another pushrod thread
10-04-2012, 12:11 AM
#1
another pushrod thread i know it has been beaten over and over, but this noob is still worried.
im getting ready to install the engine and trans back into my car. but can't find the PR checker i bought. this is a DD and need it running tomorrow! i installed tsp v2 cam, prc 2.5 5.3L heads with 63cc chambers, GM MLS head gaskets, with ls7 lifters. i installed 7.400 push rods. if i go ahead and finish my install with these then check the length when the new pushrod checker comes in, will i hurt anything in the time being if they were to be the wrong length? i was told they SHOULD be correct, but to measure, but since i lost the PR checker i can't right now
im getting ready to install the engine and trans back into my car. but can't find the PR checker i bought. this is a DD and need it running tomorrow! i installed tsp v2 cam, prc 2.5 5.3L heads with 63cc chambers, GM MLS head gaskets, with ls7 lifters. i installed 7.400 push rods. if i go ahead and finish my install with these then check the length when the new pushrod checker comes in, will i hurt anything in the time being if they were to be the wrong length? i was told they SHOULD be correct, but to measure, but since i lost the PR checker i can't right now
10-04-2012, 01:08 AM
#2
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Wait till you get the tool. If there are the incorrect length you will have valvetrain problems. Dont rush it, especially with good money invested in the motor.
10-04-2012, 02:08 AM
#3
Go ahead and check with your 7.4" PRs how many turns from 0-lash to 22ft.lb. you get with the rocker bolt. IMO, you'll want at least 1 full turn(preferably 1.25) but no more that 1.75 turns. So between 1 and 1.75 turns I'd go ahead and run it, otherwise buy new PRs.
10-04-2012, 07:23 AM
#4
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If you're still running the net lash rockers, then the base circle of the cam, the gasket thickness and head decking (if applicable) can be added up. Provided the cam has ~1.49" base circle I think you'll be close.
10-04-2012, 07:56 AM
#5
Exactly what 99BluZ28 said. I have the Comp adjustable PR checked and haven't even used it.
Copy and paste this into Microsoft Word, print it out, and bring it to the car with you.
From Shane at Thunder Racing.
The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:
FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
Check it using the above method and see where you are.
Thanks,
Shane
Copy and paste this into Microsoft Word, print it out, and bring it to the car with you.
From Shane at Thunder Racing.
The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:
FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
Check it using the above method and see where you are.
Thanks,
Shane
10-04-2012, 05:24 PM
#7
okay...so...
i went out there and tested this. with the exhaust all the way open (spring compressed) and the intake closed (spring tall) i tightened the rocker bolt down to zero lash. i was only able to get 1/4 of a turn until 22ft/lb was reached.
so, i obviously need to get rid of the 7.400's...but what size PR does that mean that i need? im thinking the 7.450's?
i went out there and tested this. with the exhaust all the way open (spring compressed) and the intake closed (spring tall) i tightened the rocker bolt down to zero lash. i was only able to get 1/4 of a turn until 22ft/lb was reached.
so, i obviously need to get rid of the 7.400's...but what size PR does that mean that i need? im thinking the 7.450's?
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05-14-2014, 04:15 AM
#13
Re-check. I found that it takes about 1/3 turn after the rocker bottoms to reach the 22 lb-ft. If you got 1/4 turn, did you check to see if the pushrod was loose? You may have been only measuring the bolt rotation to hit the torque value with no actual preload.
05-14-2014, 07:58 AM
#14
Put the rocker on just holding your finger and spin the bolt until all the slack is taken out of the rocker. But no more than that. That means no up and down motion anymore. As soon as it's not loose, stop! You’re at 0 lash. From there, torque to 22-ft/lbs.
And, yes, vettenuts is right, the final 1/3 doesn't actually move anything, which is why 1 turn is .047" in actual preload.
And, yes, vettenuts is right, the final 1/3 doesn't actually move anything, which is why 1 turn is .047" in actual preload.
