Measuring Pushrods
Thread Starter
Staging Lane
Joined: May 2009
Posts: 96
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Measuring Pushrods When you give a manufacturer a specific pushrod length do you just measure the end to end (of course taking into account additional length for preload) or do you take into account how it is actually a spherical end that gets flattened out because of the oiling holes and add additional length of the spherical end did not have holes in them. In other words the true length of the pushrod is how long it would be if there were no holes on the end.
A buddy mentioned to me that this was how crane spec'ed out their pushrods. Too me it would seem kind of silly to spec them that way because it makes it so difficult to get the exact length.
A buddy mentioned to me that this was how crane spec'ed out their pushrods. Too me it would seem kind of silly to spec them that way because it makes it so difficult to get the exact length.
How did you measure. Some manufacturers (Trend who makes many of the other companies) uses gauge length which is measured from the location on the ball end where it is 0.140" in diameter. However, if you call Terry Manton, he prefers overall length which is the measurement with the oiling hole in the pushrod. The difference between the two measurements is about 0.017" with the overall length being longer. So in the end, it depends on how you measured, which pushrods you are buying, and how accurate you need the measurement.
Thread Starter
Staging Lane
Joined: May 2009
Posts: 96
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I measured with a ruler on a table with flat edge on the top, so from oiling hole to oiling hole. I double checked my measurement on a flat granite table in a similar manner since I don't have a caliper that big. I was just curious because if you take into account the sphere without the oiling hole, it looks like it would add about a sixteenth of an inch.
Aren't you using an adjustable pushrod? If so, there should be two marks on it that close when the pushrod is at its shortest measurement. You count turns to get the length in gauge length.
Thread Starter
Staging Lane
Joined: May 2009
Posts: 96
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Yes, I am using an adjustable pushrod. I'm not sure what you mean by two markers. The range of my adjustable pushrod is from 6.125 - 7.5, but I don't know if that guarantees the closed or shortest position is actually 6.125. They may just be approximations.
I'm going to call TSP. I got a set of 7.4's. I think they measure out to 7.4 oiling hole to oiling hole.
I'm going to call TSP. I got a set of 7.4's. I think they measure out to 7.4 oiling hole to oiling hole.
Here's a quick check. Put the 7.4 in the intake position and hand tighten the bolt on the rocker until it stops. Now count turns to 22 lb-ft. Make sure cylinder is on firin position so lifter is on base circle of cam.
Thread Starter
Staging Lane
Joined: May 2009
Posts: 96
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I tried that the other day and it was several turns from zero lash until the rocker finaly seated. There was roughly 3/16 difference when I pulled the 7.4 pushrod out and compared it to what I moved the adjustable pushrod to. So I measured 7.25. If I go with a preload of .05 that puts me right at 7.3 which is what I ordered.
Keep in mind, this is with a set of Jeg's roller rockers, not the stock rocker arms. I think with the stock rocker, the 7.4's would have been okay. I can double check that as well tonight.
Just for a sanity check (see what you think): I define zero lash as where the pushrod just starts to compress in spring in the lifter. The spring inside the lifter has quite a bit of travel (about a 3/16 of an inch) before you collapse the lifter. With oil inside the lifter (from a presoak) it's much more difficult to feel the spring in the lifter. If you compress the spring and squeeze the oil out. It becomes obvious where the spring starts to push. This is where I think there is a lot of confusion. BTW I am running ls7 lifters.
Keep in mind, this is with a set of Jeg's roller rockers, not the stock rocker arms. I think with the stock rocker, the 7.4's would have been okay. I can double check that as well tonight.
Just for a sanity check (see what you think): I define zero lash as where the pushrod just starts to compress in spring in the lifter. The spring inside the lifter has quite a bit of travel (about a 3/16 of an inch) before you collapse the lifter. With oil inside the lifter (from a presoak) it's much more difficult to feel the spring in the lifter. If you compress the spring and squeeze the oil out. It becomes obvious where the spring starts to push. This is where I think there is a lot of confusion. BTW I am running ls7 lifters.
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Didn't know you had other rockers. I usually lift the rocker until the tick tick just goes away rather then feel for movement of the lifter plunger. You can count turns with an aftermarket rocker as well, as long as it is not stud mounted. What bothers me is you said "several turns with 7.4" yet ordered shorter pushrod, which will increase the turn count.
Also, did you shim to correct the rocker wipe pattern before measuring?
Also, did you shim to correct the rocker wipe pattern before measuring?
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Didn't know you had other rockers. I usually lift the rocker until the tick tick just goes away rather then feel for movement of the lifter plunger. You can count turns with an aftermarket rocker as well, as long as it is not stud mounted. What bothers me is you said "several turns with 7.4" yet ordered shorter pushrod, which will increase the turn count.
Also, did you shim to correct the rocker wipe pattern before measuring?
Also, did you shim to correct the rocker wipe pattern before measuring?
Thread Starter
Staging Lane
Joined: May 2009
Posts: 96
Likes: 1
Anyway I ordered a set of 7.3 pushrods and will recheck the wipe when they arrive. BTW antiseize to check a wipe pattern works pretty well. It gives a pretty definitive read and it wipes off easily. I hope the rockers clear the valve cover!
Also, my TSP 7.4 pushrods were right on the money at 7.4.
