Troubleshooting BMW N45, N55 and M57N Engine Problems

We explore N45, N55 and M57N engine problems, plus rusty subframes on relatively modern BMWs.

BMW Engine N45 Timing Chain

Troubleshooting BMW N45, N55 and M57N Engine ProblemsI heard of a problem recently that I hadn’t encountered before – a 2006 BMW 116i with the N45 non-Valvetronic engine that ran like a pig after timing chain replacement. The garage had done everything by the book – a proper febi Bilstein timing chain kit (the same as on the N42 and N46), the camshaft locking tools and everything else done properly – flywheel locked at TDC, cams locked and so on. Yet the EML was glowing and would not be extinguished, and the car kept coming up with camshaft timing as a fault code. Could it be a faulty Vanos pulley? I’ve had those before that don’t work after being refitted.

The answer was very simple and it’s one that would have had me foxed. It turns out that the N45 has a different locking set to the N42 and N46. The crank and cam locks appear to be the same (but take nothing for granted) and the bit that actually differs is the bit that bolts to the front to hold the cam sensor reluctor discs in the correct place. The locking kit the garage had – and the one I have – states quite clearly that it’s for the N42, 45 and 46. Luckily I borrowed a BMW locking tool set when I did an N45 years ago before prices came down enough for me to buy a cheap eBay kit.
Now I know, and so do you…

BMW Engine N55 Burnt Exhaust Valves

A mate in the trade told me about this – the N55 being the straight-six turbo unit that’s appeared in all kinds of cars such as the 535i, 640i and of course the M135i. A superb thing when it’s working and to be fair, they seem to be quite decent for reliability so far. However, one had a very slight misfire that a couple of dealers couldn’t fix despite having the usual coil pack and injector swap.

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A compression test was done and the rearmost cylinder had a compression reading way down at around 80psi when it should be at least twice that. A damaged bore was almost ruled out immediately because the car didn’t use oil or smoke at all. Instead, an airline was plugged into number six spark plug hole with a screw in adaptor and 40psi fired into it – sure enough, with an ear to the exhaust pipe you could hear it, and with the exhaust manifold removed (a real fun task) it was more obvious. By this time we’re well into taking the head off and with this done, you could see that one of the two exhaust valves was burned in one place. The head was stripped, the two exhaust valves on the cylinder replaced and the seals recut plus a head skim. What caused the valve to burn is a mystery, but it’s possible that a dodgy injector caused it to run lean. The joys of direct injection, hey?

BMW Engine Rusty Rear Subframes

No, you haven’t picked up a classic Mini magazine by mistake. Those things used to rot like a bean can in a salt mine because they were made from KitKat wrappers and given a breath of paint to ensure a long life of at least five years. The E87 1 Series, E90 3 Series and their derivatives have been around for quite a long time now – the E90 was launched 15- years ago. Fifteen crappy wet British winters will take their toll of course and it’s now not unknown for a rear subframe on one of these cars to rust enough for it to break. The result will be a rear wheel that assumes some bizarre angle and with luck it will happen at a low speed after hitting a savage pothole.

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It’s by no means a common issue and I have only seen one that’s done it – a really ropey 2005 120d, but others have been spotted on eBay. The answer is to get under the car and examine the subframe thoroughly, preferably with the wheels off. Replacing a rusty one is a fair old weekend job, exhaust off and you have to ask yourself if it’s worth the bother, but with a good used subframe costing just £50.00 and not much more for a complete rear axle assembly, it’s not going to be a pricey fix.

BMW Engine M57N Diesels

Worried about N47 diesel timing chains on an E90 purchase? Well, you can avoid most of that by buying something better, that being a pre-2010 325d. Whilst the good old M47 (and it was good, mainly) was dropped in 2007 to be replaced by the somewhat troubled N47, the six pot diesels retained the ‘M’ prefixed oil burners until late 2009. This engine goes back to the days of the E39 and it’s still a very good engine. The timing chain is much beefier and rarely gives an issue and even if it does get noisy, it’s at the front of the engine so you don’t have to take half the car apart to fix it. The 325d is in fact a 3-litre with a 2993cc capacity and not a 2.5-litre.

Pre-LCI (facelift) E90s look a bit dated now and there’s no doubt that the LCI versions launched in late-2008 look somewhat better – the Coupé and Convertible always looked better without that ‘pig in lipstick’ grille the pre LCI saloons and Tourings were foisted with. The 330d went straight to the N57 with the LCI facelift and as such you have the expensive and inevitable replacement of the rear timing chain (it’s just a six cylinder version of the N47), but the 325d kept the old engine until the end of 2009 meaning you have a one year window of manufacture to get the better looking E90 with the best engine. The M57D30TU2 is a great unit and worth looking out for – it’s not quite as good on fuel as the 2-litre but it does have just over 200hp so it will rattle along at a fair old rate. It has the same 2993cc capacity as the totally different N57 so you need to go by visual appearance when scanning the classifieds but of all the 3 Series diesels made in recent years, this is the one to have.

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