Push rod length for my set up....
07-22-2010, 12:13 PM
#1
Push rod length for my set up.... OK so Im trying to figure out if I need to go with a different length push rod for my new set up. I have a 6.0 370ci with flat top pistons and -2cc valve relives. The heads Im using are 64cc and the cam is a 240/244 608/596. Stock rockers with ls7 lifters, but Im wondering if I could get away with using 7.425 push rods. I know the best way to check is to get a push rod length check tool. But I was hoping someone is running a similar set up and what PR size are they running. Any help would be awesome.
07-22-2010, 05:16 PM
#5
The thing is that I don't really feel like waiting for someone to ship me a PR length checker, and then if I do need different rods I don't wanna wait for those to come in. I guess I should ask if it's ok to run for now, im just wanting to get the car back on the road asap. I will order the PR length checker today but I guess I won't get it till the middle of next week.
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07-23-2010, 06:00 AM
#9
11 Second Club
no i thought my setup was right because i had stock heads, stock lifters, and a cam. with that everyone says you need a 7.4 pushrod so thats what i used. my valvetrain was always noisy but after i put the ls7 lifters and trickflow heads i measured for proper preload and now no noise :-)
07-23-2010, 07:48 AM
#10
You can use the turn method for the time being. Get the intake on the base circle of the cam, you know this is the case when the exhaust valve starts to open. Install a PR of known length and set the rocker to zero lash. Keep in mind it will be fairly easy to continually tighten the bolt beyond zero lash with your fingers and start compressing the lifter. So, with that in mind, wiggle the rocker as you tighten the bolt to make sure you are @ zero lash. Now, get out the 8mm torque wrench set @ 22 lb-ft and count how many turns it takes to get there. I did 1/4 turns and carefully made sure the socket did not rotate backwards skewing my results as I went. 1 full turn is ~0.047" of preload and the ideal # of turns is between 1 1/4-1 3/4 turns with stock style lifters. You can now repeat on the exhaust. When the intake valve is closing, you know the exhaust valve is definitely on the base circle of the cam and repeat the process.
FWIW, this is not my method, just sharing it since you do not want to wait for a PR checker. A sponsor on this board, cannot remember who exactly, came up with this idea. It worked for me, as I did the adjustable PR and this method and it worked great. The only thing you need to be careful of is the zero lash. I cannot tell you how easy it is to turn the bolt beyond zero lash with your fingers. This will skew the results everytime.
FWIW, this is not my method, just sharing it since you do not want to wait for a PR checker. A sponsor on this board, cannot remember who exactly, came up with this idea. It worked for me, as I did the adjustable PR and this method and it worked great. The only thing you need to be careful of is the zero lash. I cannot tell you how easy it is to turn the bolt beyond zero lash with your fingers. This will skew the results everytime.
07-23-2010, 09:09 AM
#11
You can use the turn method for the time being. Get the intake on the base circle of the cam, you know this is the case when the exhaust valve starts to open. Install a PR of known length and set the rocker to zero lash. Keep in mind it will be fairly easy to continually tighten the bolt beyond zero lash with your fingers and start compressing the lifter. So, with that in mind, wiggle the rocker as you tighten the bolt to make sure you are @ zero lash. Now, get out the 8mm torque wrench set @ 22 lb-ft and count how many turns it takes to get there. I did 1/4 turns and carefully made sure the socket did not rotate backwards skewing my results as I went. 1 full turn is ~0.047" of preload and the ideal # of turns is between 1 1/4-1 3/4 turns with stock style lifters. You can now repeat on the exhaust. When the intake valve is closing, you know the exhaust valve is definitely on the base circle of the cam and repeat the process.
FWIW, this is not my method, just sharing it since you do not want to wait for a PR checker. A sponsor on this board, cannot remember who exactly, came up with this idea. It worked for me, as I did the adjustable PR and this method and it worked great. The only thing you need to be careful of is the zero lash. I cannot tell you how easy it is to turn the bolt beyond zero lash with your fingers. This will skew the results everytime.
FWIW, this is not my method, just sharing it since you do not want to wait for a PR checker. A sponsor on this board, cannot remember who exactly, came up with this idea. It worked for me, as I did the adjustable PR and this method and it worked great. The only thing you need to be careful of is the zero lash. I cannot tell you how easy it is to turn the bolt beyond zero lash with your fingers. This will skew the results everytime.
07-23-2010, 09:17 AM
#12
Originally Posted by Shane @ Thunder Racing
The TDC method is NOT always accurate. Try the EO/IC method to check pushrod length. I have posted directions on this forum numerous times... Here it is again:
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!!!
Check it using the above method and see where you are.
Thanks,
Shane
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!!!
Check it using the above method and see where you are.
Thanks,
Shane
07-23-2010, 09:54 AM
#15
Has the deck been milled at all? What style heads are they? If the deck hasn't been milled, and the heads haven't been milled and they are 799/243 style heads, and with that cam, I would guess 7.4500 based on the base circle. BUT if the heads have been milled, and the deck has been milled for flatness, then 7.425 would probably be right about on target. The block deck I used in my 408 was milled a wee bit, thinner gaskets, stock 799 heads, unmilled, and the MS4 which is a 239/242 0.649/0.609 111+1 cam, I ended up with 7.425.
07-23-2010, 05:15 PM
#16
Has the deck been milled at all? What style heads are they? If the deck hasn't been milled, and the heads haven't been milled and they are 799/243 style heads, and with that cam, I would guess 7.4500 based on the base circle. BUT if the heads have been milled, and the deck has been milled for flatness, then 7.425 would probably be right about on target. The block deck I used in my 408 was milled a wee bit, thinner gaskets, stock 799 heads, unmilled, and the MS4 which is a 239/242 0.649/0.609 111+1 cam, I ended up with 7.425.
07-23-2010, 05:28 PM
#17
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This so so simple. You have stock length pushrods laying around ok, put those in it and see how things turn out? Then make determination from there. 9 times out 10 people are to long then short from what I see.
