Checking PR length?
08-09-2015, 02:15 PM
#1
Checking PR length? Hey all, had a question about checking PR length.
From what i've read, to check pushrod length you have to have the rockers set to zero lash, but to set the rockers to zero lash, you have to have the correct Pr length.
So how do I do one without the other? Sorry if this is a dumb question, but all of the how tos I was reading were just leaving me
From what i've read, to check pushrod length you have to have the rockers set to zero lash, but to set the rockers to zero lash, you have to have the correct Pr length.
So how do I do one without the other? Sorry if this is a dumb question, but all of the how tos I was reading were just leaving me
08-09-2015, 02:35 PM
#2
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With an adjustable pushrod. You start too small and work your way to tighten up the gap until you just hit zero lash. Measure the rod at this length. Then, add your desired preload and order that length. You'll need a good caliper also.
08-11-2015, 09:58 PM
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mine aren't indexed. I had to measure them
08-12-2015, 11:04 AM
#6
Comp has two styles of checker (Hitech and Magnum) One has increments and one needs to be measured with a caliper. Either way I would always verify with a caliper.
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08-13-2015, 12:07 PM
#8
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once you're preloaded there is no lash. The hydraulics take that up. What I did was to measure at exactly zero lash then add the desired preload.
08-14-2015, 07:40 AM
#9
Here is my method, hope it helps:
This is for the Comp adjustable pushrod, which has increments of 0.050" per turn.
Each turn of the pushrod is 0.050". When fully closed, it is 6.800". This is pushrod "gauge length" so you can't measure it directly as the pushrod length is actually based on the length between the ball ends where the ball end measures 0.140" in diameter. I you use a caliper to measure the length, that is Overall Length (OAL) which some manufacturers like Manton use. This can be a little less accurate only because the flat on the ball end can cause a variation, however OAL is approximately gauge length + 0.015".
Assuming you are using stock rockers or a non-adjustable rocker.
1. Open the adjustable pushrod to the same length as your stock pushrods
2. Close it down two turns
3. Put your rocker rail on the head
4. Make sure you cylinder (typically #1) is at top dead center on the firing stroke so both valves would be closed
5. Put the pushrod in place on the intake valve and make sure it is in the lifter cup
6. Install the rocker and snug down the bolt (don't need to torque, just make sure it is snug)
7. Lift rocker tip up and down, if it "ticks" the pushrod is too short. If you can't easily move the rocker the pushrod is too long.
8. You can try and adjust the pushrod in place but my fingers are too fat so I end up pulling the rocker and adjusting the pushrod length. Go either shorter or longer 1/2 turn and try again.
9. You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.
To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".
Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:
6.800 +10.5 X 0.050 = 7.325"
This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.100" lifter preload, you add that to the measured number and you end up with 7.425" pushrods.
Now repeat for the exhaust valve to verify the length. If you have something like Yella Terra's, it is the same procedure but you must snug down the rocker pair rather than the single rocker.
This is for the Comp adjustable pushrod, which has increments of 0.050" per turn.
Each turn of the pushrod is 0.050". When fully closed, it is 6.800". This is pushrod "gauge length" so you can't measure it directly as the pushrod length is actually based on the length between the ball ends where the ball end measures 0.140" in diameter. I you use a caliper to measure the length, that is Overall Length (OAL) which some manufacturers like Manton use. This can be a little less accurate only because the flat on the ball end can cause a variation, however OAL is approximately gauge length + 0.015".
Assuming you are using stock rockers or a non-adjustable rocker.
1. Open the adjustable pushrod to the same length as your stock pushrods
2. Close it down two turns
3. Put your rocker rail on the head
4. Make sure you cylinder (typically #1) is at top dead center on the firing stroke so both valves would be closed
5. Put the pushrod in place on the intake valve and make sure it is in the lifter cup
6. Install the rocker and snug down the bolt (don't need to torque, just make sure it is snug)
7. Lift rocker tip up and down, if it "ticks" the pushrod is too short. If you can't easily move the rocker the pushrod is too long.
8. You can try and adjust the pushrod in place but my fingers are too fat so I end up pulling the rocker and adjusting the pushrod length. Go either shorter or longer 1/2 turn and try again.
9. You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.
To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".
Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:
6.800 +10.5 X 0.050 = 7.325"
This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.100" lifter preload, you add that to the measured number and you end up with 7.425" pushrods.
Now repeat for the exhaust valve to verify the length. If you have something like Yella Terra's, it is the same procedure but you must snug down the rocker pair rather than the single rocker.
