How do I rid myself of that annoying 2 stroke pipe rattle that makes my '13 250SX sound like a '77 RM 125?

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1/8/2019 1:21 PM
Edited Date/Time: 1/8/2019 1:21 PM

Hey gurus! I come to you for your knowledge and experience.

I have a '13 250SX that sounds rattly and old and it's all from the exhaust pipe. I have replaced the pipe O -rings, the entire exhaust port on the cylinder (they are replaceable on KTM cyclinders), verified everything is tight, nothing is touching, and so on.

When I install the expansion chamber with fresh O-rings the bike sounds like Dungey's factory 2 stroke from Straight Rhythm, for about 15 minutes, then goes back to sounding more like a clapped out '77 RM125.

What's the secret? Gasket sealant at the head pipe possibly?

Please advise.

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2013 KTM 250SX on Ohlins, 314cc built stroker engine with 56 very smooth and easy to ride rwhp.

1/8/2019 1:42 PM

Hi temp silicone?

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1/8/2019 1:47 PM

What he said. Silicon around the o-rings and where it goes into the silencer

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2011 Yamaha YZ 250 -MX
1996 Yamaha Banshee 350 -Trails
1982 Chevy S10
2005 Pontiac GTO -451rwhp

1/8/2019 1:52 PM
Edited Date/Time: 1/8/2019 1:54 PM

Buy a four stroke...you're giving two strokes a bad reputation. But seriously, try using Viton o-rings that are slightly oversized. They'll hold up to the heat much better and longer than a standard butyl rubber o-ring.

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1/8/2019 2:00 PM

And what the hell is wrong with the way a 77 RM125 sounds, may I ask??? cool

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1/8/2019 2:01 PM

I loved the sound of a 77 rm 125!

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1/8/2019 2:04 PM

Forty wrote:

I loved the sound of a 77 rm 125!

DAMN RIGHT !!!! LOL My first real race bike

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1/8/2019 2:16 PM

Suns_PSD wrote:

Hey gurus! I come to you for your knowledge and experience.

I have a '13 250SX that sounds rattly and old and it's all from ...more

Buy a counterbalanced new bike!

Im not for sure on this - but after x amount of hours I've noticed the steel frame bikes just ring and rattle a ton!

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1/8/2019 2:35 PM

2007 CR125 was pretty common with this concern.
From memory, they ran thin rubber washer behind the stainless ones on the mounts. But i would check the carbon build up and then run a slightly thicker O-ring. as mentioned the gasket sealant wont do a lot. rubber hose over the expansion chamber springs was another trick used to help reduce that "ting" sound.

On my CR we would run a gasket that was cut out for the exhaust port onto the cylinder as well as the O-ring and then we changed the springs to a different style that was a lot thicker. the OEM springs where pretty thin and would stretch and vibrate heaps.


all the best!



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1/8/2019 2:39 PM

deanwhite51 wrote:

2007 CR125 was pretty common with this concern.
From memory, they ran thin rubber washer behind the stainless ones on the ...more

Those are good suggestions.

Thanks!

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2013 KTM 250SX on Ohlins, 314cc built stroker engine with 56 very smooth and easy to ride rwhp.

1/8/2019 2:44 PM

Silicone the joint between the pipe and silencer as well. Sometimes that's a spot for rattling and the sound may propagate down the pipe toward the cylinder.

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Braaapin' aint easy.

1/8/2019 2:45 PM

OldPro277 wrote:

And what the hell is wrong with the way a 77 RM125 sounds, may I ask??? cool

Not a damn thing, they sound awesome!

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1/8/2019 3:48 PM
Edited Date/Time: 1/8/2019 3:48 PM

Usually they are actually hitting the rh side of the engine due to a slight bend. Crank up bike and pull out on expansion chamber and rev and see if it still does it. Also, Most use rtv on the muffler as well as o rings. Your flange may be worn too.

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1/8/2019 3:59 PM

Buy kreft moto o rings. The bills pipe is the only one I've ran that doesn't rattle with stock o rings. Even the kreft last only a few hours with a pro circuit because the shitty fit. I had a friend tig weld part of a destroyed bills onto a stock pipe because the part that goes into the cylinder fits so nice. I heard fmf fits well too

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