Measuring Pushrod Length & Clearance

I started working tonight on testing proper pushrod length using a Twisted Flow adjustable push rod, Comp Cams check springs, and my Comp Cams High Energy roller rockers.

To test, I marked the valve tip with a dry erase marker.  I then installed the lifter, head gasket, head, rocker, and adjustable pushrod.  I set the preload at one turn past zero lash per the instructions with the lifters.  I turned the motor over clockwise for two full rotations, removed the roller rocker, and then checked the witness mark left on the valve tip.  The goal is focus the rocker's roller tip on the middle of the valve tip while minimizing the width of the pattern caused by the roller.

I just set the adjustable push rod by estimating and did a preliminary test.  Using the 7.100 push rod, I found the witness mark was a little low on the valve tip.  Additionally, the pattern was a little wide.

I decided to go ahead and try one of my stock push rods (6.800) to see if it by chance would still be long enough.  Unfortunately, the resulting witness mark was too high on the valve tip.  As a result, I need something in the middle of the two.

I set the adjustable push rod to between the two and ran another test.  This time the pattern was right in the middle of the valve and was quite narrow.  This looks about perfect to me.  I posted it on the SBFTech.com Forum and a poster named Woody who builds stroker engines commented that it looks perfect.

I searched the Internet while waiting for a response on SBFTech.com.  I found many suggesting a solid lifter should be used instead of a hydraulic lifter.  The hydraulic lifter would bleed out during the process from the pressure of trying to move the valve components since there is no oil pressure. 

I pulled out one of my old lifters and took it apart.  The lifter fills with oil which holds it firm.  Additionally, there is a spring in the middle.  I filled the area inside the lifter with washers such that it essentially became a solid lifter so I could repeat the push rod tests.

Using the solid lifter, I duplicated the results I found with the hydraulic lifter.  I could tell there was much more movement at the rocker.  When going through the process, I expected the width of the witness pattern to be larger with the increased movement of the rocker.  However, I was wrong and it is exactly the same as the first test with the hydraulic lifter. 

With this final test out of the way, I was positive I had exactly the right push rod length.  After a little checking with a digital dial caliper, I found it was almost exactly 6.950 so I ordered a set of Magnum Comp Cam push rods.  They should be here on Monday.

While I had the solid lifter installed, I put a little Play Doh on the pistons to check piston to valve clearance.  I then put the engine back together without the gasket (for extra clearance if it is close) and then rotated the engine over two full rotations.  I then did the same with the exhaust valve.  The intake valve has .256" clearance and the exhaust valve has .268" clearance.  In short, I've plenty of room in case I ever want to switch to 1.7 ratio rockers or a different cam with more lift.