Rover 420 - Mark (RLBS)
I bought an old 420 (about 1995 I think) for my Brother in Law to use as a run about while he's visiting.

It had been standing outside unused for about 2 months before I bought it having been part exchanged. Its in excellent condition with no rust or accident damage and has a service history for its whole life. (boxes of receipts for everything, who has the time to keep that lot ?)

Yesterday the rear silencer box exploded. And I do mean exploded, it looks like one of those old joke cigars after they've gone bang.

I've had a new box put on the back which was no big deal, but the man said I needed to worry about why it happened, in case it happens again.

The box itself, from the outside, looked pretty new as does the whole system. It seems to have been fitted about a year ago. However, whatever ever the contents of that box would be, they had all rusted away.

The car revved and ran more freely than it did before it blew, and still seems to do so even with a new box back on.

The car doesn't misfire, and whilst I know that a misfire isn't always obvious, I'm pretty sure its not.

The exhaust fumes do not smell of petrol and the timing does not appear to be out; although that last is a little difficult to be sure about.

Was the back box just blocked and built up pressure, or is there possibly a more serious problem ?

I have only one requirement of the car, and thats that it keeps running until the middle of December. At that time it will be thrown away so I have no intention of worrying about any long term problems nor of spending any serious money on it.

Your thoughts would be appreciated....

Mark.
Rover 420 - SjB {P}
I would say that it can only really be either collapsed internals, or unburnt fuel reaching something hot like a catalyst, and then igniting.

Of the two, I think the latter would have been obvious as poor running (for example if one spark plug stopped working it would be immediately obvious).

This leaves the former, which seems more likely given that the car has stood for a while, with nothing to warm through and dry out the exhaust internals. An old colleague of mine suffered what you describe, and when they cut the apparently good nick back box in half, one of the internal plates had dropped out of place due to rust, and partially blocked a pipe.

I also had it happen to a much lesser degree on an old Austin Aggro 1750 Sport that I ran many years ago. Above 4500 RPM in third gear, the exhaust started to blow. Below this operating condition, it didn't. The cause was a rusted tailbox with loose baffles that had moved and partially blocked the system. When sufficient pressure built up, it escaped through the joint between the first and second halves of the system.

Horrid car!
Can't believe I ever owned it (albeit for six months).

Of course there is the less likely chance that some toe rag stuffed something up the tailpipe, too!
Rover 420 - Mark (RLBS)
So, reasonably safe to ignore it now its got a new box and not think it likely to happen again ?
Rover 420 - ShereKhan
I had the same problem with my previous car Rover 214 SEi mk2. The baffle just blew up on the rear box. Mind you the box only cost me £20 from a local garage and it ran for two years to the dot.
306 2.0 SE Cabriolet
Rover 420 - king arthur
If the car has been used for short journeys, or perhaps if it's been sitting around in the garage being started and stopped, the condensation from the engine won't have got dried out properly and will have rotted the box from the inside out. Check the Car-by-car breakdown, it's noted in there as a common problem on these.

Just take it for an "italian tune-up" and all will be fine!
Rover 420 - madf
I used to work for an exhaust manufacturer. I would agree with above.. but one other cause is the sound deadening (fibreglass) coming loose and blocking it - probably with help of rusty debris.

BUT you may have a problem with overfueling allowing petrol to condense in the back box and then ignite. I think the chances of that are unlikely but if it happens again:-)
madf

 

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