Pushrod length and lifter pre-load on LSx

[redhat]

Will need to determine the correct pushrod length for the LSx I am building. Also, I have always thought my LQ4 valve train was noisy. I just threw in stock length pushrods and truly do not know if my aftermarket cam has a different base circle than the OE LQ4 cam. Very well could. So I figured I'd measure and see what I should be running.

So I bought an adjustable pushrod and an 8" caliper.

Looking it up online, seems easy. Get intake or exhaust (depending upon which one you're measuring) on base circle, install adjustable pushrod and rocker arm, tighten/torque rocker arm and expand pushrod until you have zero lash. Remove rocker and adjustable pushrod and measure length with the caliper. Easy, makes sense.

Then you add whatever preload your lifter manufacturer specifies to that length and you order/install that length pushrod. Correct?

Is the measurement skewed if the engine is cold (sitting overnight) or if you check it an hour after running? Is there a best time to check this?

Also, what would be a safe or good preload for stock OE lifters in an LSx? Say LQ4, LM7... any junkyard or OE motor. Also, what about LS7 lifters?

 

[PontiacHO]

Sounds like that will work however also check where the rocker tip makes contact with the valve stem (at lift).
Assuming these are positive stop rockers etc. you may not have too much of a choice anyway…

 

[clinebarger]

Cams with greater lift will need a smaller diameter base circle, Meaning 9/10 times you will need longer pushrods......Surfaced cylinder heads & decked blocks can at times require a shorter pushrod.

The correct answer to lifter preload is you want it in the middle of the plungers travel.....If the lifter plunger has .100" of travel, You want .050" preload.

I check lifter plunger travel using my Arbor Press & a Dial Indicator.

I run GM# 88958689 on all my LS builds & .050" preload is perfect.

 

[redhat]

Cams with greater lift will need a smaller diameter base circle, Meaning 9/10 times you will need longer pushrods......Surfaced cylinder heads & decked blocks can at times require a shorter pushrod.

The correct answer to lifter preload is you want it in the middle of the plungers travel.....If the lifter plunger has .100" of travel, You want .050" preload.

I check lifter plunger travel using my Arbor Press & a Dial Indicator.

I run GM# 88958689 on all my LS builds & .050" preload is perfect.

Thanks @clinebarger. Great info as always.

Will measure Christmas Day (supposed to be 51 degrees here... warm!). Also going to replace rockers with trunnion upgraded GM OE rockers when I replace all pushrods. Have Melling trunnion upgraded units in there now, but somehow got into reading about aftermarket rockers breaking. I know Melling does inherently mean Worst Case China, but I think I'd feel a touch better about GM OE being in there.

 

[redhat]

@clinebarger Is it possible that a higher but mild-er-ish lift cam could have a larger base circle? My cam lift is .500/.500.

Measured pushrod length— 7.250 and with preload that’d put me at 7.3. When any rocker was on base circle… I did not have any play in the rocker bodies. And I did see, again when on base circle, the valve spring compress a touch. I’m thinking I have way too long pushrods? Currently have 7.395 in there.

I did measure with one of my new rockers with a BTR Trunnion kit in there. Are there variances in trunnion bodies enough to change pushrod length?

 

[clinebarger]

You soaked the Lifters in oil? If so they're likely pumped up.

Rotate the engine where one of the rocker is at full lift, The spring pressure should slowly bleed off the oil in the lifter. Now rotate the engine where the lifter is back on the base circle.....Can you now collapse the lifter plunger by hand using the rocker?

 

[redhat]

You soaked the Lifters in oil? If so they're likely pumped up.

Rotate the engine where one of the rocker is at full lift, The spring pressure should slowly bleed off the oil in the lifter. Now rotate the engine where the lifter is back on the base circle.....Can you now collapse the lifter plunger by hand using the rocker?

Thank you. No, not soaked in oil, but in the engine in the truck that was running last night. So yes probably still pumped up. Will do and measure again.

 

[clinebarger]

For some reason I thought you're working on the 5.3L build, Not the 6.0L in your Tahoe. Yes....They were pumped up.

 

[redhat]

For some reason I thought you're working on the 5.3L build, Not the 6.0L in your Tahoe. Yes....They were pumped up.

Yessir. Got a valve open and waiting for it to bleed down.

Something is up though. Top is an an OE LS1 rocker arm with BTR V2 trunnion. Bottom is melling OE replacement with their trunnion upgrade. The melling when torqued and zero lash has side to side play. The GM with BTR when torqued will open the valve.

Using an OE 8mm rocker bolt. I know the BTR kit says about using their bolts. Is that super crucial? Seems like the OE bolt fits in the trunnion body OK.

 

[redhat]

I rolled the motor over until a valve was on full lift and let it sit for a half hour. Then put it on base circle and couldn’t press it down. Also couldn’t press down other valves. Maybe I’m not waiting long enough… so I rolled it over and have a valve open and put the valve cover on it for the night.

Thoroughly confused now. Going to do some digging and reading around. Must be a difference between a melling OE replacement rocker and a GM one ever so slightly. That and the trunnions…

 

[redhat]

 

[clinebarger]

Might try loosening the oil filter.

