This seems as good a thread as any to post pushrod length checking questions in. Sorry for the length, just trying to be thorough. Combo - stock LS6 short block, TEA-ported 243s w/PAC 1518s and stock LS6 valves, stock rockers, stock lifters (plus 1 converted to solid), EPS cam (222/226 115LSA).

Before I get into my conflicting results, let me start with a couple basic/stupid questions... How does one bolt down the head when doing pushrod length checks? Since I'm using a lifter I converted to solid, I obviously will need to get it back out. I don't want to use my new head gasket or new head bolts, since they're single use. So, for now I've installed the head with the old head gasket and old head bolts. (Note that these "old" parts are from a zero-miles new long block.) Is there any issue with using the old head gasket? Do I need to go through the full pain-in-the-*** torque sequence for the head bolts, or is it enough to just do the initial 90deg turn in sequence?

OK, with that out of the way, here's my issue. I'm getting conflicting results using 2 different techniques and would appreciate some assistance.

I took 1 lifter out of my dead LS6 and converted it to solid. I measured the plunger depth on the solid lifter and compared it to 4 of the new lifters from the new engine - good to go, the solid lifter has the plunger at 0 preload.

I put the solid lifter in the #1 intake, normal lifters in #1 exhaust and #3 int and exh. Using a Comp adjustable pushrod (6.800 - 7.800") I come up with 9.5 turns to get me to zero lash. If I go to 9.25 turns, the rocker still has some jiggle in it when the rocker bolt is snugged down; if I go to 9.75 turns, the intake valve starts to open as I snug the rocker bolt down. So, I'm pretty certain 9.5 is the right answer. 6.800 + (9.5 * 0.050) = 7.275" with 0 preload. There are, of course, a million opinions on what preload "should" be, but if I go with 0.075" I get a 7.350" pushrod.

I then decided to try "Shane's method" on the #3 cylinder. I put stock LS6 pushrods in for both intake and exhaust and went through the procedure. For both I got ~1.4 turns to get from zero lash to 22ft-lb. Assuming I've read this thread correctly, that means (per Shane's method) that the stock pushrods are the correct length. I've read here that the stock pushrods are either 7.400" or 7.385"; either way, Shane's method gives me a longer pushrod than the solid lifter + adjustable pushrod gives me.

Any thoughts on where I should go from here? Obviously I need to check my results a couple more times to ensure they're repeatable. I also have TFS 7.400" pushrods (which Geoff @ EPS supplied, as he figured they would probably be the right answer), so I can try those rather than the stockers, just to see if that gives me a different answer. My initial inclination is to think the solid lifter + adjustable pushrod is the "right" way to do this and should give the more accurate answer, but I was surprised that the length I came up with using that technique was quite a bit different than Shane's method.

 

If I run the numbers based on my motor (1/3 turn after rocker seats to reach 22 lb-ft) I come up with 0.083" preload for the 1.4 turns you measured on cylinder #3. Do you have a dial indicator by any chance to measure the preload on cylinder #3 as you tighten from zero lash. Neither method is real accurate (down to thousandths) but I would agree the two measurements are outside what would be expected for a difference. If you don't have a dial indicator, using the 7.400" pushrods to re-check on cylinder #3 would be interesting second point. Also, one note on the method of counting turns, the zero lash point is critical. Are the lifters new? I found when using new empty lifters finding zero lash was a delicate procedure because the plungers were so easy to move. If you are using the method of rotating the pushrod to find it, try moving the rocker tip instead (get rid of any "tick" "tick").

 

ok...again...here is the single best way to measure your pushrod length. Get a couple of adjustable pushrods. Put the cam on the base circle of the cylinder you want to check. I use a hydraulic lifter because it has the plunger at the top of it's travel and is the lifter I will be using in service. Now, with the adjustable push rod installed and adjusted short, install and torque your rocker arms for that cylinder. Carefully adjust the pushrod out until you have zero lash. You tell that by a slight drag first noticed on the push rod...or by the clearance in the rocker being gone. You can do that with all the cylinders you want. With each cylinder, once you have found zero lash, measure the push rod. Mark it down. When done, find the average length of all cylinders and order the push rods with the depth you want added to the length. Say you want .050 into the lifter and the pushrod measured 7.327 at zero lash. You would order 7.375 push rods as that is the closest. You can order special length if you want...you can order different lengths for each cylinder if you want. That is overkill, but you get the idea. This method ensures you have the exact depth into the lifter you are looking for. No guessing about how much each turn...quarter turn...etc. gives you.

As for using old head gaskets...yes. As long as you are using the same used gasket you are going with new, that is the way to go. If you are changing gasket compressed thicknesses, you must measure and compensate with your final measurement.

