Question: I have a JDM ZC 1.6L engine I just put in my 1994 Honda Civic LX. Everything is working all right. No loss of power, performance or anything. However, I can hear this dull knocking noise when the engine is running. I am pretty sure it is not the timing or the gas I am running (timing set to 16 DB TDC and 92 octane). I’d say it sounds like piston slap but the again I never heard what piston slap sounds like. By the way, the sound is always there, whether the car is cold or at normal temperature. I did a compression test and here are the results (from cylinder 1 to 4): 150psi, 184psi,182psi,184psi I did some more testing on cylinder 1 and the pressure build up quickily during the first two strokes but at the third stroke the pressure maxed out and further strokes only increased the pressure buildup marginally. After this I added three squirts of oils through the spark plug hole and retested, and the pressure came out to be the same. No increase. I thought I might have been hearing piston slap at cylinder 1, but I guess this means it is probably not the piston rings? Could the noise come from one the accessories? Could it be the valve or the camshaft? Thanks in advance for any help,

I use an automotive stethoscope to find strange knocks. Most auto parts stores sell them cheap.
Mike 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ‘00 88 Cherokee 235 BFG AT’s
I just bought a automotive stethoscope and listened to the engine. I can’t be sure, but it seems like the sound is strongest when I place it on the engine block near the bottom where the #1 piston is. The waterpump, however is very close to it, so it is hard to tell whether is the waterpump or piston slap. I’d say, nonetheless, it DOES sound like it is the piston slapping against the block. What do you guys think? Any ideas to try to pinpoint it? Should I be worried if it IS piston slap. I just swap this engine into the car and I would hate to have to yet swap it again. You should do a good valve adjustment for the hell of it just to rule out valve clatter. May be your timing belt is off one tooth? Take off your accessory belts and check them for bad bearings or noise. It could be a bent rod or valve even. It could be alot of things.

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