One of my co-workers has a Dodge Challenger with a built 340 V8. Cool car, and he loves it like it was his only child.
But it has a problem, and from his verbal description, it sounds like a bent pushrod–at least, the upper end of the pushrod isn’t engaged with the rocker arm any more; it’s off to one side. We briefly discussed how one would go about replacing the pushrod (pull the rocker pivot shaft, pull out old pushrod, drop in new, adjust as necessary), but my engine rebuilding experience is about nil, and his is even less (he bought the engine already built), and when he asked what could have caused it, I came up blank.
So: What could cause a bent pushrod? Or is there a possibility that the pushrod isn’t bent at all, but just needs to be realigned witht the rocker arm and adjusted, or something? Any words of wisdom when replacing pushrods?
A common reason for bent pushrods is too many RPM. If you turn the engine too fast, the pushrod/lifter gets out of sync with the valve/rocker and/or cam lobe and the pushrod gets bent. High performance engines use extremely strong valve springs to keep any “slack” from developing in the system (and they use stronger pushrods, as well).
That’s a common reason. Wear or a bad lifter, anything that can introduce any play into the system, can result in a bent pushrod.
Overhead cam engines get away from pushrods, the valves basically run directly off the cam lobes.
Since you were discussing how you would go about replacing it* I assume you haven’t actually looked at it yet. What are the symptoms that are making you think it’s bent? There could be lots of ways it could happen.
*Assuming it’s generally the same as the last time I was that deep in an engine…
Remove valve cover.
Use a special tool to compress spring.
You may have to use a hammer to tap the valve to get it loose from the spring.
Pull off retaining thingies from valve (carefull, they’re tiny and hard to find under a car in the gravel at night).
Remove special tool.
Remove rocker arm.
Pull out push rod.
Reverse to reinstall.
Make sure to replace the valve cover gasket with a new one before reinstalling it.
As for your words of wisdom there are two things.
First don’t do this at night in a gravel parking lot, very hard to find parts if you drop them.
Second, when you figure out which pushrod/valve set it is, you’ll want to rotate the engine to a point where that valve (actually all valves in that cylinder) are closed and all the way UP. Then you can remove the sparkplug and use a special fitting on an air compressor to keep that cylinder pressurized. If you skip this step, you run the risk of that valve falling in. That would be bad. If you don’t have an air compressor, just make sure that valve is in the up position and when you pull the retaining thingies off it, put a rubber band around the stem to keep it from dropping back in.
PS if you’re comfortable working in an engine, but not sure about this procedure, pick up a haynes or chilton manual for this vehicle (and/or ask questions here, I’m sure there’s people that know that specific truck better then I do). If you’re really uncomfortable, have a mechanic work on it. If you mess it up too much you may find yourself having it towed to a mechanic.
Disclaimer: I’m not a mechanic, and the only time I’ve pulled pushrods out of a vehicle was last summer on a 1972 Ford LTD. This car could be and most likely is quite different. This post is based on the assumption that the procedure is basically the same.
The owner has since told me that “…I forgot to [mention] the part where I was accomlplishing a very major burnout on my street that attracted attention from all the concerned neighbors. It was after this event that I noted the noise. Needless to say - high RPM’s may have been a factor.”
:rolleyes:
JoeyP, I don’t understand why the valve spring compressor would be needed. From looking at pics, the rocker arms all pivot on a long shaft; it seems as though one could just unbolt and remove the shaft, rocker arms and all, and have unfettered access to the pushrod.
But in any event, the owner says his mechanic says that the problem is under warranty and he’ll fix it for free. The mechanic said that it sounds as though the lifter collapsed, resulting in the pushrod disengaging itself from the rocker arm.
Like I said, I only have expierence with the one car I mentioned. The reason you need the spring compressor (on my car) is becuase the valve stem comes up, goes through the spring, through the rocker arm and then has a retainer on it. What you need to do (again on my car), is compress the spring so that you can remove the retainer and then release the spring and remove it. …
…
Ignore everything I just said. I had a brain fart. I just realized that the rocker arm DOES come off on it’s own. You don’t need to compress the valve spring unless you’re trying to remove one of the parts over there (valve, spring, retainer, little plastic umbrella thing (forgot what it’s called) etc…) So nevermind, no valve spring compressing involved. Just pull off the rocker arm and the pushrod should slide right out.