So, had what I think was a lifter tick so the heads came off the LS2. I had the heads inspected, cleaned and rebuilt. We took .004 off the faces of the heads. Did a very light valve job. Machinist had to slightly shim the springs to get the installed height we wanted. I used GM MLSS head gaskets, I think they were .041 compressed. I previously was using 7.400 long pushrods. Not that it matters, but I have Comp 1.8 roller rockers, Lunati springs with about 400lbs @ .600 lift and a TVS2300 blower on the engine. The cam is the stock LS2 cam.

Anyway, I have it all back together and checked the pushrod length since so many small things have changed. I was hoping to reuse my existing Comp Magnum 7.400 pushrods but it looks like I shouldn't.

I installed GM LS7 lifters to hopefully cure the tick.

With my Comp pushrod checker I found that 7.300 was too long and 7.250 was too short so arrived at 7.275 at zero lash. That equates to 9-1/2 turns out (each turn is .050).

So, since I want about .080 preload, 7.275 + .080 = 7.355

So I want 7.350 pushrods.

 

If I stayed with my 7.400 pushrods that would be about .125 preload, I'd think that would be too much.

 

Your math seems correct but….valve jobs…even light ones…make pushrods shorter, because the valve sinks. Thinner headgasket makes pushrods longer, because the valves get closer to the deck. I’d think the thinner headgasket would override the valvejob difference, and you’d need longer pushrods, not shorter than OEM, even with the stock base circle camshaft. LS7 lifters, no matter the brand usually have a similiar cup height. Bottom line here is trust your math, because math doesn’t lie.
I just wrapped up another build today, and I can attest that if your measuring PR length with a caliper, you’ll notice that the OEM PR is 7.396-7.398. Aftermarket PR’s…in the case I ran into on this build, I used BTR PR’s…they measure longer with a caliper than advertised. His 7.375 PR measures 7.398 with a caliper. Most aftermarket PR builders go by gauge length, not caliper length. In comparison, I pulled a set of BTR 7.425” PR’s out of the cabinet and they measure 7.448” with a caliper. Just something for you to consider here when ordering new PR’s.

 

Pretty sure the head gaskets are the same compressed thickness as the OEMs I took off. Both were GM MLSS. The originals looked exactly like what I was putting on. I don't think the gaskets caused any change. Both exhaust and intake measured the same at the pushrods so confident I got accurate measurements there. Both the surfacing of the heads and the valve job would relate to needing shorter pushrods if all other things stayed equal. If I recall, when I originally put on the new rockers and springs, I ended up using a fairly deep preload (like .090) as that was the closest to what I was attempting to achieve. Anyway, I didn't just do math and calculate, I actually measured, three times, and did the appropriate math from there to get to the preload I want. Just a little surprised that the surfacing and valve job added up to that much. I really thought the 7.400s I had would still work.

7.350 pushrods have been ordered. I should be at a .075 preload.

Comp had something in their instructions about not being able to just measure the overall length of the pushrods, you have to measure somewhere farther down the rounded end of the pushrod ends to get the actual functional length. I don't remember all the details.

 

As long as you were able to repeat the measurements, then 7.350" is what you need. I get the propensity to doubt the result because it differed from the expectation, though. When I was assembling my dad's 5.3 using all factory components, I was coming up with a 7.350" length. I went over the method a few times because I was expecting 7.400", but I always came to 7.350". It was correct, and I learned to let go of preconceived results because that's exactly why we measure.

 

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