1980 Jeep CJ5 Engine Noise; popping, from one cylinder

ABARKERERER

MEMBER
1980 JEEP CJ5

Engine Mechanical problem
1980 Jeep CJ5 6 cyl Four Wheel Drive Manual

Noise sounds metallic. Doesn't seem to be coming through carburetor. Its very loud - hard to pinpoint location. Sounds like top half of engine though.

Sounds fine at idle. Very loud popping when reved up. Not driveable - too loud. Noise stops when cylinder #5 spark plug is unplugged. Checked compression with gauge (thread into spark plug hole, crank engine through full cycle). #5 has same compression as the other cylinders. Changed #5 spark plug and spark plug wire - no change. Distributor cap and rotor look good. Ran in it the dark. Didn't see any sparks or sparks in the carburetor. Cranked engine with valve cover off - intake and exhaust valves open and close. Added a second head gasket - no change.

Head was re-worked 2 years ago; machined flat, cleaned, new valves and rockers. The popping occurred gradually over 2 summers of use.

Thanks.

1 Reply

MHPAUTOS

MECHANIC
31,937 POSTS

Hi there,

With the plug lead off you greatly reduce combustion pressures, this sin turn will relieve the load on non oil pressurised components and often a fault can be located this way, you have identified Cyl No 5 and this can often be narrowed down to a cracked piston skirt or a worn gudgeon pin.

Mark (mhpautos)