s10xtremist

iTrader: (7)

Not another pushrod thread! Yes, I have a checker. This one should be easy but I overthink what I'm not so experienced with.

'08 LMG (5.3)
799 heads
TSP Stage 2 Truck cam (212/218, .550/.550)
Stock "LS7" lifters (looked identical in every way to originals)

Simple, preliminary calculations:
Heads have been shaved .020 and I'll be running .045" gaskets, so .006" thinner than stock. The cam's base circle is .050" smaller than stock. Assuming stock preload is/was perfectly fine, I simply subtracted .020" and .006" from the stock pushrod length then added .025" for the cam's smaller base circle. This gives me 7.384". So, these numbers say I should just stay with the stock pushrod length.

Physically checking:
I installed a "solid" lifter I made to simulate a pressurized lifter.
With a head on and using an old stock .051" gasket and 9 bolts (each end and center) cinched down with a 1/4" cordless impact, I put one of the best looking original pushrods in and torqued the rocker bolt to 22 ft.lbs. Turning the crank about 3 revolutions, I noticed the valve spring looked really close to binding. More accurately, all but 1, maybe 2 gaps appeared closed. With the rocker removed, the wipe pattern was too far down, which confirms the pushrod is too long. This would be even worse had I had the .045" gasket in place.

I stopped at this point since I don't have an easy way to remove the valve spring to use the checker with a lightweight test spring. I'm also not so sure about my using of the "solid" lifter. I've read so many forum posts from early 2000s to recent and about all I've concluded is to not bother with trying to count rocker bolt turns.

1) I can't explain why the simple calculations didn't coincide with actual testing with a stock pushrod. Any ideas?

2) Not understanding why the calculations didn't jive kinda killed my moral to proceed with the next hurdle- using the checker. I'm not so thrilled about finding more confusion and questions. Any words of guidance from the pros?

Darth_V8r

iTrader: (4)

Part of it is the solid lifter. It cannot preload so it opens the valve.

Leave the solid lifter in. Use the checker to find the length that gives you no valve lift but it fits snug. Measure that length. Then add .070 for preload. You will likely be in the 7.350-7.375 range.

Once you get your final length, double check yourself. Make your checker the final length including preload. Install on a normal lifter. Find dead soft touch with the rocket bolt. Where you just feel the pushrod tighten up but no preload. Then mark the bolt at 12:00. Tighten the bolt but do not torque it. Just until you feel it hit home. If you did it right, your 12:00 mark should now be somewhere between 9:00 and 12:00. Then you will get another half turn from bolt torque, which is where the 1-1/4 to 1-1/2 turn rule comes from.

RB04Av

I think you would be best served by getting an adjustable push rod, finding the length you adjust it to that gives zero lash by testing for play at the rocker and NOT the "twist the push rod" method, and buying push rods that are .070" - .080" longer than your adjustable at that point.

I'm personally not a fan of the "turns of the bolt" method, although some people seem to be able to get good results with it. It just always comes out too vague for my liking. I've had the right tool for decades, have lots of experience using it, and feel very comfortable with the results I get. Not least because, I've NEVER had it fail to find the right length.

I agree with Darth, you are most likely to end up with push rods that are slightly shorter than stock. Seems to be the most common, but BY NO MEANS universal, outcome.

s10xtremist

iTrader: (7)

So, with the engine running and with pressurized oil in the system, the lifters don't go fully solid?


I figured it should be something as simple and straightforward. Actually, 7.350 was one of the last figures I calculated in my head before I crashed from mental exhaustion last night.


Me trying to double- and triple-check by using various methods is likely why I'm confusing myself. I'm probably missing a number here or there or adding when I should be subtracting factors. I like this straightforward attack with marking the bolt and having target "checkpoints" for reference. Now that you mention it, I recall hitting ~1.25 turns on multiple occasions as I was playing around with it. Didn't take much stock in it since that wasn't what I was investigating, but I did take note of it.

Thank you for the clean-cut directions. I'll report back with the results!

s10xtremist

iTrader: (7)

I agree! Can't twist the adjustable pushrod since that would change the length. I'm convinced my difficulties and confusions are self-induced. Can't overthink this, but still have to "think" it.


Again, I agree. I don't believe it's defined enough for what we're measuring with this. I'm comfortable with using it as a "reverse-engineering" check of sorts, just to have that one extra facet of coinciding results. This isn't something I want to be vague about and I don't see how ANYONE would want to!


...Which makes people like you who I need to follow. It's not simply "practice makes perfect", it's "perfect practice makes perfect". The right tool means nothing if I don't know how to use it. Your and Darth's reinforcement is a breath of confidence. I just need to hit it again but with a clear conscience and organized plan.

Thank you guys!

