Technical Loud knocking/rattling after replacing engine mount

[WildFeraligatr]

Hi gang

I recently replaced the lower rear dog bone engine mount on my 500. I had to remove the middle exhaust pipe off the catalytic converter to actually get to the bolts, so I've refit that too.

Since doing all this, there's been a really loud knocking/rattling coming from under the car when driving around. I lifted it up and found the exhaust had slipped back - so I refit it and the same thing happened again. Did it again and did the U-bolt clamp up REALLY tight, left it overnight for the threadlocker and exhaust paste to settle, and it's still doing it. I've not jacked up the car yet to have another look because I'm also having issues with my Panda and frankly I'm a bit knackered today.

One thing I did notice is that there are slots running up the pipe of the cat, which, since replacing the engine mount, the exhaust no longer fits over. I've sanded it down, checked for blockages on the inside of the pipe, but it just won't budge any further up.

The engine mount bolts are torqued to spec (130nm to the body and 80nm to the gearbox) so I don't think this is the issue.

Any advice would be appreciated, but I suspect where the engine mount was very loose before, that either gave me more clearance to get the pipe onto the cat - or I just did it before I reconnected the rear muffler so I had more clearance there.

Posting this in case I've missed something completely stupid and obvious, or if anyone has done this before and can give any advice

 

[Ralf S.]

It could be that the engine mount is now holding the engine (and hence the manifold) in a different position... further forward by the sound of it.

If you have managed to separate the exhaust (the flexi section back) from the manifold/catalyst section then I would take the whole exhaust off and then re-hang it. If you have the exhaust rigidly mounted, then it may be vibrating backwards, away from the front pipe. Fit the exhaust to the front pipe while there's no other tension on it, and then re-hang it. It's a good time to look at the hanger rubbers too.

It could also be that the exhaust was trimmed to fit onto a pipe that was too far rearwards and the exhaust is not "too short"...? If there are cut marks on the end of the exhaust that might be a clue.

Failing everything.. look on eBay for an exhaust connector sleeve that you can fit into the system to make it longer, although it might be more cost-effective to just replace the exhaust pipe, if yours is looking hacked about or shabby.


Ralf S.

 

[WildFeraligatr]

It could be that the engine mount is now holding the engine (and hence the manifold) in a different position... further forward by the sound of it.

If you have managed to separate the exhaust (the flexi section back) from the manifold/catalyst section then I would take the whole exhaust off and then re-hang it. If you have the exhaust rigidly mounted, then it may be vibrating backwards, away from the front pipe. Fit the exhaust to the front pipe while there's no other tension on it, and then re-hang it. It's a good time to look at the hanger rubbers too.

It could also be that the exhaust was trimmed to fit onto a pipe that was too far rearwards and the exhaust is not "too short"...? If there are cut marks on the end of the exhaust that might be a clue.

Failing everything.. look on eBay for an exhaust connector sleeve that you can fit into the system to make it longer, although it might be more cost-effective to just replace the exhaust pipe, if yours is looking hacked about or shabby.


Ralf S.

Hi Ralf - thanks for the reply

The middle pipe and muffler are both only about a few months old, same with the rubber hangers as I replaced them all myself as part of my project to get this car back on the road I didn't trim them myself at all.

I suspect I'll have to take the middle pipe off the muffler, put it all the way forward on the cat, then clamp it down and reattach to the muffler again.

I wonder if maybe the front heatshield is knocking now because of the engine being a bit further forward - although the noise definitely sounds like it's coming from underneath i.e. where the engine mount/exhaust are

 

[Ralf S.]

Hi Ralf - thanks for the reply

The middle pipe and muffler are both only about a few months old, same with the rubber hangers as I replaced them all myself as part of my project to get this car back on the road I didn't trim them myself at all.

I suspect I'll have to take the middle pipe off the muffler, put it all the way forward on the cat, then clamp it down and reattach to the muffler again.

I wonder if maybe the front heatshield is knocking now because of the engine being a bit further forward - although the noise definitely sounds like it's coming from underneath i.e. where the engine mount/exhaust are

You can also try grabbing the silencer and shaking it from side-to-side to see whether it hits anything. The exhaust should have very little movement once it's in place but it could be the pipe is touching the body over bumps.

