How BMW Replaced One Of Its Best Engines With One Of Its Worst Engines – The Autopian

It should go without saying, buying a cheap, heavily-depreciated German car is probably a bad idea. Buying a decade-old heavily-depreciated BMW is an extremely dumb idea because although BMWs have always had at least minor issues, there was a period of time where the firm’s mainstream entry-level N20 engine offered a major problem without a whole lot of love back.

BMW went through a rough patch in the early 2010s, and one little four cylinder sought to derail the firm’s Motoren middle name with a coarse turbocharged four-banger that offered drivers plenty of timing chain problems but few reasons to jump for joy. This is a little backgrounder on what came before, what happened, and the liminal space between.

The Last Of The Real Ones

Alright, so the N52 inline-six wasn’t strictly the last naturally-aspirated inline-six. That would be the rest-of-world N53, which offered all of the problems of the bi-turbocharged N54 with none of the power. However, the N52 was the last naturally-aspirated inline-six BMW sold in America, and it fixed several of its predecessor’s issues while shooting for the moon.

The oil pump nut issue found on M54 engines isn’t found on the N52, and since the N52 doesn’t use high-pressure variable valve timing, the dreaded VANOS service simply consists of pulling two easy-to-access solenoids and cleaning their filters, rather than internal engine work. The cooling systems attached to N52s aren’t stupidly pressurized to 2.0 bar, meaning plastic components are more durable. Oh, and did I mention that the N52 brought more power and more revs?

This was BMW’s mainline naturally-aspirated moonshot. With a magnesium-aluminum composite block, variable valve timing on both cams, variable valve lift on the intake cam, an available three-stage variable-length intake manifold, and one of the highest-flowing cylinder heads BMW’s ever installed on a non-M production engine.

In three-liter, three-stage manifold form, the N52 made 255 horsepower, revved to 7,000 RPM, and offered buckets of low end torque. Perhaps most impressively, the 215-horsepower three-liter version with the single-stage intake manifold made a plateau of peak torque from 2,750 rpm to 4,000 rpm, and it kept pulling past 6,000 rpm on the way to that 7,000 rpm redline.

Oh, and the crazy part of it all? The N52 was fairly reliable. It’s extremely common for these engines to last more than 200,000 miles with just regular maintenance. Sure, that regular maintenance may include a water pump, an easy-to-change valve cover gasket, and an oil filter housing gasket, but most of that stuff wouldn’t be uncommon to do on a mid-2000s Toyota or Honda on the way to 200,000 miles. In fact, this engine only has two real, unique problems, one of which affected a small range of model years and one of which requires willful neglect to produce.

If you’ve spent some time poking around N52 forums, you’ve probably heard cam ledge bearing wear mentioned once or twice. These days, it’s essentially a non-issue, but broken VANOS bolts are a real issue on a small run of cars. According to a technical service bulletin, engines built between Sept. 2009 and Nov. 2011 may have been equipped with substandard bolts for the variable valve timing phasers. Those bolts can snap, leading to internal VANOS unit oil leakage and engine malfunction. Needless to say, this isn’t fun. While many of these affected engines were fixed under recall, some weren’t. However, you can avoid buying an N52-powered car with this issue with proper maintenance records, or by going to an older model year.

The second problem is related to the oil filter housing gasket. Over time, this gasket for the cartridge-style oil filter housing on top of the engine will dry out and eventually leak. Ignoring the eventual leak could be catastrophic. Not because you’ll lose all your oil pressure, but because a severe enough oil leak from the oil filter housing gasket will find its way onto the serpentine belt. Once that belt gets all slippery, it can slide off of its pullies, get caught behind the crank pulley, and get sucked through the front main seal. Goodbye engine. This final failure mode takes forever to manifest, so if it happens to you, you probably deserved it.

