Knocking from OHC engine

[Ext User(David \(one of the many\))]

G'day,

The beast is a 2.5L V6 TX5 4WS Telstar circa 93-94.

There is a distinct "rattle" noise coming from under one of the rocker
covers at the front (belts) end of the engine. These motors always make
some noise (in fact the owners manual has a note that some noise is normal)
but after having the vehicle for 5 years it has never been as loud as it has
become recently. The rattle becomes less noticeable as the revs increase but
doesn't go away completely. Previously the "normal" rattles would dissapear
completely as the revs went over 1000. Also, after blipping the throttle,
the rattle becomes a clatter as the revs die down again. The car drives
fine, fuel economy is same as always, no oil leaks but oil consumption has
increased slightly this year - but after 350,000 kms that'd be expected).
The noise is definitely in the top end so I have don't think its slap or
bottom end.

I was thinking broken intake valve spring as the noise is on the intake side
of the rocker cover. I can't think of much else that could go wrong with an
OHC engine that would make a noise like this. Great car. It'd be a shame to
have it put down.

Any ideas?

[Ext User(OzOne)]

On Sun, 04 Jun 2006 10:39:12 GMT, "David \(one of the many\)"
<none@none.none> scribbled thusly:

>G'day,
>
>The beast is a 2.5L V6 TX5 4WS Telstar circa 93-94.
>
>There is a distinct "rattle" noise coming from under one of the rocker
>covers at the front (belts) end of the engine. These motors always make
>some noise (in fact the owners manual has a note that some noise is normal)
>but after having the vehicle for 5 years it has never been as loud as it has
>become recently. The rattle becomes less noticeable as the revs increase but
>doesn't go away completely. Previously the "normal" rattles would dissapear
>completely as the revs went over 1000. Also, after blipping the throttle,
>the rattle becomes a clatter as the revs die down again. The car drives
>fine, fuel economy is same as always, no oil leaks but oil consumption has
>increased slightly this year - but after 350,000 kms that'd be expected).
>The noise is definitely in the top end so I have don't think its slap or
>bottom end.
>
>I was thinking broken intake valve spring as the noise is on the intake side
>of the rocker cover. I can't think of much else that could go wrong with an
>OHC engine that would make a noise like this. Great car. It'd be a shame to
>have it put down.
>
>Any ideas?
>
My guess?
It's sludged up like they all do and blocked an oil feed to a camshaft
bearing.


Oz1...of the 3 twins.

I welcome you to crackerbox palace,We've been expecting you.

[Ext User(Mike)]

In article <4482c0f3$1_3@news.peopletelecom.com.au>, none@none.none says...

>I was thinking broken intake valve spring as the noise is on the intake side
>of the rocker cover. I can't think of much else that could go wrong with an
>OHC engine that would make a noise like this. Great car. It'd be a shame to
>have it put down.
>
>Any ideas?

Take the rocker cover off and have a good look see, if you have a compressor
and plug attachment you can even pull out the springs whilst head still
on block and give it a fairly good inspection, even a service...

Face it, if people are compelled, you are going to get lots of opinions,
in any case - localising a sound without a stethoscope and associated
prongs is far more difficult and very misleading. Had, what I and several
other people thought was a top end lifter noise, didnt make sense as I'd
serviced the lifters but they persisted in saying - everything sounds
like a top end problem. Decided to use a stethoscope with a couple of
different sized rods (tubes) and discovered noise was more prevalent
on block side of exhaust just under where head meets block, so couldnt
have been anything in head. Jacked up engine in body, took sump off
and voila - overheated big end on cyl 1 and 3. Expected I guess as oil
pickup had remnants of gasket cork around it....

Anyway point is, sound hard to localise without useful tools and
may as well take rocker off to inspect and can probably service a heap
if you know how to use a compressor and a spark plug attachment etc

--
Regards
Mike
* GMC/VL Commodore, Calais VL Turbo FuseRail that wont warp or melt !
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[Ext User(Jason James)]

"David (one of the many)" <none@none.none> wrote in message
news:4482c0f3$1_3@news.peopletelecom.com.au...
> G'day,
>
> The beast is a 2.5L V6 TX5 4WS Telstar circa 93-94.
>
> There is a distinct "rattle" noise coming from under one of the rocker
> covers at the front (belts) end of the engine. These motors always make
> some noise (in fact the owners manual has a note that some noise is
normal)
> but after having the vehicle for 5 years it has never been as loud as it
has
> become recently. The rattle becomes less noticeable as the revs increase
but
> doesn't go away completely. Previously the "normal" rattles would
dissapear
> completely as the revs went over 1000. Also, after blipping the throttle,
> the rattle becomes a clatter as the revs die down again. The car drives
> fine, fuel economy is same as always, no oil leaks but oil consumption has
> increased slightly this year - but after 350,000 kms that'd be expected).
> The noise is definitely in the top end so I have don't think its slap or
> bottom end.
>
> I was thinking broken intake valve spring as the noise is on the intake
side
> of the rocker cover. I can't think of much else that could go wrong with
an
> OHC engine that would make a noise like this. Great car. It'd be a shame
to
> have it put down.

The Hemi 6 engines had a habit of doing that when their piston slap got to a
certain extent. You bring the revs up to about 2000, release throttle and
the pistons would drop thru some sort of resonance zone as the engine revved
down with a distinct light rattling sound for about 200 rev wide band.

Some OHC engines use rocker-arms to operate canted valves. After years of
use, the rocker face which operates the valves can become worn, and are no
longer flat or slightly concave, instead having a "V" shape. Worn valve
guides contribute to this. This can cause light overhead rattle. Severely
increased valve-lash, another cause.

Excessive camshaft end-play is another possibility.

If you remove the valve cover and check the rigidity of everything while
turning the engine to check valve gear for looseness. Hand turning or
blipping the starter, will allow you to check the entire valve trains when
they are not under tension.
Check there are no oil-slingers on the cam-drive ends to rattle.

If thru misadventure a piece of piston-skirt has come off, that piston will
make noises which are wierd. Cracked piston-skirts only make a noise under
load.

Jason