[grivera]

I measured for pushrods this past weekend and came up with an interesting pattern. Because I am using HR lifters, I had to get creative - so used the method Cliff recommends. This involves extending the adjustable pushrod until it bottoms out the lifter, then adjusting accordingly for the best pattern while keeping the lifter bottomed out. Once best pattern is obtained, one subtracts the extra length ( beyond the manufacturer’s recommended preload amount) to come up with proper length. In my case, that length is 9.0375. Using a Comp Cams 7704 adjustable pushrod .
The lifters are Comp Cams Evolution lifters which have .125 of travel and recommended preload is .0625

The cam is an OF1 (236/245, ..627/…632 with Harlan’d Sharp 1.65 rockers.) Valve spring installed height is 1.83”, heads are KRE 310 cfm, originally 85cc, shaved .030 for 81cc.

Following this I contacted JBP for recommendation on pushrods to buy and sent in the pattern. The tech said with 1.65 rockers I can’t go by the sweep pattern and that I should use a 9.2” pushrod. Any thoughts/experiences with this?

Pic attached is the pattern a 9.0375 - the left of the spring is the intake/rocker stud side

[steve25]

I am at a complete loss as to why with any rocker ratio being used you can’t go by the sweep pattern seen.

Maybe the person you spoke to knows that the sharps are much closer to being 1.7 and has seen that length he told you to use work better on average in actual use because that’s the only reason I think of for him to give you that length recommendation.

[grivera]

Here his message:

“With a 1.65 rocker my best guess would be a 9.200” pushrod (there’s more to it than a pattern on the valve tip) The longer rod should bring it slightly back towards center but more important the geometry through out the rocker travel will be much better.”

[4dblnkldude]

I'd go by your gut and what Steve said. That pattern looks perfect!

[chuckies76ta]

You have no way to make a solid lifter to check your work? It looks like pattern is on the inboard which I understand is better than on the outer area of the pushrod. https://www.youtube.com/watch?v=o5is9BsH5OU

[grivera]

Chuck - As explained in opening post, the HR lifter is made “solid” by bottoming out its travel. In this case .125” of travel. A little math afterwards to determine pushrod length. This is a method Cliff uses with HR lifters.

Yesterday I lengthened my pushrod tool to 9.2” as suggested by JBP, then added .125 for to bottom out lifter travel and checked the pattern - it was way to the outer edge of the valve tip. I’m thinking 7 rotations out even though more towards the outside is the thinner pattern.

I also checked at various lengths of the pushrod tool which has a range of 8.8 - 9.8” - each rotation out is .050 . Below are pics for 9.05” (5 rotations on tool), 9.1” (6 rotations on tool), 9.15” (7 rotations on tool). For the final length I will subtract .0625 to arrive at the center of plunger travel based on Comp Cams instructions.

[chuckies76ta]

I'm not disputing your work. In your original post you asked. Any thoughts/experiences with this? I've never done the measurement with bottoming out the lifter. I have always made a solid lifter and measured that way. I also made a mistake in my original post. The first pic is showing the pattern out board, which is not desirable. I included the video as this guy talks about the relationship of rocker travel. He says that at mid lift you want you roller in the center of the push-rod. My understanding is you want a narrow as possible pattern with it starting inboard, then mid point in the center then finishing out board. The other way I've checked for push-rod length is removing the inner and outer springs and using a checking spring. I believe the checking spring prevents the H/L lifter from collapsing. Just some Thoughts.