L78 Original Push Rod diameter

[Gary C.]

My L78 broke a pushrod guide. Were the original push rods 3/8"?See photo.

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[Gary C.]

Re: L78 Original Push Rod diameter

If you look at Rockauto pushrods they mention, 3/8, 7/16 & 5/16"

[Ray K.]

Re: L78 Original Push Rod diameter

Gary,

Original push rods for L78 were 3/8. L88 motors used 7/16. Some engines ( low performance _ hydraulic cam ) beginning in 1967 used the 5/16.

Ray

[Joe L.]

Re: L78 Original Push Rod diameter

Gary,

Original push rods for L78 were 3/8. L88 motors used 7/16. Some engines ( low performance _ hydraulic cam ) beginning in 1967 used the 5/16.

Ray

Ray and Gary------


Yes, it's like this:

---all 1965-66 big blocks used 3/8" pushrods

---early 1967 L-36/L-68 used 5/16" pushrods (early= L-36/L-68 assembled prior to September 1, 1966)

---late 1967 L-36/L-68, all 1967 L-71/L-89, and all 1968-72 (except L-88 and ZL-1) used 3/8" pushrods

---all 1967-69 L-88 and ZL-1 used 7/16" pushrods

---all 1973-74 LS-4 used 5/16" pushrods

In addition, the pushrod guide plates were specific to the pushrod diameters.

[Duke W.]

Re: L78 Original Push Rod diameter

Did someone "upgrade" to 7/16" pushrods, but NOT install the corresponding guide plates?

Duke

[Gary C.]

Re: L78 Original Push Rod diameter

Thanks Joe.

[Mark E.]

Re: L78 Original Push Rod diameter

Gary,

This requires more than replacing the push rod and its guide. Investigate why this happened and address root cause. The offset wear on the valve stem tip and broken push rod guide suggest the valve train geometry may not be centered causing lateral load. Worn or improperly installed valve guide? Bent valve? Broken spring? Piston contact??

[Leif A.]

Re: L78 Original Push Rod diameter

Gary,

This requires more than replacing the push rod and its guide. Investigate why this happened and address root cause. The offset wear on the valve stem tip and broken push rod guide suggest the valve train geometry may not be centered causing lateral load. Worn or improperly installed valve guide? Bent valve? Broken spring? Piston contact??

Agree with Mark. Also, could be a lifter has come apart...been there, done that.

[Mark Z.]

Re: L78 Original Push Rod diameter

Retainer, too!