Camshaft install tips and tricks

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5. Failure to use the proper valve springs for cam break-in. You can't use the 300 lb over-the-nose springs that you'll eventually use in the motor and expect the cam to live at break-in. Assemble the heads with stock or weak single springs to break in the cam, then use one of the many tools available to change the springs with the heads on the motor. Those without shop air to hold the valves up through this operation can feed some clothesline cord through the spark plug hole and then bring the piston up to smash the rope and hold the valves up. Alternately, assemble the heads with the springs you will run and use reduced-ratio break-in rockers, then change out the rockers after break-in. Although pretty "spendy", these are available from Crower in different ratios for different motors. A popular ratio for a small block Chevy would be a 1.3:1 rocker. In other words, let's say the lift at the cam is 0.350" and the theoretical lift at the valve with 1.5:1 rockers is 0.525". Using the 1.3:1 rockers would result in lift at the valve of only 0.455", thus reducing stress at the camshaft/lifter interface during the crucial break-in period. Of course, you would have to elongate the pushrod holes to accomodate the shorter pushrod cup to pivot dimension and maybe alter the slots in your guide plates as well.  

5. Failure to use the proper valve springs for cam break-in. You can't use the 300 lb over-the-nose springs that you'll eventually use in the motor and expect the cam to live at break-in. Assemble the heads with stock or weak single springs to break in the cam, then use one of the many tools available to change the springs with the heads on the motor. Those without shop air to hold the valves up through this operation can feed some clothesline cord through the spark plug hole and then bring the piston up to smash the rope and hold the valves up. Alternately, assemble the heads with the springs you will run and use reduced-ratio break-in rockers, then change out the rockers after break-in. Although pretty "spendy", these are available from Crower in different ratios for different motors. A popular ratio for a small block Chevy would be a 1.3:1 rocker. In other words, let's say the lift at the cam is 0.350" and the theoretical lift at the valve with 1.5:1 rockers is 0.525". Using the 1.3:1 rockers would result in lift at the valve of only 0.455", thus reducing stress at the camshaft/lifter interface during the crucial break-in period. Of course, you would have to elongate the pushrod holes to accomodate the shorter pushrod cup to pivot dimension and maybe alter the slots in your guide plates as well.  

7. Failure to check for retainer to valve guide/seal clearance. 1/16"-1/8" clearance at full valve lift is considered sufficient. This is the limiting lift factor with the stock L31 Vortec heads. Most uninformed fellows will say they can run a 0.500" lift cam with them stock. That leaves ZERO clearance between the retainer and the seal. Not good. GM says the limit is about 0.420" with the stock pieces. Ricky Racer down the street will tell you differently, but the GM engineers say 0.420" lift allows 0.030" retainer-to-seal clearance.  

7. Failure to check for retainer to valve guide/seal clearance. 1/16"-1/8" clearance at full valve lift is considered sufficient. This is the limiting lift factor with the stock L31 Vortec heads. Most uninformed fellows will say they can run a 0.500" lift cam with them stock. That leaves ZERO clearance between the retainer and the seal. Not good. GM says the limit is about 0.420" with the stock pieces. Ricky Racer down the street will tell you differently, but the GM engineers say 0.420" lift allows 0.030" retainer-to-seal clearance.  

8. Failure to check for binding at the rocker/stud interface with stamped steel rockers. Long slot rockers are made specifically to cure this problem. Quality roller rockers with a needle bearing trunnion are as good as it gets with a stud-mounted rocker.  

8. Failure to check for binding at the rocker/stud interface with stamped steel rockers. Long slot rockers are made specifically to cure this problem. Quality roller rockers with a needle bearing trunnion are as good as it gets with a stud-mounted rocker.  

9. Failure to check for piston/valve clearance..... 0.080" on the intake and 0.100" on the exhaust is considered by many to be the minimum clearance acceptable. You will probably find the closest near-miss at the exhaust valve on overlap, when the piston is chasing the exhaust valve back onto its seat.

9. Failure to check for piston/valve clearance..... 0.080" on the intake and 0.100" on the exhaust is considered by many to be the minimum clearance acceptable. You will probably find the closest near-miss at the exhaust valve on overlap, when the piston is chasing the exhaust valve back onto its seat.

10. Failure to run the motor at high rpms (2500 or higher, alternating 500/1000 rpm's up and/or down to allow the crank to throw oil in different places at different revs) for the first 40-45 minutes of its life. NO IDLING. NO IDLING. NO IDLING. The motor should not be run at less than 2500 rpm's for a minimum of 40 minutes. If a problem develops, shut the motor down and fix it, then resume break-in. The main source of camshaft lubrication is oil thrown off the crankshaft at speed, drainback from the oil rings and oil vapors circulating in the crankcase. At idle, the crank isn't spinning fast enough to provide sufficient oil splash to the camshaft/lifters for proper break-in protection.  

10. Failure to run the motor at high rpms (2500 or higher, alternating 500/1000 rpm's up and/or down to allow the crank to throw oil in different places at different revs) for the first 40-45 minutes of its life. NO IDLING. NO IDLING. NO IDLING. The motor should not be run at less than 2500 rpm's for a minimum of 40 minutes. If a problem develops, shut the motor down and fix it, then resume break-in. The main source of camshaft lubrication is oil thrown off the crankshaft at speed, drainback from the oil rings and oil vapors circulating in the crankcase. At idle, the crank isn't spinning fast enough to provide sufficient oil splash to the camshaft/lifters for proper break-in protection.