Well, I did it.
Removal:
Run the van up some nice bits of 9x3 making ramps with old wheels, front wheels up on this about 300mm off ground - a bit more would have been nice.
Undo the single "U" bolt holding the cat. section to the mid section.
Undo the 10mm nuts holding the cat. section to the inlet manifild - holding the bolts at the other wnd with a 10mm ring spanner. A 1/4" drive with a nice 300mm extension and ratchet would have been useful, a 1/2" one with a very slightly shorter extension sufficed. Awkward. Nearside harder to get at than O/S.
Pull off rubber hanger of mid section - O/S, just forward of rear wheel.
Drop cat. section in preparation for separating from mid section.
Gently ting ting ting wiggle pull ting wiggle pull wiggle push fit joint of cat. section and mid section with a hammer - careful not to distort pipe. After five or ten minutes, joint separated. Mid section seems to be galvanised & in good condition. Old cat. section cracked nearly all around at weld upstream of cat., lucky it didn't fall off on the road!
Note - getting the flange (manifold joint end) of the cat. section past black anti-roll bar (I think) a bit tight. Could possibly "unhang" tail exhaust section box as well as middle for more play.
Check new section - OK, but some differences from manufacturer's one - cat. ends simple cones rather than flared ones - mfct'rs had fatter expansion chamber downstream of manifold, new one has pipe of even cross-sectional area.
Observation: Why not make the whole downpipe and cat. section out of stainless, rather than just the cat.?
Replacement:
Check bits. OK.
Check and clean manifold end. Tap out rusty steel cups using drift and care. Superficial clean of surfaces. Remove old black conical compressible gasket. from manifold flange.
Clear out end of mid section, annoint end of cat. section and inside of mid section with 3-in-1.
Push in cat. section to mid flared mid section. N.B. check that nothing's fallen into the front end of the cat., gravel or whatnot.
Push on new compressible gasket (locates easily on manifold flange, but does not fall off - great!).
Warning: notice on cat. packaging, do not use any exhaust cement upstream of cat. as this could damage your cat. and will invalidate the warranty anyway.
Note: On cat. packaging, notice: ensure reason for cat. failure determined before fitting new cat. Simple on mine: welds on cat. section rusted and cracked. Whole thing about to fall to pieces.
Offer up flange on cat. section to manifold. Hold gently with jack, or preferably board sticking out at right angles to body on O/S over fulcrum of blocks, weight to balance weight of cat. on outer end of board.
Fit retaining bolts on manifold. Awkward. 1) Bolt head end through 2) Retaining cup, fit through manifold holes in flange, through exhaust flange. Below exhaust flange 3) Fireproof washer, 4) Spring, 5) cup washer, 6) nut.
Note: New bolts were shorted than old. New springs were shorter than old. New nuts ordinary M6 by the look - old ones cone-ended lock nuts. I re-used the old bolts, springs, locking nuts, due to difficulty in fitting new shorter bolts/springs with new fatter conical exhaust gasket. I should think that the new gasket will settle, allowing fitment of new bolts if desired.
Give the exhaust a wiggle when progressively tightening manifold bolts.
Re-fit mid-section rubber exhaust hanger.
Re-fit and tighten "U" bolt pinching mid section onto cat. section. Give the exhaust a wiggle as progressively tightening to ensure all lined up properly and strain-free.
Run van off ramps. Go for test drive, gentle 8 miles to warm up new cat. for the first time.
Beer time.
