Adjusting Oil Pressure

      Our John Deere 420 ran good, but the oil pressure was low.  Was it really low, or a gauge problem?  We tried a different gauge and got the same result.  Was the engine worn out or was the regulator just set too low?  We noted that the oil pressure was the same when hot, cold, idling or wide open.  That told us it was the regulator.

     Dropping the pan, we noted how clean the engine was.  We think maybe someone reworked the engine and set the pressure too low.  Most engines are similar to adjust.

     To adjust, drop the pan.  Locate the plug on the oil pump (see arrow) and unscrew it CAREFULLY.  There is a spring and other things in there!  Remove the spring.  Find some washers (or shims from the dealer) just the right size and shove them into the hole with the spring.  Replace the plug, which may need to be tied with wire.  Now, more force will work against the popoff plug.  Put the oil pan back on, refill with oil and try it.  We put in 2 washers and brought the pressure to the middle of the green on the first try!



    Sometimes, you may lose pressure when you go to idle from hard running.  That may be a piece of trash under the valve head.  In this case, go ahead and coax all the parts out of the hole and spray it out with WD40 or solvent.  Then reassemble and give it a try.