irregular 'clack' sound from front of engine? HELP

[shorty123]

Hi guys, havent posted for a while, ive noticed an irregular clack (mettalic knock) from the extreme front of my engine (4.0 serpentine late 1995)

It is not regular, like big ends, and doesnt appear throughout the rev range, and for that matter doesnt appear on overun at low revs like small end bearings... But if i pulse the throttle, at very low revs i hear this noise, its almost as if its in the cats, it that sort of sound (ball bearing in a tin can)

There has been no loss of performance, and the engine is not producing any nasty smoke, it has a genuine 52k miles on it also. idle is not over-lumpy.

Has any one got any thoughts, i need to get the car serviced so will get it checked out.

Thanks in advance for any help - Shorty

[poorpeet]

Loose/broken matrix in one or both cats?

[shorty123]

Thanks Poorpeet, i just took the car to the garage to check the engine under the lights, oil level is fine, and suprisingly clean. On further ivestigation, i am 90 % sure the knock is coming from one of the cat cans. Whilst rapidly pulling on the throttle assembly (causing the car to choke and pop slightly the knock can be heard) definately not an engine knock it seems...

Is the possibilty of a cat matrix loose or broken a costly repair? or is it non- life threatening?

Thanks again for replies!

[Corin Denton]

Hi Chris, not normally life threatening but will get worse, the monolith inside the cat is ceramic therefore the more that chips away the more gets stuck in the rest of the exhaust.
Worse case scenario is when the monolith turns inside of it's housing and if you can imagine it lets the gases through what is like a honeycomb structure, when it turns sideways it blocks the gases from escaping and loss of power. You stop!
The problem is with the cat at the front it does all the work as far as emissions are concerned for the MOT, you can remove the pre-cats with no effect but not the front one unless you have a very friendly MOT tester. I personally would ditch the whole assembly for some ACT manifolds (£1000) not sure what a replacement TVR part is probably about £400.
First thing to do is put a wanted on the PH classifieds as there are loads of people who have gone the ACT route and may have a bargain cat gathering dust in their garage.

Hope this helps.

Corin

[2 Smokin Barrels]

Might be as simple as a damaged alternator belt, or some debris caught in it? I've had that a few times.

[shorty123]

Corin Denton said:

Hi Chris, not normally life threatening but will get worse, the monolith inside the cat is ceramic therefore the more that chips away the more gets stuck in the rest of the exhaust. Worse case scenario is when the monolith turns inside of it's housing and if you can imagine it lets the gases through what is like a honeycomb structure, when it turns sideways it blocks the gases from escaping and loss of power. You stop! The problem is with the cat at the front it does all the work as far as emissions are concerned for the MOT, you can remove the pre-cats with no effect but not the front one unless you have a very friendly MOT tester. I personally would ditch the whole assembly for some ACT manifolds (£1000) not sure what a replacement TVR part is probably about £400. First thing to do is put a wanted on the PH classifieds as there are loads of people who have gone the ACT route and may have a bargain cat gathering dust in their garage. Hope this helps. Corin

brilliant, thanks corin, it seems quite minor at the mo, but will keep an eye on her, she will be laid up in my garage over the worst winter months so shouldnt get much use. will keep my eyes open for 2nd hand cats, was thinking of going down the carbon plenum and throttle upgrade route with ACT, may look at the cat replacements too, but not till the spring i guess.

thanks again!

[dlc]

The same sort of noise on my Chim (1995, Serp) last month was traced to the "idler" pulley on the opposite side of the engine from the alternator. The bearing had begun to collapse and the noise was due this, but it took a while to locate it as it sounded as it was from the front end. I was on route from Dundee to Aberdeen, so stopped of at a garage and got a suitable replacement for six quid and borrowed a spanner and and vice from the mechanic. I hope this helps you locate the noise.
Cheers Derek.

[shorty123]

dlc said:

The same sort of noise on my Chim (1995, Serp) last month was traced to the "idler" pulley on the opposite side of the engine from the alternator. The bearing had begun to collapse and the noise was due this, but it took a while to locate it as it sounded as it was from the front end. I was on route from Dundee to Aberdeen, so stopped of at a garage and got a suitable replacement for six quid and borrowed a spanner and and vice from the mechanic. I hope this helps you locate the noise. Cheers Derek.

Thanks Derek, I originally had suspicions about a pully, but since - it seemed more likely that it was in the cats, i wont overlook the pully though, and will have a prod around this w/e.

If it is a pully bearing, its gonna be a cheaper fix i guess which would be good.

[2 Smokin Barrels]

shorty123 said:

dlc said: The same sort of noise on my Chim (1995, Serp) last month was traced to the "idler" pulley on the opposite side of the engine from the alternator. The bearing had begun to collapse and the noise was due this, but it took a while to locate it as it sounded as it was from the front end. I was on route from Dundee to Aberdeen, so stopped of at a garage and got a suitable replacement for six quid and borrowed a spanner and and vice from the mechanic. I hope this helps you locate the noise. Cheers Derek. Thanks Derek, I originally had suspicions about a pully, but since - it seemed more likely that it was in the cats, i wont overlook the pully though, and will have a prod around this w/e. If it is a pully bearing, its gonna be a cheaper fix i guess which would be good.

Did you find the problem?