Im not sure if im goin crazy but i need someone to confirm;

With an adjustable pushrod length checker im measuring for pushrod length. With zero lash you can still pivot the rocker and compress the plunger on the LS7 installed lifter. This will go away once there is oil pressure, correct ? Im just adding .070 to zero lash and when the lifter is pressurized the remaining slack will be gone.

 

Zero lash is the point at which the push rod is just long enough that there is no play all the way between the rocker tip and the push rod seat in the lifter, with the lifter plunger fully extended and the roller sitting solidly on the cam. There is no "slack" whatsoever in anything at that point, but the lifter plunger is not depressed at all either.

Yes you can generally push the lifter plungers down by hand when there's no oil pressure; especially new ones or if they've sat around for awhile. That has NOTHING to do with zero lash. Once they fill with oil they get quite a bit harder. Oil pressure will NOT take up any "slack": it can't push the plunger out any farther than the retainer will let it go.

Use the adjustable push rod to take up all the "slack", WITHOUT depressing the lifter plungers. Do this on both valves of several cylinders; I like to use #1, #7, #2, & #8. Then add your desired preload to that length and order that. Since you can buy push rods in .025" increments, and in half-sets even, it should be easily possible to get all of them to within a range of .075" - .090". Remember, as parts wear, preload goes away; therefore slightly more than "ideal" (emphasis on slightly) is better than too little. The LS7 lifters seem to want about .080" or so, so that's why the range above is a good goal. Stock push rods are 7.400" long; you should come up with a zero-lash length of something in the 7.300" - 7.350", most likely, meaning you'll end up probably wanting to buy them somewhere in the 7.350" - 7.450" range. If you come up with something very far outside of that with stock rockers, go back and re-check your work.

 

I needed this confirmed. Thank you. Slack was a poor choice of words. I just switched from Lunati High RPM Link Bar back to LS7 and the plunger seemed to depress a lot at zero lash. It kind of freaked me out.

 

I just read this and I also just went through the measuring process..... and I'd like to be sure I'm going to order the "correct" length pushrods.

OK, I want to know how you "pick" the preload to be used. Is it different for different brands of lifters? I'm using Trick Flow hydraulic rollers.

I've seen people using .050, .070, etc. SO, what determines what preload you want/need to add in to your measurement.


Thanks

 

Different lifters have different requirements. Also different people have different thoughts about what constitutes "ideal". Not so much that one is right and others are wrong; as, suitability for purpose. For example it's often better to run less preload if you intend to run continuous high RPMs. But some people just get fixated on a # for no particular reason, and that's OK too, as long as it's within the lifter's design limits.

On top of that, in many ways CONSISTENCY among them all, or at least between all int and all exh, is sometimes more important than the absolute #.

Generally though, "stock" lifters want around .050 - .060". LS7 ones want more like .075 - .080". Some of the aftermarket ones want FAR less than that; like Morel if memory serves, want .010 - .015" or some such. But don't take my word for it, trust your lifter mfr.

 

Yes, Does anyone know what Trick Flow recommends for preload on their LS Hydraulic Roller Lifters?

I want to order pushrods and I can't find any information on this.

Their tech info group ignored me when I asked about why their timing chain dampener didn't have the "snug fit" it was supposed to have. Ended up pulling it and going without one, so I'm less than impressed with that result.

 

It’s a good idea to measure each/all the valves. You never know what you have until doing so. When my engine arrived, I didn’t realize that water had found it’s way into the intake & valves. Several valves were affected, and cleaning them, or a valve job would not remove the rust. The valves were replaced, leaving me with several new valves, combined with the existing valves. This left me with a couple of different valve lengths, even after valve job. After measuring all, I am sure that everything is proper, and all power is delivered.

 

Zero lash is the moment you no longer have any up and down slack in the system. So, with an adjustable pushrod checker, it's when you've extended the pushrod to the point where the rocker tip no longer can move away from the valve.

I like to do it with the trunnion just snugged to the head with no preload in the bolt. Then you adjust the pushrod checker until you have no movement. From there, you can add the desired preload to the length of the checker.

Torquing the bolt will add a slight amount of preload, but it is generally bolt stretch and not enough to really throw off things. Even when I ran .058" travel Johnson short lifters I didn't really worry about it.

