Main bearing replacement, the easy(er) way
written by: maxAbout this Guide
Replacing main bearings isn't easy, but here's a guide to doing it in your watercooled VW without having to pull the engine, separate the transmission from the engine block, or having to completely remove the crankshaft. In this particular example, I'm working on an OBD-II A3 with the ABA (2.0, 8 valve, 4 cylinder) engine, but the procedure won't vary too much between different years and engines.
Step 1: Background info
Earlier this year, our 1996 Golf had an oil pressure problem. After the engine was really warm (after a half hour or so of hard driving), the low oil pressure light would flicker on at idle and then go off when the engine RPMs were raised. Oil pressure is maintained by both the oil pump and the main crankshaft bearings (bearings between the crankshaft and engine block). It's sinfully easy to pull the oil pan off an A3 Volkswagen, so I pulled our oil pan to investigage the oil pump and inspect and plastigage the main bearings. Here I'll walk you through the steps I took to show you that it's really not that hard to do without having to pull the engine or separate the transmission from the engine. The key to being able to do this without splitting the transmission from the block, as you'll see later, is a thin-walled 17mm socket. You can buy this specialty tool, or do what I did and make one out of a regular 17mm socket by turning it down (a lathe would work great, but mine was made using a bench grinder). Steel your nerves, and let's go.
Step 2: Drain the oil
Yes, drain the oil. This is a messy job to begin with - it will be much worse if you pull the oil pan without draining the oil first.
Step 3: Remove oil pan
All the A3s I've worked on have all used torx bolts for the oil pan, but they're no ordinary torx bolts - they are also hex bolts on the outside, so you can use a six point or twelve point socket on them. It's kind of nice because if the head gets stripped out, you still have a good way to remove it. The only two bolts that are tricky to get to are the ones closest to the transmission bellhousing. You will need to remove the small aluminum plate at the bottom of the bellhousing, and then the bolts aren't too bad to get to. Oil pans can be difficult to break loose even when all the bolts are removed, because the gasket material usually sticks. With enough persistence, though, you'll get it.
Step 4: Remove oil pump
With the oil pan out of the way, the oil pump should be staring you right in the face. The two larger bolts that go up through the body are what fasten the pump to the block, so remove those and the pump will slide right out.
Step 5: Oil pump inspection
Do not remove the plastic baffle piece from the end of the pickup tube unless you absolutely have to, because it will probably break. Your vehicle may or may not have the plastic piece - that depends on the year of the car. Inspect the plastic piece (if you have one) to make sure it is intact and that no pieces are missing from it - they are known for breaking into pieces, which can then clog up the screen on the end of the pickup tube. Speaking of that screen, inspect it also to make sure there is no blockage. Make sure the clean out the bottom of your oil pan too - stuff likes to collect down there. Consult your Bentley book for backlash and lateral tolerances of the oil pump gears - you will need to separate the two halves of the oil pump to check them (that's easy, it's just a few bolts).
Step 6: Main bearing cap removal, caps 2, 3, and 4
With the oil pan and oil pump removed, you have a clear view of the crankshaft, main bearing caps, lower connecting rods, and rod bearing caps. Plastigaging the main bearings is quite easy, you just take one at a time - remove the bearing cap, wipe the wear surface of the bearing shell clean, wipe the crankshaft journal clean, place your piece of plastigage across the surface of the bearing shell, then carefully reinstall the bearing cap and torque it down (see your Bentley book for correct torque values). Now remove the bearing cap again, and compare the width of the squashed plastigage against the chart on the paper sleeve that the plastigage comes in - it will give you a clearance value, which you can then compare with the specs in the repair manual to determine whether the bearings are worn past their limit. Also, visually inspect the crank journal and wear surface of the bearing shell. The bearing shells have a copper layer that gets exposed as the bearings wear - when the copper starts to show through, the bearing is pretty well worn (but not necessarily out of spec). Also look for scoring - scored bearings will result in low oil pressure. If the bearing shells are scored, then go ahead and replace them... if you're crank journals are scored then that's more serious. In that case, you'll need to remove the crankshaft and have the journals reworked. In some cases the surfaces can just be polished, but in others they will actually have to grind the journals down to a smaller size before polishing them, which means you'll neet to use oversized bearing shells. But that's another topic for another time. If you've just found out that your crankshaft needs to be worked on and you don't know what to do then just put it all back together (using plenty of assembly lube in the bearings) for now and at least you'll be no worse off than you were.
Step 7: Main bearing cap removal, caps 1 and 5
You may have noticed by now that the number 1 and number 5 main bearing caps seem impossible to remove. The bolt heads for #1 are so close to the front main seal cover plate that you can even get a socket onto them. You can get an open ended wrench on them, but that's really not a good idea (even if you get them out that way, you won't be able to accurately torque them back down). Number 5 is even worse - it's bolt heads are too close to the rear main seal plate on one side, and the toothed crankshaft position wheel on the other side. This is why you need a thin walled 17mm socket (on the A3 ABA engine I was working on, the main bolts are 17mm - that may vary on different types of engines). My dad was visiting at the time I was doing this, and he's actually the one that used a bench grinder to turn down one of my 17mm sockets for me, and it couldn't have worked out any better. It gave me just enough room to work with those bolts for the #1 and #5 bearing caps.
Step 8: Swapping out the bearing shells
If you're going to replace your bearings, then oil them up with plenty of assembly lube (you can get the stuff at any auto parts store worth it's salt). Obviously, the lower bearing shells are easy to replace - they're right there in the bearing caps. The upper shells are tricky because they're between the crankshaft and the block. I suggest loosening all of the main bearing caps a little bit. That will make it easier to case the upper bearing halves out. They'll only slide out one way (there's a tab bent up on one end, so that end has to come out first), and you'll need something to chase them around from the opposite end. Once you get it chased out an inch or two, you should be able to pull it out by sliding your thumb along it. It may be hard to understand what I mean, but if you're actually in there and performing this work then I think it will make sense. Sliding the new upper shells into place will take some patience because you'll have to get it in perfectly straight and perfectly aligned. It took me several attempts on each one. The picture you see in this step is a closeup of one of my crank journals before I chased the old upper bearing shell out. Note the residue from the plastigage still on the journal.
Step 9: Installation is reverse of removal
From here on, start reassembling. Squirt some more assembly lube into those lower bearing shells as you install the bearing caps, and make sure to torque everything correctly (refer to the Bentley book for those specs).
Step 10: Before you start that engine...
Before you start the engine again, make sure to add oil and then prime your oil pump. You can buy adapters for your electric drill that will drive the oil pump - keep spinning it until you get some resistance (which means it's starting to pump oil). To get to the drive for the oil pump, just remove the ignition distributor (for VWs without Motronic engine management, make sure to mark it's installation position so you can put it back without having to redo your ignition timing) and look down in the hole. All you need is something that will fit onto that oil pump drive and chuck into a drill. You can buy it or make it - your choice. We made one out of a piece of round teflon stock - it was awkward to use, but got the job done. Don't run your engine without doing this, because it can take a really long time for the pump to start pumping oil again... and in the meantime your engine will be slowly killing itself.