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1974 260z timing issue


Dolfinz

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I recently had my stock engine rebuilt.  When I got it back I put the remaining parts back on and I can't get it to start.  First things I checked were compression and fuel; which were good.  Lastly I went to check the spark and I had spark but wanted to confirm the timing.  I set the number 1 cylinder to TDC and pulled the distributor and found the shaft to be at factory spec with the small lobe forward and positioned at 11:25.  I also checked the crankshaft pulley timing mark and found it to be at 10:00 and not near 3:00 as it would need to be to be at zero on the timing plate.  Thus I suspected incorrect mechanical timing so I removed the timing chain cover to verify. Please review the attached pictures of the crank and cam shafts showing the timing mark locations.  Per the service manual they appear to be correct, cam at 2:00 and crank at 3:00 and there are 42 chain links between them as specified.  Please let me know if I'm interpreting the service manual incorrectly or any suggestions as to why the timing mark on the crankshaft pulley isn't where I think it's supposed to be.  Thanks.

zcam.jpg

zcrank.jpg

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1 hour ago, Dolfinz said:

I recently had my stock engine rebuilt.  When I got it back I put the remaining parts back on

Which parts did you install?  The 42 links don't really matter once the engine has cranked over a few times.  And how did you verify TDC?  Did you actually check the piston height or did you assume because the cam lobes were up?

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The woodruff key is present on the crank, so the crank pulley can only go on in one position. And if the engine is at TDC then the crank pulley is in the right position and maybe the pointer is in the wrong position. on earlier engines, the pointer on the timing cover and the pulley marks are on the left (10 oclock) at TDC and on later engines, they're on the right (3 oclock).  so it sounds like you've got an early pulley with later timiny cover/timing marks.

Edited by jonbill
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19 hours ago, Dolfinz said:

I recently had my stock engine rebuilt. 

I set the number 1 cylinder to TDC and pulled the distributor and found the shaft to be at factory spec with the small lobe forward and positioned at 11:25. 

I also checked the crankshaft pulley timing mark and found it to be at 10:00 and not near 3:00 as it would need to be to be at zero on the timing plate. 

If you're sure that the #1 piston (the front piston) is at TDC, and that the camshaft is at "valves closed" on #1 then there are two possibilities for the missing or incorrect timing marks. 

Some of the aftermarket timing sprockets don't have the notch on the sprocket.  They just rely on using the 42 links for installation and there's no way to monitor chain wear over time.  So you might have to trust the builder on that.

On the damper ignition timing marks you might have the wrong combination timing mark plate/pointer and damper.  Some were on the left and some were on the right.

jonbill just replied but I'm going to post this anyway.

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Here's the thing, the crankshaft pulley and the timing mark plate are original.  Another note is that with the current set up the engine doesn't even attempt to fire.  Hopefully a better unobstructed picture of the cam shaft will help determine the problem.  I will post as soon as I can get it.

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18 minutes ago, Dolfinz said:

Here's the thing, the crankshaft pulley and the timing mark plate are original.  Another note is that with the current set up the engine doesn't even attempt to fire.  Hopefully a better unobstructed picture of the cam shaft will help determine the problem.  I will post as soon as I can get it.

The damper rubber can fail and the outer pulley will slip.  If you were 100% positive that you were at TDC, you would mark a new pulley to know where zero is.

All of the timing marks, both cam and ignition, are based on top dead center of #1 on the compression stroke.  So, either the damper has failed or you're on the exhaust stroke on #1 or the builder installed the pulley in the wrong spot.  Maybe he pushed the key out of its keyway.  We were just talking about that possibility in Wally's thread.

Anyway, everything starts with TDC on #1, valves closed.

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