(G) What exactly is pinking?

I'm really confused as to what pinking is.
Is it knocking? e.g. when I use tesco fuel there is a knocking from my car at around 60 to 70 mph
Or is it in the lower revs, becuase when I put my put down in lower revs the car accelerates fine, but it sounds a bit like someone is russling a plastic bag or something, or is this just a characteristic of an older engine?
I'm sure my ignition timing is almost perfect, as I had a garage do it with a stroboscopic light.

Thanks

Will

Hi, it will sound like a light rattle, your paper bag sound could just be gearbox noise and is fine at lower revs. Pinking should happen at lower revs under heavy load such as climing hills etc or at higher speeds when giving it some welly! Basically its very bad news as the spark plugs are firing before the piston reaches the end of its upward stroke, so waht happens is the piston is being forced down early and it rattles. eventually you will damage the piston so it needs sorting. check your points gap is correct and re timing, even if its set up exactly right you may still need to retard it a bit, modern fuels arent as good at burning as they were and most older cars need some retardingof the timing, trial and eror is the way with pandas!

Can also be caused if the cam lobes or shims on the tappets are worn.

I usually get a knocking sort of sound when I let off the accelerator at around 65mph, I'f i press down on the accelerator the knocking goes away.
I would say that the plastic bag sort of sound gets louder if I press the accelerator further down when in lower revs, its more noticable when the car is still quite cold. Does this happen on all carbed pandas?
Maybe I will go to a garage and have them see what they think and do the ignition timing again.

THanks

Will

With that description it's not pinking as it's the reverse press on the accelerator you get pinking release it and it goes away.

'Pinking' is pre-ignition. What happens is that the fuel is starting to combust under compression before the spark plug fires, such as when the piston moves up to the cylinder head for the compression stroke.

If the timing is too advanced or the fuel is of too low an octane then pinking can occur. Also, if carbon build up in the cylinder head has taken place then the carbon can stay hot enough to ignite the fuel before the spark plug fires, much like a glow plug in a diesel.

Two ways round this. Retard the ignition until the pinking stops, or use a higher grade of fuel (like Shell Optimax).

Pinking is bad news because it can cause a messy burn of the fuel leading to hot spots and ultimately holed pistons or burnt valves. However, if it only occurs rarely then I wouldn't worry too much about it, but I would try retarding the ignition a degree or two to be on the safe side.

doesnt sound like youve got pinking, as I said the rustle sounds exactly like the gears, check your gear oil level. as for the other sound, could be anything, maybe even a rattly exhaust, loose something, bit too little info to diagnose!

The knocking gets worse when I advance the timing, however if I retard it the performance of the engine is quite bad and it gets flat spots, at the moment I rarely get any knocking, it only happens sometimes if I am cruising at 60 to 70mph.
The plastic bag sort of sound could be the gears. I have just renewed the manual gear oil with 20w50 engine oil, should i maybe put a gearbox additive in it?

thanks

will

also if pinking was occuring, would there be any signs on the spark plug.