Hey guys - I am installing a TSP Tsunami cam and stage 1 LS6 heads with stock rockers and LS7 lifters and .04 cometic gaskets. I am trying to measure for the pushrod length I need and get a different answer depending on the way I measure.

Using this method: https://ls1tech.com/forums/12843999-post7.html
I get that the length should be 7.275 + .05 preload = 7.325" pushrod

Using this method: https://ls1tech.com/forums/12529924-post3.html
A 7.425" pushrod gets me just over 1 1/4 turns to get to 22 lb/ft (and he says "EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods")

Please help - I don't know what to order.

 

subscribing, i am orderering my cam kit next week and need to know the answer to this also. I need to know how long of push rods to get.

 

The first link is the method I wrote. The second is Shane's from TR. I tried Shane's method and get the same answer as mine. When I tried Shane's method, I found I got approximately 5/8 turn to close down the clearance in the rocker (bring the rocker from where the bolt was just starting to move it until it bottoms on the rocker support) and then 1/3 turn that is tightening the bolt (no further preload during this 1/3 turn as the rocker is already bottomed) so at 1 turn from zero lash to 22 lb-ft you get 0.050" inches of preload. Now, you measured over 1-1/4 turns so that extra quarter turn on the bolt needs to be corrected for the rocker ratio to include it and I get just under 0.020" preload from that 1/4 turn (the 1/3 turn of bolt tightening remains constant). Therefore with the 7.425" pushrod you are at greater then 0.070" preload.

I would measure both ways again very carefully and see if you get the same results. I think the results are closer then you think but they are still off a bit between them.

 

I would go with the first method, and that length sounds more reasonable to me.

 

If you do some simple math, stock length is 7.385". You reduced your based circle by 0.025" and your gasket by 0.013" so that results in 7.347" and most stock measurements I have made on preload were 0.080"-0.100". Subtracting 0.030" because you are shooting for 0.050" results in 7.317", close to what you measured.

 

Thank you vettenuts. I think my problem is I'm not exactly sure when to say when while taking the slack out of the rocker. I'll try what you said above and test again.

I like the idea of doing the math to determine it - isn't stock length 7.4"? (the heads do not have the sodium or hollow valves) adding .015 back in would get me 7.332" - in that case is it better to get the 7.350" pushrods so they are not too short?

I'm not sure what preload should be on LS7 lifters, I read .050-.060?

 

What do you do once you get the preload where you want it, but the wipe is all wrong?

 

Ok - I did it again -

Vettenuts way: Came up with the same number - 7.275 + .05 preload = 7.325" pushrod
Shane TR way: 7.325" took almost 1 turn until 22 lb/ft
Doing the math: 7.4 - .025 - .013 = 7.362 Difference between 7.362 and 7.325 is .037, so if stock preload is .080-.100 subtracting .037 gives me a preload of .043-.063?

Everything sound right?

 

Stock GM pushrods are actually shorter then 7.400", I measured and got 7.385" as have several others.

 

If you used Shane's method and got one turn, he states that is 0.047" (also what I measured using his method) so it now sounds that both methods match and you should be good if your target is 0.050" of preload.

 

Called TSP today - they recommended anywhere from .040 to .080 preload. Said the higher preload may be a bit quieter. I ordered a set of 7.350 - that should give me .075 preload.

Thanks again for the help!

 

Ok I am bringing this topic back from the dead!
Have been reading through this and some other posts in order to get some advice on my measurements I am doing.

The three methods seem to confirm one another which confuses me when I think about the math method.
If you are taking the stock length of 7.385 and adjusting for Sad's changes (reduced your based circle by 0.025 and reduced head gasket thickness .013) wouldn't you take the 7.385 and minus the 0.013 and add the .025 instead of subtracting both like you did?

My thinking was the cam has a smaller base diameter, distancing cam from rocker so you add .025. Head gasket is thinner, bringing rocker closer to cam so the .013 would be subtracted.

