i didnt check my stuff properly after my rebuild and i need help figuring out whats wrong. well i milled te heads .025 and used cometics .040 but used my old pushrods 7.4's today i set piston 1 to compression stoke and loosened the rocker bolt and my spring came up a bit. now i double checked to stroke and hand tighted the rocker bolt and there was no more play on the pushrod and when i went to torque it the valve started to compress is my lifter not preloading? or is this normal or is my pushrod too big i will b ordering a pushrod length checker soon but hope there is nothing wrong with my lifters even though it doesnt seem normal to me.

 

Even with the correct pushrod length, if the lifters are full of oil when you tighten them down the valve will slightly open until the spring force bleeds the lifter down. Having said that, it sure appears your pushrods are too long and I personally wouldn't attempt to run the motor and likely wouldn't turn it over by hand unless I knew things clear. Now is not the time to make a costly mistake, get the length checker and verify things.

 

The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:

FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.

Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.

I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.

Here it is again in a nutshell:

1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.

For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...

I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.

If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.

THIS METHOD ALWAYS WORKS!!!

Check it using the above method and see where you are.

Thanks,
Shane

 

^^^ so, with new lifters, after soaking them in oil are they ready to perform this test? Do you need to sub the valve spring for a dummy "helper" spring as not to collapse the lifter. Should you take an old lifter and weld it so it doesnt collapse?

 

Shane,

Have you measured this? With one turn on the bolt, the pushrod should deflect more due to rocker ratio (once the lifter plunger settles). Difference should be about 60%.

 

You want the lifters to collapse. That's what preload is.

Yes, measured at the tip of the pushrod with a dial indicator.

Thanks,
Shane

 

It can't be the same value as the bolt turn calculations, the rocker ratio will change the value.

 

I measured the preload at the pushrod tip of the rocker. That is a direct preload measurment. This was measured with 1.7 rockers. The difference between 1.7 and 1.8's would be negligable. This measurment was taken with a stock rocker and the stock 8mm X 1.25 rocker bolt.

Thanks,
Shane

 

I guess my point is if you move the bolt say one turn (0.049") then the pushrod end of the rocker must move more because the valve spring is the pivot point as the bolt brings the rocker pivot point down onto the support. In other words the bolt movement is less then the pushrod movement. I understand the measurement at the pushrod, that is the true preload and how I verify mine when I assemble as well.

 

I am not saying the 1 turn equates to .047" of bolt movement. I am saying 1 full turn of the bolt equals .047" or lifter preload as measured with the stock 1.7 rockers and stock 8mmX1.25 bolt.

Shane

 

One turn of the bolt is 1.25 mm or 0.049" at the bolt (1.25/25.4). I think the real point to emphasis is you guys actually measure to ensure correct preload as opposed to asking for a pushrod length without measuring and then finding out the hard way the length is not correct. This seems to be the method that many follow here rather then buy a $20 adjustable pushrod so the correct value can be obtained.

 

Although I sell many of the pushrod length checkers, I will tell anyone that you do not need one. I have done the math and the actual measurments for you. If you are dealing with stock rocker arms, the above calculations are correct. Anyone can achieve very accurate pushrod length measurments by using this method. As a matter of fact, it is much easier to get the correct pushrod length than with a length checker. The point is, you still need to make sure lifter IS on the base circle of the cam when checking by any method. Since most customers use pushrods that are only available in .025" increments, they will have to shoot for an acceptable preload range anyway. The method described above is very accurate and no special tools are needed if you have a known length pushrod within the common range for these engines.

Shane

 

When XtraCajunSS (Shane) talks about this...

2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
Is he referring to the old "tighten down the rocker and spin the pushrod till theres resistance" thats how you get zero lash?? Cause in here sounds like he's talking about the rocker arm bolt.

Probably a dumb question but hey "theres never a dumb question". Haven't been on here for a long **** time nor have I been under my hood for awhile but changed out cam and lifters (huge *** job) on sat. and now I read up on this whole LS7 lifters deal and probably having to buy pushrods as well so I gotta check.

thanks

 

If you soak your lifters you are going to get a wrong measurement. Why because the lifters tend to act more like solid lifters than hydraulic lifters when measuring. Set your lifters in no soaking, that way they are already collapsed. Then put your pushrod checker in place. Once you have one measurement do it again 3 times. If you get 2 out of 3 readings that are the same then use that length if you get 3 different reading then you are doing something wrong. I have done it like this just a couple of times since its not my first goat rope and I have never had issues.

