I am planning on doing an in frame engine rebuild to my 4.0, what bearings can be replaced while keeping the crankshaft installed?
thanks.

 

All bearings (main, rod & cam) can be replaced without pulling the block. However, it is highly recommended to leave all of the bearings alone. These engines do not have lubrication issues, imbalance issues, they operate at a low RPM range and they are low compression. All bearings, almost always look brand new on teardown. But there must be something wrong with the engine to be planning an in-frame. Do you suspect excessive bearing wear?

The primary objective on an in-frame rebuild is ring seal. A quick ball hone and new rings. You could buy a set of rod bearings from Summit Racing just in case, since the piston/rod assemblies have to come out anyway. If the rod bearings look great, like they usually do, you can just return the bearings back to Summit. It's best to leave the camshaft and lifters alone as well, unless you plan on replacing both and taking a wild chance on today's flat tappets.

Secondary objective is the cylinder head. It's amazing what cleaning out the ports does to restore power. So a good cylinder head cleaning, new springs and seals and a flat sanding the sealing surfaces. Install an oil catch can when the rebuild is finished to prevent the need for future rebuilds.

 

From my compression test it show signs of worn rings.
The plan is to put new cylinders, rings, oil pump amd timing chain along with freshening up the head as you described.

I was looking at getting a enginetech rebuild kit but I guess I don’t plan to use the bearings and freeze plugs.

 

New cylinders?

 

One should always replace the cylinders.

 

I always do on my Alfa Romeos. Aluminum block with steel liners.

I also did it on my 78 Kenworth with a Cummins 400. Steel block with steel liners.

 

I meant PISTONS! HAHAHA

 

We knew that!!

 

Informative post as usual

A friend of mine who was a mechanic for over 60 years, including over 10 years as an engine rebuilder, and rebuilt untold Jeep and other engines told me that one bearing does show wear and he considered it a bit undersize, he said it was a small end, maybe a conrod ? I cant remember

As to the catch can, do you suggest replacing the PCV valve system or just modifying it somehow?...do you have a link I can read up on