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Knock at start-up (Hex Head)


_Brock_

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Need help diagnosing an odd thing. My R1200R hex head engine under specific conditions will make one knock at start-up. Details...

  • The knock ONLY happens when the bike is started hot. No knock when cold.
  • Knock always comes from left cylinder.
  • The knock happens a split second before the engine fires (video below, listen carefully).
  • If the hot bike rests for 5-ish minutes, the knock won't happen when started.
  • If I briefly tap the starter button prior to starting, the knock won't happen. Perhaps this partial engine turn expels gasses and prevents the knock???
  • Gas type has no affect on situation. I've tried non-ethanol, 90, 92, 93, etc.
    Bike runs really well, otherwise. No other symptoms. Valves are adjusted, TBs are synch'ed... current on all service.
  • 23K miles.

Video: https://youtu.be/rYZd3jjp14A

(The knock is more prominent in person than heard in the video.)

 

Thanks in advance your your comments.

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Evening _Brock_

 

I can't hear enough in your video to tell much but your symptoms could point to a dripping fuel injector after hot shut down.

 

Pretty difficult to diagnose over the internet but if you have the time & will power you can try a hot shut down by pulling the power plug form the FPC (Fuel Pump Controller) as that allows the fuel manifold to run to 0 pressure as the engine shuts off.

 

Then re-connect the FPC & do the same hot-engine re-start that now gives you the knock.

 

If it doesn't knock upon restart with a 0 fuel pressure shutdown then look for the possibility of a dripping L/H injector.

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That sound like good advice. I just need to figure out where the FPC power plug is, but I get the concept.

 

The knock can be clearly heard on the video if you know when to listen for it. It's less than a half second before the engine fires. Sounds like a come of wood blocks being "clapped" together.

 

If it's a faulty injector, I'm guessing it's not hard to replace since it's exposed on the side.

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  • 3 weeks later...

If it's a faulty injector, I'm guessing it's not hard to replace since it's exposed on the side.

 

You might just swap the two injectors and see if the symptom moves to the other side. I am assuming they pop out of there as easily as the ones on my '03 (which may not be a very good assumption).

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Don_Eilenberger

If it was a cold start that gave the knock - I'd say the timing chain tensioner on that side is leaking down. That also ties into the noise not happening if you give the engine a tap with the starter button.

 

A knock at startup is not at all uncommon on R1200's. But it's commonly heard on a cold startup when the oil has leaked out of the timing chain tensioners (there is one per cylinder.) What you're hearing - 1 knock - is really not something I'd stay awake nights worrying about.

 

Next oil change I might switch to my favorite oil (Castrol TWS - 10W-60 full Euro synthetic - spec'd for the HP2 by BMW.) That quieted it down on my '07 (which I had replaced both tensioners on, achieving nothing.) Have been using it continually on my '12 - and have never heard the knock.

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Who makes the aftermarket cam chain tensioners? I have the knock on cold starts and would like to have the newer tensioners on-hand.

 

Thanks,

Joe. '06 RT

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Who makes the aftermarket cam chain tensioners? I have the knock on cold starts and would like to have the newer tensioners on-hand.

 

'06 RT

 

Morning Joe

 

No aftermarket tensioners. The chain tensioners are just stock BMW parts. The updated 1100/1150 L/H tensioner was to use the 1200 hexhead tensioner.

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My local dealer says there's nothing abnormal about the sound or the bike, so no sleep lost. The bike runs great so I ride. Thanks!

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My 2008 R1200R had the knock at cold startup. If I left the bike on the center stand it would not knock at startup. Might be something to try.

 

Roger L

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Last Saturday I changed the engine oil and trans fluid. The PO had over-tightened the trans drain plug and split the sealing washer causing a leak that would leave a drop on the ground after a ride. A new washer on refill fixed that. I replaced the 10-40 oil with 20-50 and the knock is obviously reduced. Next oil change I'll give 10-60 a try.

 

Joe

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I had the same thing occuring ocasionly,, the right cam chain tensioner will bleed down at certain crank positions putting a reverse load on the cam chain and causing the bleed down resulting in the rattle untill it fills with oil. my solution was to cut to length a round head screw and install throught the spring for an OAL of 2.285" compressed, limiting compression . No more rattle.

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