 

OK, thanks for the confirmation.

That is essentially what I did last night, as my converted solid lifter is just a hydraulic lifter with the plunger at the top of its travel. Unfortunately, with just the 1 solid lifter and 1 adjustable pushrod, it's not particularly convenient to check and compare multiple valves. I could use the adjustable pushrod with my hydraulic lifters, but they're so soft that I'm not sure how repeatable my results would be. I guess it can't hurt to try - I've got all hydraulic lifters in there now.

Yes, new lifters from the crate long block. I did notice that I can push the plunger down pretty easily, so I'm trying to be very gentle when getting to zero lash. What I've been doing to get to that point is grabbing the tip of the rocker between my thumb and index finger and lightly moving it straight up and down as I slowly tighten the rocker bolt until I can no longer feel or hear the "tick tick" on the valve tip. When I get to what I'm calling zero lash, I can still move the rocker side-to-side (since the bolt really isn't all that tight), but the up-down movement is gone.

I did the 7.400" pushrods on #1 and #3, and the stock pushrods on #5 and #7. (My fractions of a turn are just based on eyeballing it, so 1.4 is 20-30deg short of 1.5 turns, 1.6 is 20-30 more than 1.5 turns, etc.) I did each one twice and got...

#1 intake - 1.75, 1.7
#1 exhaust - 1.7, 1.7
#3 intake - 1.75, 1.75
#3 exhaust - 1.6, 1.6
#5 intake - 1.35, 1.35
#5 exhaust - 1.4, 1.4
#7 intake - 1.35, 1.35
#7 exhaust - 1.4, 1.4

Based on these results, and based on holding the two pushrods side-by-side, the stockers are not 7.400" (or maybe they are but based on different gauges for gauge length or something like that?).

 

OK, reattacked using the adjustable pushrod, although I had to do an iterative approach rather than the way OldCobraGuy spelled it out since I can't adjust the length with it installed. (Tried various tricks, but the whole pushrod wants to spin.)

So, I checked all 8 valves and got 9.75-10.0 turns. They're close enough that I could probably make either one work (it's hard to tell if the plunger might be compressing a bit at 10.0 turns as I tighten the rocker bolt). Working the math, with a 7.350" pushrod I would end up with ~0.05-0.0625" preload, which seems reasonable. Thoughts?

 

Good thread. I will be needing to do this soon. But I'm not sure there was a concensus on how many thousanths of an inch movement of the pushrod there is for x turn of rocker nut. Is the excel sheet on page two accurate (every 1/4 turn = ~.020") assuming the last 1/3 of a turn is bolt stretch and doesn't count towards preload so count the turns until snug right?

 

Yes. Each turn is 1.25 mm so a 1/4 turn is 0.3125 mm. Converting to inches (devide by 25.4) results in each 1/4 turn being 0.0123 inches. Correct for rocker ratio (2.7/1.7) and you get 0.020"

 

If you use 0.35 turns as an average difference, the change in preload is 0.027". The measurements I made on the stock pushrod several years ago were 7.385" gauge length. The best thing to do to know for sure would be to use a dial indicator and measure the rocker movement at the oil hole of the pushrod end to measure from zero lash to full preload. Dial indicator must be in line with the pushrod.

 

Unfortunately, my dial indicator setup is pretty cheesy, and I don't have any way to mount it to the head.

Although it's going to cost me time (and I'm already slower than molasses as doing all this ), I'm going to reinstall the stock cam and a stock head and see what preload I get with that setup. That should give me a warm fuzzy about what the factory thinks preload should be with the factory lifters and factory pushrods. That's all going to have to wait until after the weekend, though, as I'm heading out of town.

 

Rather then go through all that work, is there anyone local with an LS1 that would allow you to check their car?

 

After being out of town for the long weekend, the last two evenings I got around to swapping over to stock stuff to see what the factory thought was right.

Stock LS6 243 head, stock head gasket, stock LS6 cam, stock lifters, stock pushrods.

#1 exh - 1.3, 1.25
#3 int - 1.15, 1.25, 1.25
#3 exh - 1.125, 1.125
#5 int - 1.125, 1.125
#5 exh - 1.1, 1.1
#7 int - 1.15, 1.15
#7 exh - 1.15, 1.125
I had put my solid lifter in #1 int, which is why it's not included above.

(For those that might wonder how I'm "eyeballing it" to 3 decimal places , 0.125 is 1/8 turn, so that's pretty easy to pick off.) Average there is 1.16 turns, so somewhere between 1-1/8 and 1-1/4 turns. By the table posted earlier in this thread, that's ~0.07" of preload.

