The Stovebolt Site Forums The Shop Area Engine Shop KNOCKING NOISE

Hey guys,

My 54 pickup 235 motor makes a knocking noise when I accelerate. At idle I don't hear it. I put my hand on the valve cover and I feel the knock when i accelerate. I just had the head rebuilt and valve adjustment about 3 months ago. Any ideas why its doing this?

Thanks!

sometimes an exhaust leak sounds like that, I don't know how you can hold your hand on the valve cover while you accelerate, unless you have very long arms

Easy enough. Stand beside the truck on the carburetor side. Put one hand on the throttle linkage, the other on the valve cover.

With the truck in neutral and running, open the throttle with one hand to accelerate the engine while feeling the valve cover with the other hand.

LOL Okay..... maybe I shouldn't have done that to ya.

You may be right about the exhaust leak. Could the timing be fast enough to have ""preignition knock"?

I believe a bad wrist pin will do that. You can pull the plug wires one at a time and see which cylinder it's coming from--or if it's coming from someplace else altogether.

I can actually stand at the center of the grill and have my left hand on the valve cover and reach the carb with my right hand to accelerate. I guess I do have long arms haha..

I'll check the timing, but that was also set prior to the valve adjustment.

If its a bad wrist pin, is that an easy fix?

Thanks all!

Ok..I pulled out one wire at a time and found the one causing the knocking sound. I started from the right to left. Once I pulled the wire next to the coil it stopped knocking when I give it gas. So what is it? bent rod or i something to tight? Am I going to need to rebuild the engine?

Your input would be greatrly appreciated.

Thanks!

rebuilding only the head often results in trouble with the bottom end .... time to open that up and find what got overstressed in it's old age

Bill

I had that back in March and they had not replaced the push rod guides when they redid the engine just knurled them and put them back in.

Knocks that stop when the ignition is disabled are most often caused by a cracked or broken piston skirt. Very rarely, you'll find the wrist pin has worn excessive clearance into the piston. Since the rod clamps onto the wrist pin on a stovebolt, a worn upper rod bushing is not a possibility on these engines. A connecting rod knock will change pitch, or sometimes become a double-knock noise, but they seldom disappear entirely. Bottom line, you need to pull the cylinder head and oil pan, and find our what's going on. Once it's that far apart, you can decide whether to do a patch-up job or go ahead with a full rebuild.
Jerry

Jerry,

Now that you mention it, it does sound like a quick double knock when I accelerate then it will continue to run rough. When I drive it it sounds bad. When I unplug the ignition wire and accelerate it sounds smooth. At idle I don't hear the knock or it isn't that obvious maybe. Could it be the "connecting rod knock" you mentioned?

Thanks!

A rod knock is caused by excessive oil clearance, either from a badly worn bearing, an out-of-round crankshaft, or both. The oil film between the crankshaft and the bearing can't cushion the rod's tendency to hammer up and down as the crankshaft turns. That problem can turn serious in a hurry, with a ruined crankshaft, a locked-up engine, or even a broken connection rod that knocks a hole in the block, so don't continue to run it much until you discover the cause of the noise. It's not going to get better by itself.
Jerry

Get that thing torn down as hotrod said. If it is a connecting rod bearing failing, it won't last long. Maybe right now you can get away with replacing the rod and crank. Or may can have both repaired.

But if it runs much longer you may have some pretty serious damage. Especially if the rod comes out the side of the block. I have seen them tear up camshafts as they tore through the block.

Did you ever find the problem? My 216 is doing the same thing

His problem was all of the above & he hasn't posted since 2012.

Brad