Help with Pushrod length
Thread Starter
Melting Slicks
Joined: Jan 2007
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From: Athens OH
Help with Pushrod length
I have read some threads about checking pushrod length and I am not sure if I am doing it correctly.
I put two stock pushrods and rotated the engine until both valves were closed. I then removed them, installed the length checker at it's shortest setting and torqued down the rocker arm. I then lengthened the checker while simultaneously rocking the rocker back and forth until it wouldn't rock anymore. I measured the checker and it was around 7.250. Does that sound right?
I have just changed the cam to a comp cams blower cam and ported 243 heads.
I put two stock pushrods and rotated the engine until both valves were closed. I then removed them, installed the length checker at it's shortest setting and torqued down the rocker arm. I then lengthened the checker while simultaneously rocking the rocker back and forth until it wouldn't rock anymore. I measured the checker and it was around 7.250. Does that sound right?
I have just changed the cam to a comp cams blower cam and ported 243 heads.
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
I assume that is by counting turns? Now you have to add your preload, so you are looking at 7.350" pushrods with 0.100" preload. I would have expected it to be longer. Are the heads milled and what gasket?
Thread Starter
Melting Slicks
Joined: Jan 2007
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From: Athens OH
I expected it to be longer as well. As far as I know, the heads have not been milled and I am using the GM MLS gaskets.
Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Figure out if there ZO6 heads. I have Patroit Performance Stage II heads and the valves were changed out with larger stainless steel valves and are standard LS1 length.
BC
Thread Starter
Melting Slicks
Joined: Jan 2007
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From: Athens OH
I'm not sure how to tell if they are Z06 heads or not and I have never seen a sodium filled valve so I don't know what they look like. I believe they are just stainless valves. When I took them to the machine shop to get them redone they had two different size valves in them and they just ordered 4 2.02 manley valves to match the larger sized valves .Here's a pic if it helps:
Thread Starter
Melting Slicks
Joined: Jan 2007
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From: Athens OH
I suppose it's possible to use the stock length pushrods.I just checked oit again and came up with 7.400. I then installed the stock pushrods and the wipe pattern on the top of the valve appears to be very close.
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Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
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From: Athens OH
Hmmm...Maybe I am misinformed then. I thought the purpose of getting the right length pushrods was so the rockers were pushing down on the valves at the angle which would be the center of the stem at mid-lift.
Thread Starter
Melting Slicks
Joined: Jan 2007
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From: Athens OH
OK. I did it one last time and took it a freind of mine that has large micrometers. It measured end to end at 7.269. That makes 7.369 with preload added. I have 2 questions:
1. Am I supposed to compress the lifter any? Or just until the rocker has no play (without compressing the lifter, of course)
2. I measured overall length so what size pushrods do I need to order?
Thanks
1. Am I supposed to compress the lifter any? Or just until the rocker has no play (without compressing the lifter, of course)
2. I measured overall length so what size pushrods do I need to order?
Thanks
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
If you are measuring overall length, you need to correct unless you are ordering from Terry Manton who uses overall length. The other major manufacturers use gauge length, which is measured from a diameter on the ball of 0.140". You can approximately gauge length by subtracting 0.017" from your measured value, but you are better off counting turns to obtain the correct length. I would shoot for 0.080" - 0.100" of lifter preload if they are stock lifters.
Here is a write-up I posted on another board, hopefully this will help:
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. Assuming you are using stock rockers or a non-adjustable rocker with a correctly established wipe pattern.
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 buy 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. Lets 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 lets say you want to have 0.075" lifter preload, you add that to the measured number and you end up with 7.400" 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.
Here is a write-up I posted on another board, hopefully this will help:
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. Assuming you are using stock rockers or a non-adjustable rocker with a correctly established wipe pattern.
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 buy 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. Lets 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 lets say you want to have 0.075" lifter preload, you add that to the measured number and you end up with 7.400" 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.
Last edited by vettenuts; Feb 20, 2008 at 05:55 AM.
Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
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From: Athens OH
I have to wonder if my tool has different specs. It is a Jegs tool and it's just a 2 piece rod with no markings on it.
If each turn is .050, then ten turns should make the tool 1/2 inch longer. It was shorter than that. I counted the number of turns it took to get .250" and it was 7. Divide that and it came out to .035 per turn. Also, when the tool is said to go from 7" to 8."1 but when fully closed it was shorter than 7". I am thinking I may go buy a more accurate tool.
If each turn is .050, then ten turns should make the tool 1/2 inch longer. It was shorter than that. I counted the number of turns it took to get .250" and it was 7. Divide that and it came out to .035 per turn. Also, when the tool is said to go from 7" to 8."1 but when fully closed it was shorter than 7". I am thinking I may go buy a more accurate tool.
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
Sorry, can't help you there. Also, the issue with the tool you have is what is it actually measuring. I have the one from Comp, which is actually I believe made by Trend. You could use the OAL method and simply call Terry Manton. His pushrods are a step above as well.
Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
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From: Athens OH
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Don't forget to add the pre-load. If you call Terry Manton, they can turn them around it two days. I just got a sample from him for my work I am starting in April and I can tell you the pushrod is beautiful (well, at least as beautiful as a pushrod can be) 
Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
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From: Athens OH
Thanks again.
