Proper pushrod measurement procedure
 

I'm finishing my 383 homebuilt project. I ran into an issue with the pushrods. Pushrod measurement procedure with hydraulic lifters is needed, thanks.

The following is what I found in GMHighTech (summarized): Adjust the pushrod checker so it butts squarely against the inside of the rocker's lash adjuster cup seat. (Note: during this process, the lifters should not have any oil in them as this will throw off the reading. But if you've already soaked them, the lifters are easily bled down.) Adjust the pushrod checker so it's firm against the inside of the adjuster cup and the end of the pushrod checker is difficult to spin (thanks to friction). Remove the pushrod checker and write the resulting length. Repeat the process on the exhaust valve.

Any other way ?

While there have been several "write-ups" on this procedure that can be found on the internet, here is one that is pretty straight forward:

http://www.compcams.com/information/Products/Pushrods/

If you don't like Comp Cams procedure, just try googling "checking pushrod length" and you will find some other well written descriptions. Most will agree that an adjustable pushrod is a must in order to find the proper length for your specific engine combination.

Get yourself one of these:

http://www.compperformancegroupstore...y_Code=PSHRDTL

Those are great, because it doesn't require a dial caliper to check the length. Then follow this (post #2):

https://www.camaroz28.com/forums/sho...shrod+geometry

Not a bad write-up.

It's worth noting though, that the roller-tip "sweep pattern" on the valve stem shown in that paper may not work in all situations, and probably isn't possible in most LT1 applications.

This is a whole thread unto itself... and it "may" be possible to set up your stem-sweep differently with the same length pushrod (depending how low you crank down the rocker) but there are many threads on this idea in this forum.

I'm partial to the idea of a "return sweep" placement that starts closer to center-line, rolls across it as the valve lifts, then returns back to midline as you approach max valve lift (and max spring pressure)... this makes the total sweep pattern tighter (keeping th roller from the edge), and places the max pressures closer to the valve stem center-line.

Thanks for the suggestion. I have the CompCam procedure, and it cannot be performed with hydraulic lifters and strong valve springs. Notice that with a hydraulic lifter, the valve spring would need to be soft enough to prevent the compression of the lifter spring. Either a solid lifter with the exact same dimensions as the hydraulic lifter or a soft valve spring are needed in order to check the sweep of the roller rocker tip on the valve.

Any suggestions?

What lifter and valve spring combo did you use to check the sweep?

Yes, I have the adjustable pushrod tool, and I followed the sweep check procedure. The problem I ran into was the lifter spring compressed (lifter discharged), reducing actual valve spring compression, and not allowing proper sweep.

Any suggestions?

The method I use is to convert one of your hydraulic lifters to a solid lifter by disassembling it and use small washers in place of the spring. I also use checking springs in place of the regular valve springs.

That's smart, I have plenty of spare lifters. BTW, why the checker spring if the lifter will no longer discharge?

I also used a "fused" lifter... but I used the springs in place, that's the advantage of a fused lifter imo.

You could make a case that spring pressure is a moot point, and a checker spring would make it easier to turn the engine over to do the sweep, but from a practacle standpoint, you'd have to remove/reinstall a spring on an engine with the heads mounted... easy on an engine stand, but kind of a pain in the engine bay (IMO). A lifter is much easier to swap than a spring IMO. :)


BTW... make sure the lifter you fuse solid, is the same as the set you'll be using. there are concerns of plunger-height differences between different lifter types (i.e. caddy racing lifters vs. stock vs. comp R's, etc...).

Just the same... it's important to check the sweep with a valve cover off once the engine has bee run and the lifters are pumped up. Cardboard comes in handy to catch the oil... as does a bump switch or a helper to tap the START position with the keys. Granted, by that time it's a bit late to change pushrods or lifters unless you plan on tearing off the intake... but it's good to check anyway before going WOT.