I have a Yamaha R1 sport bike. I dropped one tooth in front and added two to the rear sprocket for more wheelie power and it was just silly! I was not concerned about highway because I rarely ride very far on the highway and it tops out around 175MPH. First gear you could tap the throttle and the front wheel was in the air. I went back to the stock sprocket in front and left the +2 in the rear and it calmed it down a bit but still pulls wheelies easily and tops out at 165 MPH!
 
The last rule of thumb I was aware of, with “modern” bikes, not a good idea to drop more than 1 tooth on the front sprocket.
OM
 
You're what? "Put it on stand, loosen rear axle nut, pull tire snug, re-tighten nut. then readjust the tension screw at the back of the swing arm....everything fine for another 100 miles. I cannot get the rear axle nuts any tighter and it is tight when I put it on the stand."


Hopefully you aren't doing what you've typed. You need to loosen the rear axle nut as you do, THEN adjust the adjusters, then re tighten the axle nut. You're saying you re tighten the axle nut than adjust the adjusters....how is that even possible?
 
For my F700GS the manual says to put it on the side stand for adjusting the chain tension. The gear should be in neutral to be sure there is no stretch on the chain.

Chain sag is 30..40mm and torque on the axle nut is 100Nm. This might be different for the F650.

/Guenther
 
Guenther said:
For my F700GS the manual says to put it on the side stand for adjusting the chain tension. The gear should be in neutral to be sure there is no stretch on the chain.

Chain sag is 30..40mm and torque on the axle nut is 100Nm. This might be different for the F650.

/Guenther
Click to expand...

I have seen that when a center stand was an option. With a side stand check, I would check, adjust, roll it around and check again.
OM
 
I just looked at the Owner's Manual for the G650GS and it says "Motorcycle unloaded on center stand".

/Guenther
 
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