Timing marks on crank pulley/damper is reversed?

[Kennymonster]

I've had no problem in the past setting the ignition timing on few different L6 motors, various 240z/280z style timing marks, etc. so I'm kind of stumped on what's happening.

 

Quick overview: this motor was actually built by another owner, I bought it and had it crated over, dropped it in to replace my dead blow through set up. I was told the specs for it, complete bottom rebuild/head/cam setup to my liking.

 

Crank pulley that came with the motor is a single groove, I can't tell if it's the euro version (the ring portion looks different), and doesn't seem to match any aftermarket pulleys either, so confused here as well.

There are multiple grooves / timing marks on the pulley, which look like this:

 

- Big gaps are increments of 10 degrees (verified with 280z timing scale tab), smaller gaps are increments of 5 degrees

- I checked for TDC via spark plug on #1 on compression stroke, it was the highest at the black "0" mark on the pulley, farthest to the left if looking from the front

 

- When I go to set the total advance timing at 3k+ rpm, it looks like the above pic.... which shows the supposed 35 degree offset mark based on the established TDC, way off from the timing marker/pointer, it's reading almost 10 degrees full advance which is not correct. Note at this setting, the motor runs very healthy.

 

- I've tried adjusting to the referenced black 35 mark to coincide with the black 0 TDC mark at full advance: loss of power and heard detonation.

 

- The red numbers are what makes more sense to me, as I think the total advance is already correct, but that doesn't jive with what I saw to be TDC (the #1 piston was higher on the stroke on the black 0, vs red 0 mark)

 

 

I'm just running it as is right now, but would like to find out once and for all what's really going on here.. any feedback is appreciated. Power level is great,  also getting a lot of exhaust popping when I let off (though the afr is fine) which I'm not sure is related to the ignition timing or not.

 

 

Pic of the crank pulley:

 

 

[TimZ]

Maybe I'm missing something, but it sounds like you still have the stock timing tab on the front cover - is that correct?  

 

If so, why not just ignore the marks on the pulley (at least for the time being), note/mark the point on the pulley that lines up with the tab's "0" mark when the engine is at true mechanical TDC, and then use the tab to verify timing?  Alternatively you could use a "dial-in" type timing light and _only_ use the zero mark.  

 

In fact if you have a "dial-in" light, then you could just put the engine at true TDC and make your own corresponding Zero reference marks on the pulley and front cover...

[Kennymonster]

Yes it has a single pointer tab (stock l24 style) on the block, and I did verify the (black 0) mark on the pulley as lining up at TDC.

 

Couple of other variables I didn't mention, I'm using an MSD 6al2 for ignition, and taylor wires, I guess that could also do weird things to getting an accurate reading, especially using a dial back light. I'm planning on swapping in a different spark wire for cyl #1 away from all the others, to rule out an interference reading maybe... another possibility I read was that if using the msd with zx dizzy, and I have the green/purple polarity reversed, it could do funky things there as well - though I've had it reversed way back once before and it just made a 50 cal noise when trying to start.

 

The car runs pretty good right now so I'm not convinced if it's just reading incorrectly due to the reasons above, or if it's truly off that much.

Edited May 14, 2015 by Kennymonster

[NewZed]

Never mind.

 

This is an odd thread.  Put the 280Z tab on and make a zero mark on the pulley.

Edited May 14, 2015 by NewZed

[Kennymonster]

^lol, odd thread indeed.

 

Just reporting back for purpose of search results in the future:

 

I got it to run well using the proper marks. I did take some measures though to ensure an accurate reading, even with a barebone timing light I think the multiple sparks from the MSD have a way of fudging the reading.

 

- Swapped in a separate wire (of different brand just to rule out the existing wires as issue), routed it away from all the others to prevent any interference

- Bolted on the L28 tab with multiple scale marks to double confirm the TDC mark, offset mark, and total advance mark

 

- Set the total advance to ~35, it was a bit more touchy to adjust with the precautions taken above, I can only guess the previously seen '35' was off by few degrees

 

 

Still getting some exhaust popping but that might just be pilot jet settings, definitely less than before however. The reading I checked before the adjustment showed 2.5 degrees at idle (which would mean only ~20 degrees full advance), to my surprise ran reasonably well but it did struggle at the top end occasionally. Now with the newly set timing, it's pulling strong past 6k in fourth, and I'm a happy man.