Correct way to measure pushrod length question
#1
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Ok, first off I did do a search but did not find a clear answer so here is my question. I bought the comp cams adjustable pushrod to measure for the proper length pushrods, and I know each full turn is .050 . What is the correct way to measure for the proper length? If possible please list the procedure steps . Thanks in advance for your help!
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This is just the tip of the iceberg. If you want more threads to check out, go find them.
https://ls1tech.com/forums/generation-iii-internal-engine/749143-how-do-you-check-preload.html
https://ls1tech.com/forums/generation-iii-internal-engine/748577-can-someone-help-me-pushrod-length.html
If the regular search function is not working, try doing a keyword search (Ctrl-F) in the archive section, page by page in the Generation III Internal Engine forum.
https://ls1tech.com/forums/generation-iii-internal-engine/749143-how-do-you-check-preload.html
https://ls1tech.com/forums/generation-iii-internal-engine/748577-can-someone-help-me-pushrod-length.html
If the regular search function is not working, try doing a keyword search (Ctrl-F) in the archive section, page by page in the Generation III Internal Engine forum.
#5
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Originally Posted by bsf
Since you are installing new pushrods, you want to determine what pushrod length gives you a preload that falls within the acceptable specification for your lifter design. This is done using a pushrod length checker. A PR length checker is basically a 2-piece PR that can be unscrewed to make it longer. The Comp Cams version is 6.80” screwed down, and increases in length .050” for every turn it is unscrewed. Once you have your new cam and timing set installed, and degreed it if you go that route, you have multiple routes you can choose.
This is the route I chose. I am installing new LS7 lifters and LS6 heads. I installed my new lifters on the driver side after having previously cleaned them and soaked them in oil. I then installed my new gasket and assembled heads according to specifications. Then, I did the following on 2 intake and 2 exhaust valves to get an average. Unscrew your PR checker about 8 turns. Place it in the head for the first valve you will check. Rotate the crank to get the PR on the base circle (off the cam lobe). You will have to push on the PR checker with your finger to keep the lifter pushed down on the cam. Otherwise, the lifter tray may hold the lifter off the cam and you will not see your PR checker move. Place your rocker stand in place. Install your rocker on the valve you are checking. Torque to ~22ft-lb or a little less. If the spring starts compressing the PR checker is adjusted too long. If there is slop in this portion of the valvetrain, that means the checker is too short. Remove the rocker and PR checker and adjust it to achieve zero lash. Zero lash is when you have taken up all play, but you have not compressed the lifter or started opening the valve. You may have to do this a few times to get it right. When you do get it right, write down how many turns on the PR checker you made. You should be able to measure at least to the closest ¼ turn if not finer. Like I said, I did this on 4 different valves and took the average. My spread was slightly less than half a turn. Average as many or as few as you are comfortable with.
Now, take your average and apply your multiplier to it. The multiplier of the Comp Cams checker is 0.05”. then add this to the 0 turn length, which is 6.80” for the Comp Cams checker. If your avg turns was 10, you would have this: 6.80” + 10*0.050 = 7.30”. Now add the specified preload. Let us say it is 0.080” for your chosen lifter. Then you have 7.30” + 0.080” = 7.380”. Buy the pushrods that are closest in length to 7.380”, which would be 7.375”.
Disclaimer: I have only recently done this for the first time myself. If I made any mistakes in my write-up, feel free to correct them. Also, some people will tell you that you need to use a solid checker lifter, and they may be right. I actually just did this earlier today on the other side of my engine with solid checker lifters, and I got the same result as I did with the regular LS7 lifters. Your results may vary.
This is the route I chose. I am installing new LS7 lifters and LS6 heads. I installed my new lifters on the driver side after having previously cleaned them and soaked them in oil. I then installed my new gasket and assembled heads according to specifications. Then, I did the following on 2 intake and 2 exhaust valves to get an average. Unscrew your PR checker about 8 turns. Place it in the head for the first valve you will check. Rotate the crank to get the PR on the base circle (off the cam lobe). You will have to push on the PR checker with your finger to keep the lifter pushed down on the cam. Otherwise, the lifter tray may hold the lifter off the cam and you will not see your PR checker move. Place your rocker stand in place. Install your rocker on the valve you are checking. Torque to ~22ft-lb or a little less. If the spring starts compressing the PR checker is adjusted too long. If there is slop in this portion of the valvetrain, that means the checker is too short. Remove the rocker and PR checker and adjust it to achieve zero lash. Zero lash is when you have taken up all play, but you have not compressed the lifter or started opening the valve. You may have to do this a few times to get it right. When you do get it right, write down how many turns on the PR checker you made. You should be able to measure at least to the closest ¼ turn if not finer. Like I said, I did this on 4 different valves and took the average. My spread was slightly less than half a turn. Average as many or as few as you are comfortable with.
Now, take your average and apply your multiplier to it. The multiplier of the Comp Cams checker is 0.05”. then add this to the 0 turn length, which is 6.80” for the Comp Cams checker. If your avg turns was 10, you would have this: 6.80” + 10*0.050 = 7.30”. Now add the specified preload. Let us say it is 0.080” for your chosen lifter. Then you have 7.30” + 0.080” = 7.380”. Buy the pushrods that are closest in length to 7.380”, which would be 7.375”.
Disclaimer: I have only recently done this for the first time myself. If I made any mistakes in my write-up, feel free to correct them. Also, some people will tell you that you need to use a solid checker lifter, and they may be right. I actually just did this earlier today on the other side of my engine with solid checker lifters, and I got the same result as I did with the regular LS7 lifters. Your results may vary.
#6
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The above post pretty much sums it up. Install the checker with cam lobe on the low side for that cylinder, unscrew it until you get to zero lash, add your preload to your meashurement and get the PR closest to that value. Repeat for two cylinders on each bank at a minimum, or even better, check every cylinder.