LS7 push rod length, what am I doing wrong?
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Joined: Jun 2022
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LS7 push rod length, what am I doing wrong? Stock cam , Johnson dogbone lifters ,.045 decked heads. I have measured these 1000 times. On a cold motor, Rotate the cam until the valve no longer moves. I use an adjustable push rod. I tighten the rocker until it fully seats, I get just enough side to side motion to let it barely slide back and forth. Then I use a 12” caliper and measure the new length. Then I add .045 (Johnson dogbone lifters). That puts me at 7.895. Ran the car like this for a year, it sounds like a sewing machine which drives me nuts so while I had the transmission out I decided to measure the push rods since it there would ne some downtime.
they mostly measured out the same, I had a couple shorter and a couple longer, not by much so I decided to swap them.
im chasing a sputtering issue after I got it all back together, I really haven’t changed anything on the motor side since putting it back together other than 4/5 new push rods and getting the injectors cleaned.
I verified the injectors are fine, according to the data sheet they didn’t get them much cleaner than what they started out so I don’t believe it to be a tuning issue.
i decided to pull the valve covers to verify everything was ok under there. Motor is maybe 20 degrees warmer than usual as I took it for a trip before pulling it back apart.
now when I check the rockers, it’s like they are at zero lash, I can move them side to side like I never added the .045 .
should I add another .045 at this point since they are at zero lash? Even the longer ones I ordered after the “recheck” have side to side movement.
I plan to check them again after the motor cools down more to find out if that is what was throwing off my other measurements.
are FED .700" Dual Springs w/Ti Retainers a problem on a stock cam?
they mostly measured out the same, I had a couple shorter and a couple longer, not by much so I decided to swap them.
im chasing a sputtering issue after I got it all back together, I really haven’t changed anything on the motor side since putting it back together other than 4/5 new push rods and getting the injectors cleaned.
I verified the injectors are fine, according to the data sheet they didn’t get them much cleaner than what they started out so I don’t believe it to be a tuning issue.
i decided to pull the valve covers to verify everything was ok under there. Motor is maybe 20 degrees warmer than usual as I took it for a trip before pulling it back apart.
now when I check the rockers, it’s like they are at zero lash, I can move them side to side like I never added the .045 .
should I add another .045 at this point since they are at zero lash? Even the longer ones I ordered after the “recheck” have side to side movement.
I plan to check them again after the motor cools down more to find out if that is what was throwing off my other measurements.
are FED .700" Dual Springs w/Ti Retainers a problem on a stock cam?
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Joined: Dec 2017
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Put the pushrod checker in the exhaust lifter, rotate the engine until the pushrod barely starts to go up, from the base circle (valve opening). Now measure the intake pushrod length of the same cylinder. To do the exhaust measurement, put the checker in the intake lifter and rotate the engine until the pushrod starts to barely go down, from max lift (valve close).
Doing it the way you are saying, can vary the measurement since you won't always end up on the center of the base circle all the time.
When you are doing the measurement, use the same rocker that is going to be installed for that valve. The rockers can vary some and throw off the measurements. (I know mine did).
What pushrods are you using? Off the shelf stuff can also vary up to .012"-.015" longer. Manton stuff is usually within .003" or better.
Don't just blindly add length to what you already have. That can cause even more issues that can be costly to fix.
Doing it the way you are saying, can vary the measurement since you won't always end up on the center of the base circle all the time.
When you are doing the measurement, use the same rocker that is going to be installed for that valve. The rockers can vary some and throw off the measurements. (I know mine did).
What pushrods are you using? Off the shelf stuff can also vary up to .012"-.015" longer. Manton stuff is usually within .003" or better.
Don't just blindly add length to what you already have. That can cause even more issues that can be costly to fix.
Last edited by jayyyw; Oct 24, 2024 at 06:08 AM.
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Joined: Jan 2017
Posts: 1,758
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Rockers will move side to side a bit at base circle, should have no lash from tip to stem. They are zero lash because they are preloaded. Sewing machine sound is common, if it isn't ticking I wouldn't worry about it.
