David Balfour

I know diagnosing rattles over Usenet is asking the impossible, but I'll
give it a shot anyway.

The car is a 1991 UK spec 240 SE. B200F engine. 157000 miles (give or take).

There is a _horrible_ rattle between 2000 and 2500 rpm from the underside
exterior of the car. I cannot find the source of it. Thought at first it was
the exhaust but a good bashing didn't leave me suspicious. Everything
visible is tight on the underside. It does only seem to happen when the
vehicle is moving.

Before I start the wild goose chase, has anybody had a similar problem that
they've fixed? It may just help me locate this thing which is letting the
car down - at all other speeds it's a silent as the grave.

Many thanks, David

Randy G.

"David Balfour" <davebalfour@hotmail.com> wrote:

>I know diagnosing rattles over Usenet is asking the impossible, but I'll
>give it a shot anyway.
>
>The car is a 1991 UK spec 240 SE. B200F engine. 157000 miles (give or take).
>
>There is a _horrible_ rattle between 2000 and 2500 rpm from the underside
>exterior of the car. I cannot find the source of it. Thought at first it was
>the exhaust but a good bashing didn't leave me suspicious. Everything
>visible is tight on the underside. It does only seem to happen when the
>vehicle is moving.
>
>Before I start the wild goose chase, has anybody had a similar problem that
>they've fixed? It may just help me locate this thing which is letting the
>car down - at all other speeds it's a silent as the grave.
>

I have one of those myself- the rattling is at just over 2000 RPM.

Take a rubber or rawhide mallet and get under the car. If yours is the
same as my 1990 you will find a curved, dual header pipe (tweo
parallel pipes as one) leading from the cast exhaust manifold towards
the catalytic convertor (if so equipped). Give the double pipe a rap
or two and you will probably hear the rattle.

CAUSE: this is a double walled pipe with an insulating layer between.
The insulation breaks down and allows the inner pipe (or the
insulation) to rattle together.

CURE: get some self-tapping sheet metal screws and install a few
through the outer pipe so they push against the inner pipe to stop
them from moving and thus rattling.

__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"

David Balfour

> Take a rubber or rawhide mallet and get under the car. If yours is the
> same as my 1990 you will find a curved, dual header pipe (tweo
> parallel pipes as one) leading from the cast exhaust manifold towards
> the catalytic convertor (if so equipped). Give the double pipe a rap
> or two and you will probably hear the rattle.
>
> CAUSE: this is a double walled pipe with an insulating layer between.
> The insulation breaks down and allows the inner pipe (or the
> insulation) to rattle together.
>
> CURE: get some self-tapping sheet metal screws and install a few
> through the outer pipe so they push against the inner pipe to stop
> them from moving and thus rattling.

Randy, many thanks for that - I'll take a look tomorrow. It does sound
likely, as the rattle is absent when the car is cold. I don't really
understand the magic behind these Volvo cats, but it could be this double
pipe you speak of that's causing the problem.

David

Randy G.

"David Balfour" <davebalfour@hotmail.com> wrote:

>> Take a rubber or rawhide mallet and get under the car. If yours is the
>> same as my 1990 you will find a curved, dual header pipe (tweo
>> parallel pipes as one) leading from the cast exhaust manifold towards
>> the catalytic convertor (if so equipped). Give the double pipe a rap
>> or two and you will probably hear the rattle.
>>
>> CAUSE: this is a double walled pipe with an insulating layer between.
>> The insulation breaks down and allows the inner pipe (or the
>> insulation) to rattle together.
>>
>> CURE: get some self-tapping sheet metal screws and install a few
>> through the outer pipe so they push against the inner pipe to stop
>> them from moving and thus rattling.
>
>Randy, many thanks for that - I'll take a look tomorrow. It does sound
>likely, as the rattle is absent when the car is cold. I don't really
>understand the magic behind these Volvo cats, but it could be this double
>pipe you speak of that's causing the problem.
>

The rattle has nothing to do with the cat itself but the pie that is a
ways in front of it.

The other likely places are:

1) The heat riser pipe (aluminum duct work leading from the heat
shield to the air cleaner box. These will vibrate and rattle against
body work which wears the pipe as well as the paintwork.
2) The heat shield around the cast iron header
3) The heat shield that is above the catalytic convertor (less
likely). In some cars the shield is bolted to the exhaust, in others
to the body.They sometimes can come loose and drop onto the exhaust
which can make a real racket. usually not so RPM dependent.

__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"