 

I think the key (if read all this correctly) is that the 7.385 was not necessarily yielding the right (desired) pre-load result.

 

You cant do math for pushrods, IT DOESNT WORK 100%. Measure, and use what you come up with there.

 

If the heads have ever been worked on and even in general it is best to test both heads and the intake and exhausts as well since some like the LS3 / L92 have different valve tip heights. Many aftermarket heads do as well on intale and exhaust.

 

Yeah not sure if you got what I am questioning. yeah the 7.385 (stock length) is not correct in his new setup but if I am understanding it right that 7.385 is used as a baseline then the changes in his setup (cam, gasket thickness) are then mathematically added or subtracted from that 7.385 to achieve the new length (assuming of course the same preload is desired)
I understand measuring is the only sure way, which is what I am doing.

What I am not understanding is this...
I would assume if all three methods are done properly
1. math method, using stock lengths and adjusting that number for changes in engine setup
2. Checker Pushrod tool method
3. Stock or known length rod used to count bolt turns beyond zero lash method.
The results found by all three would give you the same answer (within reasonable accuracy) and confirm each others findings.

The reason behind subtracting both .025 cam diameter decrease, and .013 gasket thickness is whats not making sense to me

 

Okay, now I understand your point. The change in the case base circle decrease should not be subtracted, but added. That is consistent with my experience when I had my my cam changed with no other changes. My pushrod length went from the stock 7.400 (nominal, ignoring what it actually measured) to 7.425". (i did not check the stock preload, but the resulting preload was within the acceptable range).

 

and whats wrong with using a good ole adjustable pushrod to get ur measurement? I know im old school but do your math use the adj pushrod to what u think it should be and check it! that leaves no room for guessing and buying the wrong pushrods

 

On that note here are my findings from the measurements I did!
I used a digital caliper for measuring my stock rods and the checker tool since I found it came up at 6.812 closed when its supposed to be 6.8 exactly.
my stock pushrods came out at 7.385
I used the method posted by vettenuts for measuring
After getting as close as I could with the checker tool to getting zero lash at the same point of snugging down the bolt (didn't torque to 22). I taped up the checker tool to avoid it moving, then checked for zero lash and measured the tool upon removal for each of those respective valves, here is what I found

valve__tool length upon removal_____turns of rocker bolt beyond
zero required to snug bolt
1 E___________7.274_______________________still slight tick
2 E___________7.274_______________________1/16 turn beyond zero lash
2 I___________7.274_______________________ 1/16 turn beyond
3 E__________7.273________________________about 1/8 turn beyond
4 I___________7.274_______________________about 1/8 turn beyond
1 I___________7.274_______________________little under 1/8 turn beyond
3 I___________7.274_______________________little under 1/8 turn beyond
4 E__________7.275________________________barely snug at zero lash

Is this spread close enough?
I am concerned that exhaust on cylinder 1 was quite a bit different than the rest and I even double checked it.
What should I say my average zero lash is given the results?
I figured taking my measured average 7.274 and subtracting my average turns beyond (about 1/8) in rotational distance .0058 ( distance for 1 turn .047 times 1/8 turn .0125 = .0058) to give a final zero lash length of 7.2682

I also tried a stock length rod (7.385) on one valve to verify and I ended up with 2 1/4 turns from zero lash to 22 lb-ft. 2.25 turns X 0.47 length rep rotation= 1.0575
This gives me zero lash length of 6.3275 (7.385-1.0575) which is quite a bit off of 7.2682
This doesn't surprise me since I am comparing rotation of rocker bolt to snug in one method and toque to 22 lb-ft in the other but how do I compensate for this?

 

Bingo you got my question completely. In their figures (vettenuts and Sad) they subtracted both cam diameter and gasket reduction, when the cam should be added and gasket subtracted. In the end though, that math calculation netted the same figures as the two measuring methods which is what baffles me!
Racerrit That makes perfect sense and I agree, I am just trying to understand the whole concept and figure out how all the methods relate to each other and if they will net the same results if determined properly!