Rattle at start up - 355

It can be the cats, heat shields, or even the tensioner thingies on which the tensioner bearings/rollers are mounted. The fact that it goes away when warmed up says that either the idle rpm is moving to an rpm where it doesn't resonate with whatever is rattling, or that it's the tensioner (they apparently work better when warmed up). These are bits of information I've picked up second or third-hand from reading various posts here. I'm sure someone will come along and clarify.

Let us know if you figure it out though!

 

Crap...I had this exact problem and something near the bypass rattle needed tightened but I can't remember what it was!!! My tech did fix it though.

I would check the components near there cuz it annoyed the hell outta me and it was the exact same situation you described.

 

I know you said that everything was replaced at the major, but are you absolutely certain that both hydraulic tensioners were replaced (in addition to the tensioner bearings). Does your bill show the fitting of two "hydraulic tighteners", part number 157356. I only say this because the symptoms you describe match exactly those of a sticking tensioner which loosens off when the engine is warm.

 

I'm with you Ron.

 

I'm sorry, but my tech did it and I know so little about cars.

 

this guy... between the end of the spring and the copper nut (to include the "tin can" just to the right).
Image Unavailable, Please Login

 

Press the clutch petal when starting, do you still have a rattle? If it stops the rattling at the start than you clutch disk needs to be replaced or aligned.

 

I have 99 (20 K) and all service/major was done at dealer (not that it is better), the rattleing seems to come from behind the passenger/driver compartment closer to the fire wall.

I do not belive it is the clutch as it would be from the back of the car. Also if you depress it and it goes away, then it is your throughout bearing. My understanding is that it is normal (my other BMW car has the same) and no negative impact.

The belt tensioners seem to be the most possible cause ......i have searched on this forum and others and nowhere could I find if that is bad or not. My understanding is even new ones will do this when cold ! (could be wrong though).

Anyone can ellaborate on the effects of this temporary lose belt tensioner, can the belt jump/out of timing during those few minutes ?

process of elimination I guess.

Thanks

 

I have also seen a number of discussions regarding a metallic noise at start up from cold which disappears after a couple of minutes. I too had this noise which could be attributed to a sticky/ineffective/incorrectly adjusted tensioner.

The sequence of photograph were taken during the work I did during winter 2007'

The first picture is where I found no gap between the tensioner body and the tensioner bearing bracket.

The second picture shows the bearing too loose on the belt requiring the tensioner to work too hard to add pressure on the belt resulting in a large gap.

The third and fourth picture shows the old and new tensioner with the retaining pin installed. In this position the gap is too small, approximately 1.5mm.

The final two pictures show the gap as per the WSM, i.e. 2.5mm.

After reading about this start up noise and a few theories elsewhere, if the tensioner gap is too small, the bearing bracket could chatter on the tensioner causing the metallic noise until sufficient heat was in the tensioner to extend the plunger moving the tensioner bearing bracket away from the tensioner housing.

It would seem if the pin is left in whilst the belt tension is applied to make the initial setting, the gap would be too small running the risk of chatter.

After I refitted the engine, and ever since, there has been no more chatter from cold.
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

Found these pictures (with new belts, Hill bearings and Ferrari belt bearing tensioners) which show the system quite well.
Image Unavailable, Please Login
Image Unavailable, Please Login

 

"under the heat shielding over the exhaust" sounds to me like the bypass valve.

 

Hi Mike. We are all hoping that your rattle is coming from the very rear of the car - something around the heat shields, by pass valve area 'cause that will be easy to fix. The tensioners are at the front of the engine, just behind the bulkhead separating you from the engine. They can only be accessed when in there doing a major (belt change for example).
What made us suggest the tensioner is that the noise goes away after a few minutes (and that you only get it when the engine is started from cold).
Let's hope that you get it sorted soon - and let us know what it was!
Ron

 

Another thing to try....

Get out and have someone gently rev the motor.

Does the rattle sound like it is moving from the front of the engine to the back?

 

On my 348 I have the same problem, But I know it's just the heat shield. Need to tighten it up. Does it stop rattling when you hold the heat shield? Hopefully that's all it is.

Cheers

 

Had similiar noise on my '90 348....sounded like a metallic rattle for a few minutes until things warmed up...then it disappeared.
Turned out to be the alternator... noisy bearings. Rebuilt the alternator and no more noise.

 

Good news Mike. So something in or near the exhaust system touches when cold and moves out of the way when the heat comes along. Glad that it's an easy fix (and will be at zero cost!). Thanks for updating us.