bowtiedad_z28

iTrader: (4)

Do check it at zero lash or or with the preload? Also should i use 1/4 or 1/2 turn after zero lash? I am sure i will get different opinions on this but let me hear them.

They are oem lifters and 1.6 rockers. Of course i will also be using a solid lifter to be checking it with as well as starting on the cams base circle. I have seen where guys have done it with and without the preload. I just want to know which is actually the correct way to do it.

Rodinator1234

Zero lash, and I think you will find with stock lifters, and roller rockers they will be noisy at 1/2 turn preload and a warm engine, cold they will be quiet. I did 3/4 turn on mine, they are pretty quiet warm, and real quiet cold.

Wicked94Z

iTrader: (26)

Why check with zero lash when its likely the lifter will be slightly collapsed while running? as well as expansion when the engine heats up, seems to me you could end up with a pushrod .050 too short

Rodinator1234

Have you ever used a pushrod length checker? Go ahead and put some preload on a solid lifter then turn the adjusting screw out on the pushrod.

Wicked94Z

iTrader: (26)

I doubt the pushrod cup height in a solid roller lifter will be the same as a HR lifter. Typically one would use a shimmed hydraulic lifter for checking pushrod length. Who pissed in your cheerios?

wrd1972

iTrader: (12)

Whenever I checked length by either soft test spring or just existing lifter, I got a range of results. When I used a solid lifter, results were more precise. Bottom line is if you want precision, use a solid lifter for measuring.

I disassembled a stock lifter and shimmed it up with a screw. When finished, simply put it back together.

I preload my LS7 lifters to 3/4 TPZL.

bowtiedad_z28

iTrader: (4)

I tore apart a lifter and added washers to make it a solid, so it will be the same as the lifters i am putting in the motor. I also know i should add .030-.050 to the pushrod length i come up with to make up for the preload. Relax guys.

Alex94TAGT

bowtiedad,

I don't personally see anything wrong with performing the pushrod test at zero lash with a 100% solid lifter, and then subsequently calculating the preload into your pushrod length. It's just a little more complicated.

Perhaps Wicked et.al. can verify my thinking on this -- I believe it to be correct:

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After performing the pushrod measurement at zero lash, you should have a good wear pattern on the valvestem. In order to retain that good wear pattern, the geometry of the rocker arm must be maintained in relation to the valve and pushrod. Simple, right? So, as not to disturb that geometry, you need to make pushrod calculations assuming preload has already been applied to the rocker arm nut.

What rocker studs are you using? Factory 3/8"x24tpi or aftermarket 7/16"x20tpi?

Some simple math here: Threads per inch / number of "starts" on the bolt = turns per inch. Most rocker studs have only one start, so threads per inch = turns per inch. In other words, you would have to turn a rocker nut 24 times to get it to move 1" on a factory 3/8" rocker stud with 24tpi.

-For a 3/8" x 24tpi stud: (1" / 24 tpi) = rocker nut moves down 0.0416" every full turn.
-For a 7/16" x 20tpi stud: (1" / 20 tpi) = rocker nut moves down 0.05" every full turn.

Now, those numbers need to be corrected for the rocker ratio being used, as one turn of the rocker nut will not precisely move the pushrod-side of the rocker by the same distance. The pivot point becomes the closed valve in this case, instead of the rocker trunion. For 1.6 rockers, use a correction factor of (2.6 total unit length / 1.6 unit ratio) = 1.625 correction factor. In other words, for every turn of the rocker nut, the pushrod side will be moving about 1.625 times that distance, creating your actual lifter preload. I found this to be verified by forum member speed_demon24 on CZ28 via this link -- .050" movement of the rocker nut yielded .080" movement on the pushrod side -- a ~1.6 ratio.

So, for a half-turn preload on an OEM lifter and stock 3/8" studs, just add (0.5 turn preload * (1"/24tpi)) = (+0.0208" * 1.625 correction factor) = +0.0338" needed on your final pushrod measurement to account for preload. For 7/16" studs, add (0.5 turn preload * (1"/20tpi)) = (+0.025" * 1.625cf) = +0.0406" needed on your final pushrod measurement to account for preload.

If you want a quarter-turn preload instead, those final bolded numbers would be halved. If you want a full turn preload, those final bolded numbers would be doubled.

Passes the sanity check, as we are not changing the rocker nut or rocker geometry at all -- only changing the pushrod length to account for the lifter plunger preload. Perhaps a good idea to submerge a hydraulic lifter in oil for a while and retest it with the final pushrod length you calculated.

bowtiedad_z28

iTrader: (4)

I came up with 7.165 with a solid lifter and no preload. So with the preload it would be basically a stock length pushrod. Before i order new ones i will try one of the lifters i have had soaking in oil with the preload and one of my old pushrods and check the witness mark. Thanks guys.

Rodinator1234

What did you do that made you think you may need a different length pushrod?

bowtiedad_z28

iTrader: (4)

The heads where milled, thinner gaskets plus the 1.6 compared to 1.5. Just double checking with valvetrain change.

SS RRR

iTrader: (2)

So have you already checked the sweep using the original pushrods or are you guessing you need new ones? If guessing, put original pushrods back in, mark two or more valve tips with a sharpie, adjust rockers, run engine for a few seconds and then check sweep.

bowtiedad_z28

iTrader: (4)

Yep i checked the sweep with one of the original pushrods as well. I am using guideplates hense the new pushrods. Going chromoly hardened. This is a complete 383 build so the motor is out of the car so it is getting turned over by hand.

SS RRR

iTrader: (2)

Just curious, what did the sweep measure and where was it located on the valve tip?

bowtiedad_z28

iTrader: (4)

The sweep was dead center on the valve. I didnt measure the sweep but it wasnt to bad. I had some sweeps better and some worse using a adjustable pushrod but they were either to much to the exhaust side or intake side of the valve.

IronOutlaw

iTrader: (4)

Could I do this with stock pushrods and NSA rockers just to test length? I dont think my heads have ever been off so I think Im going to need stock length but need to check first.

quik95lt1

iTrader: (7)

base circle of the cam also has alot to do with it so you should ALWAYS measure......ive seen too many guys say 'Oh well i took .020 off my heads and .010 off my gasket i just need a pushrod .030 shorter".........they forget the notion that the base circle of the cam is smaller than stock........then they start the car up and it sounds like my grandmother on her sewing machine and they dont know why

SS RRR

iTrader: (2)

Sweep width is pretty important. It is best to have a narrow sweep and to favor the exhaust side than to have a wide sweep dead center. If you measured the sweep using stock length PR then I don't see the need to go to anything else unless you really want to dial it in.
Yes.