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Old 11-30-2002, 01:26 AM   #1 (permalink)
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bending push rods!!!

I have a 1972 400 block and it keeps bending push rods, same cyclender. valve is not stuck and nothing seems to be preventing the rocker arm from moving, yet it doesn't and in turn bends the push rod. I noticed that the rockers are non adjustable. Is there some kind of trick to these that I need to know about, what is the torque spec on them and so on???
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Old 11-30-2002, 01:29 AM   #2 (permalink)
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bending push rods!!!

Uhm..your valve is probably contacting the piston, and your pushrods must be the correct legnth.
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Old 11-30-2002, 01:51 AM   #3 (permalink)
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bending push rods!!!

Lifter
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Old 11-30-2002, 02:18 AM   #4 (permalink)
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bending push rods!!!

I'm assuming the engine doesn't start and is bending the pushrods while cranking-right or wrong? If so, probably the timing chain has jumped way out of time and so the cam is banging the valves into the pistons (max valve lift is occuring when the pistons are at TDC). Set the timing mark at TDC on #1 cylinder (the distributor rotor will be pointing at #1 plug wire or sort of in that area). #1's companion cylinder-#6, I believe, will be on it's overlap cycle-that is, the exhaust valve is just closing as the intake is just starting to open. Watch the rocker arms as you rotate the front pulley back and forth a couple of inches or so. If the valve timing is right you can 'balance' or match up the rocker arm movement so both valves are equally open and neither rocker arm is higher or lower than the other. With the rocker arms matched, the timing mark should be on TDC or very close. If not, the chain has jumped.
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Old 11-30-2002, 09:27 AM   #5 (permalink)
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bending push rods!!!

That would bend more than just one push rod I would think.

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Old 11-30-2002, 10:55 AM   #6 (permalink)
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bending push rods!!!

Pull the spark plugs, run compression test. This should tell you if the valves are operating/sealing correctly. How many miles on the engine?

Questions: have you changed anything lately, new cam, lifters, head? If not, when did the problem start...what happened to make you pull the valve cover? Mechanically, it has to be either a 1).stacked valve spring set, 2).rocker arm adjustment problem (there are shims to get non-adjustable rockers to correct height). 3).Push rod length-too long.4). cam out of phase (jumped timing chain).

I'm betting on stacked valve spring or rocker set too tight.
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Old 11-30-2002, 11:59 AM   #7 (permalink)
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bending push rods!!!

spring...
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Old 11-30-2002, 12:05 PM   #8 (permalink)
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bending push rods!!!

Well it hasn't jumped timing and the pushg rods are the correct length. Nothing has been doen to the motor it's all stock with 51K on it. It rans great until this happened. I went out one morning to crank it and CLANK CLANK CLANK, But it was running. So I pulled the cover and there she sits a bend push rod, I replaced that one and it ran great for the rest of the day, then figured ah what the hell I'll replace them all. Then #7 just kept bending them, (5 in a row to be exact), The vavle does not move AT ALL. when i compress the valve and then try to crank it, the rod does not bend untill the second rotation of the motor. I am starting to think it's a hung valve. Seeing as the spring does not even think about moving, the rod just bends. Whatcha think???
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Old 11-30-2002, 03:26 PM   #9 (permalink)
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bending push rods!!!

If you fired t up with old gas in it, could very well be a sticky valve. Had it happen on an old 400. What I did was rig a pry bar that let me work the valve manually, and (with the intake off) kept hittin the stem with wd 40 untill it moved with very little effort.


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Old 11-30-2002, 05:03 PM   #10 (permalink)
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bending push rods!!!

A buddy of mine who uses a hydraulic cam in a 351C (with nonadjustable valvetrain) has the same problem if he revs the engine too high.

If there's too much lifter preload and the lifters pump up, the valves get opened up too far, and can contact the pistons.

At least, this is one possible scenerio. He carries spares in his moypos. (my old yellow piece of sh*t)

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Old 11-30-2002, 07:27 PM   #11 (permalink)
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bending push rods!!!

Weak valve springs will do the same thing. Happened in my work truck 351W. I put a small cam in it and the springs were junk kept bending two push rods not from the valves hitting the pistons but from coil bind. The spings could not keep the pre=load.

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[ This Message was edited by: 393Clevor on 12/1/02 6:28am ]
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Old 11-30-2002, 07:43 PM   #12 (permalink)
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bending push rods!!!

Had a 302 with the wrong spark plugs do the same thing. Plug was too long. Good luck.
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Old 12-01-2002, 08:09 PM   #13 (permalink)
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bending push rods!!!

well I finally did get ir running. Don't know what changed, but it just didn't bend one. Best I can figure is that is was a lifter. Guy at the show says it happened to him. I bought some new heads at the Rod Run in daytona anyway. 351C head. Anyone know what the valve size is for a 1972 400? These are 2.04 in. 1.67 ex.
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Old 05-23-2010, 01:20 AM   #14 (permalink)
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Re: bending push rods!!!

mine has done the same thing and the motor still stars but runs like crap
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Old 06-14-2010, 07:42 AM   #15 (permalink)
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Re: bending push rods!!!

The next time it starts doing this, pull that spark plug and see if the cylinder is full of gas or water. I know of a few instances where the plugs in the bottom of the old Quadrajets would leak fuel into the cylinder and cause hydrolock. The pushrod was the weak link and it (same one) would bend.
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