After tearing down our car’s 1.8 liter engine and finding a fair bit of carnage, we decided to treat tragedy as opportunity and take this opportunity to not just rebuild our engine, but make it stronger, better than it was before.
Our engine’s deflection wheel–which is really a gear–had broken out of the cast aluminum lower timing chain cover. Since this part is no longer available new, we needed to solve our problem with either a used or aftermarket part. In addition, since this is an interference engine, we had a bunch of bent valves to contend with.
The BMW engine specialists at Metric Mechanic told us they had some tricks to not only fix our engine with parts from a later one, but also bore and stroke it using the crank from that same later engine.
M/M Good
The engine in our 318is was introduced in 1988 as an all-new and quite modern design. Designated the M42–because BMW, oddly enough, used mostly “M” designations for the engines in their non-M models, while M-model engine designations began with an S–this 1.8 liter engine features a cast iron block with an 84mm bore and 81mm stroke, and an alloy 16-valve head with twin overhead cams mounted in replaceable cam carriers. Sodium-filled valves controlled by hydraulic lifters finish off the rather high-tech specs. Instead of a timing belt, a double row timing chain was used. Output was rated at 134 horsepower and 127 lb.-ft. of torque.
Six years later, BMW introduced an upgraded, 1.9-liter version of this engine called the M44. Significant differences included the bump in displacement, a move to roller rockers, and a redesigned head that did away with the cam carriers–the cams now rode right in the head. Other improvements included replacement of the troublesome deflection wheel and a larger oil pump.
The M44’s bore and stroke came in a bit larger than the M42’s at 83.5 and 85mm respectively, but output was only slightly higher at 138 horsepower and 133 lb.-ft. of torque.
The M42 debuted in the 1989 318is and 318i sedan and continued with the E36 318is and 318i, while the M44 was introduced in the 1996 model Z3 and then appeared in the four-cylinder E36 sedans.
Fixing What Broke
Following the Metric Mechanic recommendation meant we would essentially be combining elements of the M42 and M44 engines.
At this point you might be thinking that if the bigger, better engineered M44 fits in the car, then why not just swap the entire engine?
There are many reasons not to do this, but first and foremost is the hassle of switching engine management systems. BMW introduced OBD II on all their engines in 1996, and the complexities of reengineering our OBD I car to work with the more modern M44 engine, while possible, are not what we had in mind for the scope of this project—and not nearly as good a solution as what we ended up doing.
Follow along as we outline the parts needed and the procedure to update an M42 engine with a more modern M44 timing lower timing chain cover and solve the common deflection wheel failure.
Comments
So you're rebuilding instead of buying a motor from Metric mechanic?
The M42 was made with a forged crankshaft, while the M44 internals are cast. M44s were designed to be better commuters with less NVH (noise vibration harshness) and better economy. One other way to improve performance on the M42 is to switch from a dual-mass to single-mass flywheel. From what I've read, the dual-mass flywheel was mostly exclusive to US.
I have a spare M42 (w/a hole in the block) if you need any parts off of it. I'm also local.
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