bent push rods
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Freshman User
Joined: Jun 2007
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bent push rods
I finally got to tear into my new 78 broncos 460 to figure out what was knocking. After removing the valve covers I found that their were two bent push rods. I'm in the process of finding replacements but in the mean time I was wondering if I should assume that I need more parts or do the push rods just sometimes get bent without something else being broken. I was told that once I get the new push rods that I should try pressing them down the hole to see if the spring at the bottom still moves. I don't know a ton about engines but am willing to tear into things as long as someone can give me some guidence. What could cause the push rods to bend and should I assume that the rest of them will bend after replacing the two that are bent. The truck will hardly ever be driven on the road but I would llike it to be somewhat reliable on the trail.
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Freshman User
Joined: Jun 2007
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Should I check Like I was told, pushing the new push rods down the hole (what is the hole actually called) and check for movement or should I just pull the intake off right from the start. Like I said I have not ever really messed with a motors internalls so I don't really know what I am doing or looking for but I am willing to try. What is the push rod actually pushing at the bottom of the "hole"?
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Joined: Mar 2005
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From: western montana
You can check the lifter by placing a pushrod in the 'hole' and into the lfter..there should be about 3/8ths of an inch of travel within the lifter that has spring resistance...this will not be the case if the lifter is pumped up with oil pressure...which should not be an issue...
anyway you look at it the intake will need to come off whther lifter, valve etc. UNLESS the problem is valve geometry. with the rocker arm and pushrod intalled the pushrod should be depressing the lifter about half way (of the spring travel). This is determined by the length of the pushrod...so if the engine builder did not check each lifter it's possible that the pushrod length is too long in a few of them and that would cause them to bottom out in the lifter at higher rpm but this could be fixed w/o taking the intake off although it's also possible that this would damage the springs in the lifters.
I recently built a wheezer and a 400 and both had some variability in the ideal rocker arm length...so you check them all. Also some do not use an adjustible rod to measure at all which is asking for problems such as this. I took out a 400 that was prof rebuilt...bent two pushrods...same thing. all looked ok except these two.
anyway you look at it the intake will need to come off whther lifter, valve etc. UNLESS the problem is valve geometry. with the rocker arm and pushrod intalled the pushrod should be depressing the lifter about half way (of the spring travel). This is determined by the length of the pushrod...so if the engine builder did not check each lifter it's possible that the pushrod length is too long in a few of them and that would cause them to bottom out in the lifter at higher rpm but this could be fixed w/o taking the intake off although it's also possible that this would damage the springs in the lifters.
I recently built a wheezer and a 400 and both had some variability in the ideal rocker arm length...so you check them all. Also some do not use an adjustible rod to measure at all which is asking for problems such as this. I took out a 400 that was prof rebuilt...bent two pushrods...same thing. all looked ok except these two.
