1974 260z timing issue

[Dolfinz]

Thanks for the explanation..  As soon as I get the clear picture of the cam sprocket I will post and we can go from there.

[Zed Head]

On 3/8/2021 at 1:17 PM, Dolfinz said:

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.

 

14 hours ago, Dolfinz said:

The lobes are flat and the crank is where the service manual timing mark shows it should be. 

Dolfin, you're contradicting what you wrote earlier.  You said the timing mark was in the wrong place.  How about a picture of your damper pulley and the timing plate?

Also not clear what you mean by "lobes are flat".  They should be sticking up like rabbit ears if you're on the compression stroke.

[Dolfinz]

In my prior statement I meant the timing mark on the pulley was at 10:00 and should be near 3 to line up with the 0 on the timing plate.  The timing mark on the crankshaft itself is at 3:00 as shown in the service manual.  I thought as long as the lobes were flat the valves were closed.  Do they need to be sticking up like you said?  I currently have the pulley and timing cover removed to verify the timing chain is correctly installed.  That's what I'm trying to determine.

[Zed Head]

The lobes should look just like this.  I stole this picture from a Google search that linked to a CZCC thread but the picture wasn't in it when I opened it.  In case someone recognizes it.

It's starting to sound like you're on the exhaust stroke.

[Dolfinz]

Thanks for this.  I will check.

 

Edited March 11, 2021 by Dolfinz
oops

[Dolfinz]

Let me know if these help.  Lobes on cam appear to be correct.

[Zed Head]

I think that you just have an aftermarket timing chain sprocket (three holes instead of four) with no notch so no need for the holes at the top, and either a bad damper pully, or the damper pulley has been installed with no key in the keyway.  Might be that your guy pushed the key out of the slot when he installed the damper.

I'd pull that damper and check the key and keyway.

Your sprocket only has three holes, the factory sprocket has four.  Edit - I guess it might possible also to install the sprocket without the locating pin.  I see the 1, 2, and 3 on the sprocket so something is weird there.  So, I'd pull the sprocket also.  Use the tool so you don't drop the chain.

Overall, both your sprocket and your damper don't seem to match piston location.  Might be that your builder had the piston on the exhaust stroke when he installed the parts.  So, maybe you're right but he was wrong.  This is my new theory - your builder installed the sprocket on the exhaust stroke and maybe just eyeballed the damper pulley without the key in the keyway because it didn't line up.  Either way, since you know you're at TDC on the piston, you need to get the damper and sprocket to match.  Pull them off on and reinstall and hope no valves were damaged.

Short answer - something is not right so it's best to take it apart and start over.

Edited March 12, 2021 by Zed Head

[Zed Head]

Forgot to ask - where is the damper pulley mark?  Can you post a picture of that?  Then you'll have TDC, cam lobe positions, and ignition timing marks.

[Dolfinz]

I can temporarily reinstall the pulley and post a picture but as I previously stated with it correctly installed and the keyway in place the timing mark on the pulley is at 10:00.  It should be on the zero on the timing plate correct?  That would need to be at about 3:00.  What confuses me is that's not 180 degrees out.  The pulley isn't the original but I still have the original and they are exactly the same.  Per the service manual everything appears to be correct except for the timing mark on the pulley.  I'm baffled.

[Zed Head]

Did you ever confirm/know that the damper timing mark was correct before the engine was rebuilt?  You started your story in the middle.

I don't think that any of the timing mark plates available sit at 3 o'clock.  That would be horizontal with the damper center.  Maybe you have your timing plate in the wrong spot.  10 o'clock sounds right.

I can't find a Z picture (it's the one weird thing about all of the FSM and Owners Manuals - there are no good pictures of the ignition timing marks) but here's one for a Datsun 1200.  It's about the same.  Around 10 o' clock

4 minutes ago, Dolfinz said:

That would need to be at about 3:00. 

 

[Zed Head]

Here's a grimey one.  It shows zero, but he has a later timing plate with an early damper.  A later damper would have just one notch, and sit at the zero at TDC.

https://www.zdriver.com/forums/280zx-s130-forums-77/can-i-get-crank-pulley-fit-34699/

Edited March 12, 2021 by Zed Head

[Racer X]

20 minutes ago, Dolfinz said:

I can temporarily reinstall the pulley and post a picture but as I previously stated with it correctly installed and the keyway in place the timing mark on the pulley is at 10:00.  It should be on the zero on the timing plate correct?  That would need to be at about 3:00.  What confuses me is that's not 180 degrees out.  

10 and 3 aren’t 180 degrees apart, more like 160/170.

It would be a good idea to start fresh. Set the engine at #1 top dead center. Then check the camshaft position to ensure it is in the correct position.

If it isn’t, reset the cam. A degree wheel is very helpful here, both for setting the initial timing up, and checking the opening and closing of the valves, camshaft lobe centers, etc.

If the cam timing is found to be correct, then there is some other issue.