That's such a mild cam....Different length pushrods shouldn't be needed, A OE LS2 cam has more lift.

 

[redhat]

Might try loosening the oil filter.

That's such a mild cam....Different length pushrods shouldn't be needed, A OE LS2 cam has more lift.

That's whats confusing me as well. Only thing I can think of is these Melling rockers are a touch higher up on the pedastal than these OE + BTR rockers I have here.

With a OE + BTR rocker installed, with 0 lash and no pre-load on the lifter, I am at 7.25". With .050" preload, I'd be at 7.3". I have another pushrod length checking tool on the way that has an lock nut.

I am going to check again and verify before I order pushrods. Just really odd that I need this short...

Got ahold of Summit and asked does this 8717R1 cam have smaller base circle than an OE cam, they said "We do not appear to have it listed as a small base circle in either application or part notes no". Which is vague.

I also posted on some LS Facebook groups looking for info and or if anyone has any similar experiences -- got a lot of nasty responses. I have learned two things as of late with building a motor, and going through various tasks, best practices, etc.

1. most guys slap parts together, do not check hardly anything, and have no clue on theory or how things operate and it is sheer luck everything works halfway OK for them
2. anyone who says you are over complicating it or won't give you an answer is recycling info on the internet and has no clue themselves and it was luck for them in their past

 

[clinebarger]

So you came up with the same measurement with both the OE/BTR Rockers & the Melling Rockers?

 

[redhat]

So you came up with the same measurement with both the OE/BTR Rockers & the Melling Rockers?

No, the OE/BTR rocker measured at a 7.25 with zero lash. I did not measure the Melling... yet. But what I noticed is the Melling has more lash at 7.25 than the OE/BTR.

When I get the above tool I am going to measure an OE+OE Trunnion, Melling and OE/BTR rockers and see where they all lie to give myself a good baseline and make sense of this. I am thinking I am OK in my understandings. From what I can see, so far, it seems like the OE/BTR may require a slightly shorter pushrod. I also found online people talking about the same thing, some trunnion upgrades will require a shorter rod. Probably thought, 9/10 times, a different pushrod is not used and they're just preloading the lifter more and running it. I am only speculating.

 

[clinebarger]

Just to add.....

LS rockers spitting its rollers from the races walking out is usually a result of running .600" plus lift cams & stiff valve springs, I have no issues/reservations about using stock rockers up to .560" of valve lift with Beehive springs.

Yes.....I've seen stock engines with rocker/trunnion failures.....Just about every one was a 5.7L LS1 that was dogged & dogged HARD.

Another trick.....1 full turn of the 8x1.25mm is just about .050". So if you adjust the rocker to zero lash then get 1 to 1 & 1/4 turns to the 22 foot pounds.....Preload is really close!

Rarely have I ran across a lifter that wouldn't bleed down the preload applied to it within a 10 minutes or so at the most, The last was a flat tappet small block Ford....Ended up replacing the lifters.

I do DOD/AFM deletes on a regular basis, I soak the lifters in oil before installation (Even though most "experts" say not to) making them pretty much pumped up.
Torque the rockers down with the lifters on the base circle, Gotta bar the engine a few times. And make sure I got no valve hanging open. Then I verify I have side to side movement on all 16 rockers while on the base circle.

I use cams from 3 sources.....BTR, Cam Motion, & GM. If one gets lazy grinding a mild/low lift cam.....The base circle could be quite a bit larger.

 

[clinebarger]

No, the OE/BTR rocker measured at a 7.25 with zero lash. I did not measure the Melling... yet. But what I noticed is the Melling has more lash at 7.25 than the OE/BTR.

When I get the above tool I am going to measure an OE+OE Trunnion, Melling and OE/BTR rockers and see where they all lie to give myself a good baseline and make sense of this. I am thinking I am OK in my understandings. From what I can see, so far, it seems like the OE/BTR may require a slightly shorter pushrod. I also found online people talking about the same thing, some trunnion upgrades will require a shorter rod. Probably thought, 9/10 times, a different pushrod is not used and they're just preloading the lifter more and running it. I am only speculating.

OE rockers have slack in the trunnion which will result in a longer measured PR length....It's not much though.

 

[redhat]

I use cams from 3 sources.....BTR, Cam Motion, & GM. If one gets lazy grinding a mild/low lift cam.....The base circle could be quite a bit larger.

Thanks for the above info. Really great advice. I will say this… IMO after seeing some of the parts that they sell, and many of them I’ve bought and used… I wouldn’t at all be surprised if the summit proLS cams are a cheaper product and maybe a result larger base circle. A lot of their products work OK but I’ve noticed sometimes they just that—OK.

Was gonna get their ProLS rods and pistons but heard a lot about weights being all over the board. Instead went with a BTR rotating assembly balanced.

I think from now on out I am going to seek out BTR cams.

 

[DHBWA]

Clinebarger is giving spot on info….

Hint - Listen…

 

[DHBWA]

BTW - Make sure your valve heights are similar. Not that .010-.015 makes that much difference but obviously.050 would and I have seen heads where the valve heights varied a bunch…..