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Complete noob needs help with pushrod length

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Old 03-18-2017, 02:05 AM   #1
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Default Complete noob needs help with pushrod length

Hey everyone, I f***ed up and ordered the wrong pushrods.

I bought a length tool off of ebay and when I tried to check length myself it came out to 7.175 so I ordered BTR 7.2 since thats the smallest size available.

Some of my rockers after being torqued are extremely loose when not compressing the spring, pretty sure this isn't right... take it easy on me this is my first build so...

Is my pushrod length wrong? If so could someone tell me my pushrod length based off my cam and everything?

If so, Specs:
Torquer V4 Camshaft
LS7 Lifters
PRC stage 2.5 243 Heads milled .020
BTR .660 springs
Comp cams rockers with trunion

I believe there is a mathematical way to calculate length without the tool so if someone can do that for me that'd be great.... i dont know the base circle of the cam etc so.... IDK I'm just frustrated I didn't get it right. I'm not good when it comes to these things. The tool I used is ZZperformance I believe.
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Old 03-18-2017, 04:53 AM   #2
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Are you sure your lifters were resting on the cam and not held in their lifter tray? Take your pushrod and give it a slight push to pop them out of the buckets if they are.

Drop the checker in. Torque your rocker down to 22 ft lb and adjust the length of the push rod so there is no more vertical play in the rocker tip. It may take a few tries to get the length right. Just put a piece of tape on the checker so it doesn't grow or shrink while doing this. Measure a few and check them with a caliper. Once you have this measurement don't forget to add your preload.
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Old 03-18-2017, 08:25 AM   #3
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It's possible the lifter wasn't all the way down when you measured
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Old 03-20-2017, 01:00 AM   #4
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Originally Posted by TrentB View Post
Are you sure your lifters were resting on the cam and not held in their lifter tray? Take your pushrod and give it a slight push to pop them out of the buckets if they are.

Drop the checker in. Torque your rocker down to 22 ft lb and adjust the length of the push rod so there is no more vertical play in the rocker tip. It may take a few tries to get the length right. Just put a piece of tape on the checker so it doesn't grow or shrink while doing this. Measure a few and check them with a caliper. Once you have this measurement don't forget to add your preload.
Thanks for the info I really appreciate it. I'll do that for sure. Seems simple enough.. how hard of a push? don't want to force it enough to break it lol but just a good thud? Also, what should my preload be? not sure on that lol. And do I just add the preload number to the pushrod length? IE 7.4 + .070 which would make my length 7.470?
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Old 03-20-2017, 06:51 AM   #5
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Thanks for the info I really appreciate it. I'll do that for sure. Seems simple enough.. how hard of a push? don't want to force it enough to break it lol but just a good thud? Also, what should my preload be? not sure on that lol. And do I just add the preload number to the pushrod length? IE 7.4 + .070 which would make my length 7.470?
Put your thumb on the pushrods and just keep applying pressure until they drop. Don't worry about anything breaking.
Preload is specific to the lifters you're using. Some use less some use more.
Yeah you add your measurement plus preload and that is your pushrods final length. You're really just tightening down the rocker and measuring the distance from the lifter to the rocker. Then add the distance you want the lifter to be preloaded.
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Old 03-22-2017, 09:46 AM   #6
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So what is the normal pre load people go buy when using ls7 lifters? I have to do this to mine as well. Plan on doing it today after work
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Old 03-28-2017, 02:59 AM   #7
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Originally Posted by TrentB View Post
Put your thumb on the pushrods and just keep applying pressure until they drop. Don't worry about anything breaking.
Preload is specific to the lifters you're using. Some use less some use more.
Yeah you add your measurement plus preload and that is your pushrods final length. You're really just tightening down the rocker and measuring the distance from the lifter to the rocker. Then add the distance you want the lifter to be preloaded.
So I checked on a couple different valves I confirmed were closed shut...
Snug down rocker, it had barely any side to side movement and no up and down movement (which is what I should look for according to other threads?) . It took 12 turns to get to that point. After math (each turn on my specific tool is .035) I came up with a 7.22 length.

Now I add my preload which for ls7 lifters is apparently .050 which would make me at 7.272 .... Considering how snug the rocker was when I checked.. just snugged with a ratchet. I still feel like I'm wrong because my previous length I ordered was 7.2 and when the valve was closed the rocker was able to move a lot, although I did not add preload to that length as a mistake. Will that .75 really make a huge difference and stop all that play on final assembly? Do I order a 7.275 or should I go with 7.3 or 7.25? Don't want to get this wrong... thanks..
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Old 03-28-2017, 08:41 PM   #8
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bump....
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