Rattle/knock when starting engine and using accelerator

[Brunoandrade98]

Hi all,

My 197 (60K miles) has had an issue for a while that I've been trying to figure out for a while. I've made a post a while back, but it hasn't had any activity, so I'll try again and provide more details that I now know.

When starting the engine, there is a slight momentary knock or rattle. It also happens when (for example) standing in traffic and driving off on that initial press of the accelerator. It can also happen while driving, during gear changes as you let off and press the accelerator again.
Video:

https://imgur.com/a/5BX4rqh

I couldn't see anything wrong, so I bit the bullet and took it to a garage to diagnose. They spent one hour diagnosing it and reached the conclusion that my lower engine mount was bad, as well as the torque arm.

I removed the lower engine mount and it was indeed worn, however, it really wasn't that bad. Nevertheless, I bought a new one and replaced it.

The issue persists...

I'm still waiting for a Powerflex bush for the Torque Arm, but I don't believe that will be the issue, either.
Mine has slight play on the rubber area that the bushing replaces, but people have said it's normal as they are not pressed.
I have also seen a mate's NV200, which uses the same part, and it had similar slight play (What are the odds both of our torque arms are shot?).


It's proving a tricky issue and hard to diagnose, but if anyone has any ideas, I'd appreciate it if they could share them as I'm a little lost, here.

 

[turkie172]

I would say exhaust maybe on the diffuser or touching somewhere or it sounds dull like a cable touching something flat like selector cables even brake lines on the under floor

 

[Brunoandrade98]

I would say exhaust maybe on the diffuser or touching somewhere or it sounds dull like a cable touching something flat like selector cables even brake lines on the under floor

I could be wrong, but I reckon it won't be anything suspension, steering or engine mounts, as I've gone over a lot of these components.

But what?...This is the tricky part. I've been living with it for months, now, and never managed to find the source of the problem.

I went home, earlier, and removed the diffuser. Unfortunately, the issue persists. Not too surprised, as the exhaust mounts (which would likely be the culprit if the exhaust was knocking on the diffuser) were in good shape.

 

[RSRowe]

I would suggest finding a different garage. It’s rather difficult to diagnose over video, but it sounds like engine mounts to me.

Failing that, I would check to make sure the exhaust manifold isn’t hitting the subframe, and the exhaust isn’t hitting the rear beam.

 

[Marsch]

It may would help if you could provide a video with somebody standing outside and filming the engine bay while you blip the gas?

 

[Brunoandrade98]

I would suggest finding a different garage. It’s rather difficult to diagnose over video, but it sounds like engine mounts to me.

Failing that, I would check to make sure the exhaust manifold isn’t hitting the subframe, and the exhaust isn’t hitting the rear beam.

I had the upper engine mount out recently while I did my belts, and it seemed just fine, to be honest.

It's a fair assumption that the engine mounts are bad, with a description of the problem, but from looking at the mounts and testing them by rocking the engine back and forth...it seems unlikely. I will, however, update this when I fit the Powerflex torque arm bush.

I also had someone start the car a few times while I was underneath it and I couldn't really see any real movement on the exhaust manifold. I also couldn't hear any knocking sounds, which was odd...

I've got the diffuser out, currently, so I'll check if it could be hitting the rear beam. Although, I had a quick look by trying to rock the exhaust back box, and it seemed solid, too...

Strange...

 

[Brunoandrade98]

It may would help if you could provide a video with somebody standing outside and filming the engine bay while you blip the gas?

I've had this thought, but I don't think I've recorded that yet. Will do it later if the weather allows.

 

[Marsch]

Try pushing down directly on the part of the arm of the mount that's attached to the engine and see if it moves (much). If it does it could be the problem.

 

[Brunoandrade98]

Try pushing down directly on the part of the arm of the mount that's attached to the engine and see if it moves (much). If it does it could be the problem.

I've recorded this not too long ago:

https://imgur.com/a/w8sHqSm

 

[Marsch]

From what I know it shouldn't move left and right like that. Besides that it's moving quite a lot for the little down pressure you seem to apply. If you really want to test the movement you've to apply more pressure by leaning on it and pushing downwards with some force/weight.

I'd suggest to get the yellow Powerflex insert anyway. It's cheap and makes quite the impact for what it is.

 

[R20BTG]

Yeah that looks fucked to me

 

[RSRowe]

It's a fair assumption that the engine mounts are bad, with a description of the problem, but from looking at the mounts and testing them by rocking the engine back and forth...it seems unlikely. I will, however, update this when I fit the Powerflex torque arm bush.

Don’t forget there’s 4 mounts/bushings in total…..

Like I said, you need to find another garage, otherwise you’re going to end up chucking money at replacing parts which might be ok.

 

[Brunoandrade98]

From what I know it shouldn't move left and right like that. Besides that it's moving quite a lot for the little down pressure you seem to apply. If you really want to test the movement you've to apply more pressure by leaning on it and pushing downwards with some force/weight.

I'd suggest to get the yellow Powerflex insert anyway. It's cheap and makes quite the impact for what it is.

Yeah that looks fucked to me

My Powerflex bush should arrive over the next couple of days. Lets see how it does after installing. I'd be really happy with a sub £40 fix.

 

[Brunoandrade98]

Don’t forget there’s 4 mounts/bushings in total…..

Like I said, you need to find another garage, otherwise you’re going to end up chucking money at replacing parts which might be ok.

After a 1-hour diagnostic at £85, I'd rather get back to them and hope they're willing to have another look for me.
If a Powerflex bush doesn't fix it and they can't find the issue, then, maybe...