Mating old exhaust parts

Hi there, amateur question, please correct me if I'm being daft.

Model: Freelander Mark 1 1998 2.0 TD (Rover Engine)

I'm replacing the exhaust downpipe after a leak developed in the concertina section.

The exhaust bolts are rusted to hell & pretty much welded together now. (Bugger of a job getting the downpipe off)

I've managed to separate the downpipe from the catalytic converter by grinding off the bolts on the downpipe. No damage as yet to cat. (Really want to avoid replacing that part!)

However, the bolts that continue to protrude from the cat are not budging, they're just too rusted on.

I'm going to try & drill them out if nothing else can be done, however, my question is about mating the new downpipe to the cat.

The surface on the cat is quite uneven due to its age. I was thinking of using some sandpaper to smooth down the surface that will mate with the new gasket to provide a close fit. - Is this a stupid thing to do?

Any advice & points to watch out for during this job would be welcome.

Buy a cat by-pass pipe. You don't need a cat on a diesel for it's MOT. Nice and shiney, reduce turbo lag, slight increase in power, improved mpg, easily adds 2" to your manhood. OK, that bit was a fib.

But if you really want to keep your cat, then removing the rust from the mating surface is a good idea, though the gasket on it's own is unlikely to seal without some exhaust repair putty or similar (Gunsons is one brand) to fill all the pitting and provide a seal.

oddbob said:

Buy a cat by-pass pipe. You don't need a cat on a diesel for it's MOT. Nice and shiney, reduce turbo lag, slight increase in power, improved mpg, easily adds 2" to your manhood. OK, that bit was a fib.

But if you really want to keep your cat, then removing the rust from the mating surface is a good idea, though the gasket on it's own is unlikely to seal without some exhaust repair putty or similar (Gunsons is one brand) to fill all the pitting and provide a seal.

Click to expand...

Unfortunately you do need a cat for the MOT. Whilst a diesel is only tested for visible smoke and not emissions it's still a requirement for all vehicles built since 1993 to have a cat. I know that some examiners who understand can have a touch of blindness in this area but the odd b******d could fail you.

I had to replace mine a few years ago and priced the downpipe everywhere . The best price I got was from some crowd like quickfit .
It took them hours using a gas torch,heating the nuts.
I was glad we had agreed a good price over the phone.
There were 3 of them working on it for most of the time I waited.

It's been a pig of a job, that's true. I've been at it with WD40 (did nothing as the bolts were too far gone), hacksaw & angle grinder. I still haven't got the bit that attaches to the manifold at top of engine yet, but now I've cut most of the pipe off I've got more room to get at the bolts at least.

All things being equal I'd have gone the Quick-Fit route, but they quoted me £180 when I managed to get the part & gaskets for under £50.

Fair point about mating the pipes together. As luck would have it I do have some liquid gasket in the shed. I'll use that with the gaskets I ordered.

I'm going to keep the cat on, simply because I can't even afford a bit of pipe to bypass it right now! When it does finally go I will give the bypass idea a whirl though, just to see what happens to my manhood...

Thanks for the advice. Much obliged.

I don't know what you mean by liquid gasket but there is a lot of heat on this part and so I suggest the proper exhaust type stuff.

Please forgive my appalling habit of making up terms instead of looking up the correct ones. Just dug the packaging out to check.

Liquid Gasket in my world = Granville Instant Gasket. RTV Silicone.

Back of packet says it forms a tough rubber seal, resisting temperatures from -60 Centigrade to +250 Centigrade.

However there is a note to say that it's not recommended for head gaskets & fuel systems. I'm guessing it's not good at high pressure stuff. Also seeing as I need it to seal an exhaust close to the engine it's going to need to be more than just "resistant" to heat. Please correct me if I'm wrong.

Looks like a trip to Halfords is in order! Got paid this morning, so not a problem.

Thanks for pointing that out.

Sorry, should have asked this before.

When you mean exhaust repair putty, would Holt's Gun Gum do the job to seal the joins? Just did a quick search on Halfords & that was what came up.

That's what I would use - don't apply too thick and it goes hard quickly so make sure you are ready. They also do an exhaust assembly paste in Halfords - I use that on my exhausts including bike exhausts which get very hot.

Don't use the liquid gasket on any part of the exhaust mate, it's just not up to the job! I use holts, it's ok stuff, it does the job intended of it, but if you have the right gasket it's not really needed. Its more for the slip on type exhausts, as apposed to the bolt together type. If you give the old exhaust gasket surface a decent rub with a wire brush, don't use sand paper, it should take off all the big bits and just the gasket will suffice!

Maybe I'm out of date here, but I didn't think you could use exhaust paste before the cat in case any excess paste broke away and got inside it.
David

talldavey said:

Maybe I'm out of date here, but I didn't think you could use exhaust paste before the cat in case any excess paste broke away and got inside it.
David

Click to expand...

Good point but I don't know if it is the case - I would use it very carefully in that case - assembly paste is white and very runny do just a smear on the metal perhaps

Well it's been a royal b@stard getting the pipe off, but it's done. Took me bl00dy ages.

Had to drill out the studs & replaced with honest-to-goodness nuts & bolts. Hell of a lot easier to put back together.

As it was, when I finally got the remaining bits of downpipe + gasket off the surfaces, they were a lot smoother than I thought, so managed to get away with just gaskets.

I gave it a very fine sanding with some old smooth-as-glass sandpaper & block to get any minor imperfections out. Made sure it was smooth to the touch.

Used gaskets only, bolted up, ran engine for a mo to warm up, nothing leaking. Gave all the nuts a nip when warm to make sure everything was tight.

Sounds sooo much better. Charlotte took it for a spin & said it sounds like a different car.

Much obliged for all the advice on here. Could have made a right pig's ear of it.