I then used my adjustable pushrod on #3 intake and did my best to find zero lash, and then lengthened the pushrod so that I would get the same number of turns I had gotten on #3 int with the stock pushrod. Using the Comp adjustable checker, zero lash was somewhere between 9-7/8 and 10 turns (so 7.294" to 7.300"). I then gradually lengthened the pushrod. 11.5 turns (7.375") gave me 1.15 turns from zero lash to 22ft-lb. 11.75 turns (7.388") gave me 1.25 turns. Based on the difference in adjustable pushrod lengths, that gives me a preload somewhere in the 0.075-0.094" range. Obviously, it's a small sample size (a single valve, with one guy checking), but hopefully some will find that useful.

Comparing these numbers to the numbers I got using the stock pushrods and the 7.400" pushrods with the EPS cam and TEA ported 243 heads, I definitely want shorter pushrods. Now to decide between 7.375" or 7.350". I may order both and use a mix depending on what works best for each valve. #1 exh, for instance, took more turns with both the 7.4" and stock pushrods, so maybe it would be better with a 7.35" pushrod. And I haven't done anything with the passenger side head, so maybe I'll find some on that side that also would be better with 7.35".

 

The stock pushrods are 7.400" overall length (flat-to-flat), which is the same thing as 7.385" gauge length.

Remember that the Comp Cams pushrod length checking tool gives the gauge length measurement.

 

I am going to measure my pushrods without my head gasket in because I need to do piston to valve clearance before bolting the heads down. How to account for the head gasket?

Do I directly add .054 that is the thickness of the gasket?

 

This seems to be data that can be used to try and correlate Shane's "1 turn = ~0.047" pre-load" measurement method to the pushrod length checker tool method.

So if I’m reading all this data correctly:

The original zero lash pushrod length measurement with the tool was 10 turns, giving a pushrod length of 7.300”.

Then, setting the adjustable pushrod to 11.5 turns gave you a pushrod that was 7.375” long, which when installed resulted in 1.15 turns of the rocker bolt to 22 ft-lbs from zero lash.

This would then mean that 1.15 turns on the rocker arm bolt to 22 ft-lbs would really equate to 7.375 – 7.300 = 0.075” pre-load.

But Shane’s method says 1.15 turns to 22 ft-lbs should result in 1.15 x 0.047” = 0.054” pre-load. There doesn’t seem to be much of a direct correlation going on.

Some people have also mentioned that the last ~1/3 turn of the rocker bolt during torquing to 22 ft-lbs is all going into bolt stretch and doesn’t add pre-load. If this was the case, then 1.15 turns would equate to (1.15 – 0.33) x 0.047 = 0.039” pre-load. This is even farther off than the 0.075” pre-load determined by the length checking tool. Humm ... am I looking at this right?

 

Use your old gasket. Problem with no gasket is potential to scratch machined surfaces and if the valves contact the piston and you rotate with a wrench you could bend a valve as you will be missing a lot of clearance.

 

vettenuts - any comments or inputs to my Post #94 above? Do you have any data correlating use of a pushrod length checker to the Shane method of determining correct pushrod length (given a desired lifter pre-load target)?

 

By my calcs and measurements taken on my motor, for the 1.15 turns I get 0.064". I think you have to remember that all of these methods are not exact and if you want to measure you need to put a dial indicator on the rocker. When I checked Shane's method, I got a few thousandths more than him, on the order of 0.053" rather than his 0.049". But since we are counting turns this method is not going to be accurate to a few thousandths and I find the difference acceptable. I subtract 1/3 turns based on what I observed for my motor, but the 1/3 turn is by eyeball as well. I think the thing to remember is unless you are targeting a very exact value such as required for Morel lifters or worse yet Comp R lifters, the methods should be accurate enough to buy off the shelf pushrods since their length can only be bought in specific increments.

 

it is threads like this is why i joined ls1 tech
very informative and the process is broke down
for dummies like me
"pushrod/pre-load for dummies?" LOL

appreciate the info guys

 

Some food for thought. If you're going to use rocker arm ratio to calculate preload, is 1.7 is the correct number? The factory rocker arm and aftermarket rocker arms aren't 1.7:1 throughout the cycle. This is what Crane had to say about the factory LS1 rocker arm and I suppose an aftermarket rocker arm could be slightly different:

 

If you use Crane's values, the rocker correction changes from 1.59 (using the 1.78 ratio) to 1.65 (using the Crane value of 1.54). As with any of these methods, there are built in errors due to tolerances, etc. and they should be used to estimate the preload with a final measurement made with a dial indicator.