Engine pinging

[Steve Pearce]

Hi my first post
I have just acquired a Jaguar Mk2 S type 3.4 that has some problems - most I have got over. One problem I have is that the car will ping ( knock) on acceleration over 2500 RPM. Has any one had the same problem if so how did you get over it? Any help would be appreciated

[piman]

Hello Steve,

that sounds as if the timing is over advanced for the fuel you are using?

I would first retard it using the small adjusting wheel on the distributor.

Alec

[B87UL]

Steve

I think that initially Alec’s suggestion is the best move.

I have an identical car and my past professional experience tells me that the combustion chamber design is apt to encourage pinging. Most of these cars have had block and heads shaved which raises the compression ratio and that also increases the chances of pre-ignition, again my car falls in this category.

If a distributor retard of say 10 to 12 “clicks” does not cure the trouble I would look elsewhere. Firstly, I changed the fuel over to “best” petrol 98 ? and that cured the pinging on my car.

I have also seen a number of 3.4 / 3.8 ltr cars with 2.4 ltr ignition distributors and these have a very rapid (and unsuitable) advance curve. Pull the distributor and check the Lucas number. Also check the advance / retard mechanism for freedom of movement and the advance spring tension.

Note, if the advance / retard mechanism has identical springs they usually have similar tension, but if one spring is obviously heavier and stronger, then that spring is usually slack when static. This of course does not replace the need to have the distributor overhauled if necessary.

Assuming the engine was originally 8:1 compression ratio, (you could check compression pressures to confirm) and the head has likely been shaved I would set the static ignition timing for 9:1 C/R. In a similar fashion I would have the distributor advance set up for 9:1 C/R if I had the distributor rebuilt.

Hope this helps a little.

Norman