4.0 Engine Bearing Replacement

by Scott Rozman
Posted: February 3, 2001
Last Revision:

After my Submarine Kaputnik, the oil pressure on my 4.0 engine was not up to specifications. At that point, I made the decision to see what I could repair without pulling the engine for a complete rebuild. I pulled the oil pan with the idea of first getting a good idea of what kind of condition things were in. I wanted to check the clearance on the oil pump and both the main and rod bearings for wear.

As I expected, the the main and rod bearings both had pretty extensive wear. From a visual standpoint, the main bearing journals did not show grooving and still seemed smooth. The oil pump, based on some feeler guage measurements, was still in great shape and the screen did not seem clogged.

Knowing the condition of the bearings meant that the cam bearings probably suffered the same wear, but unfortunately the cam bearings are not so easily reached.

I decided that for under $100 in parts, it was worth a try to restore some lost oil pressure and delay the bigger job of a complete rebuild.

Above are the replacement main bearings. One top are the upper halves of the bearings and on bottom are the lower halves. The lower left shows one of the main bearing caps with the bearing installed. The left upper and lower are different from the rest of the bearings in that they provide a bearing surface on 2 planes.

Also note the holes and grooves in the upper bearing pieces this is how the oil gets in between the bearing and the crank journal.

These are the replacement rod bearings. Note that they are pretty much the same top and bottom.

The actual procedure of replacing these bearings involved first removing the oil pan. The bottom bearing pieces come out easily by removing the bearing caps. The upper half of the bearing was removed by "rolling it out" from its location above the crank.

In both cases, you can see small tabs that are used to locate the bearing. With some care, a small screwdriver can be used to catch the bearing and start it rotating. After a full 180 degrees of rotation, the upper bearing piece is free.

The rod bearings provide a bit easier removal because the rod can be pushed up into the cylinder giving some room to remove the upper bearing piece. After removing the rod bearing caps, I used short sections of fuel hose over the bolts, so that I could safely maneuver the rod in the cylinder without scratching the bearing journal.

Engine assembly grease was used to coat each bearing piece before installation. I tried to coat them thoroughly, but with a thin coating. Too much of this grease would probably alter your bearing cap torque specs.

Removing the oil pump would not be necessary for this procedure, but you might wish to do an inspection or replacement at the same time. To insure that the oil pump will self prime, I filled the entire cavity of the oil pump with petroleum jelly, before installation, based on recommendation of the Chilton repair manual.

The results were about what I expected. The oil pressure is back within recommended specifications, but still in the lower end of that range. The engine has not seen many hours of use since I did the bearing job, so I can only guess what the long term outcome will be.

[MADXJ]