340 cracked pushrods

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Westtexdart

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I was in the process of installing the oil pump shaft in the 69 340. After I got it in I was turning the crank when I heard a "snap". I searched and found a split pushrod(no. one intake).There are others that look like they are starting to split.These are the ones that came on this engine.The cam is mopar no. p4452782, the new springs (recommended for this cam) are mopar no. P4120249. Lifters are same length as the originals. I cleaned and inspected these before the installation and found no damage.Could I have the wrong combination or weak pushrods ?
 
hey did the cam/spring instructions say anything about have to machine the spring seat surface due to the increased lift.
 
agreed, remove spring keeper and inspect. and again did it say to cut down valve guide due to cam lift.
 
Guys this is a .429/.444 cam.Actually lighter than the 340 4-barrel cars came with.
Is the Chain set in at Straight up?
Did you BLEED the Lifters when installing?
Did you make sure you had all the push rods seated in the lifters correctly?
Anything cut off of your heads?Block?
What Piston did you use?

I have had Rockers Split out WELL before any Push Rods..

SS
 
The cam is zeroed,the original pistons had 2 valve reliefs each, these have 4 each.I'm watching springs as I turn the crank,can't see any binding.The lifters are the ones that came with the cam,same length as originals.
 
You didn't by some chance get the rockers mixed up did you?They are left and right.Make sure they are Correct.That could make them pop and since in the small block they have the push rod guide hole in the head,they couldn't escape and would bind.

SS
 
I can say the last MP pushrods I used were the assemble your own cut to lengths, and more than 1/2 the press in ends were too small for the tubing. I haven't used them since. I think that was '93. If the PR split, instead of bent, I'd say they are junk to begin with.
 
That's what I'm hoping. I ordered a set of chrome-moly from Mancini. After all these are almost 40 yrs. old. All other components are new.
 
All of what the others said is true tho. You should make sure all's well as far as valve to piston, coil bind, retainer to guide, etc. I've seen pistons installed in the wrong holes. It gets ugly, and might explain the binding. But with such a small cam, I'd think you could open the valve to full lift, and turn the pistons right past it with a TON of room there.
 
moper said:
All of what the others said is true tho. You should make sure all's well as far as valve to piston, coil bind, retainer to guide, etc. I've seen pistons installed in the wrong holes. It gets ugly, and might explain the binding. But with such a small cam, I'd think you could open the valve to full lift, and turn the pistons right past it with a TON of room there.
Click to expand...

With the combo he has there isn't anything that CAN be wrong with the set-up.He has 10.0-1 or less pistons.Stock Cam,stock rockers,shafts,push rods.I have used this stuff on my racers with good luck..Something screwy.Like I said before I have always seen the Rocker splitting WELL before the Push rod..

SS
 
"With the combo he has there isn't anything that CAN be wrong with the set-up."
Hey, even stock stuff can be wrong or broken as new in the box. I've seen some things I'd say "no way..can't be done that way and it still run" but they do, and it does. I've learned to never say never. There should be no issues except maybe the PR themselves, I agree.
 
Sounds like you are using the old solid pushrods (40 year old parts?) - those solid pushrods arent the greatest, Id do what you plan install some new tubular chrome-moly rods.

I assume you are using the stamped non adjustable rockers ?

If you are using adjustable rockers you need to have the correct lengths, Solid lifter pushrods will be too long. Correct length pushrods are readily available from crane etc.
 
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