Ls1 pushrods question
But you are right somehow I screwed up my calculation using the length checker. I don't know how I did that because I re-did my calculation like 10 times. Now I don't know how I screwed that up so bad.
So now that screws me even more lol.
Comp Cams method = 7.325"
Other method = 7.367"
in my experience, using the length checker, it's too easy for it to turn. I set it to a length, verified that length with the digi calipers, and put something on the checker to hold it at that length. Checked to see if i got zero lash. did it over and over again until i was satisfied with the measurement.
i would try to stick some teflon on the threads on the length checker, or even use some tape to hold it from turning. set it to a length and make sure it won't budge, then insert and tighten down the rocker. Got lash? a little longer. it's tight and can't wiggle it? a little shorter. use the digital caliper to measure. when you get right to zero lash, that's it, add your preload, find out what the actual pushrod length is from comp or whoever you get your pushrods from, and order the closest size. then when you get your new pushrods, MEASURE THEM TOO.
And unless you're getting a custom size or have a set of aftermarket lifters with a short travel, just aim to be as close to the right preload as you can get. with OEM LS7 lifters, you have a little leeway. some aftermarket lifters are a little less forgiving.
even if he makes that mistake, he won't be as off with his calculations as he is now.
in my experience, using the length checker, it's too easy for it to turn. I set it to a length, verified that length with the digi calipers, and put something on the checker to hold it at that length. Checked to see if i got zero lash. did it over and over again until i was satisfied with the measurement.
in my experience, using the length checker, it's too easy for it to turn. I set it to a length, verified that length with the digi calipers, and put something on the checker to hold it at that length. Checked to see if i got zero lash. did it over and over again until i was satisfied with the measurement.
The stock LS1 pushrod is 7.385" gauge length. My calculations for 1-3/4 bolt turns should give you 0.110" of preload. If you add 0.110 to your measured 7.275 you end up with the stock LS1 pushrod length. They do seem rather short, best to find out what they did to the heads.
The stock LS1 pushrod is 7.385" gauge length. My calculations for 1-3/4 bolt turns should give you 0.110" of preload. If you add 0.110 to your measured 7.275 you end up with the stock LS1 pushrod length. They do seem rather short, best to find out what they did to the heads.
I might just go with .075 preload instead of the .050 I was using and go with an adjusted length of 7.350".
When I measured for zero lash, I made sure to first of all ensure the length checker would not turn. Last night I went and checked the overall length and it matches the new calculation (7.325"). That value just seems really short. I emailed the company that milled my heads and going to see if they still have a record of how much they had to take off. Should have made sure I got that value months ago.
And, measure the actual length with a set of digi calipers.
And it doesn't sound too short if you have a set of heads that have been milled significantly.
OK your op said ls7 lifters, that much preload should be ok. I wish i could find the lifter travel data i had saved.
IIRC, the LS7 lifter cup sits a little higher than previous LS lifter designs.
Last edited by dreadpirateroberts; Jan 29, 2018 at 12:04 PM.
I definitely made sure everything was seated properly. I probably measured and remeasured about 5 times. After the first two times I got pretty comfortable with proper seating of everything. I actually measure the overall length last night and it can pretty close to what I had calculated minus preload. I guess I'm just getting all concerned about nothing because I have never done any valvetrain work before and I know how important it is to have the correct length rods.
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Verdad Gallardo Do you have a dial indicator? If you do, you can use a check spring and set your adjustable to your final selected pushrod length and then measure the actual preload prior to buying pushrods. I would also go with a larger OD pushrod to help with flex at higher RPM.
Wipe pattern can only be adjusted with shims or removal of material from the rocker stand when using stock rockers. Be sure to report back how it goes, it might help someone in the future.
Will do. I just want to make sure I'm not rocking off the top or bottom of the valve stem at some extreme amount lol.
