Cam Timing

[neilv]

As some of you may have seen in previous threads my 2000 Griff 500 has had a problem with pinking. Originally the timing was just retarded to remove the problem, but this has killed the performance.

TVR Power have said that winding the timing back is not the way to do it, they have also said to make sure that the Cam timing is correct, for which the car is duly booked in.

Here is the question though; what way could the Cam timing have anything to do with the pinking?

Regards,

Neil V

[aovcerb]

Neil v, I read the previous notes about pinking but a question, has it only recently developed or was it after some major surgery, if not and surmising here but for pinking to suddenly occur does not lend itself to cam timing unless the chain is stretched beyond the limits of the tensioner, (Thinking hard here as it was 8 years since I stripped a V8) then again it would sound like a bag of nails.

Anyway in answer to your question it is all a question of valves opening/closing in relation to piston position, one notch out on the belt or link on the chain can have an adverse effect on performance as you will not be getting optimum compression or extraction of the gases, adjusting the timing may help the ignite the fuel at the correct moment but if the piston is not travelling up at the right time of spark that results in your lose of power.

[neilv]

I only picked this car up in March and it was pinking on the test drive, the previous owner (who has been spoken too) has said that he never noticed any performance/pinking problems and it has never had any surgery of any type.

Hoe does the Cam timing would affect the compression? Surely, at some measure of degrees before detonation, all the valves will be closed? I appreciate how performance would be affected if the exhaust and inlet are not at the correct offset.

All I can think is that there is a suspected cam timing problem AND the timing marks are all wrong. Meaning that the timing was always to far advanced (hence the pinking), but winding it back to the proper offset kills the power because of the Cam timing? But not being an engineer I really am guessing.

Neil V

[aovcerb]

As the cam is run off the crankshaft and geared accordingly through sprockets/chains etc the timing is critical, as the piston travels up fuel is injected and ignited, so the timing is set at x amount of degrees before top dead centre (BTDC). You are correct that all valves should be closed however as all the movements are critical a partially opened valve will effect the performance, by moving the timing you maybe actually firing with valves closed but with the piston at TDC so though you are establishing a clean burn you are losing power as the piston is not in it's optimum position.

If everything was OK when it left the factory then it could be a number of things, however concentrating on the cam issue first there maybe a number of scenario's I think if it has no major surgery then it is unlikely that it left the factory with the wrong timing as over a period the valves would have burnt out. If this is the case and you feel it is a cam problem then one possibility could be worn cam lobes, if these are worn your valves would not fully open and throw off your timing.

This is an easy one to check just remove the rocker covers and rotate the engine by hand, if all lobes on the cam look OK remove distributor cap, there should be a red dot for No1 cylinder, rotate by hand and look at No 1 cylinder and when the marks on the crank align with the relevant BTDC check everything is aligned, valves close, distributor pointing in the right direction etc, this is only a rough guide though but may give you peace of mind.

There are other possibilities such as the fuel injection system or firing system, weak spark etc, and if your cam looks OK I would focus on the other things, a plug in test to the ECU should shed some light on this.