Hey guys and welcome back to Part 2 of the BMW N55 Engine Rebuild Project. In this video we install a piston, new main bearings, new crankshaft and seal the bedplate. Since the original engine had chunks the size of my fist, yet still somehow ran, I bought another engine on Facebook marketplace and that’s the engine we are working on today. Check out the playlist to see the teardown video and more info on how I got it. If you’d like to see what the original engine actually sounded like despite having chunks of metal and a hole at the bottom, click the links in the description below and before we start, hit that like button like the piston hit the cylinder head on my engine for the YouTube algorithm and to make me feel a little better for spending so much money on bolts and gaskets!
Now, back to this engine that I got for cheap off of Facebook. In the last video, I disassembled it to see if it was worth saving and decided that it’s actually a rebuildable engine. Since then, I have been ordering parts and cleaning all the parts I could clean. I’ve tried a few different degreasers, but ultimately the regular brake cleaner and even the cheaper AutoZone brake cleaner seem to have been working best. I’ve also learned that using a ScotchBrite pad helped get rid of the tougher, built up stuff and smooth out the contracting surfaces. Even though this looks easy and fast on video, it took hours to do, but I WAS being careful not to damage anything as I’m fairly new at this.
Removing and installing a piston
Since this engine spun the bearing on piston 6, I decided it would be best to replace it for a couple of reasons. The most important reason was that there was damage on the connecting rod where the new rod bearing would go, which of course would not last very long even with a new bearing in pl ace. I was also worried that the connecting rod itself could have been slightly bent, internally damaged or no longer perfectly round and since I have 4 perfectly good pistons from the original engine, I decided to swap one in. I picked the best out of the bunch, gave it a good clean and then went to adjust the piston rings.
Now, it’s a little difficult to see this on camera, but the M-Flex ring is made from 3 different parts. Bearing spring being the middle and two steel band rings that go on top and bottom. The idea is to get the M-flex ring and the two steel bands to be 120 degree apart at the opening or separation point. It’s also important to make sure that the contact point is not arranged over what’s called a pin boss or basically avoid the area where the piston is connected to the connecting rod.
Once you have to bottom ring properly adjusted, you need to also adjust the middle and the top ring to be 120 degree from each other. The instructions on this aren’t super clear, but I went with 120 for the 3 parts of the M-flex ring and then again 120 degree separation between the 3 rings.
Now that I had my piston ready to go, I cleaned up the cylinder wall to make sure it was perfectly clean, oiled it and then oiled the piston as well. I don’t have any fancy tools for installing pistons, but honestly, it was much easier than I expected. I used this $13 tool from amazon and it worked perfectly. It’s a little fiddly, so if you do this a lot, spend more money on something more solid, but for me it worked exactly as I need it to. I oiled up the inside of the tool to make sure nothing got scratched and tightened it around the piston. Inserted the tool with the piston into the cylinder and gently pushed it in with my fingers. You do not want to use any tools here or force it in. The new piston is now installed… woohoo!
Having actually accomplished SOMETHING, I decided it was time for a little bit more cleaning.. I’ve definitely learned that a big part of engine rebuilding is getting rid of all the old muck and gaskets and all kinds of buildup. If I ever do this again, I might get a parts cleaner or maybe a Dremel with a soft pad or something like that. At least getting it to look new again DOES make you feel like some progress is being done, so that’s a plus.
Now that I felt better about how it looked, I removed the connecting rod bolts and the connecting rod bearing caps on the big end. It’s VERY important that these rod bearing caps do not get mixed up and go to the correct connecting rod when reused or you’ll have another knocking engine very soon. I marked them and put aside until they are needed again when we replace the rod bearings in the next video. The bolts will also be used before the final install for testing, so I’m keeping them for now. Subscribe to the channel so you don’t miss that video! Now that the crankshaft is not held in by anything, it can be simply removed from the engine. Do be careful as it weighs about 50 pounds and you don’t want to drop that on your foot.
I wanted to show you the difference between a good crankshaft and onethat has been abused. Let’s compare the crankshaft from the original engine to the one I’m installing shortly. You can see how much shinier and smoother journals are on the good part. Of course, the old one is not going to waste, it can be resurfaced and used again with oversized bearings.
Back at the engine, I removed all of the old crankshaft bearings, cleaned the area with some ScotchBrite and removed the residue with brake cleaner and a lint free paper towel. We are now ready to install the new stuff!
Installing Main Bearings
WHY am I going with aftermarket main bearings? Well, that’s a very good question with a few answers. First, these seem to have a better reputation with people that have rebuilt their N54 and N55 engines. Second, these King bearings have an improved crankshaft finish for reducing microscopic ferrite peaks if your crankshaft isn’t perfect and since I’m not installing a brand new one, it isn’t perfect. They also have improved oil clearances which should reduce wear on the engine and increase its life. Other than all of those reason, the price was also a factor as these much less expensive compared to OEM.
Installing these is actually fairly simple, put the grooved side in first, squeeze the bearing just a little and push it down with your fingers. They pop in and seat themselves when done correctly. At least they did in my case. The set with a little oil hole goes on the engine block and the solid ones are installed on the bedplate. Of course, I cleaned all surfaces to make sure there was nothing there before installing.
Now that everything is ready, we can temporarily install the crankshaft so that we can check the crankshaft bearing clearance. If it didn’t go in perfectly on the first try, don’t spin it, lift it out a little bit and put it back down where it’s not in the way of anything.
To make sure the bearings have seated correctly and are not over or undersized, it’s important to check the crankshaft bearing radial clearance. For this BMW recommends using plastigauge. I have a full video on how to use plastigauge if you’d like to see the entire process. The basic process is to cut a piece of plastigauge the width of the journal, place it on top of each journal you’d like to test and then install the bedplate back on the engine block.
We then follow the correct sequence to install the bolts and torque them to spec! I left mine for a couple of minutes and then removed the bolts and the bedplate.
Now that I’m confident with the fitment of my new crankshaft, it is time to do the final assembly. Of course, I have cleaned all of the areas again and removed the plastigauge from the crankshaft as well as the bed plate. With all the surfaces clean, I then installed some assembly lube as this will be the only oil between the journals and the bearings when the engine runs for the first time. After the oil pressure is build up, regular oil will go in through the holes in the bearings and lubricate, but we have to protect the engine for those first few rotations. I put some assembly lube on the bedplate bearings as well and even rub a little on the journals directly. This stuff isn’t going to hurt anything and it still much better to the surfaces compared to regular oil.
Since there is no gasket between the bedplate and the engine block, it has to be sealed with a special sealant. The one I got is recommended by BMW and is specified in the service manual. I applied a good bead into the groove as specified.
I really hope you enjoyed this video or at the very least learned something new. If you enjoy this type of content or just like cars, check out the rest of the channel for many more car related videos. Most aren’t nearly as technical. Thank you so much for watching and I’ll see you in part 3 where we install the rod bearings.