Noisy transmission - F650GS chain video

[Rogerborg]

Ahoy. I'm deliberately bumping this thread as it's one of the top Google hits for "F650GS chain slap".

My 2012 11,000 miler is now slapping away like an Essex hen party. It's on the stock chain, and it came from BMW (ex fleet / demo bike) with the chain drum-tight and silent. I'm seeing other folk report that their bikes are coming back from BMW servicing with chains over-tightened.

With it adjusted as per the manual, I get exactly the reported symptoms, a frenzied clattering slap onto the plastic guides on neutral throttle at around 2,5000rpm, regardless of gear. It's already conditioning me into downshifting or pulling the clutch to ameliorate it.

I'll try playing around with the tension again, and checking that the wheel is bang straight, but my current impression is that they should all do that, mister, and that it's blooming annoying.

 

[Greg Masters]

The problem is that the chain does not take a circular path over the sprocket - what's actually happening is similar to spooling string onto a multi-sided block of wood.

As each chain roller hits the sprocket, it is momentarily moved further from the centre of the sprocket. The whole length of the chain between the front and rear sprocket also has to move a little.

The effect is dampened if the chain is under tension. But then the slack side of the chain is more prone. This movement, at certain speeds, can coincide with the harmonic length of the chain and causes the problems described. This can often be seen on passing bikes as a whipping of the slack side of the chain.

All chain systems are vulnerable to this. Whacking up the chain tension simply causes different problems.

 

[Rogerborg]

All chain systems are vulnerable to this.

But not all chain systems demonstrate the effect in such a distinctive manner.

I'll note again for emphasis that my bike came from BMW over-tight, presumably so as not to put off test riders, so if you buy a GS and it's silent then it's worth checking whether it's been "optimised"...

 

[dpm]

Anyone ever considered adding a sprung tensioner?

 

[ralphy]

Glad I've found this thread.

2010 F650GS Twin, 10,000 miles and the chain-slap is very, very noticeable: only if adjusted far too tight will it quieten down. The chain and sprockets all look fine to my eye, the bike has been well-maintained from new and with plenty of lubrication to the chain. But at the correct setting it's painful to listen to. :-(

Suggestions on what to do would be gratefully received!

R

 

[outrunner]

Mine has been like that for all of the 20,000 miles I have done on it, just live with it, it's not life threatening.




Andy.

 

[Rogerborg]

Suggestions on what to do would be gratefully received!

Beats me. Short of fettling a tensioner or running with it bowstring taut (and risking the cross beam going owt skew on't treadle), I'm not sure there's much that can be done.

I might try going down a tooth on the front sprocket and seeing if that puts the gearing in a happier place.

 

[Rogerborg]

...aaaand I'm liking that. A 16 tooth front sprocket (just get one for an F800GS) shortens the gearing just enough to raise the revs to the point where I'm not constantly rattling at a "street 30", i.e. an indicated 35, the same speed as everyone else will be doing. That's with the chain even a little on the sloppy side of spec.

I haven't tried it at speed yet, but it's near-as-dammit the same gearing as the F800GS - i.e. more likely what the bike was designed for - so I can't see it being a problem.

 

[Rogerborg]

Well, well. On a longer test this morning, the chain rattle is almost entirely gone, at any combination of revs and throttle.

That's unlikely to be just down to the gearing, and I believe the big difference is that I've slackened the chain off even more.

So I'm going on the assumption that it was slapping against the bottom of the swing arm, and that can be solved by running either too tight (as delivered by BMW) or "too" slack.

I "quote" that because I've always subscribed to the theory that a little slack is better than a little tight - I'd rather put wear on sprockets and cush drives than on the driveshaft and gearbox.

Anyway, that's me all smiles again now, until I find the next thing that absolutely needs to be meddled with (bars seem a bit wide...)

 

[brianya]

Mine does that as well in exactly the same circumstances ie load and speed that Tim describes. Its a horrible flaw to what is for me a perfect bike.I had the chain and sprockets replaced by main dealer on a recall apparently when it went in for a service after I got the bike at about 3000miles and it continued to do this afterwards so chain sprockets /adjustment could be excluded.Deales says they all do this!! oK but bikes have had chain drives since bikes were invented and one would expect better from BMW.I believe it must be a design issue. One point to note is that my bike is the factory lowered chassis model and I have read elsewhere on the web that the problem is more prevalent with this model. Guys I know who have the standard height don't have or won't admit to the problem.I now have 14000 mile up and just back from a 3000mile trip in europe, you get used to it but it did it as i pulled up to customs and the officer heard it and told me that something was up with the bike !!!
As the bike is a tad low , sore on the knees when on a long trip, I am contemplating a different shock to add a bit of height as this might be cheaper that a bike change!

 

[Colin]

F700gs, 2014.Low suspension model. owned from new. now 9.500 miles. chain clatter ever since I got the bike. tried tightening and loosening and checked chain alignment.
I found the answer was ear plugs.

 

[volcane]

Chain slap

We have two F650 GS twins. One 2008 and one 2010. Ive put new DID gold chains and sprockets on both a few thousand kilometres ago. My 2010 is perfect, pulls from 2000 rpm whisper quiet and is a joy. My wifes suffers from chain slap (horrible racket) but as others quote is fine as long as you keep the revs above 2500. Both lubed the same, tensioned etc but very different result. Go figure!