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Discussion Starter #1
Would an expert here please define exactly what "chain snatch" is, and how you'd know if your bike exhibited this?

FYI...occasionally, I note what appears to feel like a sudden "take-up" of chain slack when, after decelerating, I apply throttle. This occurs generally at lower speeds, so I suspect it's a typical response at these speeds. My chain measures right at BMW-specified slack.
 

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Chain snatch is when the chain is too loose and you accelerate and the chain jerks because its being pulled from such a loose state too a very tight state under load from the engine. If the chain is tensioned correctly that's one thing. The other thing is if the chain is badly worn and has developed "loose" or "tight" spots. In this case the chain and sprockets need replacing. The chain is adjusted at the tightest spot which often leaves the rest of it very loose. This is only in extreme situations normally. It may also be your throttle free play. Having a tight throttle can jerk the bike a bit or it could just be surging a bit.
 

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Discussion Starter #3
Chain snatch is when the chain is too loose and you accelerate and the chain jerks because its being pulled from such a loose state too a very tight state under load from the engine. If the chain is tensioned correctly that's one thing. The other thing is if the chain is badly worn and has developed "loose" or "tight" spots. In this case the chain and sprockets need replacing. The chain is adjusted at the tightest spot which often leaves the rest of it very loose. This is only in extreme situations normally. It may also be your throttle free play. Having a tight throttle can jerk the bike a bit or it could just be surging a bit.
5500 miles on the bike...chain cleaned/lubed every 500 miles...no abuse...chain slack measured at numerous points on the chain...same reading each time.

So...throttle free play? How would I check that?
 

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Just make sure you can twist the throttle a little bit back and forth with your fingers. Don't turn the throttle so you can feel the cables moving. Or if the bike is running you should be able to twist the throttle back and forth with your finger tips while not adjusting the idle of the bike. It should no rev at all. I'm talking minuscule back and forth. The manual will tell you how to do it I think. Its up to the user. Some like there throttle with no free play some like it a bit looser. If its too tight though it can be hard to handle because as soon as you twist the throttle it comes on with no little gap before or warning.





 

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The chain sounds to me like everything is fine. The throttle will not fix a chain problem but it can sometimes make the bike seem like its snatchy. Hence why I suggested you check it. Make sure when you decelerate down to a low speed you also down shift gears accordingly. Staying in a higher gear will give you the snatching problem on throttle application. The clutch is having to work harder to maintain drive.
 

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You cannot adjust or check throttle free play on a 2015. It is fly by wire meaning no throttle cables to adjust. I don't think that is your problem. Are you getting jerky throttle response?
 

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chain is too loose. I run 25mm at the most these days. keeps the slack backlash out of the decal
 

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Discussion Starter #9
I'm running approximately 40mm chain slack (BMW says 45-50).

And that's correct...the 2015 has no throttle free play adjustment, a fact I discovered this morning when I checked.

However, I believe the idea that I may have had the bike in too high a gear for the engine speed is the culprit. Those are the exact conditions in which I experienced the snatch. When I kept the gearing appropriate for a superbike in the canyons...no problem.

Thanks, guys...super input, and much appreciated. Learn something new every day!
 

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Discussion Starter #11
Another question:

The 2015 manual has a section dealing with chain stretch. They say to put the bike in 1st gear, and rotate the wheel forward to tension the chain...then measure the distance between 10 rivets. It should be a MAXIMUM of 5.7 inches. I measured mine, and it was just over 5.5 inches...but closer to 5.6 than 5.5.

What is the distance measured on a NEW chain? Is 5.5-5.6 inches on a chain with 5500 miles close to needing replacement, or is the amount of stretching that occurs so small that it will take many more miles to reach the 5.7 inch "threshold"?

Thanks!
 

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To gain a tenth of an inch over 10 links would be a massive amount of wear, in my opinion. I would try to pull the chain off of the back of the sprocket, that will tell you if the rollers and/or sprocket teeth are worn Any movement there would be bad news. There is a lot of "snatch" if you're on and off the throttle in a low gear with high revs (say 5 or 6 k in first), that's the nature of a chain drive and high compression engine. You might just be overthinking this, ride the bike and enjoy!
 

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Discussion Starter #13
To gain a tenth of an inch over 10 links would be a massive amount of wear, in my opinion. I would try to pull the chain off of the back of the sprocket, that will tell you if the rollers and/or sprocket teeth are worn Any movement there would be bad news. There is a lot of "snatch" if you're on and off the throttle in a low gear with high revs (say 5 or 6 k in first), that's the nature of a chain drive and high compression engine. You might just be overthinking this, ride the bike and enjoy!
I have checked the chain by trying to pull off the sprocket, and it was tight to the sprocket, so no issue there. One of the first things I checked...

I think you hit the nail on the head, skapan...everything checks out "five-by-five", so it is more than likely just what you said.

Thanks.
 

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Also, all the play in the gears intermeshing in the transmission add to this "snatch". I'm amazed that the BMW wants as much slack in the chain as it calls for. On my Gixxer it was only 20-30.5mm, but the overall driveline lash feels less.
 

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Agreed, had to triple check the spec. Looks/feels like a lot of slack to me as well.
 

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I have checked the chain by trying to pull off the sprocket, and it was tight to the sprocket
That's not a good indicator of chain tension. The chain wraps around it, so it'd artificially make a loose chain feel tight. Do it the way the manual details it.
 

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You would think that, but the wear on the sprocket teeth is equal for all, as is the wear on the rollers and pins on the chain. The result is that the chain links are slightly longer than the sprocket teeth centerlines when they are worn. No matter how tight the chain is, it will still be loose on the sprocket, as it only tensions the first few links on each side. Try it when your chain is worn out.
 
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