Hey guys, I'm caught in-between 2 pushrod lengths and need to know if I should err on the longer or shorter side...

Building an LS3;
BTR Centri Supercharger cam
Johnson 2110R lifters
BTR dual valve springs
Stock rockers w/BTR trunion upgrade
Stock valves
Stock heads w/no milling
LS9 head gasket

Got the heads on and torqued...

Measuring for pushrod length using the Comp 7702 checker tool.
On base circle I get zero lash with the tool turned out about 11.25 turns on on average on all the valves.
According to my math, that equals about 7.3625"... + 0.035" (which is what Johnson recommends for preload on the 2110Rs) = 7.3975"
Round up to 7.400" (Which is apparently stock length.)

Now, if I double check using the "tighten to zero lash, then torque to 22ft/lbs" method... with the stock pushrods, I'm getting just over a half turn of preload.
Apparently 1 turn = 0.047", so I'm at about 0.0282" of preload (0.047"x0.6 turns).
If I do the exact same using the checker tool (turned 12 turns out, which is supposed to be 7.400") instead of the stock pushrod, I get more like 3/4 of a turn with my torque wrench...
Which would put me at almost exactly 0.035" of preload.

So, which #s should I trust? The factory pushrod length of 7.400" giving me 0.028-ish preload, or the checker tool's 7.400" which is giving me 0.035" of preload?
The "tighten to zero lash, then torque" method seems a little less precise considering variance in "zero lash" and slack in the ratchet turning, etc...

Planning on using BTRs 11/32" pushrods and my closest options are 7.400" or 7.425".


TL;DR
7.400" and risk them being a hair too short or 7.425" and risk them being a hair too long?
Which direction seems like the smartest way to err, and why?

THANKS!!!!

 

If you really want to be exact, Manton can make you pushrods in any length you want.

But you will be fine if you go with 7.425 length. That is what I would do. It will put you at .050 preload which is just fine for those lifters.

 

Is there any concern about piston to valve clearance going with the 7.425?

 

How would pushrod length affect piston to valve clearance?

 

No, the lifters have at least 0.2 inches that the plunger can travel.

 

Ok, thanks for the help guys! I pulled the trigger on the 7.425, 11/32" ones a couple days ago.

I'll let you guys know how it goes in a few weeks after everything is up and running.

 

how did it work out? im going through the same process?

 

 

Like someone else said ... The total plunger travel in the stock LS3 / LS7 lifter is approx .200" (200 thousands of an inch) so you have a lot of leeway when setting the preload. Obviously, .100" (100 Thousands of an inch) would put the preload right in the middle of the lifter's internal plunger travel.

In my case, on my LS3, I use a set of pushrods that get me .090" preload.

This may be helpful to you:

 

Setting LS3 Valve Lifter Preload when Using Stock GM Lifters

1. First, you will need to find the cam’s intake lobe base circle on any one of the cylinders you choose.

Remove both rocker arms on that particular cylinder. With just the stock 7.40”exhaust pushrod installed, turn the crankshaft clockwise until that exhaust pushrod just starts to move upward from it’s full down position. Now, that cylinder’s intake lobe will be on it’s base circle.

2. Remove that exhaust pushrod.

3. Install the stock LS3 intake 7.40” pushrod and the intake rocker arm.

4. Run the rocker arm retaining bolt down until you achieve ‘zero lash’ ... This is easily done with your fingers wiggling the rocker arm back and forth while tightening the bolt. Pay attention to the rocker arm contacting the valve tip, the point at which all the slack is gone is ‘zero lash’.

5. Tighten the rocker bolt from this zero lash position until the bolt reaches 15 Lb /Ft torque, while counting and recording the number of turns the bolt makes (see lifter preload chart below). Tightening to only 15 Lb /Ft insures that there will be no bolt stretch effecting the lifter preload measurement.

6. We are looking for between 1 -11/2 turns, which will insure the correct lifter preload.

7. After recording the number of turns, finish by torquing the bolts until it reaches the required 22 Lb /Ft.

8. There really is no need to check all of the rest of the cylinders. Once you have determined what length of pushrod you need in order to achieve the correct lifter preload, all the others should require the same length pushrod.


Note:The total plunger travel in the stock LS valve lifter is approx .200” (Two Hundred Thousands)

Note: If the bolt rotates less than 1 turn, you will need a pushrod that is .025” longer than stock (7.425”)

Note: If the bolt rotates more than 11/2 turn, you need a pushrod that is .025” shorter than stock (7.375”)

 

Either my brain is thinking backwards (common for me), or your last two notes are backwards.

 

Rodney ... It's right

If the bolt rotates less than 1 turn from zero preload, you don't have much preload ... using a longer pushrod will push deeper into the lifter and obviously give you more preload.

 

Yep, backwards brain strikes again! Read it twice before making my post. Ate texmex dinner with one (1) margarita and it looks correct now. Shoot.

 

I can't just drink one (1) margarita ... or anything for that matter . .

 

I don't think you will be getting any updates from the OP since it's been about 1 1/2 years since he posted last here on the Corvette Forum.

 

If you're on the fence about being in-between sizes, I would err towards the longer pushrods.
I went with the longer ones, and I still get valvetrain noise when the engine is hot.
It wasn't very noticeable for the first year, but after everything broke-in more, it's louder now.

I'm to the point where I think I'm going to go up ANOTHER size in length.

 

Mwahahahaha!! I've made a liar out of you!