knocking after fitting new exhaust

[bowman]

hi guys


on friday i decided to go back to OEM backbox, and had an unsilenced b-pipe put in at the same time (loving the sound by the way!!)


ive noticed over the last couple of days, once the car is nice and warm, when I decelerate and go over slight bumps Im getting some knocking coming through the drivers seat

is this likely to be the exhaust, and they have fitted it too close to the chassis?

 

[Loxy]

It's the B-pipe.

My Spoon one used to do it, particularly if it was raining. Water used to get between the body and B-pipe and kettle off the B-pipe. As the B-pipe is a bigger bore there was less room for the steam to escape and the force would move the pipe around.

If yours is rattling about in the dry, I wish you luck in the wet!

You could try double checking the back box is on straight. If the bit that meets the B-pipe is too high, it could be holding the B-pipe up unnaturally high and close to the body.

 

[Suits]

Hangers might need adjusting.

 

[You Jay]

Same is happening to me when in wet.

I could feel mt seat vibrating. But nothing on dry conditions.

I got supersrpint unsilenced.

 

[eptrois]

My DC sports rattles loads when it is soaking - it has to be really really wet so it doesnt happen often but when it does, it worried me - until now, as I didnt have a clue how water could cause such an awful noise. Thanks Loxy for the above post!

 

[bowman]

looks like they just fitted it too close to my body.... theyve adjusted the hangers slightly to give it a little bit more clearance


going to test it out over the weekend see if it still happens



thanks for help guys

 

[Suits]

K20's, well most Honda VTEC engines to be honest move a lot, due to the high reving and due to this, the exhaust can move about a good bit too.

Normal practice is to hang the system as close to the underside as possible for better clearance but with Honda's they should be hung a little lower to avoid them getting to close to the underside under drive.

That's my thoughts and experience anyway.

 

[Harv]

If it's popping from the middle of the car when wet then its the water evaportating and popping on the stainless steel b-pipe. If its knocking from the back then its the backbox on the anti-roll bar.

Both common, both nothing to worry about.

 

[Harv]

 

[Suits]

Yar'ly.

Fujitsubo RM01A.

Happened to mine too.

Hangers fixed it.

 

[Harv]

yeah powerflex ones, can't remember the product code. :lol:

i went through all this in 2005

#feelsold

 

[bowman]

had it back in today has knocking happening quite alot.. and they have noticed that one of the bolts between my cat n manifold has completely corroded away, and all that is remaining is a slight bit in the manifold flange
they recon this missing bolt is causing more than usual sway in the exhaust, and have advised that trying to get the bolt out would not leave enough of the flange behind???? so they have recommended getting another manifold

this sound about right? or do you recon i could get the bolt out and not have to replace the manifold?

 

[mikerj]

If it's popping from the middle of the car when wet then its the water evaportating and popping on the stainless steel b-pipe. If its knocking from the back then its the backbox on the anti-roll bar.

Both common, both nothing to worry about.

If you get a knocking or rattling noise after driving through a puddle it's not caused by steam (though granted it will produce a bit). Having water splashed onto to the underside of a hot exhaust will cool the underside of the pipe and as the metal contracts the entire pipe will bend upwards like a banana. If it's already quite close to the floor pan it will touch and cause the rattling/knocking noises. It's quite a common problem, especially (but not limited to) after-market stainless exhausts that tend to have thinner walls than mild steel ones. As the exhaust heats up and the water is evaporated the pipe will straighten out and the knocking stops.

I have seen the same thing happen on a number of different cars (including my old Civic VTi). If the system can be adjusted to increase the clearance around the pipe (not always possible) then it can be prevented or at least reduced. The thicker the wall of the pipe, the better it will retain it's heat and the less it will bend.