5 replies to this topic

[connorj]

So I had a problem with ECU in my mini and after posting on here a few days ago managed to diagnose the problem and the ECU is shortly going off to be fixed, all thanks to the guys on this forum. Since that problem was solved so quickly and helpfully I thought i'd post about another issue that's been bugging me.

 

I have a 1995 1275cc SPI mini sidewalk with a cat. I've had it for about 3 months and since I bought it has had a very distinctive knock. I don't mean a small knocking sound on the engine, I mean it sounds as if someone has just punched the bottom of the car. This happens when throttling off. The quicker you release the accelerator the stronger the knock. It doesn't happen however when you just dip the clutch.

 

My first thought was to remove the engine mounts as I know they can cause knocking, but they were fine, no wear at all. The knocking feels like its coming from right between the two front seats, just behind the handbrake.

 

I suspect the exhaust. Once the car was raised and I could get underneath it there were a few areas which I thought could be knocking. It is worth mentioning I firmly shook the whole exhaust system and there were no obvious contact points apart from where the exhaust exit at the rear hits against the bodywork but that's only with sideways movement.

 

I'm guessing that someone took this over a speed bump too fast and the exhaust has shifted back and up.

Would be great to hear what you think and whether anyone else has had this problem!

 

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Whole system, standard?

 

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First box clearance ( the upper section that is resting on is the handbrake "y piece" seperating the cable to each wheel)

 

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Bent back too far?

 

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Rear box clearance (side)

 

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Join at rear of cat

 

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Bubble joint clearance

Edited by connorj, 23 July 2014 - 02:00 PM.

[6joshh6]

You want to look for play vertically if it occurs when lifting off as the engine shifts when you lift off, causing the exhaust to move up and down. I had a poorly fitting exhaust on my mini when I bought it which caused banging on the overrun and adjusting the angle at the front made little difference. I looked underneath and saw that the drivers side rear seatbelt bolt protruded about 3/4 of an inch into the exhaust tunnel and was knocking on the silencer. In the end I just shortened the bolt so that there wasn't as much excess length and that solved it for me. 

 

Hope this helps!

[Carlos W]

Did you check the engine steadies as well as the engine mounts?

[RedRuby]

It certainly looks as though there are a number of areas on the exhaust that could be causing the problem, particularly the cat which is not sitting as flat as it could and the box on to the handbrake bracket. Carlos has mentioned the engine steadies but there is also the mounts for the rod change gear linkage that may be part of the problem.

[greenwheels]

You want to look for play vertically if it occurs when lifting off as the engine shifts when you lift off, causing the exhaust to move up and down. I had a poorly fitting exhaust on my mini when I bought it which caused banging on the overrun and adjusting the angle at the front made little difference. I looked underneath and saw that the drivers side rear seatbelt bolt protruded about 3/4 of an inch into the exhaust tunnel and was knocking on the silencer. In the end I just shortened the bolt so that there wasn't as much excess length and that solved it for me. 

 

Hope this helps!

Ditto - had that on my estate (ok it's not an SPI) worth checking as you say 'just behind the handbrake'.

[connorj]

Thanks for all your replies guys! Turns out to be the cat banging on the tunnel, it's broken through the heat shield but I cannot find one of these online for sale. Think I will have to wrap it into thermoprotective material to pad it out.