push rod length...
12-29-2009, 08:19 PM
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push rod length... hello all i am just hear for a few min... and wanted to post a question... i am about to undertake my cam install this weekend, i have everything i need put do not know what pushrods i need. i know that i am going with the trick flow ones but i do not know if i should get stock or longer or shorter... i have a all stock ls1 with 241 heads and my cam is a 233 239 tsp cam on a 112lsa. what should i go with... 7.40 larger or smaller... thanks mark
also looking for a part number for the trick flow rods...
thanks
also looking for a part number for the trick flow rods...
thanks
12-29-2009, 09:05 PM
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I personally would run the 7.425s. Stock length is 7.400, but the aftermarket cams are slightly smaller then a stock cam, hence the reason for the slightly longer pushrods.
12-29-2009, 10:41 PM
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Best case get a pushrod checker and and measure. Having said that 7.4 will probaly work fine. But the stockers are actually 7.385. But the 7.40 should make up for the slightly smaller base circle of the aftermarket cam. As stated 7.425 could possibly be the ideal length hence the advice for a checker......
12-29-2009, 11:21 PM
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All stock cams I have measured have been like 1.53. And the aftermarket cams I have measured have been 1.48. So thats .050 difference. Now divide in half bc my measurement was diameter and we need radius. So 0.050/2 = 0.025. So add 0.025 to the factory length of 7.400 and get 7.425. If only doing a cam swap only, without removing heads or changing lifters, rockers, head gaskets etc etc. Its not really needed to measure for some special length pushrods. Only one piece of the equation has been changed and its been accounted for. However I speculated on pushrod length after I had a valve job and mill, got LS7 lifters and went to a different head gasket and my predicted numbers were way off what i ended up measuring. But, that is way different then a simple cam swap.
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01-10-2010, 05:54 PM
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do a search about lifter preload. i did a custom comp cam install on my buddies vette. 590-600 i used 7.4s at first and they wound up being too long and it had the sewing machine noise.(search topic dreaded sewing machine noise). i swapped them out to 7.350 and the noise went away along with the idle issues it was having. basically its like this. get a pushrod length checker. adjust it to match a stock length pushrod and install it on a cyl where one of the valves is closed while the other is open. tighten the rocker bolt down by hand until the rocker is just snug enough to the point where you can lift the rocker off the pushrod. now take a torque wrench and set it at 22 ftlbs and count the turns it takes for the torque wrench to click. stock is 1 full turn which equals to .047 of lifter preload. say you count 1-3/4 turns like i did with the stock pushrod it comes out to .082 lifter preload which is too much. 1-3/4 x .47 = .082. good builders shoot for .050-.060 of preload. i dropped in the 7.350s and got 1 full turn again just like it would be stock.... the motor is stock 806 heads that have never been off. cam swap only. car runs like a dream now....
01-10-2010, 10:11 PM
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Here's the original quote, courtesy of Shane at TR
FWIW, 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 for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
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.
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.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
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.
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.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
02-08-2010, 12:20 PM
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Im also in process of a cam swap. I will be using a push rod length checker and the procedure above. My question is the base circles. My stock 99 measured 1.553 and the TSP Torquer V2 circle is 1.451 (+- .003). My how-to book says aftermarket cams are around 1.45x but is that right where its 0.100 less than stock?
If so and I have my research right, Id be looking at about a 7.425 to 7.435 rod length? It will be another week or so until I can actually measure on the engine (going on vacation).
If so and I have my research right, Id be looking at about a 7.425 to 7.435 rod length? It will be another week or so until I can actually measure on the engine (going on vacation).
