Thread: 4.0/4.6 Timing Pointer/Marks

Are you pulling the motor down, if so you can use the marks on the timing chain gears.

Make a U-tube manometer out of an old spark plug body and a length of clear plastic tubing. Watching the water level gives you a quite accurate TDC indication. Then mark TDC whatever way works best. I'm wondering if a front pulley off a serpentine 3.9 would give you a suitable scale.

Originally Posted by Stu_B

Are you pulling the motor down, if so you can use the marks on the timing chain gears.

Unfortunately no - stupid me did not think of this while the engine was being built - is straight forward then.

Cheers

Garry

Originally Posted by bee utey

Make a U-tube manometer out of an old spark plug body and a length of clear plastic tubing. Watching the water level gives you a quite accurate TDC indication. Then mark TDC whatever way works best. I'm wondering if a front pulley off a serpentine 3.9 would give you a suitable scale.

Hmmm - I know what a U-tube manometer is but having trouble linking it to TDC. I assume your logic is that as the piston rises the increasing air pressure will force the water up the other side of the U and will stop when the piston gets to TDC and then start to drop as you go past TDC. If this is what you think you mean - yes it would work but a combustion chamber is not totally air tight - some air pressure might escape through the valves (if the head guy did a good job not much) but a lot of air will escape past the rings.

Also when measuring at TDC you get a fair bit of angular movement at the crankshaft but barely measurable vertical movement of the piston top. That was one of the reasons I used a mechanical adjuster inside a drilled out spark plug to measure further down the bore where there is more piston movement for every degree of rotation of the crank.

I have an old 3.9 here but the harmonic balancer looked a lot different and of course it has the dissy timing cover. As you suggested, I was also thinking of using the 3.9 pointer and pulley but because it looks so different I did not pull it off the engine.

Cheers

Garry

The sensitivity of the u-tube manometer means that leakage past rings and valves is negligible. I actually have a commercially made one somewhere, it came with a timing light I bought a few years ago off a forum member.

I know that there is probably more to your post, but why would you want to check the timing on a 4.0 4.6.

The timing is set by the position of the flywheel Vs the sensor on the RH rear of the engine. If you had the flywheel out by 90-180degrees it would not go AFAIK.
The only way you can adjust the timing would be to elongate the sensor holes, but the engine in any case works off the knock sensors which if knock is detected will retard.

That is why there are no timing marks and /LR/BMW/Bosch do not want any adjustment.
Regards Philip A

Originally Posted by PhilipA

I know that there is probably more to your post, but why would you want to check the timing on a 4.0 4.6.

The timing is set by the position of the flywheel Vs the sensor on the RH rear of the engine. If you had the flywheel out by 90-180degrees it would not go AFAIK.
The only way you can adjust the timing would be to elongate the sensor holes, but the engine in any case works off the knock sensors which if knock is detected will retard.

That is why there are no timing marks and /LR/BMW/Bosch do not want any adjustment.
Regards Philip A

My guess is because Garry is running an aftermarket ECU and wants to check what it's actually doing.