Clunk noise help

[ThomasJ]

Have a 01 1150GS with just over 50k and here what's happening...

 

Before its well warmed up (choke engaged) do a quick rev to about 2-3k and as

the revs go back to idle there is a clank/clunk that happens that appears to come

from the Cat converter.

 

Does anyone have an idea what's up...is this a cat problem or something

worse?

 

thanks,

Tom

[dan cata]

Does it sound like a backfire? Between the cat and where it connects to the pipes coming from the headers?

 

When I had my 1100 gs, same exhaust on the RT, when going uphill, I used to hear something close to grains of sans inside the cat But only when going uphill No clunk noises though...

 

Dan.

[ThomasJ]

Does it sound like a backfire? Between the cat and where it connects to the pipes coming from the headers?

 

When I had my 1100 gs, same exhaust on the RT, when going uphill, I used to hear something close to grains of sans inside the cat But only when going uphill No clunk noises though...

 

Dan.

 

It sounds like a piece of metal striking the inside cat shell...just one clunk per rev.

[dan cata]

Could have someone put small rocks inside your exhaust pipe?

 

PS: like your photo of the Gs rear tire, I one had that on a Anakee 1 tire

 

Dan.

[AndyS]

Is the noise definately from inside the cat?

Could it be the righthand throttle body shaft rattling?

or maybe the cam chain tensioner.

Try using a long metal bar. put one end in your ear and the other on or near where you think the noise is coming from. This 'stethoscope' may help you track down the exact location and identify the culprit.

 

Andy

[Jim Moore]

That sounds like a classic left-side cam chain slap. I'd put an updated cam chain tensioner in there and see if it goes away.

[OldBMWMaster]

That sounds like a classic left-side cam chain slap. I'd put an updated cam chain tensioner in there and see if it goes away.

 

I have been ignoring a similar noise for about 40,000 miles now.

[dirtrider]

Morning Tom

 

Without actually hearing the noise about all we can do is guess at it's cause.

 

Seeing as your noise is on dropped throttle decel & coming from the cat. area it most likely is some post firing in the exhaust from a lean-out on decel.

 

If it is, then nothing to worry about as that is harmless-- but (you really should have it listened to by a qualified technician to verify it is only a harmless post firing)

 

On your 1150 you might also have a TPS learning issue from a low battery or previous battery disconnect (TPS re-learn can have an effect on post firing as it effects the dropped throttle fuel shut-off point).

So you might try a TPS re-learn as a remedy to your issue.

 

To do that -- first remove the Motronic (usually #5) fuse for about 30 seconds, then re-install the fuse, then turn the key on (do not start engine), then simply (fully) open & close the throttle twice (make sure the choke is OFF during the re-learn process).

 

Also look closely at the cat area & all around on the cat. for signs of cracking or leaking. Any cracks or air leakage into the cat. can really increase the chance of dropped throttle post-fire in the exhaust. (cracking cat. or cracking pipe is somewhat common on older BMW exhaust systems.

 

[Galactic Greyhound]

Might be worth while checking that there are no air leaks at the throttle body/cylinder head stubs - check the securing clips are tight. Also, check that there is not a missing sealing cap at the throttle body vacuum take-off pipes.

[Jim Moore]

That sounds like a classic left-side cam chain slap. I'd put an updated cam chain tensioner in there and see if it goes away.

 

I have been ignoring a similar noise for about 40,000 miles now.

 

Most folks think it's a moderately annoying, but largely harmless noise. I can't believe that it's good for the chain or the rail. IMO there have been enough instances of broken cam chain rails over the years to warrant replacing the old tensioner with the upgraded one. Especially when you consider that the upgrade is pretty cheap, and a broken cam chain rail = new engine time.

[AndyS]

As you can see Tom, already there are a few good suggestions here, and you are going to have to do a little more delving to identify geographically where it is coming from.

Keep us posted on what & where you find with relation to your clunk or clack.

Andy

[ThomasJ]

I'll be getting to it this next weekend...will report back

[OldBMWMaster]

I'll be getting to it this next weekend...will report back

 

It must be a California thing.