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Staging Lane
Joined: Jul 2016
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I just swapped in a new cam with some PAC-1218 springs. The base circle RADIUS of the new cam was 0.050 smaller than the stock GM cam. Since I did not have the tool to check for pushrod length, I thought I would torque each rocker down with the stock 7.385 pushrods (lifter believed to be on the base circle) and record the number of turns from zero lash. Expecting to be at least 0.050 short!
To my surprise I recorded values between 1.25 and 2.25 turns. The 1.25 turns I think is good but a few at 2.25 turns is puzzling. I did a quick test fire without the balancer and water pump. Fired right up, 60 psi, sounds great, but looking for explanation on apparent pre-load variability.
In this case it would appear that using the pushrod length checker would yield a whole range of pushrod lengths ??
To my surprise I recorded values between 1.25 and 2.25 turns. The 1.25 turns I think is good but a few at 2.25 turns is puzzling. I did a quick test fire without the balancer and water pump. Fired right up, 60 psi, sounds great, but looking for explanation on apparent pre-load variability.
In this case it would appear that using the pushrod length checker would yield a whole range of pushrod lengths ??
Last edited by slarsen47; Mar 7, 2018 at 03:58 AM.
Not sure how you tightened the pushrods, did you place each cylinder at TDC of the firing stroke when you counted turns? If not, then some of the lifters were up on the lobe and not the base circle.
Staging Lane
Joined: Jul 2016
Posts: 98
Likes: 3
I started with the cam and crank sprocket "dots" lined up as when you do the cam change. I took that position to be top dead center for 1 and 6. Then turned crank 90 degrees to do 5 and 8, another 90 to do 4 and 7 and finally another 90 for 2 and 3. This worked for changing the valve springs. Seemed to be just a bit of normal base circle preload when loosening rockers to swap out springs.
UPDATE: Just put a cam gear on the old cam and positioned it as described above. Clearly the lobe was NOT always on base circle, sometimes onto the ramp just a bit. A cam/sprocket on the bench is a really good visual tool to see where the lobes are at various gear "dot" positions. Comparing my detailed turn notes per rocker it was evident that the ones on the base circle were all 1.25 turns.
So the bottom line is that with the lobe for sure on the base circle 1.25 turns which is perfect.
Other values that were up to 2 turns reflect that there was just a bit of lift that had to be compressed from being just off the base circle.
Learn something everyday!!
UPDATE: Just put a cam gear on the old cam and positioned it as described above. Clearly the lobe was NOT always on base circle, sometimes onto the ramp just a bit. A cam/sprocket on the bench is a really good visual tool to see where the lobes are at various gear "dot" positions. Comparing my detailed turn notes per rocker it was evident that the ones on the base circle were all 1.25 turns.
So the bottom line is that with the lobe for sure on the base circle 1.25 turns which is perfect.
Other values that were up to 2 turns reflect that there was just a bit of lift that had to be compressed from being just off the base circle.
Learn something everyday!!
Last edited by slarsen47; Mar 7, 2018 at 03:37 PM.
https://ls1tech.com/forums/generatio...ll-advice.html
this thread has the correct gm rocker torquing procedure.....aka how to know when the lifters are on the base circles.....aka how to be sure to know what cylinders to measure and when
this thread has the correct gm rocker torquing procedure.....aka how to know when the lifters are on the base circles.....aka how to be sure to know what cylinders to measure and when
As indicated 2 posts above...when the dots are facing/lined up, this is TDC for cyl #6, although offhand, cyl #1 might be exhaust closed at this point (don’t have the chart in front of me to verify this), allowing the intake pushrod for #1 to be calculated.
Don’t go by TDC/dot to dot to calculate lengths. Please make sure that the intake is on the base of the cam/exhaust closed/past TDC, and vice-versa when measuring exhaust).
Don’t go by TDC/dot to dot to calculate lengths. Please make sure that the intake is on the base of the cam/exhaust closed/past TDC, and vice-versa when measuring exhaust).