924Board.org

[gegge]

I hade my head ported and checked because of a head gasket failure. The mechanic told me that the cam and followers were ok and everything worn was exchanged for new parts. He is an true expert (but maybe not on this particular engine).

The engine is very easy to start and relative silent. Oil and water looks good by color and level. Compression was low but even, a bit more than 100psi for all cylinders with a cold engine and bad battery. Ignition when idling is approx 20 deg BTDC.

BUT, when the engine gets warm and I let go of the throttle, there is a loud hard metalic sound (clash, slack, click). It is definetly from the head, not from the turbo, popvalve or CIS. Sounds almost like the piston is hitting a valve. But nothing at constant revs of if I let the revs slow down gently.

I have no idea what it is, but is scary. Please help me out! Any ideas?
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[924turbo_sout_africa]

well not sure how load it is but ,my trhottle cable makes a cluck noise when i release it i had a fright the first time until i checked what it was and worked it out and now it's normal ....

my race car had the piston hitting the valves and let me tell you that is no funny noise if it does it twice the velve is bent and it's all over the car will not perform and probably start to smoke and you wil hear a noise at idle and at reving the motor
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Porsche ...where dreams are a reality
'79 924 turbo canada spec
'98 Formula Vee (M3 eater)

Time in the 931 is a dream come true !!

[gegge]

I also thought that the throttle housing made the noice, and it is very similar, but louder and a harder. Sounds like there is a gap between two parts and it occurs when the load is released. An instant noice just like slamming a hammer into the headcover.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[Rasta Monsta]

Sure it's not your recirc valve? It makes a noise exactly as and when you are describing.
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[gegge]

Thanks Rasta,

That is exactly what people are telling me, but the location of the sound is more from the head than the turbo. Is the pop valve working when you rev the engine standstill? I can´t hear the noice when the engine is cold, or maybe just rev it enough...

Maybe I am just paranoid, but the noice can´t be right.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[Smoothie]

The recirc valve should "clack" every time you open or close the throttle.
-And yes, it'll do it when you rev the engine standing still. A sharp rise in manifold vacuum as in when you release the throttle, pulls the recirc valve open with a "clack". Same when you open the throttle - you get a sound again as the recirc valve closes..
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Smoothie]

Well waddayaknow, my recording of it is still out there -
http://www.geocities.com/smoothies931sounds/PopOffValveClick18sec-48kHz16bitStereo.mp3
It sounds tinnier, like a tick on my little laptops' speakers. In real life it's more like a clack sound.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[gegge]

Hmmm, I don´t have that. Dead silent. But, that is what I would expect from a valve.

The noice I get is only when you rev the engine and instantly shut the throttle. It is harder, heavier and (maybe) louder.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[Rasta Monsta]

Revving the engine and shutting the throttle is what Smoothie is doing in the recording. The valve makes a pretty loud clacking sound when it opens and when it shuts.
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3