Exhaust advice

Horizon81

A friend of mine has just had her catalytic convertor and mid section of her exhaust replaced. The back box was not changed as this was already replaced a year or so ago.


I've been in the car the new set up doesnt sound good. With the car idling I put my hand over the tail pipe and I could leave it there quite easily. No pressure at all pushing my hand off.


Underneath the car, the join between the mid pipe and the backbox looks very poorly made. Its been joined by a lot of dry putty like substance which was cracking and crumbling off, and with my hand over the exhaust I felt heat coming from this area so I think this is at least one place it's blowing. What sort of gasket should they have used? Is this putty stuff basically a bodge?

philgr

Doesn't sound good.. could you see gas escaping from this point when blocking the tailpipe?

Phil

UsernameAlreadyExists

Have they splattered this stuff all over it?
http://www.amazon.co.uk/DESIGNED-SILENCER-EXHAUST-SYSTEM-REPAIR/dp/B002SHD1IQ

Horizon81

philgr wrote: »

Doesn't sound good.. could you see gas escaping from this point when blocking the tailpipe?

Phil

Yes, only when I blocked the tailpipe which I know you never do in normal use, however I was always told that when you put your hand over the tailpipe, pressure should quickly build up and push it off, which doesn't happen here.


And yes, the join is covered in a liberal amound of that goo, which has hardened, dried, and gone crumbly.

philgr

Horizon81 wrote: »

Yes, only when I blocked the tailpipe which I know you never do in normal use, however I was always told that when you put your hand over the tailpipe, pressure should quickly build up and push it off, which doesn't happen here.


And yes, the join is covered in a liberal amound of that goo, which has hardened, dried, and gone crumbly.

That does sound like it's poorly fitted. Does the car sound louder than one would expect it to normally?

Horizon81

Can anyone tell me if its normal practice for a garage to use exhaust paste or is it more of a DIYers bodge? I realise the aftermarket mid pipe and the aftermarket backbox may not be exactly designed to fit together as they're likely from different manufacturers, but isn't a 'proper' way of connecting them with a gasket rather than liberal amounts of paste? (which is already cracked and crumbling away)

Richard53

It's normal to use paste as an assembly compound, to create a gas-tight join between two pipes. However, even if the pipes are from different makers, they should be the same nominal size, and any paste is simply to create a seal. There should not be large amounts around the join. If they have had to use a mass of paste, either the pipes aren't designed to go together or it's been done by someone without the necessary skill. For your description, it sounds like a bodge.


Blocking the exhaust outlet may not 'blow your hand off', but it should certainly kill the engine within a short time. If it doesn't, there's a leak, and that is an MoT fail and a danger.


(ETA: if the pipes are of different diameters, the normal practice is to use a metal reduction piece between the two, basically a short cylinder with the O/D of one pipe and the I/D of the other. Fitted properly, it would look neat and clean.)

Horizon81

The mid pipe to back box connections are like the top one on the page below. It's not a case of one sliding into the other, it's a union that is joined by 2 bolts with (it would seem) a gasket inbetween. Perhaps there isn't a gasket on the car in question and the 2 bolts have been tightened up with a mass of paste inbetween instead?


http://www.catalogue.bosal.com/pages/exh_system_list.php?query_nr=2&make=TOYOTA&model=Yaris

Joe_Horner

Richard53 wrote: »

[...] If it doesn't, there's a leak, and that is an MoT fail and a danger.

Agreed with most of the above, but the MOT rules were "clarified" a couple of years ago and a leak is only a fail if it's "significant". An exhaust that won't create pressure at idle (especially with a petrol engine) can easily be a pass under that description.

Incidentally, from the danger point of view, most catalyst equipped cars don't produce enough carbon monoxide to be a problem once the cat's lit up and it'd take a VERY big leak to fill the car with enough CO2 to suffocate you!

Joe_Horner

Horizon81 wrote: »

The mid pipe to back box connections are like the top one on the page below. It's not a case of one sliding into the other, it's a union that is joined by 2 bolts with (it would seem) a gasket inbetween. Perhaps there isn't a gasket on the car in question and the 2 bolts have been tightened up with a mass of paste inbetween instead?


http://www.catalogue.bosal.com/pages/exh_system_list.php?query_nr=2&make=TOYOTA&model=Yaris

Looks like it's an olive joint - there's a very short fibre tube with tapered ends that goes between the two pipes. As the joint's tightened the tapers seat into the pipe flanges and seal.

It's very unlikely indeed that the whole space has been filled with paste - it'd be virtually impossible to keep it there while it set and you'd end up with a very big, and very obvious, blow.

More likely is that the flange on the old section was slightly damaged or distorted (common when a pipe's been fitted then dismantled again) and that, rather than insist on replacing that as well, they've used paste to try and seal around the distortion.

Bear in mind that a new (especially aftermarket) exhaust is going to sound different to the old one. They often sound a little "tinny" until they've been run for a while.

UsernameAlreadyExists

Joe_Horner wrote: »

Incidentally, from the danger point of view, most catalyst equipped cars don't produce enough carbon monoxide to be a problem once the cat's lit up and it'd take a VERY big leak to fill the car with enough CO2 to suffocate you!

Depends where the leak is!