Hello, I'm piecing together the rebuild of my LS6 and I want to understand the correct method for measuring pushrod length.

Here are some details on the engine:
'03 LS6, factory block, pistons, rods, crank
Port & polished 243 heads that have been milled .010
.040 Cometic MLS head gasket
Comp Cam, Johnson 2116 link bar hydraulic lifters
BTR springs, BTR shaft rocker kit, GM factory rockers

OK. Now, are the pushrods square in the block so that I can just subtract the difference in the height of the heads? I took off a total of .021 between between the thinner head gasket & the head milling. So, factory pushrod length -.021? I suspect this isn't entirely accurate.
If I'm right in assuming this doesn't work, I want to see if my other method is accurate.
Install cam & complete heads. Install lifters. Use pushrod length measuring tool to check length when on base lobe of the cam. BUT, if this is accurate, a 2nd question comes to mind. This has to be done cold, are there warm up tolerances that need to be considered? Is there a certain amount of preload to add? If so, how would one add that?

Thanks!

 

Are those 2116 link bars the short travel ones? If they are I highly recommend to measure for custom lengths. To do so, put #1 cylinder on TDC on the compression stroke ( both rockers on the base circle of the cam). I assume the rockers come with shims, and if they do I would go ahead and install them for less stress on the valve. Take both pushrod length check tools and remove the jam nuts completely as there isnt room to utilize them. Apply some thread locker to the threads of the length check tool and re-assmble. The thread locker is to keep the tool from moving while you remove it to measure length. Install check tools. Run the bolts down for the shaft rockers into the head with just your hands, dont go all Hulk and ram them down as tight as possible. Now you can measure for zero lash (rockers have no movement front to back or side to side, basically just resting on the valve tip with no preload). I had to remove the check tools each time I want to make an adjustment, took a long time. Here is what I came up with:

Intake Exhaust

1. 7.5425 7.5400
2. 7.5570 7.5515
3. 7.5425 7.5495
4. 7.5440 7.5410
5. 7.5435 7.5525
6. 7.5445 7.5440
7. 7.5425 7.5495
8. 7.5375 7.5455

Convert these to three decimal places and then ( 7.5375 bumps to 7.538) add in your preload. For my Johnson 2116lsr short travel lifters I added in .045 preload ( Mamo suggested this length) but the box actually states a .035 preload. once this is done you can order your custom pushrods. Here is what my list looked like after placing it with Manton ( machining tolerances made some if the measurements I had round up or down to the nearest .005)

7.585-3
7.590-8
7.595-3
7.600-2

 

The correct length for one should be correct length for all, IF not Machine shop did not do the correct work on the heads.
Note : all stock push rods come in the same length, If your having to use diffrent length push rods for each cylinder you have serious issues with the heads.

Cutting Valve seat depth should be the same on all intake valves and exhaust valve seats. To add to it cutting Valve tip length should be the same for all intake and exhaust valves.
Putting strait edge across valve tips to check if they are not all touching strait edge some sitting higher some lower you know you have issues and head is not acceptable.
(IE all intakes should be same all exhaust should be the same.)

Checking heads for amount milled : On some heads There is a couple of the Head bolt holes that have reamed twice creating a step in the bolt hole this is for measuring head before and after milling. On other heads their may be a machined surface others you go off the valve cover rail regardless of point to measure from. Measuring from one side of the head to the other side should be the same on both sides if not the head was not level in the Mill when machined.
Again Different cylinder heads have different points to measure from.
Regardless if head was set up correctly in Jig before milling and level they should be the same from one side of head to the other unless they were angle milled then one side of head will be thinner than the other side from the intake side to the exhaust side. BUT will be the same thickness from end to end.

Almost all machine shops offer cylinder head Work NOT all machine shops should!
Rebuilding cylinder heads correctly is Very time consuming!!! And very costly to be done correctly and for many not worth it,
Such is why you get variations in measurements, Valve seats not cut to same depth, valves not cut accurately.
Your Grocery getter will never know the difference but in a High performance motor or for a racing motor when you are trying to squeeze every available HP out of motor small variations add up quickly and is why accuracy in measuring AND correct machining means every thing.

For me even on a basic hot rod engine or a grocery getter a head that's been machined .020 and had a basic valve job I will just throw the heads on it with out even checking as I already know they are not machined correctly and its not worth the time and effort to measure and fight with the machine shop or to adjust pushrod length they are close enough.
For a head milled .020 the engine wont even know, The push rod will ride a little lower in the lifter or ride a little higher and provide a little more lift or less in one or two cylinders no big deal if engine doesn't see Red line or knock on Valve float RPM continuously after all its not Pro stock engine.

My Point is you get what you pay for with cylinder heads if you didn't come away from machine shop Crying after getting a set of heads rebuilt They were not done correctly.
Their are Variation in even some of the Big name brand heads even when new that is why Shops that build racing engines say to always have their experts inspect and correct them before use.

If i were building an LS6 for my Vette and wanted an accurate set of heads worth the effort I would buy a Brand new set of Bowtie heads from Chevy and call it good.

 

The internet is a wild place

 

Your right it is But whats your point? If you think I am full of Sh t call it say so say your full of B S please don't be shy I have thick skin.
If you think its cool to have 16 different length push rods in an engine say so.

 

dont calculate. measure. are you going to shim the rockers to midlift/square or just bolt them in?

 

If he wanted to get preload perfect, especially with those aftermarket lifters he would almost certainly need different length pushrods. However he can probably get within range with one length for all 16. I believe its the 2116r that is short travel, 2116 should have a more forgivable preload range

 

It is accurate, and you are correct about warming up. It will change by about .015 cold to hot I believe. Call johnson and they will confirm but I believe preload for those should be .035 +/- .015 which ends up being .050 +/- .015 when you add the .015

 

In a perfect world, yes, pushrods length/lifter preload should be the same for all cylinders/valves. It never is EXACTLY the same. Tolerances. If the machine shop was shooting for an ideal PR length of 7.5925" for proper lifter preload, they did a pretty damn good job. In this case, you have all pushrod lengths@7.5925, plus/minus .0075", which means the shortest is 7.5850", and the longest needs to be 7.6000" This is one reason why they make hydraulic lifters. I see no problem with all 16 valvestem tips within .015" of each other. When setting up installed height, you find the shortest length, lets say 1.7950". Then you shim the rest to equal the same spring tension (theoretically) as the one thats 1.7950". Example: You have one.thats at 1.8100". This spring would require a .015" shim in the spring cup/locator. 1.8100"-.015"=1.795", same as the shortest one with no spring. The preload may be plus/minus .0075" from each other, but the engine will never know the difference, and neither will the OP, or you, or I, or......

 

Woah, woah bug 'un. I am only referencing that you can literally get two different answers when it comes to asking questions on the internet. I agree, ideally all the push rods would be the same length. It worked for GM when they made the LS1 with a 7.400 pushrod length.

 

Just making sure couldn't make head or tails of the post ( you know the internet being devoid of all emotion and all )
And I agree with you as well GM knows what they were doing.