Hotrodder

Hello.
I would like some second opinions on my push rod length checknig.
Chevy small block, faktory roller block. Vortec heads with Beehvie springs, TRW roller self aligning roller rockers 1:1.6.
Standard push rod length 7.2 inches.
When changing rocker arms, I decided to do a proper check of the valve train geometry, and to make it short: 7.6 inches push rod length gives the perfect geometry.
But by using this length, the wear mark will be placed very close to the edge of the valve tip.
Because of that, I did some testing with different lengths, including the 7.2" stock length.
I tested 7.6", 7.4", 7.3" and 7.2"
The shorter push rod , the wider sweep and the closer to centre of the valve tip, the wear mark ended.
What of the alternatives should I choose?
To make a visible mark in the valve tip, I rugged the pus rod a bit side to side during the test. Maybe that have widened the mark a bit, I don't know.

AlkyIROC

As long as it's not riding on the edge of the tip, any location is fine. The goal is to get the narrowest sweep possible.

Just buy one of these to determine proper pushrod length.



Drop it on the stud and let it sit on the valve tip. Adjust the pushrod until it's just about to push the tool off the valve tip. That's the pushrod length you need.

Those pushrod holes through the head are pretty small. Are you sure you need self aligning rockers? 1.6 rockers will move the pushrod closer the the rocker stud.

Hotrodder

Thank you for your answer.
I have this tool as well.
According to this, the standard 7.2" push rods are fine - contrary to what the mid lift measurments say.
That's why I got uncertain.

Push rod holes were widened with a 13 mm drill a long time ago before I assembled the heads.
I have driven with1.6 rocker arms earlier a short period, witout any clearance issues for the push rods.
With stamped rockers, tow. But still...

AlkyIROC

Using the tool will provide the length for the narrowest sweep on the valve tip.

BOOT77

Hard to tell from the pic angle But are you using a lightweight test spring to check?

Hotrodder

Yes.
Very light weight.
To avoid the hydraulic lifters to collapse.

According to information that I have been able to find, there must be (at least) two ways of "thinking" when it comes to push rod length:
1. Based on the mid lift method, the wear mark on top of the valve stem should be as narrow as possible, and a more narrow mark out of center of the valve tip is better than a wider mark in center of the valve tip. As long as the rocker arm don't goes off the tip, of course.
2. Wear mark should be at the center of the valve tip, no matter the width of the mark.

In a perfect world like on YouTube videos, the most narrow mark is achieved when is centered at the valve tip.
My experience so far is that this is not possible to achieve. One must compromize.
Personally I start to lean against my point 2, the "centered wear mark, no matter" version.
Especially with a full roller rocker arm, where the roller tip rolls back and fourth and therefore won't create so much back and fourth forces on the valve stem as if it was a non roller tip.
But I'm just an amateur with not much exeperience, so maybe that's wrong thinking.