Still, if you do your diligence on model year and maintenance history, and then just maintain an N52-powered BMW like you would something that isn’t a fiddly European beast, it won’t be a fiddly European beast. Reliable, silky-smooth, makes power everywhere. What’s not to love?

Less Is Less

Well, maybe the tested fuel economy numbers of vehicles with the N52 weren’t great. Look, the end of the N52’s run coincided with the downsizing craze, and instead of another silk-ripping naturally-aspirated six, BMW replaced it with a two-liter turbocharged four-cylinder engine. This is the story of the N20, and why it was so disastrous.

The N20 had all the soul of a DMV administrator, but it got solid posted fuel economy numbers, was smaller than the N52 and easier to package. Most people who leased one were perfectly happy with the off-the-line torque, the fuel economy figures, and most importantly, the badge. This was good news for BMW, since the N20 engine was spreading like gonorrhea in The Villages through the brand’s expanded lineup. If we’re talking about total global availability, customers could order the N20 in a 1 Series, a 2 Series, a 3 Series, a 4 Series, a 5 Series, an X1, an X3, an X4, and X5, a Z4, and a partridge in a freakin’ pear tree. In America, it was the corporate entry-level engine, and everything was going according to plan. Then timing components started to go boom.

In 2017, a small group of BMW owners filed a class action lawsuit over N20 timing chain problems, and made some pretty damning claims. For instance, the suit’s introduction claimed that

The primary chain plastic guide assemblies in class engines are defective and prematurely fail. The primary chain plastic guide assemblies become brittle and break apart because the guide assemblies are made of defective polycarbonate composition and other materials. Pieces of broken off plastic from the chain guide become lodged in the crankshaft drive sprockets causing chain breakage or chain skip sufficient to cause severe engine damage or complete engine destruction.

Yikes. Oh, and unsurprisingly, BMW apparently knew of this defect by the time the lawsuit was filed. Superseding parts numbers show that BMW revised the timing chain hardware for the N20 in 2015, well before people filed suit. Yeah, this was going to be a disaster of epic proportions.

In the years between filing and settlement, the failures piled up, but a resolution was eventually reached. In 2021 (the legal system moves slowly), a settlement was agreed on that included a limited warranty extension covering the timing components on, well, you take a look.

Yep, it covers just about everything with this engine made between the beginning of this engine’s life and late February of 2015. That’s a massive model year spread.

As you can probably expect, customer awareness of most service bulletins isn’t crazy high, and now there are N20-powered BMWs running around on original timing chain components well outside of the limited warranty extension period. As a result, when the timing chains on these often buy-here-pay-here-fodder vehicles go, they end up for sale online with gnarly front end noises or catastrophic engine damage.

Now, you might be thinking, didn’t the older BMW V8s also have timing chain issues? They certainly did, but the old V8s gave you something back for that unreliability. They gave you character, soul, astounding performance relative to common engines of the time. The N20, well, it was just another gravelly, economy-minded two-liter turbocharged four-banger that falls off up top. The N20 is competent when it works, but nothing more. An unreliable engine that doesn’t give the enthusiast anything back.

The Inbetweeners

Tech transitions are never seamless, and the space between the N52 engine and N20 engine was weird indeed. Generally, vehicles introduced in the mid-aughts had the N52 and vehicles introduced in the early 2010s have the N20, but there was a weird gap. The then-new 2011 BMW X3 28i, 2011 BMW 528i, and early E89 Z4 sDrive30i used the N52 instead of the N20 because the N20 just wasn’t ready yet. As a result, they meld the reliability of the old N52 with the mod-cons of a BMW from the 2010s. Sure, these vehicles aren’t exactly what I’d call the Ultimate Driving Machines, but they’re luxurious, comfortable, fairly practical, and have seriously fun engines. More proof that rare and good doesn’t always equal valuable.

(Photo credits: BMW)

Support our mission of championing car culture by becoming an Official Autopian Member.

Got a hot tip? Send it to us here. Or check out the stories on our homepage.