Hi there... I have a 2001 KLE 500 with about 46 000 km on the clock.

The bike is making a weird engine noise: it almost sounds like valve clatter or a worn cam chain. The noise does not go away when the bike is warm. It is particularly noticeable when the bike is idling, and does not sound very happy.

Otherwise the engine runs fine, and is not giving me any hassles.

Last service was about 1000km ago.

How normal is this type of noise? Should I be worried? What could the reasons be?

Would appreciate your advice!

Please could some people with KLE 500s post some replies...?

Well, it could be that the engine just needs new oil, mine is much smoother and quieter when i change the oil.
However previous to this kle500, I had another one which I bought brand new after six thousand miles it developed an engine rattle. I took it back to Drayton Croft motorcycles in Hinkley where I had got it from. They said the oil pump had failed and as a result had done a great deal of damage to the big end etc. They were so surprised as the bike has a reputation of being ultra reliable, they were also embarassed.
So much so that they replaced it with a brand spanking new kle500. I Can't praise them and their after sales service enough. BMW and Touratech could learn a lot from them.
I am happy to report that my Kle has now done 22000 miles , been to europe and the arctic and is used every day in all weathers including snow, it lives outside and nothing has gone wrong, its such a good bike. Really reliable and the chain has only needed tensioning four times, the engine is so smooth.

valves arent too much of an issue - if they are noisy it means loose, which is better than quiet (tight) and burnt valves. Doesnt sound like valves though.

My bet (if it is a slapping whacking noise) is cam chain tensioner!!!!! remove and readjust. Many bikes need this done. If its at its limit of adjustmnet you need a new camchain and sprockets, but that unlikley at those km's. At idle it is often more noticeable, but as you accelerate the centrifugal forces helps tension the chain a bit (expand it) - or flings it off your cam sprockets and stuffs your whole engine!!!

Last one is knocking/pinging from pre-detonation - run good fuel and check jetting.

Is your idle speed set correctly?
Mine seems a little noisier when I try and set the speed much below what the manual says.

From what your saying it really sounds like the cam chain tensioner needs adjusted, If you have not done the valves in the last service I would do them also they are really easy to do and also adjust the cam chain tensioner as above if its still noisy replace the chain and tensioner. I would not neglect this as Jimmy101 says if you don't sort it, the chain could jump a sprocket tooth and destroy your valves - and engine.

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If it is good to have one foot in England, it is still better or at least as good, to have the other out of it. jake