Exhaust Leaks

BISavage

BISavage

champion rider
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Oct 8, 2020
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Do any of you have, or have had an exhaust leak?

After fitting my stock pipe again today and adjusting everything to make sure there is not tension, I got one. It blows out between the cat and down pipe in the direction of the brake reservoir and it makes that puff puff puff as I pass by sound reflective things.

My new gaskets have on back order since June, (I know because that's when I ordered them) and I'm not sure that taking it apart again will help the gaskets get any newer, atleast not until the new ones arrive.

I see quite a few out there with after market pipes, some of which dont have the thick flanges like the factory pipes, and I was wondering how you all go about keeping it all exhaust-tight?
 
As I like to take it apart and put it back together, RTV probably is not the best choice for me.

The 401 uses the graphite donut thing that slides over the pipe and squishes between the flanges.
 
So, after taking it all apart, turning the gaskets, cleaning everything with wd40 and reinstalling the Leo pipe I was able to get everything to seal.

I am amazed how much quieter the bike is now.

Once the seals arrive I will swap them, but for now the pft pft pft house is gone!
 
Just for reference, I’ve used the Ultra Copper on other bikes in the past, and disassembly afterwards wasn’t an issue. It worked well at sealing slip-on joints.
 
So, I will finally be getting around to doing my gaskets and had a question:
I am going to take the Cat, chamber, and muffler off to change the gasket at the front of the Cat.
Does it make sense to loosen up the header bolts on the motor?
And what is the best tightening order?

I figured I would leave the header bolts alone, and hand tighten everything from front to back, and then torque it down from front to back; header/cat clamp, cat/box clamp, box/frame bolts, box/slip-on clamp, slip-on bolt.
 
So, the tightening order I mentioned was wrong.
The correct order is found in the manual.

This is how leaking gasket looks:
 

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Totally my fault, not the bikes.

They were backordered or idda changed em 6 months ago.

Fixing exhaust leak makes a huge difference in noise and power.
 
BISavage,

I've ordered a replacement exhaust but I don't know what I'll need for seals until I get it. And then I remembered your post about the seals...
Can you describe those gaskets? I'm wondering if I can get generic parts for the seals/gaskets?
For the 2017-2019 bikes:
I think there are 2 of these: 93805005100
And 1 of these: 93805005000

Are they flexible or hard metal/graphite seal? inside diameter? Are the symmetrical and can be fit either way, or are they "one sided"?
Is there any chance you still have the old seals and can measure them and post some additional pictures?
 
I would recommend the original ones, which are always sell out this time of year.

I did find a pic, will have to go and measure them later.

As you can see from the pic, they are all in different conditions, and all three had a leek.

The cat leak as the small one was noticeable due to the carbon build up on the clamp.

The top of box to the cat clamp was pretty rough cause i didnt have the clamp on right and tightened into the gasket.

The bottom one from chamber to slipons was destroyed by a thin metal pipe which bent alot under the clamp and deformed it, pieces fell all over when took it off. Then After installing a different slip on the cat water always dropped from there at cold start.

Now knowing very well how to mess up those fragile things, I kinda like em.

20210329_003003.jpg
 
Last edited:
Vintage Veloce said:
Are they flexible or hard metal/graphite seal?
Click to expand...
I didnt bend them, they flake off if you abuse them.
Vintage Veloce said:
inside diameter?
Click to expand...
Need to check.
Vintage Veloce said:
Are the symmetrical and can be fit either way, or are they "one sided"?
Click to expand...
Look like they are reversible the first time you put them in.
Vintage Veloce said:
Is there any chance you still have the old seals and can measure them and post some additional pictures?
Click to expand...
Yeah, Ill have dig them out of the "on the way to the trash" pile.
 
I just installed the Competition Werkes mid chamber replacement pipe and I’m waiting for my Coffman slip on to arrive. I was barely able to save the stock seals since they fall apart so easily. Since I’m pretty sure that the KTM 390 Duke exhaust is almost identical to the 401, I found replacement seals here:

www.ktmpartsnation.com

2020 KTM 390 DUKE ORANGE Exhaust System

Shop online for OEM Exhaust System parts that fit your 2020 KTM 390 DUKE ORANGE, search all our OEM Parts or call at 269-385-1540
www.ktmpartsnation.com www.ktmpartsnation.com

My plan is once I get the slip on, I’ll use these to replace the stock ones. If they don’t fit (doubtful) I’ll just have to be super careful when removing them again.
 
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