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Originally Posted by cmitchell17
Attachment 1146872
So I emailed Johnson and told them I was shooting for 0.035 and they didn't correct me so I guess this is correct preload maybe not though.
So looking back on my notes you may be right, apparently I was shooting for around 0.050 because right now I am using a 7.750 pushrod, which gives me an average of 0.056, 7.725 would have been very close to nominal 0.035 Johnson recommendation though. I looked back on all my receipts and I think I tried pushrod lengths: 7.725, 7.750, and my original TSP 7.800. I sold all of them though and stuck with my 7.750s:
Attachment 1146873
I think I was trying to increase the preload to make it quieter, but got tired of changing back and forth and just settled with the 7.750s. But you may be right maybe I had some other knowledge somewhere that 0.050 worked better than 0.035, either way its been too long ago to remember.
I am still looking for my preload measurements done just by the rocker arm screw finger tight method, then counting screw turns. I think preload measurement is very subjective from person to person and seems like it would also be very subjected to the state of the lifter height. In the case above all of the lifters would have had miles on them from the TSP cam and recently ran in the engine.
I really think I have more measurements I did with screw turns somewhere I just have to find them, but I think both methods were consistent though
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The .035 spec is for a hot engine. You have to factor in heat expansion when taking a cold preload measurement, so you need add .012-.015 on top for aluminum engines to account for expansion. Iron block stuff is different.
Also, you definitely want to measure both intake and exhaust on a few different cylinders because I have seen ported heads that had valve jobs done end up with slightly different valve lengths.
Nothing wrong with the screw turn method to verify, but I prefer to use an adjustable push rod with H/C custom lifter stuff. Start by finding base circle, find zero lash, then measure the adjustable push rod with a digital caliper, add the target preload to that number, and order the correct pushrods.
The only way I would rely on screw turn method is if you are installing a cam in a engine with stock heads, head gaskets, and factory spec lifters. Otherwise, you really need to go through the entire process as I mentioned above or a lot of times you end up with a noisy valvetrain that wears prematurely. This was a huge topic back in the day on LS engines. The LT stuff is no different in that regard.
Cam motion stuff is generally known for having smooth lobe profiles with quiet valvetrain. So if it was noisy I would look into this more. You seem to be knowledgeable, so I am not saying you did anything wrong. Just putting this info out there as food for thought. It may or may not add any valuable information for when you put the new combo back together.