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MG MGF Technical - Exhaust removal

Does anyone know how to remove an exhaust which has been in place for three years?
I have bought an SP performance exhaust with the apparently naive intention of fitting it myself. After gaining reasonable access to the underside of the car (a feat in itself as the ground clearance wasn't enough to get the car on the lift I intended using), I discovered the exhaust retaining nuts are, unsurprisingly, solid lumps of corroded steel. The easy answer would be to cut or grind off what's left of the nuts and the studs they are attached too but how do I then go about fitting the new exhaust with no mounting studs or would I have to drill out the entire stud in order to use bolts ?
Finally how did this blindingly obvious maintainence nightmare fail to be spotted by the boffins who designed the car in the first place?

True of just about any car you'd like to name these days. Short of using special materials at considerable expense, the heat and proximity to the road will always lead to this. The only answer is to apply heat until almost cherry red and then put a socket to it WITH CARE. Easier once you have some experience of how it feels just *before* a stud shears ! I've done an exhaust swap for an F'er from Surrey, if you are in North Ham,pshire you could bring it over if you are stuck.
David Smith

As an aircraft engineer I have plenty of experience of 'almost'shearing bolts and studs!
How does one heat such an inaccesible area without setting fire to the rest of the car (come to think of it no bad thing in this instance!) and anyway the threads are totally gone, corroded away to ragged metal.

No consolation now, but MS does what he calls his "KatKit" which is basically a set of 6 blanked off alloy nuts to replace the ones either side of the cat. These nuts effectively sheath the exposed thread & protect them from corrosion. Such a simple idea and incredibly effective for aroung 15.00 UKP - i think that all F's should be sold with these as standard.

Fitting an aftermarket exhaust to an F older than 6 months (sans-KatKit) is not a job for the in-experienced. Having fitted numerous MGF exhausts in my time i can say that the dreaded "rusty nuts" syndrome has been the bain of my life for some time. There are 3 potental solutions to the problem, the first is the heat them up routine described above. Not for the faint hearted, this method requires carefull use of a blow torch, nerves of steel, welding gauntlets and either a hydraulic ramp or inspection pit as it needs plenty of room. Method #2 depends on the severity of the corrosion and basically involves spending an entire day with some WD40 & intermittantly working it into the thread. Older cars will not find this method at all effective, but say, <1 year old, then you may have some luck. Lastly, shear all the threaded studs off of the cat, drill them out and replace with stainless steel nuts and bolts. Drastic, but guaranteed to work!!

SF (with a KatKit on my cat & SS nuts and bolts for the cat bypass when fitted!)
Scarlet Fever

(1996 VVC Fitting a Daytona SS Exhaust) I have just managed to remove 2 of the higher nuts from the right side by using a blow lamp and WD40, I only used the blowlamp after the WD had soaked in and dried off. DO NOT use a blow lamp on any area that still has wet WD40 on it as will go up in flames.
As I am a plumber I have a quality Blowlamp that can be tuned to a neat small flame, so it was quite easy for me to heat the nuts. The lower of the 3 nuts was not going to shift as this was just a lump of rust, so I managed to saw the side of the nut off,then knock the nut away. I have now fitted 3 of Mike Saturs nuts to my car. I still have the 3 from the left side to do yet. Can remove the exhaust and the cat in one piece and then work on getting the other nuts off as they are all lumps of rust ?



Yes, by undoing the nuts prior to the cat, you can remove both at the same time to make working on the "post-cat" nuts easier.

Scarlet Fever

Luckily I have access to a hydraulic car lift that gets the car clean off the ground. To clarify the situation with my car, the exposed section of mounting studs are totally corroded to the extent they do not even appear to have any thread on them whatsoever. So I guess it's out with a cold chisel tomorrow!

Thank's Scarlet, That's put my mind at rest on that one.

What I did was to get my dealer to fit the SS cat nuts to the car. I then later got an SP and fitted it my self without problems. So you can get someone else to do the hard part and do the rest yourself. It would not cost too much to get a dealer to fit the whole thing for you anyway.

The FAQ was my guide, but it is not the first exhaust I have changed in my life, the easiest, but not the first. I managed to get just enough room underneath with a trolly jack and axle stands. The easier way is to use ramps, I just did not have any.

