When diesel engines lose oil pressure and start knocking, it may be time to replace the rod bearings. These small but crucial parts help connecting rods move smoothly around the crankshaft and servicing them may prevent damage while increasing the engine’s lifespan. Whether you’re servicing one vehicle or an entire fleet, this guide will help you replace diesel engine rod bearings effectively and safely.
Rod Bearings: What They Are and Why They’re Important
Before working your way through our rod bearing replacement guide, take a minute to learn what these parts are and what they do. Rod bearings reduce internal friction and allow connecting rods to rotate smoothly as pistons move up and down. With time, bearings may wear out due to heat, high pressure, and oil degradation.
If left untreated, rod bearings may spin or seize, leading to sudden, catastrophic engine failure. Replacing rod bearings at the earliest signs of trouble or easier yet, during an engine rebuild, is a vital part of diesel engine maintenance.
Is It Time to Replace the Rod Bearings?
Before getting into the nitty-gritty of rod bearing replacement, ensure that the bearings are the problem. The most common trouble signs include:
- Decreases in oil pressure
- Tapping or knocking sounds from the bottom end of the engine
- Metal flakes in the oil filter or pan
- Discoloration of drained oil
If your heavy-duty diesel is showing one or more of these signs, consider inspecting and replacing the rod bearings.
What You’ll Need
To do the job right, you’ll need these tools and supplies:
- Torque wrench
- Socket set
- Engine hoist
- A gauge to measure bearing clearance
- Assembly lube
- New rod bearings and bolts
- Oil pan gasket/sealant
- Degreaser
- Plenty of clean rags
By gathering tools and supplies in advance, you’ll save frustration and time during disassembly.
Preparation
Begin by draining engine oil and disconnecting the battery. Remove the oil filter and pan to access the connecting rods and crankshaft. Depending on the engine’s design, you may have to lower components or remove crossmembers to reach the bottom end.
Rod Location and Inspection
Rotate the crank slowly, exposing the connecting rods one at a time. Inspect each rod for signs of scoring, heat damage, and discoloration, all of which indicate bearing wear.
Rod Cap Removal
Mark connecting rods and caps with a paint marker, so they’re reinstalled in the same position. Then, remove the cap bolts and separate caps from the crankshaft. From here, the bearing shells should be visible on the rod ends.
Crankshaft Journal Inspection
Before installing those new bearings, inspect all crankshaft journals for grooves and scratches. Light scuffs can sometimes be buffed away, but severe damage may require crankshaft refurbishment or replacement.
Bearing Clearance Measurement
Next, place a Plastigauge strip on the crankshaft journal and reinstall a rod cap to the manufacturer’s torque specs (don’t add oil). Remove the rod cap and compare the flattened strip to the provided scale. If there’s too much clearance, the bearings are worn; too little, and they may seize.
Bearing Installation
Once clearances are finalized, make sure surfaces are thoroughly clean. Apply a thin, consistent coat of assembly lube to each bearing half and press it into place on the cap and rod. Ensure that oil holes are aligned.
Reassembly
Reinstall rod caps in their marked positions and torque all bolts to factory specs with a torque wrench. It’s crucial to follow the tightening sequence closely. After all bearings are reinstalled, clean the oil pan and apply a fresh gasket before reinstalling the pan and filter. Finally, fill the engine with fresh, clean oil.
Break-In and Final Inspection
After reassembling the engine, turn it over manually a few times to ensure that it rotates smoothly. Then, reconnect the battery and turn the key to start. Listen for strange noises and check for oil leaks or pressure problems. When taking the vehicle back out on the road, avoid heavy loads and high RPMs for the first several hundred miles; it seats the new bearings properly and ensures their continued reliability.
Keeping Diesels Running
Rod bearing replacement isn’t an easy task, but with precision, patience, and the best parts, it’s doable. Regular fluid changes, proper break-in, and oil pressure monitoring will extend the life of new parts and minimize the risk of future failure.
