E36 M50 Replacement
Summary
Replace failed engine.
Start Date: May 1, 2012
Odometer: 308141km
Total cost: $
When I purchased my 318is, it already had an M50 non-vanos engine swapped in by the former owner. On its first day at the track, the engine started blowing bluish smoke and lost power. The mechanics I consulted all agreed that the problem was likely a broken piston ring or valve guide.
A compression test on the failed engine yielded these results:
Cylinders 1 and 2 were far below acceptable levels, and consistent with a leak either past the piston rings or the valves. To isolate the source of the low compression, I attempted to improve the piston seal by introducing some oil into the combustion chamber, and then tested the compression again. The readings did not change, which seemed to suggest that the leak was not entirely in the piston ring, but I could not diagnose the problem further without taking the engine apart.
An oil pressure test yielded the following results. All readings were within allowable range.
To return the car to active duty as soon as possible, I decided to swap in another M50 non-vanos engine (rather than fixing the existing engine). I also considered swapping in an M50 vanos or M52, but both required more research and installation time than I wanted to spend. For future reference, I've saved some basic notes on the M50 vanos or M52 swap below.
In addition to replacing the engine, I planned to rebuild the M50 that I pulled out of the car, with the intention of eventually reinstalling it, so I kept the refresh of the replacement engine minimal. I replaced some gaskets that were leaking, spark plugs, and the oil filter.
Parts
Torque Specs
Oil pan bolts: 10 ft lbs
Oil pump nut: 19 ft lbs, left threaded, recommend tack welding to prevent backing off
Thermostat housing: 7 ft lbs
Journal
I tested the new engine compression when it arrived. All cylinders had good compression. Here are the test results:
Compression test on the failed engine:
Replacement-engine arrival:
Exhaust manifold removal:
Cleaned up. Alternator, power steering pump, starter, v-belt removed:
Refreshed cylinder-head cover and replaced cover gaskets.
Supplemental Research
How to Identify an M50 Vanos vs Non-Vanos
An M50 vanos has a hump on the intake manifold side of the valve cover (circled in red below). An M50 non-vanos does not have a hump.
Parts Required for M50 Vanos
Here are the parts needed to replace my e30's M50 non-vanos with an M50 vanos:
Harness
ECU
Run the VSS (Vehicle Speed Sensor) wire from the back of the cluster to the correct pin on the ECU
Parts Required for M52 (OBDII)
An M52 is OBDII, so it would need to be converted to OBDI to be a direct swap into my car.
Procedure:
get an M50 vanos harness and ECU.
put the M50 OBDI manifold on
drill a hole in the cylinder head to put another coolant temp sensor in since OBDII cars use one sensor. (It might also be possible to use the one sensor and wire it(?)).
The benefit to doing a OBDII swap is that the engine is a higher displacement. Usually they are M52B28's which are 2.8L as opposed to 2.5L. This provides more torque. S52 cams would provide a bit more power.
Swapping in an OBDII M52 is more labour intensive, similar to an S50 swap.