The Younger Mrs S. Cinquecento had a pattern mid-section pipe that had a horizontal S bend in it, to go around the fuel tank... but it was bent too tightly so it didn't have enough clearance. Unless it was positioned "just right", it would bump the fuel tank.

500 is a simpler system.. more or less a straight pipe, but it curves over the subframe and the silencer hanger needs to be in good condition to keep it under control. On ours, the silencer hanger had a habit of moving off the prong, until I put a cable tie around the rubber, to make it "firmer".


Ralf S.

 

[WildFeraligatr]

You can also try grabbing the silencer and shaking it from side-to-side to see whether it hits anything. The exhaust should have very little movement once it's in place but it could be the pipe is touching the body over bumps.

The Younger Mrs S. Cinquecento had a pattern mid-section pipe that had a horizontal S bend in it, to go around the fuel tank... but it was bent too tightly so it didn't have enough clearance. Unless it was positioned "just right", it would bump the fuel tank.

500 is a simpler system.. more or less a straight pipe, but it curves over the subframe and the silencer hanger needs to be in good condition to keep it under control. On ours, the silencer hanger had a habit of moving off the prong, until I put a cable tie around the rubber, to make it "firmer".


Ralf S.

I don't know if you were secretly looking at my car but you were spot on - one of the rubber hangers on the silencer had fallen off the chassis so the side was just dangling there.

Strangely the rubber hanger I got had holes in but they were closed off, so I've jabbed a screwdriver through them to make sure it doesn't come off again

 

[WildFeraligatr]

FFS - just taken it out again and the knocking is still there. Admittedly it's a lot fainter now, but I'm hearing a big knock when i change gear between 1st and 2nd (ie when there's a bit more strain on the engine mounts). The new mount looked solid when i installed it but I'm less sure now...

 

[The Panda Nut]

Is the new part the same length as the old one. Id be suspicious unless its genuine Fiat.

 

[Mike1alike]

I wonder if maybe the front heatshield is knocking now because of the engine being a bit further forward - although the noise definitely sounds like it's coming from underneath i.e. where the engine mount/exhaust are

The heat shield is bolted to the CAT, so it's not that. Anyway, I'm sure the cat didn't change position.

 

[Mike1alike]

I don't know if you were secretly looking at my car but you were spot on - one of the rubber hangers on the silencer had fallen off the chassis so the side was just dangling there.

Strangely the rubber hanger I got had holes in but they were closed off, so I've jabbed a screwdriver through them to make sure it doesn't come off again

FFS - just taken it out again and the knocking is still there. Admittedly it's a lot fainter now, but I'm hearing a big knock when i change gear between 1st and 2nd (ie when there's a bit more strain on the engine mounts). The new mount looked solid when i installed it but I'm less sure now...

Surely you left the middle pipe hanger unhooked into the rubber hanger. That has one too, towards the back of the car, towards the silencer.

 

[WildFeraligatr]

Surely you left the middle pipe hanger unhooked into the rubber hanger. That has one too, towards the back of the car, towards the silencer.

Nope - ended up taking it to a garage and i think i just hadn't put the middle pipe onto the silencer hard enough. Turns out that was causing a minor rattle, but they've found a whole host of other stuff wrong with it - I posted another thread asking follow up questions (but mods may want to merge it, idk)

 

[Mike1alike]

Where is the other post? Put link here.

 

[WildFeraligatr]

Exhaust rattle - an update | FIAT 500 (2007+)

So after being unable to fix the rattle myself, I took my little 500 down to the garage today. They managed to fix the exhaust but have found a host of other issues - worn CV boot, lower suspension arm, radiator leak, crack in the cat and leaks on both the engine and gearbox. What worries me...

www.fiatforum.com

Garage have fixed most of the issues now (with a pretty bill on top...) but strongly suspect the issue now is a head gasket which I'm planning on repairing myself when I get a chance

 

[Mike1alike]

but strongly suspect the issue now is a head gasket which I'm planning on repairing myself when I get a chance

What makes you suspect that?

 

[WildFeraligatr]

What makes you suspect that?

Details are in the other thread - but pink liquid in the exhaust and lots of white smoke coming out the back - admittedly the car hadn't been driven very far (10 mins or so) and there's no forbidden mayonnaise in the oil fill cap

 

[Mike1alike]

There are 2 words there with not enough details.
Is the coolant level going low?

 

[Mike1alike]

Is engine not firing on all cylinders? Do you experience lack of power?