Time to say goodbye ?

Once the cat is out, if you find that the matrix has broken up, you need to ask your self where has it gone? The answer is it's probably in the rest of the exhaust down stream of the cat and is probably choking the flow through a muffler.
There are a few types of catalyst matrix one is a rock like ceramic honeycomb and the other is like a foil mesh honeycomb, this latter type is often found in high flow performance cats , but it is also found in cheap and nasty ebay rubbish from China, it can brake up and bits can do a excellent job of blocking the internal baffling of your muffler.
The former type is what is found in most OEM cat converters, it is more durable, however it to can brake up into little bits with age and vibration, these bits can rattle about in the exhaust system they may just block the exit pipe of the converter. or they can be finding themselves down stream also causing other restrictions, you may however be able to shake most of it out of your muffler if you're lucky.

What also happens is if the ceramic matrix can also over heat, then it can block up as it melts.
it can overheat due to excessive unburned hydrocarbons getting into it there can be many causes for this, such as dirty injectors, poor tune, ignition problems, etc. not to mention our old favourite: a blown head gasket!

Cat converters can also fail due to poisoning, leaded fuel can put a coating on the catalyst, preventing it from reacting, lubricating oils that use zinc and/or phosphorus additives will also poison a cat, as can silica which can find it way into the cat via coolant getting into the exhaust or the use of the wrong types of gasket sealants (most silicone types, there are some that are OK for use with cat converter equipped cars, it will state this on the packet, so read it!) I myself, prefer NOT to use silicone sealants, and in the rare occasions when I do, I apply them sparingly.

 



 

Thanks Cobber, there is always some useful takeaway from one of your longer pieces.
It really didn’t matter how many summers you have seen a Cobber knowledge nugget is always informative.
Now we have Christmas in the rear view mirror & with that grump subsiding, what are you feelings on the coming new year, is that still humbuggery?
M

In a nutshell...yeah and my new year resolution is to have no bloody stupid new year resolutions! 🤣

Good on ya mate!
My New Years resolution is to keep breathing, keep thinking coherently, keep walking, keep scrabbling about under the car, keep coming up with fresh ideas & putting them into practice.
That will do.
M

Had to cut the old exhaust out today which was a pain but got it done with new backbox and cat fitted. Upon proper investigation of the downpipe I could see it had been welded very badly at least twice in the past and had holes in the welds so I've done away with that and have another ordered.

I started disassembly on the engine to replace the camshaft cover gasket and when I was removing the coil packs was quite shocked to see one of the spark plugs come out with it.

That would explain the pop and the lack of compression up that A-Road. I took the plug off the ht lead and tried to screw back in but it span with very light torque. So whoever has worked on it in the past has knackered the thread and it's eventually just unwound on what it had and blew out.

I'm looking at a heli coil to rectify the issue. Has anyone done one of these before on a K ? What did you use/how did it go/what was the outcome ?

From the research I've done this evening these seem to be the trick (Save-A-Thread) > https://www.amazon.co.uk/Helicoil-5334-14-Thread-Thread-Repair

As a side note, the cam cover gasket that was already installed seemed perfectly fine. No Damage at all. Although there is evidence of oil leaking from that location so I put the new one on anyway. The new genuine MG Rover one I had seemed to have a porous material coating the metal unlike the one I removed which was just a standard sheet metal gasket.

Pretty much all 4 of the spark plugs were oily/sooty. No signs of wearing away or anything.

Thankyou to everybody for your help so far. Any advice as always appreciated 

I don’t have first hand experience with Helicoiling a plug thread, although I’m aware of it being done with great success. Of course there will be naysayers, but hopefully not within our community.
Obviously others are invited to add to this if there’s a divergence of opinion.
Cobb’s is usually an excellent bellwether on such things, I’m sure he will have words for us.
Please keep us informed of your progress, as you have noticed we are nosey buggers.
M

Yeah a helical thread insert should do the trick, I not had the need to do one on a K series engine but I've used them on many other engines.
So whilst I cant give you a guide tailored to the MGF/TF, I can give you a generic one.
Give me a little time to write one, I can probably do it today as it's pissing rain outside so I've got bugger all else to do today!
 it will be posted in the how to section for posterity, it will be for general thread insert needs with dedicated info for sparkplug threads.
I will post a link here when done.
 

Here is the link as promised: https://www.the-t-bar.com/forum/tooltime/99341-how-to-use-helical-thread-inserts-including-tips-for-spark-plug-threads
I've didn't put it into the How To's as  there is so much stuff it in there it's likely to be too hard to find. Seeing as it's really a tool specific how to I put it into ToolTime to keep it separate from the job specific MGF/TF Howv To's
I will in time do more tool specific how to's  which
I intend to place in ToolTime.

And I should do a tread on how not to bugger up  your spark plug threads probably tomorrow if I have time.

You are a good man Cobber.

TA22GT wrote:

You are a good man Cobber.
 

That's only when I'm not too busy being a bad man!

Thanks Cobber. Love to see it. Amazing work on the guide.

One question I have is a lot of people after tapping seem to be applying high temp sealant on the insert before screwing in which I didn't seem to see you suggest on the guide.

What's you're opinion on this given that you've done these on many an engine in the past ?

I never saw the need for it, indeed I would be worried that some sealant would get through the spiral of the insert and adhere to the thread of the bolt or spark plug as the case maybe, thus creating a problem undoing it as required in the future. Spark plugs would be a serious problem given that they are a consumable component and require regular maintenance. In fact I always use an anti seize compound on spark plug threads, regardless if they are screwed into inserts or not. the inserts are easy to remove and replace if they are ever loose or otherwise suspect. They might not be so easy to remove if they were sealed in.
And given the grease reside left over from cutting the spark plug thread i doubt the sealant would adhere to to thread in the head very well anyway.
I've never had a helical thread insert fail whilst the spark plug was in place. I have had one try and unscrew with the spark plug, and then I just replaced it. it wasn't one that had been fitted by me.