Pushrod Measurement Procedure
Thread Starter
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Pushrod Measurement Procedure
Does anyone have a step by step procedure for measuring the required pushrod length if you have adjustable rocker arms? Here is what I have come up with, but I am not sure if I have to add the lifter plunger preload to the final length if the rockers are adjustable, but I would think not doing so would alter my swipe pattern.
1. Remove intake and exhaust springs on new heads, replace with checker springs
2. Install Morel hydraulic roller lifters into checking locations
3. Install head on car using old gasket and tighten enough to remove clearances (around 15 lb-ft) Note I will be using stock GM gasket on the new heads.
4. Make sure intake is on base circle of cam, install checking push rod
5. Mark up top of valve with Sharpie
6. Install Crane adjustable rocker and finger tight to zero lash point
7. Rotate motor and check swipe, once correct then push rod length is established
Repeat the process on the exhaust valve.
At this point, do I need to alter the measured length?
1. Remove intake and exhaust springs on new heads, replace with checker springs
2. Install Morel hydraulic roller lifters into checking locations
3. Install head on car using old gasket and tighten enough to remove clearances (around 15 lb-ft) Note I will be using stock GM gasket on the new heads.
4. Make sure intake is on base circle of cam, install checking push rod
5. Mark up top of valve with Sharpie
6. Install Crane adjustable rocker and finger tight to zero lash point
7. Rotate motor and check swipe, once correct then push rod length is established
Repeat the process on the exhaust valve.
At this point, do I need to alter the measured length?
Racer
Joined: Feb 2004
Posts: 251
Likes: 1
From: Sunny Melbourne FL
just got off the phone with comp cams, while valve is on the base circle of the cam.
stock push rod in place at zero lash(finger tight), scribe the point where the rod comes thru the head
then torque rocker arm to 22-24 ftlbs and scribe again.
measure distance between the two marks. Comp OEM lifters 850-16 need 0.040" preload. If your distance is larger than 0.040" then you need shorter push rods. If your distance is smaller than 0.040" then you need longer push rods.
I have the distinct advantage since my motor is installed, and running. Now I can order the correct hardened push rods.
stock push rod in place at zero lash(finger tight), scribe the point where the rod comes thru the head
then torque rocker arm to 22-24 ftlbs and scribe again.
measure distance between the two marks. Comp OEM lifters 850-16 need 0.040" preload. If your distance is larger than 0.040" then you need shorter push rods. If your distance is smaller than 0.040" then you need longer push rods.
I have the distinct advantage since my motor is installed, and running. Now I can order the correct hardened push rods.
Le Mans Master
Joined: Feb 2002
Posts: 5,970
Likes: 20
From: San Marcos Texas
just got off the phone with comp cams, while valve is on the base circle of the cam.
stock push rod in place at zero lash(finger tight), scribe the point where the rod comes thru the head
then torque rocker arm to 22-24 ftlbs and scribe again.
measure distance between the two marks. Comp OEM lifters 850-16 need 0.040" preload. If your distance is larger than 0.040" then you need shorter push rods. If your distance is smaller than 0.040" then you need longer push rods.
I have the distinct advantage since my motor is installed, and running. Now I can order the correct hardened push rods.
.
stock push rod in place at zero lash(finger tight), scribe the point where the rod comes thru the head
then torque rocker arm to 22-24 ftlbs and scribe again.
measure distance between the two marks. Comp OEM lifters 850-16 need 0.040" preload. If your distance is larger than 0.040" then you need shorter push rods. If your distance is smaller than 0.040" then you need longer push rods.
I have the distinct advantage since my motor is installed, and running. Now I can order the correct hardened push rods.
.
When I adjusted mine, I used the Zero lash method and used a magnetic base mounted dial indiactor to measure the lifter preload distance...Then you cancheck the swipe mark to see if you need a longer pushrod. 
Thread Starter
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Wow, this is an old thread. Well, since posting I have bought a set of Dart heads, disassembled them, hand polished them and re-assembled getting the spring heights withing +/- 0.005" of each other. I also installed checking springs on one cylinder (head off the car) and have found the best swipe and use a measurement of stud depth from the top of the adjustment nut. Now I can measure pushrod length in the car quite easily by getting the pushrod length to the correct adjustment nut height and adding the preload.
