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MG MGF Technical - Exhaust - Cat Studs

Be aware that the studs in an original catalytic converter will not press out. If you break one (as I have) the only option is to drill it out in order to replace with a nut and bolt.

I am told the studs are a flow fit - inserted by a machine that literally melts the housing as the stud is pressed home. The metal flows into a waist on the stud and thus there's little chance the stud will move in any direction ever again.

Drilling out a broken stud at the "engine" end of a cat still attached to the exhaust is a challenge. Due to the proximity of the silencer box, there's limited room to get the drilling equipment in line with the remains of the stud.

I took the entire exhaust+cat assembly to a machine shop with a milling machine. Using a slim extended chuck, a small drill introduced a pilot hole for a 10.5mm drill to follow and the job was done in a few minutes. However, mounting the cat on the rear of the mill's table required some special extension clamps to be deployed and the mill turrent was swung back to line up it's drill to the broken stud. The exhaust+cat is quite heavy and "hanging" the assembly from the extended clamps on the mill table is not feasible - human support (or a box would do it) is needed to keep the work steady during the drilling out procedure. Setting up took most of the time - about 30 minutes in all.

Jeff
J Lennon

Jeff that's always been the problem for anyone replacing an exhaust. Mike Satur's Cat saver nuts are a good idea since the closed end stops the stud rusting and makes it easier to get off again in the future.
David Clelland

Hi Jeff,

I took out my "cat" the other year and fitted a bypass tube. To remove the "cat" I used a dremel cutting tool to cut through the nut and stud. However an easier option, if you have one, is to use one of those "finger" grinders to grind through the nut. Cut through the offside only then you can remove the "cat" and silencer together. You can now more easily remove the "cat" from the silencer.
I had used an angle grinder to remove the head of the stud thinking I was going to need to drill out what remained of the studs, however, a few blows with a club hammer I was able to knock out the studs with ease. The studs were knurled. I supported the flange(s) on the edge of the vice jaws.

My F is an early 1996 mpi model.

I can now refit my "cat" with s/s bolts and MS "cat-saver" nuts (that the bypass tube is fitted by)should I wish to do so.

It's strange that you could not do the same.

Hope this helps anyone else in the future.

willyphixitt
W A Nixson

Thanks all for your input - and I agree that using cat saver nuts over the full length of the studs is a good way to go in future.

My broken cat stud was stuck so fast in the flange that I snapped a substantial "G" cramp in a vain attempt to press it out - hence the machine shop solution. Must have been a Far Eastern origin "G" cramp!

It's interesting Will, that stud fixings vary - yours knurled and mine metal flowed. I'm told by a local breaker that old cat's are worth good money and post 2000 worth less. No doubt to do with the amount of semi-precious metals inside and explains why this breaker will never sell a s/h cat!

Jeff

J Lennon

This thread was discussed on 25/07/2009

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