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Old 07-08-2019, 02:23 PM
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Default PUSHROD SNAPPED IN HALF
Anyone ever have a pushrod snap in half? What would cause this to happen?
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Old 07-08-2019, 03:31 PM
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bad geometry and push rod flex. what head and rocker ratio? guide plates correct? Is this a new combo or making changes?

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Old 07-08-2019, 03:42 PM
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What Brand?
Wall Thickness?
Spring Pressure?
more info needed......

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Old 07-08-2019, 09:46 PM
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Originally Posted by mysticmissle View Post
bad geometry and push rod flex. what head and rocker ratio? guide plates correct? Is this a new combo or making changes?
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.

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Old 07-09-2019, 07:11 PM
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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.

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Old 07-09-2019, 08:30 PM
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Originally Posted by Mike Davis View Post
What Brand?
Wall Thickness?
Spring Pressure?
more info needed......
.116 WALL 5/16 O.D.
PAC 1243 I think 240 on the seat and around 650 open

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Old 07-09-2019, 08:31 PM
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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.
I'm not sure I know what you mean. What is stack the spring?

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Old 07-10-2019, 02:12 AM
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That's a lot of spring for 5/16" pushrods. Just sayin'.

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Old 07-10-2019, 07:16 AM
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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!

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Old 07-10-2019, 07:40 AM
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Suspect a Tight Valve Guide

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Old 07-10-2019, 10:03 AM
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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

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Old 07-10-2019, 12:02 PM
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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...

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Old 07-10-2019, 12:28 PM
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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".

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Old 07-10-2019, 01:28 PM
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11/32 are had to find,I think I got mine from Manton?Tom

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Old 07-10-2019, 02:39 PM
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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.


.

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Old 07-11-2019, 07:32 AM
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Do you run a stud girdle?

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Old 07-11-2019, 08:25 AM
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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

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Old 07-11-2019, 09:30 PM
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Quote:
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Do you run a stud girdle?
No girdle, shaft rockers.

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Old 07-11-2019, 09:34 PM
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Quote:
Originally Posted by tom s View Post
11/32 are had to find,I think I got mine from Manton?Tom
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.

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