Replacing the Catalytic Converter/Exhaust

[Loque]

Hi all,

My cat is essentially shagged, to get it through it's last MOT, the entrepreneurs that liked to call themselves mechanics did a bit of a bodge job on the whole exhaust system to be honest.

Firstly the Cat has more holes in than Swiss Cheese, and it seems to be that the whole assembly has been pugged up with some engineering equivalent of Pollyfilla or whatever, in itself it isn't too bad, but the noise the car makes now is just getting silly. Something along the lines of a fart in tin can etc. Furthermore they decided to put a non Vauxhall rear section of exhaust on, which in itself is fine, but the damn thing is now banging against the handbrake cable just over the rear axle where the clamp is.

First up though I am going to deal with the Cat, I'm hoping that the cat might be slightly out of alignment somewhere, and that replacing it will stop the damn noises.

Anywho, anyone have any experience of doing this sort of thing? Have to confess I haven't done it before, but I'll be dragging someone that has along to do it with me. My local garage want about £300. That aint happening considering a new cat is about 60 quid off fleabay.

[haydn1987]

To stop the clamp hitting the axle loosen the clamp and twist it around to give you more clearance and check the rubber hangers they might need replaceing there are four of these two on the back box and two on the centre section that are a bit more difficult to get to. I alwas try the cheap things first.

If you suspect the exhaust is blowing anywhere mix up some water with a lot of fairy liquid and pour it over bits that you think are blowing eg manifold gaste, exhaust seals and joints then start the engine and put your hand over the exhaust, turn the engine off and have a look to see if there are any bubble where you pour the soapy water. This will tell you if it just a bad seal that can easily be fixed, oh and engine has to be cold before you do this.

Replaceing exhaust sections seems realy easy undo the clamps and pull the two sections apart, if only it was.
Most of the time you will find that no matter how hard you hit the bloody thing with a hammer you can't get the sections seperated this is ussualy because they rust together and most garages use a sealing paste that sets hard.

If the rear section hasn't been on that long you should be able to get it off, but seperating the center section from the cat isn't going to be easy. By remaoving the rear of the exhaust you will be able to get the cat and centre section off as one piece then you can have a good go at seperating them off the car.
You will need to have ramps or stands or a trolley jack to lift the car up, normal jacks are not safe enough.

Which engine is in the car I know the old 8v have a compression seal between the down pipe and the manifold I tried fitting one 3 times buying a new seal each time and couldn't get an air tight seal a garage did it for £12. I think the 16v have a much easier gasket.

[Loque]

Thanks for the reply Haydn.

I have actually moved the clamp around a few days ago, still no luck though. It's just hitting on the other side, it seems that the 'bend' in the exhaust does not go up nearly enough into the recess in the chassis.

Several weeks ago I checked the rubber mountings and found that I didn't have one on the left side/centre section, after ordering one of fleabay I shimmied under the car and put the thing on. Unfortunately, to no avail. I suppose it's a good thing to have anyway.

This is one of the reasons I don't want to leave it too long, as the sealant paste between the exhaust sections will harden more the longer I leave it. Do you know how many miles have to be done before the stuff hardens fully vaguely?

Yeah, I think sticking the car on the kerb and going underneath isn't the way forward here, I am commandeering my mates pit for a day. Good call on the fairy liquid though, definitely will check that one out

I actually spoke to a mechanic mate and he seemed to think that the noise was coming from the manifold, so you may very well be right on that one, I'm gonna have a close look at it later on today and report back. Just looking at the cat and hearing the engine, it looks pretty conclusive, may try to get some pictures up later on today.

Thanks again.

[haydn1987]

The sealant paste sets after a few hours and then realy goes hard if you heat it up so if you have driven you car for about 20mins then the exhaust would have gotton hot enough to set the paste.
You should still be able to seperate the exhaust its mostly the rusting problem them makes them impossible to get off.

Cable tie a bit of rubber to the exhaust where it hits the axle it. It will still hit but you won't hear it.

I would definately get some soapy water around the manifold here is a pic of when the gasket went on my manifold and I used the soapy water.


and here is a pic of the seal between the manifold and the down pipe