finding TDC to set valves?
Racer
Joined: May 2012
Posts: 257
Likes: 12
From: las vegas nevada
Had some difficulty doing this recently myself. I found by rotating the engine, I could tell when individual valves were closed, and just torqued those rocker arms to 22 ft lbs at that time, regardless of wherever the crank/cam was. If I could push on the push-rod side and get a little play, then the valve was closed or close to closed, no?
Team Owner
Joined: May 2001
Posts: 87,391
Likes: 1,593
From: Western NY
Had some difficulty doing this recently myself. I found by rotating the engine, I could tell when individual valves were closed, and just torqued those rocker arms to 22 ft lbs at that time, regardless of wherever the crank/cam was. If I could push on the push-rod side and get a little play, then the valve was closed or close to closed, no?
Drifting
Joined: Jan 2012
Posts: 1,341
Likes: 8
From: Hopatcong New Jersey
How much difference this would make unless your new cam has a decent amount of lift, I have no idea.
Last edited by dblerman; Jun 22, 2013 at 11:06 AM.
Team Owner
Joined: May 2001
Posts: 87,391
Likes: 1,593
From: Western NY
Why not? In the OE configuration, GM sets the preload by the pushrod length, since the OE valvetrain is not adjustable. 22 ft/lbs is nothing more than the proper torque for the rocker trunnion bolt....
Drifting
Joined: Jan 2012
Posts: 1,341
Likes: 8
From: Hopatcong New Jersey
I'd be curious to see how far off the torque would be between base circle and partial to full lift.
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Drifting
Joined: Sep 2009
Posts: 1,719
Likes: 4
From: cinnaminson n.j.
St. Jude Donor '14
I believe the reason for the procedure is avoiding piston to valve contact. If a piston is at tdc at the end of the exhaust stroke, both valves are open. How much will vary with lobe profiles. If a lifter is pumped up with oil and the rocker is torqued, the valve could hit the piston before the lifter bleeds down.