Determining TDC
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 1,234
Likes: 5
From: Herriman UT
Determining TDC
Isn't there a valve train event that will indicate that the #1 pistion is at top dead center on the compression stroke, or close to it? (e.g. cylinder #4 intake valve beginning to open) Just wondering...
Melting Slicks
Joined: Sep 2006
Posts: 2,736
Likes: 7
From: Redding CA
Yes, stick a screw driver inside the spark plug hole and let the pistons come up to touch the screw driver. You can also just spin the push rods with your fingers on cylinder number one...if you're able to spin it somewhat freely with your fingers than you are on the base circle of that lobe/and the piston is at the top.
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
At the top of the compression stroke neither vlv will open, at the bottom of the power stroke (the stroke after the compression) the exhaust vlv is starting to open. Is that what you are asking?
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 1,234
Likes: 5
From: Herriman UT
At the top of the compression stroke neither vlv will open, at the bottom of the power stroke (the stroke after the compression) the exhaust vlv is starting to open. Is that what you are asking?
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
I understand what you are asking but the ramps won't show hardly any movement at the top of the exhaust stroke on the other cylinder as it is just cracking at that point unless you have a lot of overlap with fast ramp rates. When I measured mine, at TDC of the exhaust stroke the intake and exhaust were only open 0.053" and 0.034" respectively.
6th Gear
Joined: Jun 2007
Posts: 6
Likes: 0
From: Grand Rapids Michigan
this worked for me
I did this recently while changing the valvesprings on my 02 z06. I turned the engine over by hand (in the proper direction, obviously) watching the INTAKE valve on the #1 cylinder. After it closed, I kept turning until it hit TDC. That should be TDC on the compression stroke.
Hope this helps - it's probably not the short-cut method you were looking for, but it worked for me.
Hope this helps - it's probably not the short-cut method you were looking for, but it worked for me.
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 1,234
Likes: 5
From: Herriman UT
I did this recently while changing the valvesprings on my 02 z06. I turned the engine over by hand (in the proper direction, obviously) watching the INTAKE valve on the #1 cylinder. After it closed, I kept turning until it hit TDC. That should be TDC on the compression stroke.
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6th Gear
Joined: Jun 2007
Posts: 6
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From: Grand Rapids Michigan
Thread Starter
Burning Brakes
Joined: Nov 2003
Posts: 1,234
Likes: 5
From: Herriman UT
Yes. If I remember correctly, TDC comes up fairly quickly after the intake valve closes. To find TDC, I used a little TDC finder that threads into the spark plug hole - I think I order it from Summit.
Alternatavely, what diameter / how much nylon rope would one need to jam in the spark plug hole to stop the piston at TDC?
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Pro
Joined: Mar 2007
Posts: 507
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From: Macungie Pa
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Yes the valve is fully open at (about) the bottom of the intake stroke then closes for the compression stroke. So 180 deg after that (TDC, both vlvs closed) is the cams base circle
