Working on determining my pushrod length. This is 6.3. Would you send it or go a bit longer?

 

I wouldn't send it or get longer push rod. There is something wrong with the geometry or the way you are checking the sweep pattern.

I would use a jiffy marker, cover the whole end of the valve, then get an adjustable push rod and check correctly.

The width of the pattern should be less than 1mm.

What heads and rocker arms are you using?
Pedestal mount, adjustable, roller tip, roller rockers?

 

AFR 165 heads pedestal mount and scorpion 1.6 rockers. It’s a 96 302 roller. I have an adjustable rod. Torqued the heads to 50 with head gasket. Tightened the rocker bolt till zero lash then 1/4 turn til 20lbs. Rotate the crank. I’m using a dry erase marker to check. With 6.4 the sweep is close to center.

 

That’s a pretty wide sweep.

Check your geometry at half lift—the rocker should be 90° to the valve stem at that point. If it’s not, the sweep will be wider than it should be.

Pushrod length mainly shifts the sweep pattern across the valve tip. Longer pushrods move the pattern toward center/exhaust, shorter pushrods move it toward the intake.

On a pedestal setup, shim height affects both the sweep width and where mid-lift occurs.

Based on your pattern (starting intake and moving toward center), the geometry looks too high—you’re likely hitting mid-lift too early. I’d try reducing shim height and/or a slightly shorter pushrod, then recheck the pattern.

 

Did you put the dry eraser on the roller of the rocker?

 

yes and it’s a pain. Too easy to rub off. I am going to use a sharpie this evening

 

You don't put it on the roller, you put it on the tip of the valve stem.

Or, put some scotch tape on the valve stem and sharpie on the tape.

 

Thats right. On the valve stem. I was able to do a bit of work over lunch. Here is what I have now. 6.38. Much better. Centered and narrow

 

If you have a bolt down pedestal mount rocker arm the pushrod length should not really change the contact pattern to any great degree. It will change the rocker ratio because it changes the position of the adjuster.

Either way where the contact occurs on the end of the stem makes no difference. The only thing that matters is the pattern of movement. For most rockers the contact point should sweep outward until mid lift where it stops and then starts to sweep back inward toward max lift. If it is inboard or outboard does not matter just as long as it doesn't run off of the edge you're fine.

 

Thanks. I am happy with where it is now. I can now order the pushrods and get on with the build. Would you shoot for .030 preload?

 

.030 preload should work fine.

 

Sweep pattern looks great compared to the first picture, nice.

 

Why would the sweep pattern change at all if he has a bolt down style rocker arm when changing the length of the pushrod?

 

I had the wrong lifter in during the first test and realized I had not torqued the rocker which elevated the trunnion causing the geometry to be off. I put the correct, shimmed lifter in and got the rocker torqued correctly and it fixed the sweep. I will test it on the exhaust valve and confirm. Measure 20 times and cut once.

 

That makes sense. One thing I always hate about doing this on a hydraulic valve train is that even with a soft checking spring sometimes it can be moving target.