SBC valve train issue - help

Greg Reimer 7376 · 04-07-2011, 07:09 PM

Good comment regarding rocker arm slot length.If the pushrod is too long, the rocker arm slot runs out of slot before maximum lift and binds on the stud. Too much of that and the stud breaks,pulls out, breaks the stud boss,bends the push rod, or commits unholy mayhem on the tip of the valve stem. Anytime interference occurs on the valve train, especially near max lift like that, the lifter and cam lobe become stressed, so check the cam and lifters very carefully.Push rods are available in a variety of lengths,try some around .150" short and go from there. I recently built a 327 with the usual stock eliminator stuff, a bunch decked off the block and a bunch more decked off the heads to get the deck height and the combustion chamber CC's where they belong, and valve lift with an OEM pushrod was over on eight valves and real close on the other eight. A set of -150" length pushrods brought the lift down to safe limits, but a set of -100" length pushrods would be optimum. When you deck a set of heads ,let's say, 065" to arrive at optimal CC's, and .045 from the block to correct excessive deck heights, you just increased the length of the pushrod .110". Not to mention, the intake is now too wide, and the distributor is now too tall. That can be corrected with a spacer between the flange on the housing and the intake manifold,and by cutting .060-.070 from each side of the intake at the gasket surfaces.It's easy to see that all engine assemblies are a part of a relationship these parts have with each other. Have you ever seen where some stocker motors might have a different length pushrod on the intakes than the exhausts? Sometimes, proper engine building is a matter of determining what it takes to do what you have to do in order to arrive at the desired end result.

04-07-2011, 07:09 PM	#1
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,136 Likes: 172 Liked 705 Times in 219 Posts	Re: SBC valve train issue - help Good comment regarding rocker arm slot length.If the pushrod is too long, the rocker arm slot runs out of slot before maximum lift and binds on the stud. Too much of that and the stud breaks,pulls out, breaks the stud boss,bends the push rod, or commits unholy mayhem on the tip of the valve stem. Anytime interference occurs on the valve train, especially near max lift like that, the lifter and cam lobe become stressed, so check the cam and lifters very carefully.Push rods are available in a variety of lengths,try some around .150" short and go from there. I recently built a 327 with the usual stock eliminator stuff, a bunch decked off the block and a bunch more decked off the heads to get the deck height and the combustion chamber CC's where they belong, and valve lift with an OEM pushrod was over on eight valves and real close on the other eight. A set of -150" length pushrods brought the lift down to safe limits, but a set of -100" length pushrods would be optimum. When you deck a set of heads ,let's say, 065" to arrive at optimal CC's, and .045 from the block to correct excessive deck heights, you just increased the length of the pushrod .110". Not to mention, the intake is now too wide, and the distributor is now too tall. That can be corrected with a spacer between the flange on the housing and the intake manifold,and by cutting .060-.070 from each side of the intake at the gasket surfaces.It's easy to see that all engine assemblies are a part of a relationship these parts have with each other. Have you ever seen where some stocker motors might have a different length pushrod on the intakes than the exhausts? Sometimes, proper engine building is a matter of determining what it takes to do what you have to do in order to arrive at the desired end result.