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MG MGF Technical - Exhaust - various questions

Hello folks,

I need to replace the strap that goes around the silencer on my 1995, 74,000 mile 1.8i and consequently am looking at what needs doing to the rest of the exhaust system. An archive search suggests that a lot of people leave off this strap, particularly with after-market systems, but I am told that it is needed to hold the downpipe in position and prevent undue movement of the flexible section.

So, the questions:

1) Since I've got to take the cat nuts off on one side and suspect that these will need to be ground off, I wonder if I may as well replace the (probably original) catalyst. Anyway of telling before removal whether it is knackered?

2) The woven mesh around the flexible section of the downpipe has completely broken away at both ends and the downpipe looks pretty rusty (no apparent blowing). The recommendation (before inspection) is that this will definitely need replacing as the inner wall of the flexible section is likely to be on its way out. Any experience?

PS: the bracket securing the top of the downpipe to the engine is now part Rover number WCU 100990, in case anyone needs one.

3) If the cat has degraded and parts of it have lodged in the rear box, I may need a new silencer as well! Has anyone been able to diagnose this from observations when driving and then had it confirmed when the system was taken apart? A loss of power would be indicated, but I seem to be fine.

4) Other than cat saver nuts, any bright ideas for improving the system without fitting a performance system (too expensive for me)?

5) Finally, out of curiosity, it seems from the archive that early cars were fitted with SS exhausts and later models were not. Did anyone confirm exactly when this change occurred (not that with VIN 525, I need worry)?
C Golvala

With regard to the CAT don't grind off the bolts but do grind off the nuts.

If you have a bit of the bold left protruding from the CAT it is then possible to push out the stud using a vice, socket and a long extention bar. When the old studs are out you can them simply use 6 new SS M10 x 40mm nuts and bolts to put it back on the car.

I did this on my 1998 1.8i ~ the CAT now in the garden shed (ready for the next MOT) and a CRP is on the car. The car still has the standard back box, for now, but the sound is better IMHO.

FYI the rear box looks OK, but it is starting to go on the top LHS (looking from the rear). So it will not last for ever.

My back box strap has also rusted away and I do not have any issue running with out it, but I do have the JanSpeed 4-2-1 manifold fitted which has a very short flex section, only 4" long.

Hope this helps.

Steve Ratledge

I think it should be said that anybody who gets an F should get rid of the original exhuast. You miss so much by not doing this.

....sorry is this the darkside calling again?
Neil

Quite a comprehensive question list there! LOL

>> 1) Since I've got to take the cat nuts off on one side and suspect that these will need to be ground off, I wonder if I may as well replace the (probably original) catalyst. Anyway of telling before removal whether it is knackered?<<

The cat is almost certainly going to be in perfectly good, serviceable condition. The K-series was designed to pass emissions regulations WITHOUT recourse to a catalyst, but legislation changes made them compulsary irrespective of whether this is needed or not.

An indication of this is two fold:
1. We have a 13-year old metro with 100,000 miles on the clock, and it passes the MoT, no problems
2. Some folks have reported that their cars have passed MoT emissions tests even without the cat fitted!

So the point is, the cat is not worked all that hard.

If, however, the cat makes a rattling sound when removed, indicating that the matrix has fallen apart, then yes, it'll need replacing.

>> 2) The woven mesh around the flexible section of the downpipe has completely broken away at both ends and the downpipe looks pretty rusty (no apparent blowing). The recommendation (before inspection) is that this will definitely need replacing as the inner wall of the flexible section is likely to be on its way out. Any experience?<<

Difficult to know how much life will be left in it. Could be loads more: the woven wire mesh is only there as a protective covering, and has no structural job to perform. Good second hand items can be purchased cheaply from the MGFC as and when yours does eventually give up the ghost.

>> 3) If the cat has degraded and parts of it have lodged in the rear box, I may need a new silencer as well! Has anyone been able to diagnose this from observations when driving and then had it confirmed when the system was taken apart? A loss of power would be indicated, but I seem to be fine. <<

A rattle is the only indication on the road. When taking your system apart, it would be immediately apparent if there was a problem with the matrix though.

>> 4) Other than cat saver nuts, any bright ideas for improving the system without fitting a performance system (too expensive for me)? <<

If you are talking about performance gains, then have a look at the welds on the inside of the exhaust manifold. They're a menace! They radically reduce the inner diameter of the pipe, and a quick clean with a tungsten carbide cutting bit will weap some cheap rewards :o)

>> 5) Finally, out of curiosity, it seems from the archive that early cars were fitted with SS exhausts and later models were not. Did anyone confirm exactly when this change occurred (not that with VIN 525, I need worry)? <<

Not sure, but I'd guess from the introduction of the 2001 pattern exhaust system, as all the components of the system, from the manifold to the back box, were modified at this time.
Rob Bell

VIN 525!

Blimey, could this be the earliest F on the board? (not counting Mike Satur (VIN 500))

Just curious.

FTR - SF = 4240

SF
Scarlet Fever

How do you get the vin no from the long no??
MW

>>My back box strap has also rusted away and I do not have any issue running with out it, but I do have the JanSpeed 4-2-1 manifold fitted which has a very short flex section, only 4" long.<<

I am in the procese of having a full Janspeed sytem fitted (inc manifold).
It was supplied with a strap, so Janspeed clearly feel there is a need for it. This could be down to the fact the flexy section, well, isn't very flexable and prone to braking after only a short time (Just ask Kingsley ;) )
Steve White

Thanks all. For the curious, VIN 525 makes mine the 275th car produced and I gather that the first 100 or more were turned into Japanese cup racers since the quality was not up to scratch. (MW the long number is the VIN and I'm just quoting the last six digits: 000525). Mine was a Dutton Forshaw demonstrator at the start of her life, which may or may not have been a good thing, but she keeps bringing a smile to my lips.

Rob, the list of questions approach is just 'cos I'm a lawyer - it brings a semblance of order and knowledge to things. Note I said "semblance"!

It looks as though dismantling the system and giving it a shake is the only way to tell for certain. I have some exhaust knocking sounds on start-up and hard acceleration, but nothing definitively like a death rattle. This means that my bank balance could be anything from £100 to £600 lighter when we're done. Interestingly, I suppose the change to mild steel explains the low cost of rear boxes but it will be a shame to replace the original (and none too rusty, Steve R) silencer if it has been damaged by a degrading cat. Nice to see some support for the oval bracket, thanks Steve W.

I'm really not looking to upgrade for various reasons, but if the downpipe comes off, are the welds in the manifold reachable from there or are they at the other end?

Thanks as always for the instructive responses.

Cheers

Chaz
C Golvala

Is it possible to buy the straps as a seperate item? If so can some one supply the part No.?

Thanks
Steve Ratledge

Steve

Yes, you can buy the strap on its own...

RWCU100870 EXHAUST STRAP ASSEMBLY £ 12.06 (Jan 2002)

Tony
Tony

This thread was discussed between 28/04/2004 and 05/05/2004

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