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:

 

 

[Jarvo2]

That crank pulley looks more like a harmonic balancer, which I didn't think the L series engines used.

[Zed Head]

The black numbers are ordered in the correct direction.  Imagine that you had the 280Z tab on the engine and were watching the "0" move with more advance.  It would move to the left, higher numbers on the 280Z scale.  Which would move the numbers to the right on the damper over on the pointer.

 

So, it sounds like what you're basically seeing is that the engine runs best at only 10 degrees total centrifugal advance.  Assuming that the scaling is correct (only you know what you saw with the 280Z tab as a ruler), the real problem is that the engine runs funny.  Maybe the CR is too high, or cam timing is off.  Maybe it just won't run well at high advance.

 

If you wanted to double check your marks, you could attach the 280Z tab close to the damper pulley somehow.  Whatever mark is across from the tab's zero mark is now the damper reference mark, and it should move appropriately across the 280Z tab as timing advances.  Or attach the tab anywhere, set TDC, and make a new mark on the damper pulley.

 

You could also borrow or buy a "dial-back" light and use that to check the marks.  With those you adjust a dial on the timing light to read timing and use only two marks, one on the damper and one on the pointer/tab.

[Kennymonster]

Thanks for the feedback, actually was attempting the dial back light method last night at a buddy's, and his craftsman tool conveniently died.

 

I agree with your overall assessment, though on a CR of only 9.5 : 1, 91 octane, and a .480 lift cam (all supposed numbers from PO), I would think it would just dog at only 10 degrees total advance. Currently the power feels similar to my previous 8.7 : 1 with nowhere near as built motor, which ran on 36 or so total advance as typically done. Fuel/induction hasn't changed, 44phh mikunis, fuel psi is right at 3.5 psi as it should.

 

I guess I don't really have any other ideas besides confirming with another dial back light, or maybe using the black numbers & slightly increasing the timing by 10 degrees or so to see if the power immediately drops off or gains.

[Kennymonster]

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.

[26th-Z]

That crank pulley looks more like a harmonic balancer, which I didn't think the L series engines used.

Although the pulley Kennymonster is using doesn't look like this one, Nissan competition part # 12303-E4100 with the correct front bolt and washer.

[Chickenman]

Had a dampner that looked very similar to that on my D-Production 240Z back in the late 1970's. Was a Nissan Competition number ( 12303-E4620 discontinued ) or a Tilton part. Can't remember which excatly, although I'm leaning towards Tilton.

 

Regardless, confirmation of the accuracy of the TDC mark on pulley is what you need to establish. Set the engine to TDC using a Piston stop. Or, you can also use a long thing screwdriver inserted in #1 Plug hole to confirm when piston reaches TDC.

 

Once you have established TDC, check the marking on the dampner.  If the TDC marks are lining up great. If not, scribe a new TDC mark on the Dampner and use a dial-back timing light to set your full mechanical advance. Disregard all other markings.

 

Note: VERY IMPORTANT. It may be worthwhile removing the crank pulley bolt and checking the overall length. The Nissan Comp dampner  and some aftermarket dampners ( Tilton ) required a longer crank bolt as the dampner was thicker at the mounting face than the stock unit. A stock crank bolt will be too short to provide enough thread engagement and will work loose. I bent a very expensive Tilton crank because a " Professional " engine builder made that mistake. Finding the longer crank bolt may be tricky, but ARP probably has something that will work. The current Nissan Comp crank bolt 99996-E1065 is not correct for Dampners that require the longer bolt.

[CanTechZ]

Although the pulley Kennymonster is using doesn't look like this one, Nissan competition part # 12303-E4100 with the correct front bolt and washer.

 

The crank pulley on my '70 non emissions car looks the same as your example, out of curiosity would it likely be the same comp PN?

 

Edited May 19, 2015 by CanTechZ