This results in thousands of owners worldwide having to pay for highly expensive repairs or possibly having their cars written off.
The flaps are found in the inlet manifold of the BMW diesel engines M47TU and M57TU (either 4 or 6 flaps depending on the amount of cylinders).
These numbers are intended to produce a swirl (thus the name) in the inlet manifold, which helps to improve combustion when the engine is not under heavy load. To maximize volumetric efficiency and power output under higher load circumstances, the flaps are completely open. This approach really performs worse in practice than it does on paper.
A typical BMW swirl flap has been removed in the image above to make room for an inlet manifold.
Unfortunately, swirl flaps are poorly designed and prone to malfunction. As you can see in the image below of a used swirl flap that was taken from a car with 80,000 miles on it, the shaft has been shattered (where the closest bolt meets the base).
When a swirl flap malfunctions, the debris falls into the engine and either sticks in the valve port and forces it open, pushing the piston into the valve, or it falls into the cylinder, damaging the piston, valves, and head.
The other problem we frequently encounter with these swirl flaps is that the tiny screws anchoring the flap to the shaft come loose and end up in the combustion chamber, where they cause significant harm. When they go through the turbo and CAT on their way out of the engine, they do more harm.
In the image below, a brand-new piston and swirl flap are shown next to a damaged piston and swirl flap (on the right). At 3000 rpm, when a component strikes a piston, you can see the extent of the damage.
Right side was taken from an engine with swirl flap damage; the left side is brand-new.
BMW attempted to address this issue by introducing a redesigned inlet manifold (still equipped with swirl flaps), which has a thicker and stronger valve spindle but is tragically still prone to failure. In late 2008, BMW eventually gave up on swirl flaps.
BMW only provides one solution if you are unfortunate enough to have swirl flap failure with your car. a new motor (circa PS8,500 to PS13.500 fitted).
At Grosvenor, engines with swirl flap damage can be repaired for about PS2,750 (depending on the extent of the damage).
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Which BMW engines are affected by this?
The 4 cylinder M47 and N47 diesel BMW engines are vulnerable to this. The 6-cylinder M57 and N57 engines will follow. When we removed the metal swirl flaps from the early M engines and installed blank plates in their place, the restriction and potential flap failure were eliminated.
While the manifold is being removed, we manually clean the manifold of unwanted carbon buildup.
You’d think BMW would have learned from their earlier M engine blunder with the subsequent N engines. They have used a big rod with plastic swirl flaps and fully reworked the intake manifold and swirl flaps. Unfortunately, with time, engine vibration and movement cause the plastic flaps to wear out and become loose. To avoid constriction and potential flap failure, we remove the metal bar and plastic flaps. While the manifold is being removed, we manually clean the manifold of unwanted carbon buildup.
The more recent B Diesel engines (made in 2014 and after) do not currently appear to experience the same problem. We believe that these will eventually need to be removed when they age. They resemble the earlier N engines in terms of design. At Burch Motor Works, the blank plugs are already prepared for installation.
All contain fresh inlet manifold gaskets as well as the necessary swirl flap blanks or bungs. Please be aware that possible ECU map tweaks may be needed for the later B series engines to enable swirl flap removal and prevent engine light illumination when in limp mode. A Remap of the DDE-ECU software is an additional PS199.00 inc. VAT if this is necessary.
SWIRL FLAP FAILURE IN A BMW
We are accustomed to benefiting from German automakers’ excellent design as BMW owners. German automakers have established the bar that everyone else merely aspires to. So why is it surprising that the automotive industry powerhouse BMW could make a mistake in engine design?
Inlet manifold butterfly flaps are an unique design flaw in all BMW diesel engines built between 2000 and 2006. (commonly known as swirl flaps). The BMW M47tu and M57tu diesel engines’ inlet manifolds feature swirl flaps to adjust the length of the tract depending on the load and predicted demand. This enables the delivery of the best performance (on a dynamometer!).
BMW/Pierburg decided to make the swirl flaps for diesel engines out of steel back in 2000. BMW swirl flaps frequently malfunction in such a way that they drop the upper spindle part or an attaching screw. If this doesn’t stop the engine, the last swirl flap will collapse completely. Such failure does not have a pleasing end in the least. The piston of a diesel engine spins at least 60 times per minute, thus any swallowed metal fragment that falls off the butterfly flap will be smacked by the rotating internal parts. The cylinder head is typically extensively damaged, along with numerous valves, an injector, and one or more pistons; it’s also likely that collateral damage has spread to the turbo?
