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1976 Top Dead Center - how to find
I have a 1976 2.7L motor that I am converting over to ITB and fuel injection. I am adding a Clewett CAM sensor.
Instructions say " rotate engine through a cycle stopping 120 degrees before Z1 on the compression stroke" Assuming this is for cylinder 1 I have the engine out of the car and the valve covers off I can find TDS for cylinder 1 using a stick to see when the valve is up. How do I know if I am on the compression stroke (vs exhaust) Does anyone have a good method. I need to know before I drill for my CAM sensor. 
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Jared 73 Porsche 911 Targa 57 Chevy 3100 |
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05-11-2025, 10:42 AM
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Just went through this.
Check the valves on cyl 1- if they’re loose or wiggly then you’re on compression for cyl 1. Confirm that cyl 4 valves are not loose. Sent from my iPhone using Tapatalk
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-Julian 1977 911 S: Backdate, EFI/ITB, AC project in the works: http://forums.pelicanparts.com/porsche-911-technical-forum/1106768-when-well-enough-cant-left-alone-backdate-efi-itb-ac-more.html |
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05-11-2025, 11:36 AM
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Is there anyway that is a little more confirmed to check besides if they are wiggly. I need to drill the Cam sensor location and don't want to be wrong. Was hoping there was another way to do this to be certain.
thanks
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Jared 73 Porsche 911 Targa 57 Chevy 3100 |
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05-11-2025, 02:09 PM
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Location: Nash County, NC.
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If the valve is closed, the rocker is loose and the intake on #4 is opening so it’s not loose.
Bruce |
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05-11-2025, 02:53 PM
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You can look at the rockers to see if they’re on the lobes. Other than that, the wiggle method is the best way. Do it a few times and it’ll make sense. If the rockers aren’t loose then you’re either not at cyl 1 compression or they’re too tight and it’s time to adjust.
Sent from my iPhone using Tapatalk
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-Julian 1977 911 S: Backdate, EFI/ITB, AC project in the works: http://forums.pelicanparts.com/porsche-911-technical-forum/1106768-when-well-enough-cant-left-alone-backdate-efi-itb-ac-more.html |
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05-11-2025, 03:54 PM
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It's a 914 ...
Join Date: Jan 2008
Location: Ossining, NY
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Yep agree. You'll be able to tell if the valves are open (it would be about 1 mm on your engine) vs. totally closed. If closed, you'll have the .004" valves lash like when you check your valve clearance. I assume that's what is meant above by wiggly.
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05-11-2025, 08:29 PM
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Thank you everyone. I believe I have it figured out. That wiggle is slight, but I can feel the difference. Now on to drilling for the CAM sensor. appreciate all the replies.
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Jared 73 Porsche 911 Targa 57 Chevy 3100 |
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05-12-2025, 08:31 AM
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Need to use piston stop and degree wheel or you are just guessing
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05-13-2025, 11:03 AM
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If you haven't disturbed the distributor, pull the cap off and see if the rotor is pointing to #1.
You can also remove the other 5 plugs, leaving the #1 plug in, then rotate the engine over until you feel and hear compression on the cylinder. |
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05-13-2025, 11:32 AM
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Porsche
Chevy
