Hey guys, looking for some insight, advice on pushrod length. I included a screen shot of my general engine specs. For context, the valve train that I reused was pretty new, and didn’t appear to have any issues at the time of the rebuild, primed the motor for a while before starting, and one of the lifters bottomed out and caused a push rod to bend….now I’m on summit looking at new push rods and lifters. Ig my question is if you guys think that the push rod length of 7.2 seems correct. When I bought this motor that was the push rods and lifters that came with it. Along with the cam. I had called comp cam for there input but the tech was kinda rude and didnt really wanna help once I mentioned it was a crane camshaft. When looking at the geometry there was plenty of coverage on the tip of the spring/valve stem. And I had called AFR to ask why there I/E are clocked towards each other and the tech was super helpful and said that was normal for there heads. I do have an adjustable pushrod checker and can double check but I’m just trying to make sure this makes sense before I order a set of hardened pushrods and lifters

 

There's no way of knowing if what you have is correct unless you revisit the geometry in it's entirety.
You're halfway there with the adjustable pushrod and using whatever geometry method you're comfortable with, take some measurements and then verify the new length, or old length for that matter, as a starting point, and observe the contact pattern on the valve tip (via a magic marker "painting" of the valve tip). Narrow is key and centred is generally a hopeful thing.
Narrow indicates the pushrod length is there or thereabouts. Centred demonstrates that all of the components are working with one another. Both is best but historically in these engines, with the myriad of aftermarket and OEM parts involved, often difficult to achieve.
I prefer the Miller Mid-Lift Method for geometry verification. There are links posted throughout 3rdgen.org to the paper he published. If I can find it, I'll post it.
And for the record, his method does NOT involve the little plastic widget that some use to get the wrong result.
On a similar note, how do the valve guides feel at this point? Poor geometry will take out the guides and it's always worth a look to see if you've damaged anything. The aftermarket bronze guides aren't necessarily the most durable.

 

Nobody could guess what length you need. For all you know, stock length may be perfect.

Using lightweight checking springs, you're looking for the smallest sweep pattern on top of the valve tip. It doesn't need to be exactly center but should not sweep right to the edge of the tip. Using an adjustable pushrod, you can lengthen or shorten the pushrod until you get that perfect sweep then check the length and order proper length pushrods.

Building an engine is not the same as assembling an engine. Expect to tear it down a few times before it's finished.

 

What I like about Miller's mid lift method is that when done properly it guarantees the minimum contact patch across the valve tip. Even the rocker roller tip placement can be observed because the measurement is done with the valvetrain in a static position and no rotation is required. No checking springs either although admittedly, I double check my results with a full rotation using the conventional marker marker method and light springs. However, the lighter springs invite a certain margin of error as the valvetrain isn't fully loaded as it would be otherwise.

 

I have never had an issue getting it right with the plastic tool. Geometry is Geometry and the plastic tool has the correct angles for the rockers to be correctly oriented for the narrowest contact patch. Just have to add to what you measure with your adjustable pushrod for the lifter preload when running a hydrualic lifter. If your rocker arm has a recessed cup you will need to add its depth as well. Also keep in mind that pushrods have tolerances and you will not get 16 pushrods of identical length off the shelf. In reality if you are within +/- 0.050" of the ideal length it is not hurting anything especially on a mild street engine like that. Years ago, I cannot even begin to count how many different SBC engine combinations I ran stock 7.200 or 7.800 pushrods in over the years with milled heads, decked blocks, aftermarket cams, even LS7 lifters, aftermarket roller rockers and had zero issues out of. They were quiet and ran great. I have never had valve guide issues with one either.

My version of those head castings with 0.100" longer valves worked out with 7.300" pushrods with a standard base circle cam and now has 7.400" pushrods with a 0.050" reduced base circle. The 7.300s were a bit shorter than the ideal length but close enough they worked problem free.

 

If you want to use some generic plastic gizmo that doesn't take into account those variables you mentioned then have at it.
I've ruined more that one set of guides, and intake valves, because I messed up the geometry or did it in an uninformed way. Bronze isn't particularly durable. On the other hand, the cast iron guides in factory castings such as Vortecs, will take a beating.
Engines may run "forever" with poor geometry but I'll bet that forever isn't really.
Further to that, while an engine may run perfectly well and dyno numbers being of the happy variety, poor geometry will result in lost cam lobe information as it's transmitted to the valve via the rocker arm. If less performance is the objective, then that too is a decision that has to be made and lived with.
High performance engine building and valvetrain geometry at the 100% level go hand in hand. And getting there is easy and no tool is required other than calipers and a machinist rule.

 

Just me but I will trust the sweep pattern over attempting to measure it out as well. Mathematical calculations often do not pan out in real world. I have had aftermarket bronze guides in several engines as well. Honestly I am considering going with the Mercruiser 6.2L method and using their LS style rocker setup on my future SBC engines. Just have to reduce the threads from 7/16 to 8mm with inserts and have a much more stable, easier to setup rocker design. With the fulcrum sitting in a rigid carrier you no longer have to worry about the geometry change from pushrod length or rocker stud flex. No preload adjustment necessary either, just torque the cap screw down and done.


This is the cylinder head design on those 6.2Ls.

 

To each they're own. Although after measuring, I confirm with a "sharpie" test. This is how I determined that a backset trunnion rocker was needed so as to keep the narrowest sweep resulting from proper geometry but the longer pushrod placed the contact too far towards the exhaust side for my liking. A .050" backset trunnion pulled the contact back towards centre. This left about a .030" - .040" sweep which was right in the centre of the valve tip. So far so good.

As for the Mercruiser rocker set up, that's pretty slick. It does make it non-adjustable though doesn't it? I recall the initial setup when the LSX454 landed in the shop. We had to incorporate shims under the rocker pedestals to accommodate the bigger cam and have the lifter preload set correctly. Still it certainly does tighten up the valvetrain.
If I were turning more RPM for longer instead of 6500 for 12 seconds (or less) I'd opted for a shaft system too.