Push rod Length?
FormerVendor
Joined: Dec 2011
Posts: 77
Likes: 0
From: Sandy, UT
7.4" rods probably may be approximately almost in the ball-park, but you should always measure to get the correct length, then use that length. Sucks, 'cause it adds a few days to your builds (in most cases), but you should never guess the right length and never check them. Maybe buy some 7.4"ers then measure, then install them if 7.4" is correct...
- Jeremy
- Jeremy
What is a good way to measure? If you have an adjustable length pushrod, do you adjust to zero lash, then go 0.XXXin longer to get the right lifter preload? What if you don't have an adjustable pushrod, but do have a known length pushrod?
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Comp makes adjustable pushrods...I just did this on a 370 I'm building this past weekend...I brought it up to zero lash, then I verified that I'm suppossed to run 0.030-0.050 preload on my Morel lifters...so I found that a 7.300 pushrod will work perfectly with my decked block thinner than GM head gasket and ever so slightly milled heads above my custom ground cam.
You seem to be mostly using "stock" components other than the cam...but do you know the base circle is the same as stock was (likely is, but I don't really know), and you didn't specify which head gasket you're using either.
You seem to be mostly using "stock" components other than the cam...but do you know the base circle is the same as stock was (likely is, but I don't really know), and you didn't specify which head gasket you're using either.
FormerVendor
Joined: Dec 2011
Posts: 77
Likes: 0
From: Sandy, UT
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
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
- Jeremy