RB04Av

Yes the lifters do go "fully solid"; but, only at the height that the preload sets them to. A lifter has an oil chamber under the plunger that fills with pressurized oil, and a check valve; the OP forces the plunger upward to the point of taking up all the lash; then as soon as the cam starts to move it, the oil attempting to flow back out forces the check valve closed, holding that height. Pretty clever really. When you hear of lifters "pumping up", that's what happens when the valve floats... the plunger gets forced up too far because there's "extra" lash, and then the valve can't close.

s10xtremist

iTrader: (7)

Thanks for explaining this!

So, more preload would yield less lift/valve opening, right? I mean, there appears to be quite a wide range of acceptable preload for these things. I'm seeing a range of .060" - .100" the most. If preloaded to .060", the lifter could go "solid" at a higher height than one at .100", yeah?

This can't be right- .040" variance?

Darth_V8r

iTrader: (4)

It is more common than you think due to tolerances stacking. If you use short travel lifters you can end up ordering four different pushrod lengths to to properly set preload.

And no, more preload does not mean less valve lift. It just means the pushrod is longer so the plunger in the lifter is further depressed vs less preload when the valve is closed. Too little preload generally ends up noisy.

RB04Av

No; valve opening stays the same regardless of preload. The lifter "solidifies" at whatever the zero-lash height is required to be. Preload determines the height that the lifter adjusts itself to, such that it takes up all the lash. After the engine has run for a few seconds the lifters reach a height that delivers essentially the full cam lobe lift to the push rod, minus just a few .001"s to close the check valve.

As Darth says, LOTS of things combine to affect push rod length. With lifters like the LS7, which have a fairly wide preload range, it's not a big deal; but with ones like Johnson that want .020" or something, the variation among parts becomes significant. Things like the depth that the valve seats have been cut to for example, or replacing valves, can easily have .020" of variation among cylinders, especially int vs exh. Most of the rest of the parts are fairly consistent; like, the head gasket is usually the same thickness for all 4 cyls; but there are still plenty of opportunities for things to be different.

s10xtremist

iTrader: (7)

I finally had time to check this with starting from scratch. I found two big mistakes and I wanted to post 'em here so the next noob Googling for such info won't do the same. First off, zipping down the head bolts with a 1/4" impact isn't enough. Once I used a torque wrench to cinch 'em down to 35 ft. lbs, my numbers suddenly started making a lot more sense. Second mistake was that I didn't have the rocker pedestal secured with anything other than the rocker I was working with. I mounted two old rockers, one on either side of the cylinder I was testing with to hold the pedestal in place.

Following what you listed, everything went as expected for the first time in all of this. Last weekend when I measured, I thought I had it figured out to 7.375" and was about to pull the trigger, but I just didn't feel assured. Glad I checked again! After making my corrections and starting from scratch tonight, I got 9.5 turns on intake and exhaust, which comes out to 7.275". I tried 1/4 turns on the checker to be more sure. Listing out all the preloads in .010" increments, 7.355" sounded the best at .080" preload. The next pushrod size down is 7.325", but that puts me at .050" preload. The next size up is 7.375" for .100" preload. I got all of these numbers testing with an old original .051" gasket. Subtracting .006" for the .045" Cometics I'll be running puts me at 7.349". There again, 7.350" for .080" preload sounds like a winner, right?

I did the double-check and, once again, the bolt turns worked out as they should've for the first time. With the 7.350" pushrod (via the checker), I got one full turn before the bolt bottomed out. It went only an 1/8 turn further when torqued, but that initial bottoming out may have been a hair heavy. I'm satisfied with all the numbers and actions.

You guys see anything I may have missed? I'd like to order some rods tomorrow.

Darth_V8r

iTrader: (4)

That to me sounds a lot more like it. Should be good to go

s10xtremist

iTrader: (7)

Thanks for you guys' help!

Stampede4ever

Well, this makes me feel better about my push rods. I measured and calculated - 7.375, and thought that was to short.

Stampede.

s10xtremist

iTrader: (7)

Just wanted to update for closure.

@Darth V8r , @RB04Av

Engine has been running great since first start about one month/800 miles ago. I hear nothing from the valvetrain and it revs smoothly and strongly to 6K. Thanks again for you guys' guidance!

To show my appreciation for y'all tending to yet another damned pushrod thread, here's some videos exploiting the results of your help:

Darth_V8r

iTrader: (4)

Vids sound great. I like the bottom one!!

s10xtremist

iTrader: (7)

Thank ya! I had the tuner leave as much lope as possible without causing it to load up. Makes the cam sound a little bigger than it is. It's obnoxiously loud since losing the cats, but I'm working on that.

Darth_V8r

iTrader: (4)

Lol. Come hear my car after it's running and then tell me about obnoxiously loud.

Very glad you are happy with the truck and the cam