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Single, loud, metallic *crack!* on hot starts


another David

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another David

The following has happened twice in the last week. Both times while restarting the bike after it had been run for about 45 minutes.

 

- Turn key.

- Pull the fast idle lever.

- Hit starter.

- *crack!!* -- very much like two pieces of metal striking each other.

- Bike turns over as usual.

 

It's a sharp, single sound (i.e., doesn't repeat), and there is no residual or unusual noise after it; seems to come from the right side.

 

Bike is an '04 1150RS with 32k.

 

Any ideas?

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The following has happened twice in the last week. Both times while restarting the bike after it had been run for about 45 minutes.

 

- Turn key.

- Pull the fast idle lever.

- Hit starter.

- *crack!!* -- very much like two pieces of metal striking each other.

- Bike turns over as usual.

 

It's a sharp, single sound (i.e., doesn't repeat), and there is no residual or unusual noise after it; seems to come from the right side.

 

Bike is an '04 1150RS with 32k.

 

Any ideas?

 

David, you didn’t give us much to go on here. Is the noise for sure metal on metal or could it be an exhaust post fire (popping in the R/H exhaust on initial fire up?)

 

Why the fast idle setting on a hot engine? Shouldn’t need it.. Is it better without the fast idle lever up on hot start?

 

See if it will crank with the kill switch OFF (or kick strand down in gear with clutch in).. If the noise is gone cranking hot but no ign fire then possibly an exhaust post fire problem.. If noise is still there try to identify where (exactly) it is coming from.. Hope not a broken cam chain tensioner or loose flywheel..

 

Anything out of the ordinary happen to bike just before the noise started (like dropping the bike over, or any mechanical work done?)

 

Twisty

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another David

Hi, Twisty. I'll try to give you some more info....

 

- The noise for sure is metal-on-metal.

- I pull the fast-idle lever out of habit and shut it off immediately; but, yes, when it's hot (in the last "episode" I'd only had it shut down for 10 minutes or so before starting up again). I'll try it without the lever the next time. But, this isn't something that's happening every time I start it when it's hot.

- The noise happens once -- like a single clap (of two hands clapping, not one, sensei...) -- and then it's done.

- Nothing out of the ordinary (valves were adjusted about 1k miles ago) to speak of

 

Hope this helps.

 

Thanks!

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I have also experienced this metallic "crack" on hot starts. It is not a usual occurance but from time to time it does happen. I don't use the fast idle lever when engine is hot. Engine is a 4 y/o 1150 with 35k. Also curious as to cause.

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I have also experienced this metallic "crack" on hot starts. It is not a usual occurance but from time to time it does happen. I don't use the fast idle lever when engine is hot. Engine is a 4 y/o 1150 with 35k. Also curious as to cause.

 

I have experienced this also. AFter a long ride shut down in driveway then start it up a few minutes later to pull into garage....I'd say one of our 8 times I hear that crack. Weird. What the heck is it?

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SAAB93driver

It's only a guess on my part but it could be the starter gear engaging, disengaging and then engaging on the ring gear but that would tend to come from the left side of the bike (as you sit on it). I've had a similar noise if I wasn't consciously holding the starter button down all the way for the whole start sequence and the starter would catch on the already spinning fw ring gear.

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Have you checked the turn signal fluid or muffler bearings? lurker.gif

For me it was the electric white walls.

 

Haven't had this experience, but am now curious. Perhaps it's time to go for a ride and test things out. Meanwhile... lurker.gif

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I have heard a single loud snap when hitting the starter button on a non-BMW motorcycle. I attributed the sound to the closing of the starter solenoid.

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Any chance it could be pre-ignition combustion from the fuel air mixture left sitting in a hot engine?

 

lurker.gif

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The same sound happens on my '04RT on a hot start. It seems to be coming from the r/h side of the engine. I suspect the cam-chain to have a bit of slack when the engine was turned off hence the short *clak* when the cam chain gets re-tensioned. Just my 2 cents....

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ShovelStrokeEd

Hmmmm, no answers so far, just a little speculation on possible mechanical causes.

 

Wanna know what it really is?

 

 

 

 

 

 

 

Detonation, or severe pre-ignition, which is its slightly less evil twin. Hot surfaces on the intake port, piston top and combustion chamber walls are causing the first squirt of the fuel injectors to vaporize rather than atomize. Low velocity in the intake port contributes even further to this. The result is a mixture that is explosive in nature rather than one that burns. Again, since everything is turning pretty slowly, the clank is more pronounced as the sharp pressure rise bangs things about in there.

 

It really isn't harmful as this is more or less a one time event and it takes a sustained level of this stuff to do any significant damage.

 

For accuracy, I should state that it is more of the fuel vaporized than normal that is causing this. The fuel has to vaporize to burn but normally it does so in a very progressive manner. On that first shot, it has had more time to do so and therin lies the problem. It may also be that the first shot doesn't do it but rather the second with the first one never igniting. Now you have even more vapor in there as the pumping efficiency of the motor at sub-idle speeds is even worse.

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It's only a guess on my part but it could be the starter gear engaging, disengaging and then engaging on the ring gear but that would tend to come from the left side of the bike (as you sit on it). I've had a similar noise if I wasn't consciously holding the starter button down all the way for the whole start sequence and the starter would catch on the already spinning fw ring gear.

 

I've heard this on my 1150GS under hot start conditions. It sounds very much like starter noise to me - I attributed it to the engine firing almost instantly with very little cranking and the the starter gear has trouble engaging/disengaging fast enough. I've never heard the noise on my 1100RT or K75, just the 1150. Ed's theory sounds totally plausible too. I'm no mechanic so I'll buy it!

 

Nothing seems to be hurt by this, so I shrug confused.gif and go riding.

 

Doug

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Hmmmm, no answers so far, just a little speculation on possible mechanical causes.

 

Wanna know what it really is?

 

 

 

 

 

 

 

Detonation, or severe pre-ignition, which is its slightly less evil twin. Hot surfaces on the intake port, piston top and combustion chamber walls are causing the first squirt of the fuel injectors to vaporize rather than atomize.

 

While I believe the occasional noise I hear from my right side is likely knock related, I don't think its the first squirt but rather the last squirt(as the motor spins down)

I've heard this noise even in fuel lockout (side-stand down/gear engaged) situations.

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sonofdennis

Same thing has happened to me on hot restarts. I'm going to have to go with pre-ignition because it also can blow a puff of brown carbon looking smoke out the exhaust. I would describe the sound as taking a hammer and smacking the top of the piston.

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Same thing has happened to me on hot restarts. I'm going to have to go with pre-ignition because it also can blow a puff of brown carbon looking smoke out the exhaust. I would describe the sound as taking a hammer and smacking the top of the piston.

 

Yep,

You pegged it! Just ensure it doesn't happen while you are under heavy load. Two of my riding buddies have the same start-up noise when hot. My '96RT never does it but theirs (2002 and a 2003 R1150RTs) both do it.

I think the main culprit here is carbon build-up in one or both of the heads. High oil consumption when new can leave carbon deposits and that can raise compresion ratios too. Higher than normal compression pressures can also cause it.

 

Mick

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