Causes of Pinking

[simontwithers]

My 3.5 SD1 V8 sounds like its pinking (detonating) all the time.

The exhaust note has a loud metallic 'tinkle' over the V8 rumble.

This occurs as soon as I touch the throttle pedal, whether under load or not (up or down hill)

I started with the timing at 10 BTDC @ 1200rpm with vac disconnected as per the haynes, but have been right down to 4 BTDC with no improvement.

I have tried driving with the vacuum advance disconnected, with no difference.

I know that pinking is usually under load with wide open throttle making the engine work hard, but the only time mine doesn't 'tinkle' is on overun.

I checked that the timing marks were correct to TDC when i built the engine, and the engine doesn't overheat. I also tried super unleaded with no change.

Is my engine pinking ? or does it just sound like it ?

Spec is:

3.5 SD1 V8
mild kent 200 cam
holley 390 vac secondaries
offy 360 inlet manifold
stage 1 heads

Thanks

Simon

[DaveEFI]

My 3.5 SD1 V8 sounds like its pinking (detonating) all the time.

The exhaust note has a loud metallic 'tinkle' over the V8 rumble.

This occurs as soon as I touch the throttle pedal, whether under load or not (up or down hill)

I started with the timing at 10 BTDC @ 1200rpm with vac disconnected as per the haynes, but have been right down to 4 BTDC with no improvement.

I have tried driving with the vacuum advance disconnected, with no difference.

I know that pinking is usually under load with wide open throttle making the engine work hard, but the only time mine doesn't 'tinkle' is on overun.

I checked that the timing marks were correct to TDC when i built the engine, and the engine doesn't overheat. I also tried super unleaded with no change.

Is my engine pinking ? or does it just sound like it ?

Spec is:

3.5 SD1 V8
mild kent 200 cam
holley 390 vac secondaries
offy 360 inlet manifold
stage 1 heads

Thanks

Simon

The factory method on an SD1 is to set the static timing before any advance occurs - doing it it at a specific RPM where it is on the advance curve would require an accurate tachometer. So set the idle for this purpose at under 800 RPM. However, a non standard cam might work best with a different setting.
But are you sure it is pinking? As you say this only usually happens under heavy load.

[kiwicar]

Hi
Have you done a plug check, just if it is pinking "all the time" the plugs will show it. Have you looked at the exhaust tail pipe? any evidence of fine metalic particles? If it is doing it on over run it is unlikley to be pinking. I think you have somthing else here.
Best regards
Mike

[Ian Anderson]

Slight leak from exhaust manifold to head area

Tell take is discolouration or sooty area

Ian

[simontwithers]

Thanks for the input.

it doesn't do it on over run - the only time it doesn't

I do suspect a small leak at the manifold to down pipe joint as i've had problems sealing it before.

Will this cause detonation, or simply make a sound like detonation ?

also the noise happens when holding even a few revs whilst stationary

noise is 100% from the exhaust.

Im keen to solve this as its my only form of transport at the moment so is in daily use.

thanks again

Simon

[ChrisJC]

I've also had head gasket failure sound like pinking.....

Chris.

[ramon alban]

it doesn't do it on over run - the only time it doesn't

Hello Simon, that pretty much clinches it, being a minor breach in the exhaust system close to the head/manifold.

No exhaust leak noise on overrun is because the combustion explosions are significantly reduced in quantity.

High engine speed and very lowl fuel input - results in only occasional combustion.

On overrun, you may even get loud pops and bang in the exhaust (overrun cackle) which of course would sound very different to the tinkling of a small exhaust system leak.

If you are using normal exhaust gaskets - replace them all.

On my car, with S/S headers, for example, I simply have metal to metal joints, but if a bolt loosens, the noise you describe can occur thereabouts until re-tightened.

Damaged (or not using) lock-tab type washers may allow this to happen.

[simontwithers]

Brilliant stuff !!!!!

Right, i'll go over the system head to tailpipe and look for leaks. I tig welded the whole (manifold back) system myself so there may be a few pin holes as well.

im guessing the noise is likely to be caused more by a leak close to the head / manifold area ???

read a few topics on google, and apparently high temp silicon does a good job as it flexes ??

I'll let you know how i get on.

Cheers

[DaveEFI]

Brilliant stuff !!!!!

Right, i'll go over the system head to tailpipe and look for leaks. I tig welded the whole (manifold back) system myself so there may be a few pin holes as well.

im guessing the noise is likely to be caused more by a leak close to the head / manifold area ???

read a few topics on google, and apparently high temp silicon does a good job as it flexes ??

I'll let you know how i get on.

Cheers

If you've got the normal thin wall SS manifolds or downpipes, noise goes through them much more than cast iron or mild steel and may well sound like pinking, even without any blowing. Had a P6 SS system like that - eventually cured by wrapping with special cord. It did have a sharp right angle bend at the bottom, though.