F650GS Dakar - Worrying Engine Noise....

DevonianScotsman

DevonianScotsman

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Hi Guys,

I've got a worrying noise coming from my engine - wondering if anyone can shed some light on it?

It's a whirring/buzzing sound that then worsens to a growl over a period of about a second and then fades away.
This happens every few seconds in any gear - including neutral.
The frequency of the buzzes doesn't change with more or less revs.

Any help very much appreciated!

Cheers,

Rob
 
Could it be the cam chain tensioner has failed? :nenau It's a bit of a fiddle to get the nut covering it off/on, but from memory I used a 1/2" 22m socket, flexible joint, and extension bar threaded through underneath the seat.
 
It could be, they can stick. I repaired one once by fitting a small spring inside the piston body until a new one arrived....which...had a spring inside the piston:D
 
There's a bucket like piston, makes sure it doesn't stick at all in the 'engine side' there should be a spring to assist it being pushed back against the tensioner but I found one that has no spring.

That's why I made one up, then bought a new one which came with a spring.
It could be that early ones didn't have this spring and relied only on oil pressure, occasionally sticking.

You could try undoing the plug/bolt in my photo, pushing the piston in with your finger or something, replace the plug and start engine to see if the noise has gone.

If it has, there's your answer but it will happen again.
If the noise is still there, the tensioner could still be at fault.
 
Cyclic engine noise

Did you ever resolve this? I have the same cyclic vibrational noise, starts at about 3000rpm but sometimes appears at idle, sounds like gravel in a rotating drum. It's not related to engine load, any gear, clutch in/out, I have replaced the cam chain tensioner and checked the cam chain for wear. It sounds like it comes from the RHS of the engine (from riding position). It's been there for around 15,000 miles but I don't want to assume that it's "just one of those things" and then find something explodes, taking out casings etc. The favourite (I think) is possibly the sprag clutch, but would appreciate any thoughts, experience, opinions etc before I pul it apart.
Cheers
 
Sadly he didn't - the bike got decommissioned for a spruce up + fix a lot of little issues, and then the project got mothballed when he moved house.

I've just taken it on again, and have had a look at the cam chain, tensioner, and blades, and can't see anything wrong. I wasn't actually present to hear the noise though.

If you could update me (I'll PM you) if you managed to sort it, i'd be grateful for the info!

T
 
OK, just got it all in bits. The noise was getting so bad I could hear it at 60mph! As far as I can tell the problem seems to be that the front timing chain guide is not actually secured in place - it sits on a couple of pegs at the top and a cast ledge at the bottom - and it's not a tight fit. Looking at the back of the plastic blade there are areas of chafing that correspond to shiny bits on the inside of the engine casings. My current theory is that the timing chain is worn (but not too bad) and that at certain RPM ranges (3000-4000) the chain forcing frequency matches the engine pulses, resulting in the chain resonating and transferring this to the chain guide which then vibrates against the engine casings, making a growly noise. This also explains why the noise frequency doesn't alter with engine speed and seems to wander around the front of the engine
I've ordered new chain, tensioner blades etc, and will update here with results in a few weeks.
 
HI db1did you ever solve the problem? Did replacing cam chain and blades work? I got the exact same thing/noise happening..
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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