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When I bought the cam, stock length 7.400" pushrods were spec'd and worked fantastically
Then rebuilt motor:
1 -Heads Milled .025 w/ .040 gasket
2. New LS7 lifters - but these are interchangeable part right? So shouldnt change pushrod length
So here is the confusions:
Method 1 - Using pushrod checker - zero lash at 8.5 turns = 7.225 + .070 preload = 7.300 pushrod
Method 2 - Counting turns on the bolt from zero lash. 1 1/8 turns from zero lash = preload of about .052, using .047 per turn. 7.325 Pushrod From this post
Method 3 - Math - I milled .025 from the heads and used a gasket that is .011 thinner. Factory .051 - .040 Cometic = .011. So .036" total less height from rocker arm to block (lifters).
Then how in the hell does a 7.300 or 7.325 pushrod make sense, using the other methods? I would think 7.400 - .036 -> 7.364, so a 7.350 or 7.375.
The motor is together and running, but has epic valve train noise using a 7.300" pushrod. I've been all over the valve train, rockers tight, bearings good, etc - all good.
Before milling the heads, the valve train was factory silent.
Since milling the heads sounds like a sewing machine.
Anyone share how much a mill changed their length?
I'm pretty sure my 7.300s are too short, but i'm back to lost on how much longer to go.
Ok, on method 2, preload is not .047" per rotation. It's .076". .047" is the bolt thread, but the preload is cantilevered past the bolt. Using similar triangles to calculate, .047" at the bolt is .076" at the pushrod cup. And also, there is torque. Did your 1-1/8" include torque? If it did, you have less preload than you think. Once you start actually applying torque, you are no longer adding preload, you are stretching the bolt to gain clamping force.
If using method2, you find dead soft touch with the rocker bolt, and you tighten the bolt just until it bottoms out. No further.
Usually torque results in half a rotation on the bolt. That would mean your method 2 was lacking preload by a good 030. That would put you right in the range of your math method. To tell the difference between preload and torque, use a screwdriver handle to tighten the bolt instead of your ratchet. Or use a very mall ratchet so you can't get much torque on it. You'll feel it bottom out.
On the adjuster, I'm not a fan of the counting rotation method. I use calipers and measure the pushrods. I've never had the two not agree.
I went through this recently. Honestly the best way is, make sure the lifter cups are all the way at the top of the bores in the lifters. Then using an adjustable pushrod, turn it in maybe 4 turns from stock pushrod length. Tighten down rocker arms. Adjust pushrod to 0 lash, and try and be as accurate as possible. Remove pushrod and measure. Add desired preload and be done.
I tried the counting the turns of the torque wrench method and it mathematically didn't come out right and varied between lifters.
Here's a thread to explain the bolt turns a little better, hope it helps.--->Bolt Turns Explained
I used the adjustable pushrod, counting turns (using the subtraction of 1/3 turn where no preload is applied to the lifter as explained in the link) and a dial indicator and basically came up with the same answers. I did this while my car was apart for my own curiosity. Note that the answers won't match exactly, the measuring tools are simply not that precise, with maybe the exception of using a dial indicator, but even the dial indicator method can introduce small errors.
I ended up switching to 7.350 pushrods. Got about 1 3/4 turns from zero lash with them. Rotated the engine by hand, no issues, cranked her up and a little noise at first but then pretty quiet. There is still some noise in the cabin, but I think it has to do with my headers and not having a sufficient number of hangars. These LS7 lifters must be pretty forgiving, I went from a 7.300 to a 7.350 with only a small change in noise level. So IMHO, if any method gets you a consistent answer, then don't over think it and go with a pushrod that puts you in the top range of preload (.60-.90). The lifter has a travel of like .160 so plenty of wiggle room.
The LS7 lifter are very forgiving, tho they can make some noise when under 0.050 preload. I am currently running around 0.070-0.075 preload and they are about as quiet as you can get. I really wanted to have preload in the 0.080's but the next step up was 0.090+. I am using 7.325" pushrods.
I ended up switching to 7.350 pushrods. Got about 1 3/4 turns from zero lash with them. Rotated the engine by hand, no issues, cranked her up and a little noise at first but then pretty quiet. There is still some noise in the cabin, but I think it has to do with my headers and not having a sufficient number of hangars. These LS7 lifters must be pretty forgiving, I went from a 7.300 to a 7.350 with only a small change in noise level. So IMHO, if any method gets you a consistent answer, then don't over think it and go with a pushrod that puts you in the top range of preload (.60-.90). The lifter has a travel of like .160 so plenty of wiggle room.
Originally Posted by 07NBSChevy
The LS7 lifter are very forgiving, tho they can make some noise when under 0.050 preload. I am currently running around 0.070-0.075 preload and they are about as quiet as you can get. I really wanted to have preload in the 0.080's but the next step up was 0.090+. I am using 7.325" pushrods.
The LS7 lifters are forgiving. Some of the shorter travel lifters are not. When you are trying to get preload very precise on short travel lifters, it's not unusual to see some variation between valves. THat .010-.015 variation won't mean anything on a LS7 lifter, but on a johnson short travel with only 0.058" total travel, it's a much bigger deal. But at that point you're ordering custom rods from someone like manton or manley
I ended up switching to 7.350 pushrods. Got about 1 3/4 turns from zero lash with them. Rotated the engine by hand, no issues, cranked her up and a little noise at first but then pretty quiet. There is still some noise in the cabin, but I think it has to do with my headers and not having a sufficient number of hangars. These LS7 lifters must be pretty forgiving, I went from a 7.300 to a 7.350 with only a small change in noise level. So IMHO, if any method gets you a consistent answer, then don't over think it and go with a pushrod that puts you in the top range of preload (.60-.90). The lifter has a travel of like .160 so plenty of wiggle room.
