Originally Posted by Ballpeen
I have about 100 miles on my new 327 ,it's about 10.5 to1.It just bent the pushrod on #8 exhaust valve.The motor has guide plates and every one is worn significantly by the pushrod but only on these valves-#2intake--#4exhaust--#6intake and #8exhaust.I am useing a mild hydraulic cam and lifters.Everything in the motor is new. I removed the guideplates because I don't have hardened pushrods and now the rocker arms won't stay centered on the end of the valve stems. They were doing that with the guideplates on as well.What am I missing? Please Help B.P.
A guide is necessary to keep the rocker tracking on the valve stem. There are two ways of going about this:
1) Self guiding rockers, these use a raised feature to either side of the rocker contact point on the valve stem to keep the rocker aligned to the stem. No other device or built in guide can be used without risking binding the assembly of push rod, rocker, valve stem with this set up. This is a common factory set up on all SBCs since the mid 1980s, heads for these engines have no other mechanism except the L98 and LT1/4 which have a very loose stamped guide to assist with production assembly. A hardened push rod is not required with self guided rockers. Self guided rockers are available in both sliding foot and roller tip versions.
2) Engines older than 1985, perhaps more specifically their heads, use either a cast guide where the push rod passes from the valley into the head's rocker box for ordinary production engines. High performance engines used a separate stamped guide that fastens under screwed in rocker studs. Hot rod aftermarket heads also use this method. When employed (especially on factory heads with cast guides) the cast guide is eliminated, the stud boss is milled down and tapped for the screw in stud.
- All engines using guides whether cast or stamped must use a hardened push rod.
- When using stamped guides on a head with cast guides the cast guide must be drilled out, there's a tool sold for this purpose.
- When using a high lift cam, it is likely that the guide whether cast or stamped will need to be clearanced in the manifold's direction (across the head width) for additional movement of the push rod. This movement is more exaggerated if the push rod is not the correct length. Aftermarket heads, high lift cams, milling of the block deck and or head, performing a valve job with re-used valves and seats, using extended length valve stems or lash caps are some of the things that greatly affect the push rod length. So a length checker is always required when mixing, matching, and modified or non production parts are used.
- Sheet metal guides often require modification and massaging to get the proper fit, between their manufacturing tolerances and major machined part tolerances, often things just don't line up without doing some cutting and welding of the stamped guides to get proper alignment and clearances. Isky sells a two piece guide specifically for this problem.
This is all stuff you'll have to go over to be sure things line up and don't bind.