 

By setting the lifters without soaking, then checking for preload, will you be doing all of this checking before bolting down the head? Then soak your lifters, set them in for real, and torque down the head after you get the measurements?

 

You should get all your measurements before soaking, then presoak them over night and set them in your engine when you are getting ready to do the actual install.

What you are doing is getting the correct measurements before hand. Reason being when you set them in and have everything torqued down the lifter will bleed out correctly under mechanical pressure like they are supposed to and your meassurements will be on point. Now to reduce valve train clatter I would set the tq specs to the high end if your using the LS7 replacement lifters. That will make sure that there is as little valve train noise as possible.

Also make sure to us the correct lifters with correct valve train. As basic as it seems some people use lifters like the Comp "R" and try to use stock rockers, when you have a preload of .002 -.004 when you need adjustable rockers, and then they are pist off when they have issues with things like HP and minimal things like that LOL because they can't set the lash or the preload correctly with stock rockers.

 

These pushrod length threads turn into such a pissing match. I did it just like shane said with my lifters soaked, using an old compressed head gasket, and bolting the head down with a couple bolts. Mine is quiet as ever with no issues.

 

Its not a pissing match. There are different ways that people do and have had success. How ever any one wishes to set their lash and preload is up to them, I do it how I have found it to work for me, I give my opinion and if some one has a problem with it then they can voice their opinion.

 

Shane,

I had the opportunity to check my method and yours as I was doing a pushrod swap this past week. In the end my calculations and your method are pretty close and I have sorted out in my head why I didn't understand how you got the values you did. Here's what I did.

When tightening the bolt, I snugged with my fingers to take out the lash and then gently rotated until the rocker bottomed out. Any bolt rotation after this point is not adding preload to the lifter but rather is preloading the bolt to obtain final torque. What I found was I had approximately 5/8 turn until the bolt bottomed the rocker, which comes out to 0.031" of bolt movement or through the rocker ratio 0.049" at the pushrod. (The value you stated above) I then tightened to the final torque value of 22 lb-ft, which required approximately another 1/3 turn for a total rotation from zero lash of around 1 turn. My dial indicator values are 0.054 so the two methods and measured values are within thousanths of each other.

Hope this all makes sense.

 

Please correct me if I'm misunderstanding this.

I thought the lifters had a spring in them so that if thier is no oil is in them (not soaked) they are still not "collapsed". Now with that being said its is easy to drive the lifter cup (piston) down into the lifter by turning the rocker bolt or adjuster down and not notice it. The oil on the other hand provides the resistance for the cup to not move much during normal high speed valve train operation but allows the cup to move up and down within its acceptable range to maintain Zero Lash while running.

So the reason we set a specific lash is to ensure we have our pushrods in the middle (engineered operating range) of the cup travel when the engine is at normal operating temperature. The design from GM then allows the lifter cup enough movement to maintain zero lash when running too hot (not sure how much too hot) by the cup moving up in the lifter to ensure zero lash and then still being able to move down far enough when cold to prevent the cup from bottoming which in turn would keep the valve open when the cam was on the base circle.
The aluminum LS's need the cup further down when cold then the iron blocks. This is because the aluminum block grows more than Iron one. That way as the engine gets hot and expand the cup can keep moving up (being held there by hydraulic lock and the lifter will not be asserting any pressure on the valve but still have zero lash (which makes it quiet).
I imagine there is some engineering calculations that allow x amount of pressure acting on the bottom of the cup from oil pressure which miantains the zero lask but is not high enough to open the valve.

vettenuts I like your posts as they are detailed and theory/procedure based.
XtraCajunSS Your method I was sure would work and would end up being correct as it was developed with lots of experience but was born out of the Shade tree style. Nothing wrong with shade tree but if the theory isn't also there its hard to understand the cause and effect which could make troubleshooting problems difficult.

different car people are drawn to different style wrenching!

Well after I rambled on here a final thought a fellow LS Mech and I were discussing. There are a lot of Head/Cam swap people complaining about their car sounding like a sewing machine or louder valve train noise. I'm guessing they are erroring on the short side of the lash range and with the aluminum blocks its just not quite enough. I will concede that erroring too far the other way would soon leave you with a burned valve which is way worse.

Please correct my interperation of the hydraulic lifter operation if it wrong.
thanks Ed