BMW fixed this issue in 2004 by enlarging the swirl flap supporting spindle and the attaching screw diameter (we have seen vehicles registered up to 2007 with early type 22mm swirl flaps fitted). Despite the larger spindle diameter, we have seen and heard from several customers across the nation who have had modified type swirl flap failure.
The best course of action is to just totally remove the flaps and swap them out with blanking plates, which will solve the issue.
However, if your swirl flaps have digested, you will need to have your entire engine rebuilt, which we can do for you for PS 1600 inclusive of parts.
One of BMW’s biggest design flaws is the swirl flap, which has cost thousands of owners around the world thousands of dollars in repairs or even totaled their cars.
The BMW diesel M47, M47TU, M57, and M57TU engines’ inlet manifold is home to the flaps (either 4 or 6 flaps depending on the amount of cylinders).
Another problem with these swirl flap units that we frequently encounter is when the little screws holding the flap to the shaft come loose and end up in the combustion chamber, where they cause significant damage. When they go through the turbo and CAT on their way out of the engine, they do more harm.
How do BMW swirl flaps function?
How do swirl flaps work? On contemporary diesel engines, swirl flaps are tiny butterfly valves found on the inlet manifold. They are intended to enhance emissions at low engine speeds and assist in regulating the fuel to air ratio. The flaps close while the engine is running lightly, which causes the air to swirl into the combustion chamber. The spinning effect promotes leaner air to fuel ratios and aids in combustion. The flaps typically activate to a completely open position after 2000 rpm and have relatively little impact on engine output and emissions.
The swirl flaps installed on early BMWs were very prone to failure; with time, they were brittle and susceptible to breaking. In addition, the tiny screws securing the metal flap to the spindle are prone to breaking off and coming free. Any flap or screw that separates from its resting place within the input manifold is likely to enter the combustion chamber. This frequently causes severe engine damage, including cylinder head, valve, turbo, cylinder head, injector, and piston damage.
BMW upgraded the flaps’ design in 2004 by enlarging the spindle and screws’ diameters, but failure still happened. On later editions, the design underwent another alteration that involved the use of plastic flaps rather than screws. When removing the manifold for inspection, we have occasionally observed loose or missing flaps even though failure on the plastic variety is less prevalent.
In addition to catastrophic engine damage, swirl flaps can also have a negative impact on performance and MPG during normal operation. Regardless of their design, all flaps eventually acquire a thick layer of carbon and oil buildup from the EGR and breather systems. Due to the internal size of the inlet manifold being reduced as a result of the increased flap size, performance and efficiency are lost.
Depending on the design, there are many ways to remove the flaps, but in most cases, the manifold is unbolted from the cylinder head, the flaps and connection rods are taken out, and then specially made blanking plates are installed in their place. The ECU is reprogrammed and the actuator function is turned off if the car has an electronic swirl flap actuator.
We also advise performing a Custom ECU Remap concurrently with this modification. The remap is intended to counteract the slight loss of low-end torque that may result from removal.
Very little, in our opinion. The loss of efficiency and performance at low engine speeds is very imperceptible and would only be significant in the absence of carbon buildup. The removal of the flaps is expected to lead to an increase in performance and economy because carbon buildup starts as soon as the vehicle leaves the factory. BMW ceased installing swirl flaps on the majority of its vehicles after 2010, which implies that even the manufacturers are now aware that swirl flaps have more drawbacks than advantages.
Do the BMW f30’s swirl flaps work?
Unquestionably, the F3X 30d/35d units have swirl flaps. They do have carbon build-up, which can be removed, but all they need is a thorough cleaning, along with the inlet manifold.
BMW stopped utilizing swirl flaps when?
Swirl flaps were first put into the intake manifold of BMW diesel engines in 2000, however they were plagued by several mechanical issues. BMW made changes to the swirl flap design between 2004 and 2006 to address reliability difficulties, but several problems persisted, including carbon build-up, mechanical failures, and leaks. After discontinuing the swirl flaps in the majority of its engines after 2010, BMW stopped using them in its engines at the end of 2008.