Knock In Motor
 

Hi i have a manual 1987 Ford Ranger 2.0L motor 4 valve, it has a knock in the motor as soon as it starts. it sounds like is echoing through the motor so i cant find where its coming from, i took off the valve cover and i doesnt need a tune up, so im leaning towards a rod knock, is there any way to fix this without rebuilding the engine

nope

To tell if it is a rod knocking disconnect 1 spark plug wire at a time while engine is idling.
Assuming 1 spark plug per cylinder on the 2.0l.

If/when the knock gets quiet that cylinder has a bad connecting rod bearing.

The knock sound comes from a cylinder firing, the piston pushes down hard from air/fuel igniting and slaps the loose rod against the crankshaft journal.
When you prevent the cylinder from firing(no spark) the knock gets very quiet.


You really need to pull out the engine and all the pistons and rods, then install new bearings in all and make sure rods and crank are still true, round.


I have replaced just one rod bearing before, with engine in vehicle, didn't last long, thinking 200 miles, rod cap bolt broke and I was lucky I didn't wreck the block.