How would you tackle this repair?

[David Pye]

Hi guys,

I need to repair a break in a piece of exhaust pipe between the catalytic converter and the main exhaust. The stainless pipe has corroded through between the body of the catalytic converter and the main exhaust and left a gap!

A picture of a similar (but not as bad) disaster is here (2nd one down!)

http://forums.tdiclub.com/showthread.php?t=258836

What I plan to do is to get some 2mm stainless sheet, bend it over some old exhaust pipe to make a tube... Weld this tube to the larger diameter of the outside of the catalytic converter itself (where it's a bit tapered), then tap it a bit so it tapers to the size of the smaller diameter pipe. Then weld it to the smaller diameter pipe, so I make a sleeve that completely covers the break.

I'm using TIG as a welding process..

Is this how you'd do it, or is there a much easier/better way?

Cheers,

David

 

[ford34/2]

repair options

had exactly the same problem just a couple of months ago, as I intend to keep the car golf/4 I cut my losses spending time possibly doing a repair that didnt last, new one off Euro car parts was £66.35 P/N 724440330. I kept the old one with the intention of doing a repair but I`ve been told I`ll get my money back for the new one at a scrap yard which has a dedicated catalytic weigh in desk, thought about doing the repair the same as you, an internal sleeve or an external sleeve, plenty of lee way on the joint connector.

Stan

 

[David Pye]

Heh, same car as well then ;-)

Would you make an external 'sleeve' from sheet steel then, if you were going to?

Oh, and as another question, but very job-specific - does the frontpipe/cat come off without having to drop the front subframe down?

 

[dannymac]

Yes,or easier than rolling sheet is if you have stainless pipe,slice it in half and fit it on either side,even with the taper you should manage.

 

[the snooper]

Hi guys,

The stainless pipe has corroded through

stainless corroded ? it looks rusty to me, mild steel

 

[David Pye]

Further research suggests it might be galvanised mild steel.

I think I will still use SS for the repair and paint over the welded section with high temperature manifold paint or similar.

Cheers

 

[the snooper]

Further research suggests it might be galvanised mild steel.

I think I will still use SS for the repair and paint over the welded section with high temperature manifold paint or similar.

Cheers

there will be no advantage using SS as it will just rust either side of it, also you cant protect the inside from condensation at the welded seams, so unless its a full SS exhaust nature will do its thing on the steel

 

[outofthefire]

I wouldn't bother with stainless either in fact if the exhaust looks like the one in the pic i'd probably just plug the hole, I can't see the rest of it lasting that long.

 

[David Pye]

In mine, there isn't a hole, the pipe has corroded for about 80% of the circumference! However the catalyst itself is solid as is the rest of the pipe. It is just the join that has given way...

Have to take it off anyway and as the cat is the expensive bit I was going to try to make the TiG pay for itself ;-)

 

[ford34/2]

removal

very fiddly, accessed from underneath, and I think I used a swivel headed ratchet spanner to get access, didnt drop any cross members or anything else off car will have a look again on sat, my mind is not what it used to be. corrosion was exactly as you describe, circumference weld corroded and a wee hole,annoying but 02 plate-10 yr old.
Stan

I can photograph removed front pipe/cat for you, again be on Sat.

 

[welshpug]

I had a fairly similar issue with a pug o.e cat, condensation collects as there's a dip in the system right on the bend as it exits the cat, all I did was lay LOTS of mig weld


but it was strong and worked, and only cost me the consumables!

 

[David Pye]

Ford34/2, thanks for that. Is there any chance I could be really cheeky and ask if you could make a couple of measurements from yours?

The bits I want to measure on mine are covered in exhaust repair putty while it is still on the car!

I would like to know the diameter of the pipe from the back of the catalyst (the one that corrodes). I think the diameter is 55mm?

The other measurement I would love is the outside diameter of the metal bit on the catalyst to which the pipe is welded. The bit after the taper, where it is just round again but a bigger dia than the pipe. I want that bit because I am going to make a collar over it to strengthen the repair :-)

Cheers!

 

[ford34/2]

sizes

here Ya go,
The tail end on the cat is about 20mm long and its "bulb" is 63.83mm Diam, the tail pipe that fits into the cat has a wee "bulb formed at the cat end and is 57.58mm the pipe diam varies and behind this bulb is 55.91mm, further back near the joint area is about 55.3mm dropping to 54.97 near the joint.
Its a pity you cant scrounge a piece of pipe off a good scrap exhaust at a nearby exhaust garage, about 360mm minimum,and ideally 370mm, and just weld it straight into the cat. Double check the pipe just outside of the joint on the end of the pipe as mine was a bit dodgy and would need a repair if I didnt put a complete length of pipe in.
As my cat is still good and the Daughter has the same car but 03 model, I think thats what I`ll do and i`ll have a spare.
If the pics are not what you want --shout.
Stan

 

[David Pye]

Thanks so much for these pics/measurements- they are very much appreciated!

I am in the process of sourcing the bits. Will post some pics when I'm done!

Cheers!

 

[Wozzaaah]

It's most likely aluminised, not galved. Horrible stuff to weld all the same.

 

[David Pye]

Mine are going to be stainless, and I'll grind back to steel on the catalyst wall to weld it to. As that bit isn't exposed to the exhaust gases on the inside, a good coat of high temp enamel should keep the weld OK longer than the rest of the car, hopefully!

 

[dannyp]

no point useing a stainless really. some of the vag systems are a low grade stainless i think someone once said it was 409 or something like that.


on reapairing used old exhausts you need to make the job as easy as possible it would sleeve it with some exhaust tube and spud it together with a mig.

TIGS HATE working on crappy old exhaust tube

 

[David Pye]

ford34/2 - could I just confirm one further measurement?

The length of the pipe, from where it enters the cat, to the end where it would enter the exhaust clamp - is that 370mm? I think from what you are saying that it is, but I would like to be 100% sure before I make a decision I regret!

Cheers!!

 

[pob30]

hi,im new to the site but in my early welding days(still fairly early earlier but hope i make sense) i started off my love of welding working for a exhaust manufacturer so can safely so the steel used is of eeexxxttremely poor quality as said before in other threads coated with alu..horrible to weld.plus if you repair the hole the pressure will just find the next weakest point and you will have the same problem again and again...not worth the hassle unless your really bored!

 

[ford34/2]

Length

yes correct. but it could be cut after welding. + there is a bit leeway in the clamp. good luck.
Stan
EDIT:::::
Just double checked -- 370mm would do just nice, but get it longer to have a bit practice on , a dummy run and then cut it off.