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Old 03-27-2015, 08:44 AM   #1
hennessyktm OP
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Oddometer: 48
Loud Exhaust at certain RPMs

04 950, 2:1, Akro, exhaust clamps are tight.

Symptoms: Under load, and only under load, from 3600 to 4200 RPMs, I get a sound like the header has come off/slightly come off one of the cylinders. I get a single sylinder thumper-type sound from somewhere (think XR650R with free flowing exhaust). It is very difficult to pinpoint where this sound is coming from while riding down the road. Just realized how difficult it is to describe the sound.

The bike will not make this noise when in neutral and revved to these RPMs in the driveway, only does it when in gear, going down the road/under load.

My assumption is one of the exhaust gaskets at the cylinder-to-header joint or one of the exhaust rings at the header-to-2:1 joint has failed and only breaks seal when under load.

Anyone ever experienced this, whether with a 2:1 or 2:2

NOTE: I recently replaced my un-baffled Remus can with a baffled Akro (why is another story). It happened within 120 miles of the swap. I removed the baffle in the Akro once I noticed the sound, but it's still there. My guess is the increased backpressure caused a leak somewhere.
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Old 03-27-2015, 09:17 AM   #2
zeropoint
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yes .....this is exactly how my 2:2 akras sounded when the graphite rings started to disintegrate at 16000 miles. thought i was imagining it at first.....

within a few hundred miles one blew completely followed by the other a few hundred later.....
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Old 03-27-2015, 11:04 AM   #3
hennessyktm OP
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Thanks

Thanks for the reply. I have 2 x rings and 2 x seals on order/in the mail. Which seals failed for you; the ones at the cylinder head or the ones at the header to mid-pipe junction(s)?
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Old 03-27-2015, 12:10 PM   #4
zeropoint
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the graphite rings between header and mid pipe......pt no. 60005005001

didn't do them myself and it was a while ago now but I think the other gaskets (60005005002 x 2 and 61005005000 x 2) were replaced at the same time
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Old 03-28-2015, 07:57 PM   #5
hennessyktm OP
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parts

zeropoint, appreciate the feedback; good info. I ordered the part numbers with the last digits of 001 and 002 (at cylinder and mid-pipe). They arrived in the mail today and I plan on installing over the next few days. I'll report back to close this thread out and tell of the results.
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Old 03-31-2015, 07:15 PM   #6
hennessyktm OP
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Results!!!

This evening I completed the removal/replacement of the old exhaust rings at the midpipe and the gasket at the midpie-to-can connection. It was a slight PITA, but its done. Had to buy new clamps because I broke a bolt off in one of the 2 x midpipe exhaust clamps (and broke a bolt extractor off in the broken bolt...fun).

Update: no change to the odd, "louder" sound I am getting. It sounds like it is coming from the front cylinder. I took the bike out for a 20 mile re-test/diagnostic ride and no change. I the same odd/louder sound at 3600-4200 RPM. Sounds like its from the front cylinder. I have ZERO power issues, idiot lights, etc. Bike wheelies hard in 1st and 2nd. No overheating, idle issues, oil level correct, coolant is fine, etc. Other than the noise the bike is the same as always; a blast. I find this odd.

Maybe the cylinder-to-header exhaust gasket on the front cylinder? I find it hard to believe this would all the sudden decide to give.

Thoughts....anyone? I know this isn't the most fun/interesting thread on ADVrider.....
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Old 04-01-2015, 10:40 AM   #7
chainbreaker
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Several times I have checked for an exhaust leak because of a noise as described. Never found a leak but when the noise appears I usually have very little fuel left in the tanks. I have come to think that some sort of a harmonic resonance sets up that doesn't happen with full tanks.
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Old 04-01-2015, 12:34 PM   #8
hennessyktm OP
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Not fuel

chainbreaker, thanks for the reply. I wish it were something so simple, but I just filled up last night and the sound persists. I have been reading other threads all day and did find one guy say he gets "piston rattle" in 5th and 6th when lugging it (started at 25K, he now has over 60K, no issues from teh sound). I wonder if the noise I am hearing is not exhaust related but piston related.

After re-assessing, I find the sound occurs from 3200-3400 and again from 4000-4200, then goes away.

Guess I'll drain the oil and check for debris?

I am stumped.
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Old 04-01-2015, 09:34 PM   #9
Zuber
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You are not just hearing the intake 'pulse' noise? The stock airbox makes a rapid 'poka-poka' noise at those RPM's.
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Old 04-02-2015, 08:23 AM   #10
hennessyktm OP
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Intake noise

Zuber, I don't think thats it. I've had the bike going on 4 years and don't recall this noise.

As menitoned I added the Akro shortly before I noticed the new sound. Perhaps the new pipe caused different exhaust resonance?

I guess I'll continue to flog her as usual unless I notice an additional symptom(s).
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