Hey guys and welcome back to the BMW N55 engine rebuild project. In this video, I go through the process of replacing the rod bearings with the engine out, but the process is exactly the same once you have access, although maybe not nearly as comfortable. Rod bearings fail for many reasons; mostly, due to oil starvation which causes them to overheat and spin on the journal of the crankshaft. If you catch it in time, you can simply replace the rod bearings and you are done. However, if it’s not caught in time or the rod bearing has already welded itself to the crankshaft (show n20), you’ll have to replace the crankshaft as well, just like what I’m doing with this engine. If you hear a knocking coming from the bottom of the engine, the most likely culprit is the rod bearing. This is why some people choose to do this as a preventative maintenance on their hard driven or high mileage BMWs. If you are interested in those steps, check out my previous video where I go through the process of installing a piston, replacing the crankshaft, installing new main bearings and sealing the bed plate. Before we start, make sure to hit that LIKE button for the YouTube algorithms and future DIYs.
In this video I will not be showing you a step by step on how to get to the bearings as it’s different on every car and may be harder or easier depending on the model. As an example, it would be much easier on a BMW Z4 that is rear wheel drive and has tons of space to work with, but it’s much harder on a BMW 335i e92 like this one as space is very much limited and you have to deal with the all-wheel drive system. In any case, to get to the bearings without removing the engine in this car, you’d have to remove all of the reinforcement plates and covers under the car, lower the front axle, remove the front axles and differential and remove the bearing support. ((maybe show video with engine already out ‘for clearance of what to do’). All that work has to be done just to allow you access to the Oil pan. Now, this isn’t necessarily a very complicated part of the job, but it’s important to keep safety in mind, have the engine supported at the top in the installation position and use plenty of jack stands. When I did this on my BMW Z4 with the N20 engine, I used jack stands, wood blocks, 2 jacks and some muscle to lower it. The jacks would allow me to lower and raise the subframe as needed to squeeze the oil pan out. Like I said, a little different on each car and you don’t have to deal with a differential on a rear-wheel-drive car, but you get the idea.
Once you have sufficient access, Removing the oil sump is fairly easy, you just remove the connector for the oil sensor and unbolt all of the bolts. Then, muscle it out of space and watch out for oil dripping down on you. Once the oil sump is removed, you will see the oil pump and the plastic pick up tube. Strangely, the workshop manual does not mention removing the oil pump, but obviously if you need to replace the bearings on cylinder 1, you’d have to remove it as well. That’s a process of its own, but mostly you just unscrew some bolts and you can remove the oil pump without removing the chain modules.
Clearly this video is more about the correct procedure of changing the rod bearings rather than all the preliminary work, but I hope I helped you get an idea of what it would take to get to this step. Since I had the crankshaft out on my engine, I took that opportunity to install the bearings on 5 of the 6 cylinders for convenience, but I will show you how you’d do it if the crankshaft was still installed on the 6th cylinder. The very first step would be to remove the connecting rod cap and be VERY careful not to mismatch it with another connecting rod. It’s best to do these one by one if you are worried. As mismatching connecting rods and connecting rod caps can cause rod knock or even damage. Now would be a good time to inspect the journal on the crankshaft and after removing the bearings, see how good of a condition both of the surfaces are in. You can clean them with a non-metal sponge. I used a very fine scotch-brite here to clean the surfaces and then wiped them down with some break cleaner and a lint free paper towel.
I decided to go with Calico Coated KING rod bearings instead of BMWs color coded bearings for a couple of reasons. As you may know, technically, you are supposed to look at the crankshaft marking to determine which bearing shells you are supposed to install on which cylinder and each one would be slightly different to make a perfect fit. These aftermarket bearings are more or less the average of all those values and should fit all bearing colors and provide longer life with the Calico coating and not as tight of tolerance, allowing for more oil flow. It’s important to get standard sizing as these come in the oversized spec as well and you do not want those unless you have had your crankshaft resurfaced. Standard sizing is indicated by the STD letters on the bearing itself, check every single one to make sure there was no mix up.
Now that the surface is clean, the bearing should go in very easily. The trick here is to put the end with the key in first, squeeze it just a little bit as you are putting in the other side and it should just pop in there.
I repeat the same process for the rod caps. I clean them with scotch-brite, some brake cleaner and a clean paper towel and then install the bearings exactly the same as on the connecting rod. Here you can see exactly what I meant as far as the installation goes. Very easy!
Now that we have all of our pieces ready to go, it’s time to check the clearance between the crankshaft and the bearing. It’s vital that the clearance falls within spec if you want your engine to last. Essentially, what I do here is place a small piece of Plastigage on the journal and then install the connecting rod cap on top using the old bolts. Of course, I will be installing new bolts on final assembly, but these are just fine to use for testing. Before torquing them down, double check that you have the correcting connecting rod cap. When installed, it should look like once piece, even with finger pressure on the cap. The torque specs here are 20 Nm with additional 70 degrees of angle rotation and the 70 degrees of angle rotation again. Once everything is torqued up, the cap can be removed and clearances checked. You are looking for clearance between .025 and 0.76 mm just like on the scale. Since I’m going with aftermarket bearings, I should expect a slightly looser clearance than from factory, but that’s to be expected. If you’d like to learn more about Plastigage, check out the video in the top right corner.
Now that I know the clearance is perfect on this engine, it’s time to do it for real! I repeat the steps, but this time I’m are not doing it dry and adding some assembly lube to the bearings after cleaning off the Plastigage. With the new bolts in, it’s time to torque it to spec the same as before. We are still doing 20 NM and 70 degrees of rotation, twice.
That’s all it takes to correctly replace the rod bearings on a BMW N55 engine and many other BMW engines of this era. Now, all that’s left to do is to do it 5 more times. As you are checking the clearance on each bearing, you don’t’ want to see too much deviation between the cylinders. They should all be more or less within the same range if done correctly.
Now put the car back together and enjoy another 100 thousand on your BMW. I hope you guys enjoyed this video or at least found it helpful. I put a lot of effort into these videos knowing they won’t be popular, so hitting that like button really does keep me motivated. Anyway, check out the rest of the channel for more DIY video and other car related content and I’ll see you in the next one!