Today, a mention of the BMW E30 or E36 generations of the 3-Series will most likely bring to memory their most proficient model — the M3. However, the second and third generations of the BMW 3-Series also included multiple standard models powered by smaller, less-capable engines. One such humble engine is the BMW M40 engine.
The BMW M40 engine is an inline-four unit that the German marquee produced between 1987 and 1994. It acted as BMW’s entry-level straight-four and thus found its way onto some of the company’s entry-level models.
Today, several older-gen BMW owners have an M40 engine at the heart of their Bimmer. If you’re one of them, or if you’re looking to acquire a car powered by this engine, this guide contains all the information you’ll need to stay informed — from available models to common problems you might have to deal with during your ownership.
BMW M40 Engine — Filling Big Shoes
The BMW M40 engine replaced the M10 engine. The BMW M10 was produced for over 26 years, with 3.5 million units making their way onto several models — from the BMW 1500 of the New Class to the E30 3-Series. This iconic engine was also the base for the spectacular BMW S14 engine, more popularly known as the unit that powered the E30 M3. Evidently, the engineers at BMW had their work cut out for them when it came to producing a worthy successor.
What followed was the production of two engines — the BMW M40 and the BMW M42 — that were sold alongside each other. While the M42 was developed to power some of BMW’s more performance-oriented models, the M40 was used on the company’s entry-level cars. It was made for modest, everyday applications and did remarkably well at that.
The BMW M40 engine also brought some notable technical advancements over its predecessor, including hydraulic tappets in place of the manual units on the M10 engine and a belt-driven camshaft. As mentioned above, the M40 engine powered the E30 and E36 3-Series models. BMW decided to use a different fuel injection system on both; the E30 came with a Bosch Motronic 1.3 unit, while the E36 cars used a Bosch Motronic 1.7.
With regard to overall construction, the M40 engine was largely similar to the M10, using a cast-iron engine block and an aluminum cylinder head.
BMW M40 Engine — Available Versions
Broadly speaking, the BMW M40 engine had two versions — a 1.6L iteration called the M40B16, and a 1.8L version called the M40B18. As we mentioned above, each engine used a different fuel injection system dep[ending on whether it was used on the E30 or the E36 3-Series.
M40B16
The M40B16 displaced 1,596 ccs with a bore of 84 mm and a stroke of 72 mm. It was a relatively lightweight engine, weighing around 130 kg when it made its debut. In 1991, BMW updated the car’s DME (Digital Motor Electronics) unit, adding 4 kg to its weight. The valves on the M40B16 were placed at a narrow 14-degree angle, allowing the manufacturer to incorporate finger followers supported by hydraulic valve lifters.
On the E30 models, the M40B16 produced 98 hp at 5,500 rpm and 104 lb-ft of torque at 4,250 rpm. Owing to the different fuel-injection systems it worked alongside on the BMW E36 models, peak output figures on those cars were 101 hp at 5,500 rpm and 105 lb-ft at 4,250 rpm.
M40B18
The M40B18 displaced 1,796 ccs, thanks to a larger stroke of 81 mm — the bore dimensions remained identical to that of the M40B16 at 84 mm. The rest of the engine’s construction, including the valve angles, was the same as on the smaller M40 engine.
Peak output figures were rated at 111 hp at 5,500 rpm and 119 lb-ft of torque at 4,250 rpm on the E30 models and 114 hp at 5,500 rpm and 122 lb-ft of torque at 4,250 rpm on the E36 models.
Which BMW Cars Have an M40 Engine?
Considering the BMW M40 engine acted as the base four-cylinder model in the BMW portfolio, it was used in some of the manufacturer’s entry-level models — particularly those from the BMW E30 and E36 3-Series.
M40B16
The smaller M40B16 was used on the BMW E30 316i from 1988 to 1994 and the BMW E36 316i from 1990 to 1994. It also found its way onto a non-BMW vehicle with the Bertone Freeclimber 2, an SUV built by Italian company Bertone in 1992 and 1993.
M40B18
As the more capable unit, the M40B18 was used on the BMW E30 318i from 1987 to 1994, the BMW E34 518i from 1988 to 1994, and the BMW E36 318i in 1992 and 1993.
Is the BMW M40 Engine Reliable?
The BMW M40 is from when engines didn’t contain too many complex individual components. If the overall construction was good, it was unlikely you would run into serious mechanical issues with an engine. The M40, with its cast-iron construction and the aluminum head, was one of these and isn’t infamous for being a problematic engine.
Pre-Purchase Inspection and Common Problems
Despite the reliability of the M40 engine, you should remember that even the latest iteration of one has been around for nearly three decades and has likely done several thousands of miles. As with all engines, the effects of time and normal wear and tear are unavoidable. So, if you’ve just actuated an M40-powered Bimmer, or if you’re in the market for one, here are some of the common problems you should be keeping an eye out for:
Timing Belt Issue
One of the most severe issues with the M40 engine was related to its timing belt. While the belt itself is inexpensive, you might be forced to change the timing belt tensioner, guide, and pulley. These parts can cost you upwards of $250, depending on whether you opt for an OEM or aftermarket replacement.
Worn Out Camshaft
Another somewhat common issue to look out for is a worn-out camshaft. Most examples of an M40-powered BMW out there will have over 150,000 miles on the engine, and the camshaft is bound to wear out by that time. If you notice a loud knocking sound from the motor, the camshaft has probably reached the end of its run.
Since the M40 is a relatively simple engine, you can check the condition of your camshaft yourself if you have access to some essential tools. Remove the rocker cover on the engine and run your finger over the cam lobes. If they’re not smooth and have scratches, you will have to replace the camshaft.
Noisy Tappets
If the engine is starved of oil, it can cause the tappers to wear out. In many cases, you might find the camshaft issue mentioned above is accompanied by faulty tappets. However, if your camshaft is in decent condition, you might be able to bring the car back to proper running order by just replacing the tappets.
Once the new parts are in, ensure that your engine is never starved of oil, and you will delay having to deal with the same problem again.
Get Your BMW M40 Parts at Bimmers.com
The BMW M40 engine is a prime representation of the no-nonsense inline-four engines the German manufacturer produced before the turn of the millennium. If you’re looking for a Bimmer from the era and performance is at the top of your priorities, you’ll be better off picking a car powered by the more capable BMW M42 engine. However, if you want a simple daily driver or something you want to work on yourself, you can’t go wrong with an M40.
Restoring an older BMW engine requires time, patience, and, most importantly, access to the right parts. If you use cheap aftermarket options in your engine, you might have to deal with severe mechanical consequences down the line. Bimmers.com has one of the largest portfolios of BMW parts in North America, and you can find all the engine parts you’ll need to restore an M40 engine on the site. Just enter the model and year of your vehicle to see what’s available.
