Valvetrain Geometry Question-Pontiac 400

[68nate]

I'm running 670 heads with spring installed height of 1.7 inches. With stock pushrods my rocker sweep is wide and to the exhaust side so I know I need shorter pushrods. I'm running a hydraulic flat tappet cam. My question is- Should I use a solid lifter to test the valvetrain geometry and then add the 0.020 inch to the pushrod length for hydraulic lifter preload? Anyone been down this road? Thanks, Nate

[Scott Parkhurst]

That's exactly how you do it - Just make sure the solid lifter is the same height as the hydraulic and you'll be fine. .020 isn't much- I'd add .100 if it were me. Measure how much the rocker moves with a half-turn on the poly-lock...that's your key dimension and I promise it'll be more than .020.

~SP~

[68nate]

Thanks for the info, that's what I was thinking- but 0.100" preload is too much. Comp cams recommends .020" to .040" preload- .030" being about half a turn. Nate

[Zee]

Or you can use a hydraulic lifter in a jam. Just pull the snap ring and put in washers until the slack is taken out then reinstall the snap ring.