I've done this so many times on so many different vehicles, I figured I'd post it step by step so that anyone considering doing this could get an idea of what they're in for. I've seen alot of people give up on a car because of a little bottom end noise or just keep driving it until the engine is completely wrecked.
The only reason I can see for this is that they mistakenly believe that a complete engine overhaul is the only solution and they lack the time, experience, or money. While this is sometimes the case, often if caught in time, the problem can be solved simply by swapping in a new set of bearings.
First off I'll go over how and why this works. Most modern engines use a pressurized oil system with babbit bearings. Babbit is the soft grey material on the surface of a new bearing. During normal engine operation, the only time the bearings will touch the crank is during startup. The babbit being a soft material allows this to happen without damaging the crank. Once the engine is running, oil from the pump is being forced between the crank and bearings at high pressure. This pressurized oil holds the bearings away from the crank so that there is no contact between the two.
Now here's the problem. Over time the bearings will wear from startups, debris in the oil, running the engine low on oil, etc. and the gap between the bearings and crank will increase. Once the gap becomes excessive, the oil pump can no longer maintain enough volume of flow to hold the necessary pressure. The result is that the oil between the bearings and crank will get pushed out of the gap and the bearing will touch down on the crank. This is what is happening when you hear a knock. The only solution to this is to tighten the gap back up between the bearings and crank by replacing the bearings.
Now that I've bored you to death, we'll get into the fun part.
Rod Bearing Swap
- Raise the front of the car with ramps, jack stands, or if you're real lucky, a lift.
- Drain the oil and remove the filter.
- Remove the oil pan bolts, lower the pan and set it out of the way.
- Using a socket on the crank pulley bolt, turn the engine so that the #1 and #4 rods are at the bottom of their travel.
- matchmark the #1 rod and cap so that you can be sure it goes back together the same direction it came apart.
- Remove the nuts from the #1 rod cap and using a soft drift (I use a wooden hammer handle) tap the rod bolts to free the cap.
- Remove the cap and inspect the bearing half and crank journal. If the crank journal isn't scored badly, you're probably in good shape to go ahead with the bearing change.
- Place 2 short pieces of rubber fuel line or vac hose over the rod bolts to protect the crank from nicks and using your thumbs, push the rod/piston up in the cylinder until the rod bolts will clear the crank.
- remove the old bearing halves from both the rod and cap and replace them with the new bearings making sure to line up the locks on the bearings with the coresponding notch in the rod and cap.
- Coat both halves of the new bearing with assembly lube and pull the rod back down over the crank.
- Remove the pieces of rubber hose from the rod bolts and reinstall the cap making sure to line up the match marks you made earlier.
- Using a torque wrench, tighten the nuts to factory spec.
- Repeat steps 5-12 for the rest of the rods, reinstall the oil pan with a new gasket, install the drain plug, fill with oil, and install a new filter.
- Disconnect the HEP wires coming from the distributer and crank the engine over until the oil pressure guage starts to come up.
- Reconnect the HEP wires and start the engine. After checking for leaks, lower the car and take a testdrive.
That's prettymuch it. At first, changing rod bearings seems like a big job, but after doing it a time or 2 it's really not that bad. For a first timer, I'd allow about 2-2.5 hours for the entire procedure.
Main Bearing Swap
In car main bearing changes require the fabrication of a simple "tool". I've had the best luck starting with a small cotter key. Simply flaten the head of the cotter key so that when your done it resembles a "T".
- Perform steps 1-3 of the rod bearing procedure.
- Number and matchmark the main caps and block so you can replace them in the same place facing the same direction.
- Remove the oil pump pickup.
- Remove the first main cap and inspect the crank journal and bearing half. If the crank isn't badly scored then you're probably in good shape to continue.
- Using a ratchet on the crank bolt, rotate the engine until the oil passage in the crank journal is just ready to start passing behind behind the upper bearing half ON THE SIDE OPPOSITE THE LOCK.
- Insert the "tool" you made earlier into the oil passage. The crossbar of the "T" should be the only thing sticking out.
- Have an assistant turn the crank with a ratchet while you watch from underneath. The "tool" should catch the side of the bearing and spin it out of the block with the crank. It is extremely important that you turn the bearing out away from the lock. In other words, so that the bearing comes out lock side first.
- coat the new bearing with a thin layer of assembly lube on the front side.
- Place the new bearing against the crank journal in the direction that will have the locks lined up properly when it is in place. You will probably be able to start it a good way into the block by hand.
- Make sure that the bearing is started into the block straight and then using the "tool" have your assistant GENTLY and SLOWLY rotate the crank to spin it the rest of the way in. Stop when the bearing just sits flush with the block on both sides of the crank and remove the "tool".
- Coat the lower half of the new bearing with assembly lube and install it in the cap.
- Replace the cap taking care to line up your match marks. Install the bolts and torque to factory spec.
- Repeat steps 4-12 for the rest of the mains.
- Reinstall the oil pump pickup, the pan with a new gasket, make sure the drain plug is tight, refill with oil, and replace the filter.
- Follow steps 14-15 of the rod bearing procedure.
That's all there is to it.
I should mention that the rear main isn't accessable on either the early or commonblock engines without removing the trans and rear seal plate. Also, the front main on the early engines requires removal of the front seal plate which means pulling the crank pully and timing sprocket. Unless the old bearings show extreme wear (missing babbit), replacing all but the rear (commonblock) or all but the front and rear (pre commonblock) should do the trick.
Another thing, commonblock engines require removal of the balance shaft assembly to gain access to the bearings. Any good manual should show this procedure. It's up to you if you put them back in (I don't) but just remember to plug the oil feed hole if you decide to leave them out.