Pushrod Length
Pushrod Length Since I have my 243s milled .036" and got a valve job, I wanted to know what pushrod length to run. My TRex cam package came with 7.425. It took about 3 1/2 turns to tighten the rocker arm until it was seated on the stand. The valve actually started moving down. I was testing this on cylinder 1 at TDC. My stock pushrod took about 2 1/2. So I set my adj pushrod to 7.3 and came out with 1 3/4 turns. From what I read on LS1tech you want to be between 1-2 turns. I didn't torque the bolts down to 22ftlbs but I turned them until the rockers were fulled seated. So I didn't have to take the 1/3 extra turn for the final torque. Did I do this correct?
The TRex is in there. I fly cut the exhaust and intake .090. I'm trying to get my pushrod situation figured out then I am going to measure PTV with clay.
This is what I have for pushrod length at 0 lash using my Com Cams adj pushrod.
9.25turns x .050per turn = .4625 + 6.800 = 7.2625
So if I went with a 7.350 pushrod I should have a preload of around .087 ?
This is what I have for pushrod length at 0 lash using my Com Cams adj pushrod.
9.25turns x .050per turn = .4625 + 6.800 = 7.2625
So if I went with a 7.350 pushrod I should have a preload of around .087 ?
Last edited by Rangersltw; Jun 3, 2012 at 05:21 AM.
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Ok. I went out and remeasured again to make sure I had the correct length. I came up with 9 1/3 turns on my Comp Cams adj PR.
9.333 x .050 = .4665 + 6.800 = 7.266 = Zero Lash
Then if I add a .090 preload I get 7.357
Did I do this correctly?
edit: When I put the stock PR in I could push down on the lifter end of the rocker just a little bit. According to my calculations it would have .134 preload since it is 7.400. I read some where on here that stock pushrods are only 3.87 and not 7.400. Is that true?
9.333 x .050 = .4665 + 6.800 = 7.266 = Zero Lash
Then if I add a .090 preload I get 7.357
Did I do this correctly?
edit: When I put the stock PR in I could push down on the lifter end of the rocker just a little bit. According to my calculations it would have .134 preload since it is 7.400. I read some where on here that stock pushrods are only 3.87 and not 7.400. Is that true?
Last edited by Rangersltw; Jun 3, 2012 at 04:04 PM.
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Ok. I went out and remeasured again to make sure I had the correct length. I came up with 9 1/3 turns on my Comp Cams adj PR.
9.333 x .050 = .4665 + 6.800 = 7.266 = Zero Lash
Then if I add a .090 preload I get 7.357
Did I do this correctly?
edit: When I put the stock PR in I could push down on the lifter end of the rocker just a little bit. According to my calculations it would have .134 preload since it is 7.400. I read some where on here that stock pushrods are only 3.87 and not 7.400. Is that true?
9.333 x .050 = .4665 + 6.800 = 7.266 = Zero Lash
Then if I add a .090 preload I get 7.357
Did I do this correctly?
edit: When I put the stock PR in I could push down on the lifter end of the rocker just a little bit. According to my calculations it would have .134 preload since it is 7.400. I read some where on here that stock pushrods are only 3.87 and not 7.400. Is that true?
You are measuring all wrong if the pushrod is starting to open the valve or its WAYY too long. FORGET ABOUT THE HALF TURN THIS HALF THAT BS!!! The plunger on the lifter should move down before the valve opens.
MAKE SURE the camshaft is on the base circle when you measure. TDC is not it. The intake valve is opening at at the sequence.
Once you have that lenghten the Comp Cam PR checker to zero lash.
Turns X .050 + 6.8 (tool length) = PR lenght + Pre-load = buy
Why do you want to run so much pre-load? Search after search has yielded .050-.080
Also the Comp Cam tool measure gauge length not overall.
This topic needs to be Stickied...EVERYDAY! this question comes up.
The second time I went out to measure I turned the motor until the exhaust valve was open then measured intake side. Then vise versa for the exhaust measurement.
That is how I came up with this:
9.333(turns) x .050(per turn) = .4665 + 6.800(PR closed length) = 7.266(Zero Lash)
So to have a .080 preload I would need a 7.346 pushrod?
I'm pretty sure the closest pushrod I would find to that would be 7.350
That is how I came up with this:
9.333(turns) x .050(per turn) = .4665 + 6.800(PR closed length) = 7.266(Zero Lash)
So to have a .080 preload I would need a 7.346 pushrod?
I'm pretty sure the closest pushrod I would find to that would be 7.350
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The second time I went out to measure I turned the motor until the exhaust valve was open then measured intake side. Then vise versa for the exhaust measurement.
That is how I came up with this:
9.333(turns) x .050(per turn) = .4665 + 6.800(PR closed length) = 7.266(Zero Lash)
So to have a .080 preload I would need a 7.346 pushrod?
I'm pretty sure the closest pushrod I would find to that would be 7.350
That is how I came up with this:
9.333(turns) x .050(per turn) = .4665 + 6.800(PR closed length) = 7.266(Zero Lash)
So to have a .080 preload I would need a 7.346 pushrod?
I'm pretty sure the closest pushrod I would find to that would be 7.350
And as badazz81z28 mentioned above, the Comp Cams lenght checking tool measures in pushrod 'gauge length'. But if you are buying Comp Cams pushrods then they are specified in gauge length and what you measured is what you need.
If you are buying pushrods that are measured from 'flat-to-flat' (with a 0.100" dia flat on each end - like Manton pushrods), then you would need to add 0.015" to the gauge lenght to obtain the flat-to-flat length.
Last edited by ZeeOSix; Jun 3, 2012 at 07:54 PM.
If I measured the intake side when the exhaust side was fully open would that be on the base circle?
edit: I'm going with the Comp Cams pushrods.
edit: I'm going with the Comp Cams pushrods.
Last edited by Rangersltw; Jun 3, 2012 at 08:00 PM.
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It's known as:
EO/IC = Exhaust Opening / Intake Closing
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If you are not familiar with the EO/IC (Exhaust Opening/Intake Closing) method for determining valve events in a 4-stroke engine, it’s very simple:
· 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.
· 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.
Last edited by ZeeOSix; Jun 3, 2012 at 08:26 PM.
I tried many method when I measured mine. I actually measured the lobe when the opposite was near full lift. Measure more than one cylinder to make sure.
When the exhaust valve is pushed down wouldn't it be on the lobe and the intake be on the base circle?
edit: that picture def helped me understand things much better. Thanks
edit: that picture def helped me understand things much better. Thanks
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I had an error in my statement in Post #13. The EX valve will be on the base circle and opposite the EX lobe when the IN valve just closes. I corrected Post #13 - see updated version of that post with more info.
Another way to do it is to find where the valve is all the way open, then turn the engine's crankshaft 360 degrees (1 turn) to make the cam turn 180 degrees. That would put the lifter on the base circle opposite the lobe tip.
Last edited by ZeeOSix; Jun 3, 2012 at 08:31 PM.
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EO/IC = Exhaust Opening / Intake Closing
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· 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.
· 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.
