We had a rod bearing fail on our 2003 Dodge Caravan 3.8L V6. The engine started making a bad knocking sound.
I removed the oil pan and wiggled the connecting rods to see which was the loosest. It was the fourth from the front of the engine. I pulled the cap off the rod bearing and saw that the bearing had spun. The cap doesn't just pull off. After removing the nuts, you have to tap on the bolts to separate the connecting rod from the cap.
Here's what the spun bearing looked like. Notice the wear on both the inside and outside surfaces.
The rod bearing should not rotate within the connecting rod. It is clamped in place with pressure from the connecting rod bolts. It has holes that need to line up with oil passageways. When a rod bearing spins, the hole in the center no longer lines up with the oil passageway and then oil can't squirt on the underside of the piston.
When I pulled out the spun bearing, the oil pickup tube screen had a lot of metal shavings in it. There were shavings in the bottom of the oil pan too.
Although the rod bearing is called a bearing, it's actually only half of the bearing. The other half is the crankshaft surface, called a journal. I tried to replace the bearing to see if it would work. The journal didn't look too bad, so I put a new bearing in to see if it would work.
The Chilton manual for the older model 3.8 engines says to tighten the rod nuts to 40 foot pounds plus another 90 degree turn. I really don't like that way of tightening. I don't want to over-stretch the connecting rod bolts. If they were new, I'd do that, but re-using them is different, and the book torque specs don't take into account re-using rod bolts. So I torqued them to 40 foot pounds and stopped at 50 before I went another 90 degrees.
After a day's errands, the rod was knocking again.
Here's what the replacement bearing looked like. This time, it didn't spin, but the journal was not smooth enough to prevent it from wearing.
For comparison, here's what the number 1 cylinder's rod bearing looks like after 130,000 miles.
So, I figured I'd just smooth out the journal surface and try again. So I got out some metal polishing compound, wrapped a cloth strip one and a half times around the journal and got the surface smoother. Well, it still wasn't enough. The surface needs to be absolutely flat and polished for the bearing to ride on a cushion of pressurized oil. The bearings don't rub on each other in normal operation. The oil provides a cushion that prevents the bearing from contacting the journal.
I haven't taken the second replacement bearing out yet. Here are my options:
- Replace the crankshaft. It comes with rod and main bearings. $157 + $75 core + $8 for the timing cover gasket set + oil and oil filter. That's if I do it myself. This may or may not be a great idea. If the oil loss was due to worn piston rings, I would have to eventually replace the engine anyway. Also, if there was any damage to the wrist pin from a lack of lubrication due to the spun rod bearing, that would be cause for engine replacement too. At a minimum, I would have to remove the transmission, ring gear, crank pulley, timing cover, and oil pan to get the crankshaft out.
- Replace the engine. $1880 + $360 core. I'd need time and patience for this job too, and a good supply of nitrile gloves and shop towels.
- Cut my losses and sell the van as is. Blue book value is from $3600 to $5300. I'd have to subtract $2000 for the engine, plus $500 for installation, and $500 for the hassle factor. So I'm looking at a $2300 selling price, with negotiation possible down to $600. However, this option comes with consequences. First, my wife loves this van. Second, her parents gave it to her. I'd be suffering unimaginably by selling it. The repercussions of selling it would be more painful than the blood, sweat, and tears expended by swapping engines.
- Let the van sit in the back yard. This would work for a little while. But eventually, it would only be slightly less painful than option 3. That is, unless I buy another used car that she absolutely loves. Then she may be willing to sell it after getting tired of seeing it sit there.
- Invent a way to machine the journal down 0.010" with the crank still in the engine. Then just buy a 0.010" undersized bearing, put it in and go. While I may impress my wife with my ingenuity and tenacity, I'll lose points for development costs and time. But then, if I could market this tool for $100 or less, then it may . . . never mind. This isn't going to happen. Wives may smile and nod at your dreams, but they also know your track record on following through.
- Install a junk-yard engine. Let's not go there. It's high risk.
