Thread: Until NOW !!!....TD5 ValveTiming ...

Originally Posted by bushrover

Cam timing will make bugger all difference to injection pressure unless you are out by teeth not degrees. Next time you have the cam cover off check the injector lobe.

The adjustment on the cam gear is approximately one tooth, so in theory with a very worn chain that has run out of adjustment you could move the chain one tooth and readjust to return to factory spec valve timing, in practice you would be waiting for a chain to break and resultant damage.

Rick

The injector pressure is set and does not alter, correct? We are talking the timing of the injector pulse. The correct timing of the pulse in relation to the piston placement is what determines the power.Too early or too late will result in a power loss, and possible engine damage in a worst case.

However Rick is correct with his scenario regarding teeth out.

Cheers Scott

I understand what Rick is saying, and my original post was probably a bit general, but I can't see how the big difference the OP Ian was describing could be caused by that small change to the camshaft timing.

I used to play around with camshaft timing when younger, advancing timing was a cheapskate way of getting more torque when I couldn't afford a cam grind, but it never resulted in the expected increase. There was a noticeable change but not a lot.

I have been running my old 2.6 6cyl about 4 deg. advanced for a while, it has made a difference, but not to the degree that Ian is describing.

Cheers,
Terry

Originally Posted by schuy1

The injector pressure is set and does not alter, correct? We are talking the timing of the injector pulse. The correct timing of the pulse in relation to the piston placement is what determines the power.Too early or too late will result in a power loss, and possible engine damage in a worst case.

However Rick is correct with his scenario regarding teeth out.

Cheers Scott

Yes, injection pressure is constant as is injector cam timing and cam duration. Injection pressure is set by adjusting individual injectors. Line up the cam lobe, wind the adjuster in fully and back it out one full turn.

The injector lobe has to be able to maintain full pressure over probably 30-40 deg of crankshaft rotation. (I don't have the actual figures so bare with me, this is only a generalised explanation) When you adjust the injectors at TDC you are actually setting them in a retarded state. The cam lobe must provide maximum injector plunger travel and therefore maximum pressure from up to 30+ deg of advance until after TDC. At idle injection usually takes place a few deg before TDC. When cranking, or with a cold engine the ecu advances, retards accordingly as well. At max governed rpm around 4800 the ecu advances injection timing to 10-15 deg (I am guessing, I don't have the figures, but those who play with ecu maps will know). Add a load - and various other inputs - and the ecu will adjust injection timing to 25-30 deg and volume and duration to suit as well.

Varying injection timing, volume and duration (not necessarily in that order of importance) on a TD5 controls rpm. The throttle position sensor tells the ecu what rpm you want the engine to do for the load you have, the ecu tells the injectors what timing, volume and duration is required to get the engine to your required rpm for the load. Sometimes the engine won't do it, the load is to great, like when you ask the engine to perform outside rpm range for max torque.

Very, very generalised explanation. Ultimately you press the go peddle and magic in the wires makes things happen. The injector lobe provides maximum injection pressure across the entire potential timing range.

A previous poster counted cam rotations to realign the timing marks on the chain. The first time I did a TD5 head I did the same -

21 crankshaft teeth = 16 CS rotations
42 cam gear teeth = 8 cam rotations
112 chain rollers = 3 chain rotations
336 teeth pass a particular point until it all realigns.

So now after assembly I count chain rotations, small numbers are easier for me. I only do this to ensure the pins line up again, If they are slightly out after 3 chain rotations, (cam slightly retarded) I haven't removed the slack out of the driven side of the chain correctly. On my own TD5 after replacing the cam chain and gears and doing 5000k the cam was a poofteenth retarded. Readjusted without the slightest hint of a performance increase and life has been great ever since.

And since you asked, 42 teeth on the cam sprocket means approx 8 deg of adjustment. Certainly could be a noticeable performance increase if you had the gear adjusted completely the wrong way with a worn cam drive train (or never adjusted from new with a couple of hundred k on the clock).

Rick