i'm building a 383. i have a custom ground cam and a set of dart heads. i need to find the right pushrod length.

i have a pushrod length checker. my lifters are set at the base of the cam circle. my head is bolted down. i just can't figure out how far down the rocker stud that i should bolt the rocker?

 

Comp Cams website has a tech article on measuring pushrod length.

Hope this helps.

 

To do it properly, you should be using a solid lifter. Trying to use a hydraulic lifter probably won't give you an accurate reading.

Using a solid lifter, you adjust the rocker to the specified valve lash. Using a hydraulic lifter you can try adjusting the rocker 1/2 turn from zero lash.

Before installing the rocker, use a Sharpie on the tip of the valve. Adjust the rocker then wiggle it across the tip of the valve. Rotate the engine so that the lobe is at maximum lift and wiggle the rocker across the tip of the valve.

Rotate the engine so that the lifter is back on the base circle and remove the rocker. There should be 2 scribe marks on the tip of the valve where you wiggled the rocker. These 2 marks should be centered on the valve tip. Keep adjusting the pushrod until both marks are centered.

If you don't have the lightweight checking springs, your valve springs will bend the length checking pushrod.

 

When the incorrect length is used, is an offcenter witness or wear mark a result? I noticed that 2 motors ago, I think the engine builder was a nucklehead. The motor was a custom grind Comp Cam, Harland Sharp and Dart heads as well.

 

You're almost done; start off with adjustable pushrod adjusted to the stock length. You then mark the valve stem tip with a Magic Marker. Install the adjustable rod.

Now it's trial and error time.

Install the rocker and poly lock and just tighten down the poly lock while watching the tip of the roller. When the rocker makes contact with the rod and is solid, stop.

Wiggle the rocker tip side to side to make a witness mark. Remove the rocker and look at the mark you made when you rubbed away the marker color.

The CLEAN area, with the lifter on the base circle of the cam's lobe, SHOULD BE ON the INBOARD THIRD of the valve stem tip, CLOSEST TO THE INTAKE MANIFOLD. If it's not, remark the tip, re-adjust the pushrod, wiggle and re-check.

Visually divide the valve stem tip into thirds;

INNER MOST THIRD IS WITH THE LIFTER ON THE BASE CIRCLE

MIDDLE THIRD IS WITH THE VALVE AT ITS MID-POINT OF LIFT

OUTBOARD THIRD IS WHEN THR VALVE IS FULLY OPEN

Once you nail the INBOARD position, the rest will be correct too.

Since aftermarket rods generally come in .050" increments, select ones closest to what you measure once the roller tip is correctly placed. You then add to that measurement the amount of preload you're going to run. The actual amount of preload should be the recommendation made by the lifter manufacturer.

You DON'T want the mark in the middle of the stem WITH THE LIFTER ON THE BASE CIRCLE OF THE CAM LOBE. That spot's for MID-VALVE LIFT.

Old Racer's Rule of Thumb, better to run a rod that's a little too long than one that's a little too short.

This is the quickest and easiest way and doesn't involve buying or making a solid lifter or removing the stock spring to install a low tension spring. None of that is required.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

thanks guys. i really appreciate it. that really helps.