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Mysterious Knock

Last Tuesday a problem arose with my truck. I had a meeting across town at one of our sister companies about eleven and got there with no problems. However, on the way back to work a loud clanging knock suddenly reared its ugly head out of my engine compartment. My heart sunk as thoughts of a failing engine filled my brain. I immediately pulled over and attempted to ascertain the exact location and cause of the knock. Without seeing anything obvious and knowing that it was internal anyway and thus I wouldn't be able to "see" anything, I braved the short trip home since I was only a few blocks away. It got home just fine, but made that horrible noise the whole way. I grabbed my wife's car and headed back to work. I told a couple guys what happened, and one guy said that he thought it was probably a bent push rod. That night I took off the valve cover and checked all my push rods, rocker arms and what I could see of the lifters and they all appeared to be fine. Bad luck for me. Not knowing what is wrong with your engine is almost worse than finding a major problem. At least the major problem can be worked on.

I'll admit that I'm not a real mechanic. I just play one on tv. Not to say that I don't know what I'm doing, I know more than most people about engines, but there are still many that run circles around me with their experience. Anyway, I hadn't had another chance to mess around with it yet and was in West Plains last weekend. I started brain-storming the possibilities of what it could be by pouring over everything that I knew about it (which is pretty extensive after 3 1/2 years of fixing or replacing its 50 year old worn out parts), engine theory, and what I've heard others say about it. That's when it hit me. I remembered what a co-worker suggested, "Check to make sure that you're not missing any parts from your carburetor. Parts can come off and make their way down your intake manifold and wind up sitting on top of a piston." I then remembered noticing that the wingnut that holds my air filter on my carb was gone. I took the filter off and set it aside and saw that the stud that the wingnut screws onto was hanging by a thread (literally) and was about to drop down into the carb. I didn't put any thought into this as I removed it and set it aside as well. Why should I? There's no way that the wingnut could of made it into the carb and I caught the stud before it fell into it. But, looking back coupled with the advice from a friend, I realized that there must have been a nut holding the stud tight on the underside of the filter assembly. This nut worked itself loose and dropped down and managed to find a nice home on a piston head. For those of you who haven't put it together, the clanging is when the piston is slamming the nut into the firedeck of my head.

Now, engine performance wasn't lost during this brief trip with the knocking so I shouldn't have anything worse than a scarred up head. I'll take the head off, check my piston for cracks, use the opportunity to fix my dead cylinder, put on a new head gasket, put everything back together, and fire up a 223 that has all six cylinders firing for the first time since I've owned it. (it's had a dead cylinder since I bought it, blow-by, which is a bad valve seal or broken valve that I didn't want to fix because it meant that I would have to remove the head). So, I'm very excited that I figured it out and soon I will have it running smoother that it has ever run before under my ownership.


That thing had good power with out all the cylinders so I bet its going to kick some major butt now.

I didn't know you had a firedeck in your head! :)

Lucky for you that it wasn't something really costly and you could repair yourself. It would have cost ya to take it to a mechanic and have him figure it out. Good job.

Mystery solved. What a load off!

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