Exhaust header joints

[lerk]

Evening all,

I’m after a little sanity check.

My new to me bike has developed a bit of a knock, but it doesn’t seem to be directly engine related.  It occurs under throttle openings but also occasional knocks on the overrun too (about in time with the exhaust pops)

I've tested for potential pinking by running on the choke (just about manageable) and I know the clutch makes noise until disengaged.

I decided to get a new header gasket and orings to try the cheap obvious fix first before tearing into the engine. And as I stripped away the mud deflector noticed the header looked like this.

Removed the exhaust and cleaned the header (clamp straightened in the vice) and decided against changing the gasket as the current one is not compressed to nothing as I expected.

Refitting the header, the same thing happened - the header is definitely sitting square and central but I assume the header isn’t dropping into the gasket. 

tried to pop out the old gasket and it was having none of it… how difficult should they be to come out? I didn’t try too hard for fear of damaging something but my plan is to try and collapse the gasket inwards to shrink the diameter.

The good news is refitted clean and with new orings in the slip joint, the knock has gone, but I’d like to know whether I need to sort the cylinder joint or not…

[Tr1AL]

@lerk If it bothers you take it off and flatten the flange plate again and this time do not over tighten it , if you overtighten joints you are more likely to have leaks because you are distorting things , Most of the time torque settings tables from the manufacturer  and torque wrenches can help to avoid this. 

[Tr1AL]

35 minutes ago, Tr1AL said:

@lerk If it bothers you take it off and flatten the flange plate again and this time do not over tighten it , if you overtighten joints you are more likely to have leaks because you are distorting things , Most of the time torque settings tables from the manufacturer  and torque wrenches can help to avoid this. 

@lerk When you fit the front pipe/header into the mid box put some silicone grease on the 2X orange silicone rings and on the pipe so that the pipe can move around easily and when you fit the front/header pipe to the cylinder DO NOT have the Mid box mounting bolts tightened have them as loose as possible so that you can get the front pipe to enter the crush gasket and sit correctly then tighten the flange plate just enough to hold everything square the front pipe should be able to swivel at the joint , now tighten up the mid box support bracket bolts and then  swivel the front/header into the best position to be close to the bike and leaving an even gap at the join where it enters the mid box and then tighten the 2X bolts at the flange plate.

Edited January 4 by Tr1AL

[lineaway]

Nice explanation!

[lerk]

The flange bent as I ran the bolts in with the long end of a t bar, so not a lot of torque (I haven’t looked up the torque setting for these, but it was far less than I’d guess would prevent the things rattling loose)

I did actually take it back off and jiggle it all round a couple of times, including refitting the back box on the opposite side of the mounting tab to see if that helped alignment but no bueno.

I can’t see any damage to the header to indicate it has been bent, but the gap between header and frame is tiny.

I lubed the orings and also deburred the header to avoid damaging them.

Edited January 5 by lerk

[faussy]

Every GG i had came like that from the factory. Your knocking does sound like lean mixture, but it also sounds like youre aware that it could be that

Edited January 6 by faussy

[lerk]

1 hour ago, faussy said:

Every GG i had came like that from the factory. Your knocking does sound like lean mixture, but it also sounds like youre aware that it could be that

Did you just live with it or can it be made to fit flush with the right wiggling or even bending?

[Tr1AL]

6 hours ago, lerk said:

Did you just live with it or can it be made to fit flush with the right wiggling or even bending?

@lerk I think faussy is talking about the knocking not the bent flange , something is not right with the flange plate  it should fit almost flush with the cylinder with a small even spaced gap of about 1mm , try taking off the crush gasket/gaskets ?  there should be one perhaps someone fitted one thinking there was no gasket there and you have 2X gaskets in there . They are crush gaskets and  so they come out quite easily get a long thin screwdriver with a flat blade about 5mm wide put something on the edge you are levering on like a cut piece of hose pipe or whatever to protect the cylinder and gouge the end of the screwdriver into the inner face of the crush gasket and lever it out then make sure there is not another one in there before thoroughly scraping out the recessed area and putting a new gasket back in there.

As far as knocking/ pinking goes you need the highest octane petrol / gas you can buy at the pump 98/99 RON and you can try fitting  a 1mm thick aluminium spacer available from www.trialendurodirect.com approx £25  at the head to lower your bikes compression slightly or fit a GasGas/S3 low compression head insert. Lowering the compression will obviously soften the power output of the bike which is not a bad thing if you ride in wet conditions.

Edited January 7 by Tr1AL

[faussy]

No, im talking about the bent flange, they have all come bent to a certain degree, probably because theyve been fitted with an impact gun at the factory. Ive lived with it, because ive only had to take a front pipe off once (and i did what you did, straighten it as best i could before refitting) . The others never leaked at this joint so never had a reason to touch it. 

Heres my 2022 untouched fron the factory. Sorry for the crappy pic. Ive no lights in my garage at the moment

Edited January 7 by faussy

[lerk]

Well fettling it definitely shut the noise up for the first couple of hours riding, but the seal soon opened up again as I shook the bike around and heat cycled the header a few times.

Now I know it’s not doing any damage I’m less bothered by it, but I will try to refit it again with a brand new gasket and re-straightened flange.

 

For the avoidance of doubt - bike is running on shell e95 at 80:1, I was tempted to throw some a gas at it to test - but know all too well what TEL does to spark plugs!  I’m happy that the mix isn’t lean. 

 

When I have time I will strip the exhaust and rebuild with all new seals and gasket. Although before fitting seals to the mid box I will dry fit the header to ensure alignment without risking the new orings!

[lerk]

Right then, in preparation for this weekends riding, I’ve had a fettle.

Straightened the flange just past straight so the middle contacts first - fitted a new Cylinder gasket and then tried to fit - the flange bends before the gasket compresses.  Even tapping the flange back towards the head didn’t help squash the gasket. 

So off it came again for another attempt.  I’ve now added two washers of equal thickness to the spigot on the header so I can torque the bolts without distorting the flange.  Early testing in the garage indicates the joint is gas tight, we’ll see how it goes in use.

I did consider sanding down the thickness of the gasket or giving it a bit of gentle percussive maintenance to sink it back into the cylinder where it should compress to, but we’ll try this method first.  Worst case scenario is I drop the washers out and dog it back down as it was previously!

Edited January 12 by lerk