Replace timing chain to improve economy?

rowan194 · 05-01-2013, 07:14 PM

Saw mention of timing chains that stretch after a while (150-200k+). Does this happen with the AU engine and is it worth looking at replacing it once the engine has done some decent km? Or is this supposed to be replaced anyway?

**Whoosha** · 05-01-2013, 09:41 PM

Timing chain has a tensioner fitted to keep it taught so unless it is rattling excessive or you plan on pulling the motor apart for another reason I would'nt bother .

Sox · 05-01-2013, 11:44 PM

The chains are pretty unlikely to break, and as Whoosha said, the tensioner will take up the slack.

However, the cam does become retarded with chain stretch. The quickest fix is to throw in a vernier cam gear and set it back to spec, or perhaps a couple degrees more.

FGII-XR6 · 06-01-2013, 09:18 AM

Spot on . I have seen AU I6 engines with over 800 000 Ks still on the original timing chain and no chain rattle but there would be a bit of stretching. these are a remarkably reliable engine good for well over 500 000 Ks with good routine maintenance that's why the taxi owners loved the AU.

Quote:

Originally Posted by Sox

The chains are pretty unlikely to break, and as Whoosha said, the tensioner will take up the slack.

However, the cam does become retarded with chain stretch. The quickest fix is to throw in a vernier cam gear and set it back to spec, or perhaps a couple degrees more.

Evgeni · 06-01-2013, 11:22 PM

You will need a scope to see what is going on with the timing. Given what is involved with replaing the chain, compared to hooking the car up to a scope - max 15mins - my mortgage will be paid off this year, so it is on the shopping list!!

You need to put an amp clamp on the battery - on a clear flood crank peak amp draw will occur when each cylinder is at TDC.

Backprobe one of the control wires for the coil pack. The pcm will switch each coil on by providing ground voltage.

You would then need to graph these two signals to see when each event is happening in relation to each other. Just remember that spark occurs when the coil is switched off as opposed to on - (the control wire energises the primary winding of the coil and once it is switched off, the magnetic field collapses, sending voltage through the secondary winding, producing spark).

On a graph, the 6 amp draw peaks will represent 720 degrees of crank rotation. You will then be able to see just exactly when and how many degrees btdc firing is occurring.