03worthy4link

Trying to get the right pushrods ordered for my setup. BTR cam, GM LS7 lifters and .025 milled stock heads. Measured with a push Rod checker to zero lash and came up with 7.705, I've read differing opinions on preload from ~.065 to ~.100 so I'm thinking of jumping in the middle at .080 which gives me a length of 7.785. Or I can stick with the stockers at 7.800 for a theoretical preload of .095. Most people seem to have ended up with 7.750 for .030 mills so everything is making some sense thus far.

I suppose I'm just trying to sanity check with you guys for my own peace of mind. So let's hear those opinions!

outhouse

I went simple and turned the trunion bolt 1 3/4 in


Done. Seen a few screw up the measurement with the push Rod checker


Ideally, both should be used, and turning the trunion bolt should just be back up to ensure your measurements correct.


Check the stock length, and see where your at.

redbird555

really any preload in taht window should be fine. I would try to keep it under .09 though. .065-.08 is about perfect

03worthy4link

I'm not too sure on the method you're referring to outhouse, with my checker set to 7.750 I used a method listed here somewhere that counts bolt turns but I only came out with 3/4 till torqued from zero lash and using the numbers in that thread had a theoretical preload of .049 which almodt exactly coincides with setting the checker to zero lash length (7.705) and adding .049 for a difference of only .004

outhouse

You want in between 1 1/2 to 1 3/4 turns

outhouse

Many choose 1 1/4 to 1 3/4


But not to torque spec, just until you feel it tightening.


With that said, AHP recommended to me the 1 1/2 to 1 3/4 as they like preload on the tighter side, a little possible HP gain.

jayyyw

So, finger tight rocker bolt till zero lash, then count the turns till tight?

Schred86

Yea u should be hitting 22 ft/lbs torque If you are running the factory rocker arm bolts.

Great video

jayyyw

Going to check mine for a third time.. Valvetrain is noisy. I believe I'm a little light on the preload. I am running Morel drop-in lifters. From what I've read, they seem to like .040-.050 preload.

Schred86

Just check with morel. A lot of aftermarket run less preload. My johnsons are around .041.
Check and recheck. Also check multiple cylinders

outhouse

Do not follow my instructions for those lifters, they probably have a different setting.

outhouse

Yes.


But make sure you are setting the right specs for those lifters.


They should need a more critical approach.




I only use this to make sure my math is in the ballpark

jayyyw

One turn from zero lash to 22ft lbs is roughly .047" preload? Is this correct?

C6z06man

I'm running .090 preload and valvetrain is very quiet even when hot.

Schred86

Yes. If u check my build thread i show how i came up with my pushrod length.

Nowanker

JUST went through this on an LS1 motor on Friday, same LS7 lifters. Measured total plunger travel at .160", so to set them in the middle of range is .080".
Thread pitch is 1.25mm, means 1 full turn is ~.049" at the bolt, but you need to calculate for the rocker arm ratio.

User Omega

No, you have to account for the rocker ratio (1.8:1). I believe the actual distance at the bolt is .048"/360 deg..

You will be preloading your pushrod at 1.55x that so at one revolution, one turn would be .074".

I did not use this method to decide what rods to buy. It is very very inaccurate. I measured each zero lash using a comp length checker and a quality digital caliper good for .0005". Then I added my preload. I ordered Manton rods through Mamo and he helped me group them. I think we ordered 10 different length rods. He has been a huge help.


Jayyyw, as far as meeting the suggested .045" +/-.005" spec I would suggest you use the same technique. I believe my variance was over .020" between them all. Yours could very likely be the same.

Someone chime in here if my math is incorrect.

03worthy4link

Omega, I , like you feel as if the bolt turn method with these engines is a little inaccurate. It no doubt works and even my results were close to measuring using the same zero lash method as you, but I feel more comfortable with it than counting turns. Now if I had a polylock my opinion may differ lol. But are you saying you ordered 10 different length pushrods for one engine?

jayyyw

Thank you.. Most of the info I found was for just a general LS motor. I didn't even think about the rocker arm ratio. Finding zero lash and then adding the needed preload seems like a much easier, and better solution. Thanks for the info!

03worthy4link

I don't see how you can get the zero lash and added preload method wrong. But anything is possible given human error. As I stated the counting turns method worked for me as well within .004 using the numbers I found on the forum. So either way you CAN figure it out. Like outhouse said try both to confirm and go from there.