Budget de-cat and centre box removal.
You will need;
Length of 60mm outside diameter steel tubing. I bought 2m length from my local factor. Under £15.
3x 2,1/4 inch exhaust clamps. £3
Steel bracket. £1 . See pics.
Spare 13mm nut/washer.
Exhaust jointing paste. (for belt and braces gas tight seal)
WD40.
Hacksaw (not junior!!) with a new blade ;-)
Hammer or rubber mallet.
Old long screwdriver and/ or chisel
3/8 drive ratchet
13mm socket.
13mm ring/open end spanner.
12mm ring/open end spanner.
Three cups of tea.
Sense of humour.
First, carry this out at your own risk, its your van/bus!. I’m not a professional mechanic. This work was carried out without harming any animals.
Boring but I have to say it. It is ESSENTIAL that you do not work underneath a vehicle without placing it on axle stands placed on a firm base , i.e.hard tarmac/concrete. As well as two axle stands placed under vehicle, one under rear jacking point, one under engine crossmember directly underneath rear wishbone bush , I had trolley jack placed with light pressure under front jacking point. The wheels were not removed either as it wasn’t necessary to carry out the work. Please be careful. Exhausts are heavy!!. I’m assuming you have decent tools, i.e not a socket set free with every £5 of diesel purchased.
I removed my centre box because I wanted to retain the standard back box but improve gas flow. If you just want to punch out the cat it may prove tricky to remove just the cat pipe as you will need to separate it from centre exhaust section by pulling forward. I didn’t investigate the practicality of that but I would imagine it’s a bit tricky. You may even have to remove the whole exhaust system. There may be another forum member who could comment on that. I’m no photoshop guru so pretty coloured pointers are out!!.
Ok, so I’ve jacked up my van and placed it on axle stands. Pic A is centre box in situ. pic 1 is of the cat viewed from underneath with me on my back. You cant miss it, it’s a bulbous cylinder at the front of the exhaust system set at about 75* angled upwards toward the rear of the engine. At the top you see a triangular bracket connected to the exhaust downpipe which also has a triangular bracket. They are connected with three bolts that have 13mm heads and, on my van, 12mm nuts. Soak them all in WD40 or similar. I used 13mm socket on a 3/8 drive ratchet on bolt heads and 12mm spanner on nuts. Apply firm pressure to undo but be patient. They’re not done up that tight, they’re just a bit rusty!. DON’T strip the nuts/heads by going at it hammer and tongs. They will crack and come undone if you’re sensible. If they don’t crack fairly easily soak with WD40 again and leave for longer. Try again.
Once you’ve removed them remember there is a copper gasket between the brackets. Clean for re-use. I cleaned up and re-used my old nuts/bolts for re-assembly because they were in ok condition.Now as I was removing centre box but leaving centre section pipework to sleeve my replacement pipe over the next bit is a bit basic and laborious. Get your yourself comfortable under the van and cut through the exhaust pipe with the hacksaw. I cut through about 80mm from the back weld. That point was the easiest to cut through. You MUST cut through the pipe as close as you can to the front weld to ensure maximum straight length to sleeve over. Ensure you don’t saw into your van chassis or any other components!!. Make sure your two cut pipe ends that you will sleeving are clean and are free of rust etc. Get from under van and pull away centre box…. Unhook cat pipe mounting lug from rubber bracket. (you cant miss it..its holding the pipe up!!) You should then able to carefully pull cat pipe away from van. There is a protective guard to get around but its very straightforward. Pic 2 shows the underneath of the van with the centre box removed. Pic 3 shows the cat as viewed from the top. You will see it is filled with the inside of a giant Kit Kat (ha ha..). Methodically chip away using mallet and old chisel to remove structure and wadding, Pic 4. AVOID inhaling the dust. ( there wasn’t a lot of it, but better safe than sorry !) The further you get, the bigger the lumps it disintegrates into. Eventually (about 15mins) you will be left with a nice empty bulb that just HAS to improve gas flow!! Make sure you don’t leave any debris from the operation in the rest of the cat pipe. See pic 5.
Cut yourself 620mm of steel tube using hacksaw (der) pic 6.
Cut 6 to 8 slots approx 50mm deep into steel tubing from ends that allow tube to compress on to original exhaust tube when clamped. Sorry forgot to pic that.
Re fix the cat pipe in place. Don’t forget your gasket.
Place 3 exhaust clamps loosely over your steel tube and get back under your van taking your jointing paste, 13mm spanner and 13mm socket (you wont need spanner if you have a deep 13mm socket) and a clean cloth. Now I covered the sawn ends of original pipes with jointing paste. Not strictly necessary but I wanted to make sure I had no gas leaks especially as end of de catted pipe had a limited length to sleeve on to before it bends. I then slid my new length of pipe over and down rear pipework far enough to allow me to slide back up to, and on to, my front pipework. (its obvious when youre doing the job!) Push new pipe on to front pipework as far as possible. Smooth and clean off excess jointing paste from both ends. I put two clamps on front end. First clamp placed carefully at the very end of new pipe, second clamp butted up to it(still on new pipe of course!!) but offset to allow nuts to be tightened. Third clamp is tightened on rear end of new pipe near end of the slots you cut. Nearly done!! See pic 7. Now the whole set up is very rigid but I still wanted to hang the new section off of original rubber bracket. So I just looped a bracket I could bend through rubber mount and bolted it on to thread on exhaust clamp. Obviously there are other solutions to this. Start up engine and let warm up slowly to harden exhaust paste. Check for leaks. Job done.
WARNING. I had quite a lot of blue smoke for a while and the exhaust fumes were very pungent. This clears as disturbed soot/carbon/junk is burnt away.
Sorry if I’ve missed anything or preached to the converted. Feel free to add to improve thread.
I would not consider this modification unless I was Project Powering.
PIC A
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MG]PIC 5
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)as it was impractical to cut it out of the system. Replaced the centre box with sleeved 60mm steel tubing. I have pics of the whole operation and can do a step by step if it is of use to anyone. The whole exercise comes in at less than £20. I cant run to a full stainless at the mo!
