PUSHROD SNAPPED IN HALF
 

Anyone ever have a pushrod snap in half? What would cause this to happen?

bad geometry and push rod flex. what head and rocker ratio? guide plates correct? Is this a new combo or making changes?

What Brand?
Wall Thickness?
Spring Pressure?
more info needed......

69 Ram air iv heads, 1.5 ratio exhaust 1.65 intake. No guide plates, t & d shaft rockers. Only change was 1.65 rockers on the intake. Exhaust is what broke. Pushrods have about 100 passes on them. I've never seen one break like this without being bent at all.

Did you stack the spring? Should be straight forward as you assumed. Unless the push rd is hitting the head and forcing it out of normal geometry. Then the leverage would snap it.

.116 WALL 5/16 O.D.
PAC 1243 I think 240 on the seat and around 650 open

I'm not sure I know what you mean. What is stack the spring?

That's a lot of spring for 5/16" pushrods. Just sayin'.

Well it does not look bent at all, atleast from your photo so you might just chalk it up to a defective tube section with a internal stress point, but still 650 psi open with 5/16" Rods is not something good to do I would say!

Suspect a Tight Valve Guide

RA IV heads came with 11/32 pushrods as I remember.I know your 5/16 are heavy wall but as stated too much spring for them.Tom

wow!

I would expect to see at least some bending - but that looks like a clean snap!?

I have bent one when a valve stuck on me, and have a second bent one I pulled from a grenaded engine - but have never seen a clean break like that before!

I wonder if Steve nailed it?

EDIT: I just noticed Tom's reply...

Thanks for all the replies. I agree, I need some larger pushrods. I may try to get some tapered 3/8" in there or 11/32" at the very least. I may be wrong but I think 11/32 would be around 20% to 25% stronger than the 5/16".

11/32 are had to find,I think I got mine from Manton?Tom

If you were to build a 5/16 pushrod and a 3/8 pushrod at the same length and same wall thickness diameter the difference in column strength is 96.7 percent different.

This according to Manton.


.

Do you run a stud girdle?

Buckling Anslyses separates the Mech Eng men from the boys.

When i lost an EXH pushrod it "Z"'d into 3 straight pieces. i think the CYL head prevented the high end from bowing.

Suppose you could end up with a clean 2- piece snap. As it bowed and broke at the place of maximal bow. But no constraint by the Head

No girdle, shaft rockers.

Talked to Al at Manton. He is very knowledgeable. He said that their 5 series 11/32 are about 42% stronger than the heavy wall 5/16 I have in there now. I ordered a set yesterday.