If you're not running something like the Johnsons where it's very important to get within a .010" window on all 16 lifters, checking an intake/exhaust on both sides is probably enough with the LS7 lifters. They have around .200" plunger travel.

I would aim for about .080" of preload there. Should be quiet and stable to 7000 with light valves/right springs.

 

Easiest way to do this is soak the lifter in oil then use a push rod to pump them up. They should stay up after this so there is no guessing where zero lash is.

 

Rotate the engine so the cam is on the base circle (no lift). Put some teflon tape on the threads of the check rod so it doesn't move around on you. Make the check rod too short and set it down on to the lifter. Have a very light touch and don't compress the lifter any.

Set the rocker arm in place and screw down the bolt until the rocker seats firm on the pedastal. Hand tight is fine.

Begin extending the check rod bit by bit and wiggle the rocker. Zero lash is where the rocker just gets to the point where it won't wiggle anymore. In other words, you've taken up all the slack between the check rod and the rocker WHILE HAVING A VERY LIGHT TOUCH AS TO NOT COMPRESS THE LIFTER ANY.

Remove the check rod and measure its length with a caliper. Don't use the "turns of threads" method to calculate the length of check rod. I have four Comp Cams check rods and none of them are close to the advertised length, so it just spits out junk numbers using the turns method.

Then you're going to add to that the amount of preload that the lifter manufacturer recommends for their lifter. You also need to add more length to account for growth of block and heads when hot. And you need to add one more number to account for the difference in shape of rod tip compared to the rod tip of your check tool. All this adds up to the length of pushrod you need.

Call the pushrod manufacturer to get recommendations of the growth numbers and push rod tip numbers. (Manton knows what they're doing and won't lead you wrong).

All told, all the gnats *** accuracy doesn't matter a lot if the lifter has a large acceptable range of preload. But it's still smart to aim small.

 

That's good advice on the tape. My comp pushrod check has tape on it. Makes it so it doesn't move around. They like to move. They are loose.

 

"And you need to add one more number to account for the difference in shape of rod tip compared to the rod tip of your check tool"


this is is something I wonder about every time I read "just measure for length, add your preload, and order that size". I was always taught that there are three ways to come to an overall length of a pushrod: theoretical length taking into account the curvature of radius of the tips, actual measured length across the tips, and something else that escapes me. How many people just measure straight across with a caliper (and add preload, of course), and just order that length?

 

The main confounding factor in "measuring the length" is, the tip is spherical, but the hole in the middle takes away some of the length from the complete spherical shape. The "nominal" length assumes that the tip is the whole sphere, so that variations in the size of the hole (a function of variation in the wall thickness and the mfg tolerance in the crimping process) don't matter, as well as allowing for consistency regardless of intentional differences in wall thickness.

I just kind of dodge that all with the adj pr... mine is 6.8" all the way screwed down (it's the Comp "Hi-Tech" one, says the length on the side) and is ¼"-20 thread, so it gets .050" longer per turn. (1" ÷ 20) Keeps all the rest of that out of the mix. I've never had the problem QwkTrip speaks of, not sure how that could happen, not that I don't believe him, but in all the motors I've ever built with it, it's never been an issue for me. I like his Teflon tape tip although I've never really had a problem with that either, but it definitely would help stabilize the whole thing and keep you from making that one error anyway.

Of course the "lost" length due to the hole is fairly easy to estimate; maybe .012" - .015" at each end I'd guess for most of them, which depends on the mfg details of the particular adj pr you are using. So if you try to mic it, you should probably add .025" to what the mic says, to come up with something close to the "nominal" or "trade" length, i.e. what to order.

 

The above might explain why GM says stock pushrods are 7.385, rather than the commonly stated 7.400.

 

I do that, but then I specify - as measured with a caliper. Works well with Manton

 

But not why comp 7.400 measure 7.407. The gauge length is actually measured with a cup similar to the lifter cup on each end of the PR. Again, when ordering, best to state measurement method. If you are working with ls7 lifters and .200 travel, no big deal. If johnson 2126st, then it is a very big deal.

 

Isn't the plunger spring in the lifter supposed to keep the plunger at the top, when there's nothing pushing down on it, even if there's no oil in the lifter?

 

Yes, but in lots of them it's not all that strong. It's real easy to overdo it if you get too enthusiastic.