BMW M20 Engine Overhaul, Rebuild, Restoration, and 2.7 Stroker
Specs: 2.5 block, 2.7 crank, 2.5 rods, custom 85mm Wiseco pistons, 885 2.5i head, stock cam (for now), Supersprint headers and exhaust, Bosch Motronic 1.3, custom chip, custom wiring from Motronic to the E21 fuse box. June, 2014: This BMW M20 engine was offered to me and the deal was too good to pass up. Supposedly it was taken from a parts car with 88k miles. It's from a 1988 325is. I know it's an 88 because it has the later style coolant system with the metal coolant pipe across the front. And it's an "is" because it has a oil filter housing set up for an oil cooler. I got lucky! Or did I? As I dismantle it I'm finding someone has been through this engine quite a lot. Nearly every bolt I touch is loose already. The timing cover is held on with one bolt, there are hoses missing, and the exhaust manifolds are already removed. And the kicker - the cylinder head is new/fresh. There's not a smudge anywhere inside and half the rocker arms are new! But I can't be so lucky - the timing marks between the cam sprocket and the crank pulley are off. It's off by 1.5 teeth on the cam mark. Since the M20 is an interference engine this can be BIG trouble. I'm hopeful that someone just reassembled the engine hastily and left it off a tiny bit. Update: after removing the cylinder head and inspecting it and the pistons, I think I have the whole story on what happened. As is too common on the E30 325, the timing belt probably broke, which sent the valves into the pistons. There are grooves in the exhaust valve reliefs on the pistons that shouldn't be there (the intake side looks good). So the head was pulled and rebuilt but was not milled. Then the pistons were cleaned up but not removed from the block. And the motor was reassembled with all new gaskets and driven for a little while. Then the car was sold. The last owner of the engine started taking it apart but took a different direction. That's why so many parts are removed or loose. I got very very lucky with this deal! Update, August, 2015: first drive with the new engine. A few small issues but running great! Update June, 2019: I have about 3,000 miles on the rebuild so far and it's been a joy to drive. There have been some setbacks from things that should have been done with everything off the car. But that's Murphy's Law for you. You can find the series of minor setbacks at the bottom of the last page. To see more about M20 and E21 life, check out my blog at http://www.e21323iblog.com. All images publicly shown are mine and I reserve all copyright.
Read Moreconnecting rod cap orientation. the picture is taken from the front of the engine. I was confused on this because the Bentley manual says they should all be installed in the same orientation. but as I pulled them out they were not all facing the same way. I think it's more important together the bearings lined up.
first few coats with VHT Wrinkle paint. I used the same on an M50 valve cover but not over such a wide area. The nozzle spray is narrow which made some problems. You can see the narrow streaks where the paint hasn't "wrinkled" yet. The instructions say to apply more coats until the surface is uniform. The good news is that it will wrinkle over 24 hours, no baking necessary.