You also need a couple of gaskets for the new exhaust, quite cheap from an MG / Rover dealer.
Tony Smith

For the exhaust tests, we had a devil of a job removing the exhaust on my car. For better access, we removed the rear bumper and had the car up on ramps. Usefully, the guys who owned the RR also had an oxy-acetylene torch, so job done!


PS Don't mention *almost* shearing cat bolts ;o)
Rob Bell

What do you mean *almost* ;-)

Scarlet Fever

I had a look at putting my newly aquired, second hand Daytona on over the weekend just gone. As with Bob, this exhaust I think has been on since the car was new (in my case 5 years). Anyway, I'll try and get my local ATS to do it this weekend, same time I get the tracking done.

Why spend hours trying to do it yourself when you can pay someone to do it. erm.. that is if you have the money to pay them. Sh*t, there's the hole in my idea. Grrr.

Steve Childs

You can always try the bolts before the cat and then remove the whole lot in one piece and have a go.


*almost* in the sense that Amercians *almost* lost their spy plane ;o)
Rob Bell

air filter clarification is called for here i think...

The exhaust system is divided up into 4 parts, the exhaust manifold, the flexi-pipe, the catalytic convertor and the rear silencer. The manifold has 4 threaded studs & the flexi-pipe is attached with mild steel nuts. These are located about a third of the way up the block and are therefore pretty well protected. The flexi-pipe runs under the sump & then turns through 90 degrees to mate with the catalyst. The catalyst has 6 threaded studs (3 each end) & the flexi-pipe & the rear silencer attach to these with (again) mild steel nuts. These nuts are situated close to the ground and are exposed to the elements. These are the nuts that go rusty & are replaced by MS's KatKit. To remove the rear silencer you need to remove the three nuts "post-cat". The alternative suggested by Alan involves removing the three "pre-cat" nuts and removing the cat and silencer together, thus making working on the three "post-cat" nuts easier.

There is a third alternative, that of separating the flexi-pipe from the manifold. Certainly you will have an easier job with these four nuts, however, manouvering the three components (flexi, cat & silencer) together to remove the complete assembly might prove impossible without first removing the rear bumper. Therefore, for me at least, this is not a viable alternative.

The upshot of all this is that REGARDLESS of which method you choose, eventually you will HAVE to remove the three "post-cat" nuts to fit a sports rear silencer. Furthermore, the three "pre-cat" nuts are likely to be in just as bad a state as the "post-cat" ones, given that they are essentially, in the same exposed location.

This is why i am such an advocate of Mike's KatKit, it is a very cheap & effective solution to an incredibly annoying (and potentially expensive, should damage occur to the cat) problem. I cannot recommend these enough & for me, are the best thing you can buy for your F,
Scarlet Fever

Well, a long day yesterday but teh SP system is now in place. Only eight hours work to get the old system apart!
Removing the exhaust and cat complete from the car was fairly straight forward. The upper nuts where the cat joins the manifold pipe were still in reasonable enough condition to just undo after a good soaking with WD40, and the lower one was ground off using an angle grinder.
With the exhaust and cat removed from the car the two were then separated, again grinding off what was left of the studs and nuts.
With the cat now completetly removed from both car and exhaust, it was possible to grind down the remnants of the four corroded studs (the three at the exhaust end and one at the manifold end) and then attempt to drill holes to replace the studs with bolts during reassembly.
This was what took the time.
The heat from the cat had clearly tempered the already hardened steel such that we got through six drill bits doing just four holes. A cobalt drill bit or similar is the way forward for this job. I searched everywhere and just could not find one of a large enough size (10mm).
Once the holes were drilled, we could reassemble the cat and new exhaust and the car was ready to go in under half an hour.
So.....moral of the story...the day after you collect a new MGF, fit Mike Saturs KatKit!

A good way to drill out hardened steel is to use a masonary drill, we do this quite regularly at work to drill through hardend dies (press tools). A toughend exhaut flange/bolt should be somewhat easier I would have thought.
Paul Lathwell

Not so much fun, but take the new exhaust to a friendly Exhaust shop and ask them to fit it for a tenner say?
They will use oxy-acetylene torches to get the old one off
John Thomas


Are you joking or does a masonary drill bit really work on hardened steel?


This thread was discussed between 30/03/2001 and 17/04/2001

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