The ideal is to hit the middle range of the lifters travel. I thought LS7 had upwards of .190 on travel? and several folks have ran well over .080 pre load with good results. I personally would measure each valve and make sure none are under .070.
I am in a similar situation except I am running a morel 5315 with a travel of .140ish. Preload calls for .050 but I have several lifters in the .06x range because 3 valves measure .010-.015 lighter then the rest. Currently debating switching to a set of comp ultra pro adjustable rockers to get all valves the same and I am sure that will be worth a few ponies and a even more responsive engine down low.
It blows my mind after all these years somebody has not come up with a light weight adjustable roller tip rocker for LS....there is again the comp ultra pro but only offered in a 1.8 ratio which will work for some applications but most need or want a 1.7.
HI ALL, this is good "tech" though NO ONE has added the AL block/head expansion value.
The block/head temperature effects the pushrod length specification.
I am sure all here will agree that a steel part will grow less than an aluminum part.
I too try for "center" plunger location, with no problems found.
The alloy, 319-T5, of the GM block has a different growth rate than a 356-T6 used in the RHS block.
The newer GM HP blocks get the 319-T7 for greater strength.
THUS, when checking the pushrod length, block temperature should be considered.
HI ALL, this is good "tech" though NO ONE has added the AL block/head expansion value.
The block/head temperature effects the pushrod length specification.
I am sure all here will agree that a steel part will grow less than an aluminum part.
I too try for "center" plunger location, with no problems found.
The alloy, 319-T5, of the GM block has a different growth rate than a 356-T6 used in the RHS block.
The newer GM HP blocks get the 319-T7 for greater strength.
THUS, when checking the pushrod length, block temperature should be considered.
Lance
Yay! Actual Tech!
I actually do consider this when planning preload. For the most part, you can figure from "cold" to operating temperature, you are going to gain 0.010" lash. Put another way, you will lose about 0.010" preload. Now, on higher strength aluminum, this variance is going to be closer to 0.008 or possibly even 0.006, but you will ALWAYS gain lash / lose preload with heat. Event he iron block / aluminum head truck motor should lose preload with temperature, but decidedly less vs the aluminum block.
On a LS7 lifter, That's pretty much a nuance, because there is a ton of "slop" in there. Using the Johnson short travels as an example, there's a reason you aim for 0.038" preload. You drop 0.008-0.010, putting you in the 0.028-0.030 range, which is exactly half the travel of the lifter.
For solid lifters, even more critical. Whatever your cold lash is, this is where you really need to understand the block thermal expansion, as this is the difference between 0.006 and 0.010" hot lash, which directly affects the actual perceived cam duration.
Food for thought, but what about your garage temperature. If you're doing all this and its 50 degrees in your garage in winter or its 110 in Arizona in the summer in your garage, that will impact your lash/preload by a couple thou. but again, on LS7 lifters, not that critical.
Method 4: Take the guess work out and buy an 8" digital caliper. Find zero lash, pull the checker out, measure with calipers, and add the desired preload to that value. Order pushrods.
Method 4: Take the guess work out and buy an 8" digital caliper. Find zero lash, pull the checker out, measure with calipers, and add the desired preload to that value. Order pushrods.
I've always found this to be the best. but I do use method 2 to confirm. I'll add the preload to the PR and then check bolt rotations.
The ideal is to hit the middle range of the lifters travel. I thought LS7 had upwards of .190 on travel?
LS7 lifters have 4.22mm/0.1661417" of full travel. GM recommends 2.09mm/0.08228346" of preload, which is ideal for stock type applications, although can not always happen. In my opinion, anywhere between 0.070" and 0.090" of preload would be ideal.
Method 4: Take the guess work out and buy an 8" digital caliper. Find zero lash, pull the checker out, measure with calipers, and add the desired preload to that value. Order pushrods.
I have always done this method and it has worked nicely. I do measure every pushrod maybe 5 times and have a chart to verify that measurements are stable. I'm running lunati high rpm link bars and they want preload between .030-.060, so I try to go for the .045-.050 preload because pushrods seem to have up to +\- .007 length. Though lunati didn't advise it but informed me that some customers run up to .100 preload. I'm running an aluminum headed iron block.
Personally I think the caliper is the most accurate method
LS7 lifters have 4.22mm/0.1661417" of full travel. GM recommends 2.09mm/0.08228346" of preload, which is ideal for stock type applications, although can not always happen. In my opinion, anywhere between 0.070" and 0.090" of preload would be ideal.
you are correct I had my numbers crossed with a older gm lifter.
Method 4: Take the guess work out and buy an 8" digital caliper. Find zero lash, pull the checker out, measure with calipers, and add the desired preload to that value. Order pushrods.
I really don't understand how people don't think of this. Who counts turns?
Ok, on method 2, preload is not .047" per rotation. It's .076". .047" is the bolt thread, but the preload is cantilevered past the bolt. Using similar triangles to calculate, .047" at the bolt is .076" at the pushrod cup. And also, there is torque. Did your 1-1/8" include torque? If it did, you have less preload than you think. Once you start actually applying torque, you are no longer adding preload, you are stretching the bolt to gain clamping force.
If using method2, you find dead soft touch with the rocker bolt, and you tighten the bolt just until it bottoms out. No further.
This is correct. I've also heard that about 1/3 of the last turn adds nothing as the bolt snugs. So yeah its a little whacky, luckily the ls7s are very forgiving.
01-22-2017, 02:59 PM
Help me understand lifter preload/why all methods give diff results 
I would think 7.400 - .036 -> 7.364, so a 7.350 or 7.375. 
