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1974 260z timing issue


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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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Can you explain the diagram further?  I'm going to remove the fuel lines and provide a clearer straight on picture of the cam sprocket.  Perhaps that will help.

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zed head, I had to reinstall intake, exhaust, fuel lines and carbs, oil pump and distributor and all coolant related parts.  TDC was confirmed on compression cycle and verified by piston height.

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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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4 hours ago, Dolfinz said:

Can you explain the diagram further?  I'm going to remove the fuel lines and provide a clearer straight on picture of the cam sprocket.  Perhaps that will help.

The thrust plate has a small indented line, about 1/4" long.

20210309_145225.jpg

the cam sprocket has 3 V shaped cuts on the backside for the 3 timing chain adjustments.

20210309_145329.jpg

the line should be a frog hair to the left of the V for proper chain tightness. This is also another indicator of TDC.

20210309_145521.jpg

hope this helps.

 

 

 

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I just noticed something. Your cam sprocket "window" should show the top bolt of the thrust plate. Your's needs to be farther clockwise I think. The bolt is not visible in the photo you posted.

Screenshot_20210309-155134_Samsung Internet.jpg

Edited by siteunseen
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I think you have the cam sprocket on wrong somehow. There's a couple of things that aren't right. The small dot shouldn't be above the TDC window. Looking at a sprocket I have the V notch isn't in the same spot as the dots on the front side. I'm sorry if I confuse but that's what I'm seeing. Good luck, I'm gonna hush up now. LOL

 

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Here's an old thread about the notch and groove.  Some familiar names in it.  Not sure that the windows would need to be at top if there's no notch.

 

Edited by Zed Head
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I'm remembering the ocd things I did to get tdc. With the 1st and 2nd cam lobes kind of bunny eared or the smaller ends up, I used a feeler gauge on the 1st and 2nd rocker lash pads and the cam lobes to get the same gap (thickness/thinness). When they were equal to each other that was TDC.

Smarter people correct me please but that's what I rember. 

Edited by siteunseen
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I think the question isn't the cam alignment but the crankshaft and it's associated pulley.  With the crank at TDC as shown in the picture and the fact that the pulley can't install any other way due to the keyshaft doesn't that mean the the timing mark has to be in the wrong place?

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There's only one keyway.  It's relation to piston #1 will not change.

35 minutes ago, Dolfinz said:

that mean the the timing mark has to be in the wrong place?

Maybe.  That's what I meant when I said the damper pully might have slipped.  They tend to slip before they come apart completely.  You can pry on it and see if it moves.

Here's what they look like in two pieces.

 

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What other method is there?  We turned the motor to verify compression stroke and the piston was verified at TDC by using a screwdriver inserted through the spark plug hole to insure it didn't fall once it rose to it's maximum height.  The lobes are flat and the crank is where the service manual timing mark shows it should be.  i still question that since the lower end was rebuilt by one shop and the head was installed afterwards if the lower end wasn't 180 degrees out with the new head possibly putting the timing mark on the pulley out of alignment?  Perhaps the lower end was on the compression stroke and the head was on the exhaust?  I'm not a mechanic and this is confusing.  I have personally rebuilt this engine 3 times and this has always been the most difficult part.  Having others involved has only clouded the situation regarding the work that was done.  I don't believe the damper has slipped on the pulley as I have two pulleys that are exactly the same.  I really appreciate the help y'all are providing and I think we'll figure this out.  Keep the ideas coming and thanks.

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at the bottom end, there isn't a difference between compression stroke or exhaust stroke. theres just pistons going up and down. the cam timing determines whether a piston up stroke is compression or exhaust. 

so if the piston #1 is at TDC (determined by your screwdriver) and the cam dowel is correctly engaged with the cam pulley and the marks line up on the cam pulley and the thrust plate, then #1 is at TDC on compression stroke. 

Then if the distributor drive spindle is aligned 11:25 with the tang offset to the correct side (which side? can't remember!) then the spark timing is in the right ball park and the engine should attempt to run if you have sparks and fuel. 

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