Exhaust Flap Update 2


Editor Bob Mack

The more I look into this sticking exhaust flap problem the more I’m amazed that BMW still haven’t found a reliable cure for this problem, which has been with us from the introduction of the overhead cam 1200’s right through to the current 1250 shift cam engines. It seems that the fundamental problem is likely to be the materials used in its construction. Similar valves have been used in cars, particularly, to cut noise emissions at low revolutions, for years. My car has 2 in the exhaust system.

The short video below, kindly supplied by Carl, illustrates that a correctly assembled and working version has clearance above and below the butterfly. The scrap one had no clearance at the bottom and led us to believe that this deficiency contributed to build up of carbon and seize up.



That theory was blown out of the water when it was found that Geoff’s example had the clearance but was seized slightly again after very little use, since freeing it off.

The scrap valve is now completely apart and creating a method of reassembling and lubrication is being undertaken.

A big surprise is that after removing some of the carbon build up, between the spindle and the bearing, there is quite significant clearance. Might be better with less?

Photo of parts of Exhaust Flap

There appears to be a slight difference in the start up test regime on the valve of a 1250 and a 1200. On a 1200 the valve sweeps shut and then open each time the ignition is turned on. A 1250 does this randomly which may lead you think it has stuck if you were checking. Below is a short video of the start up test.



The obvious thing to do with this exhaust valve setup, when it seizes in the open position, would be to disconnect the servo and plug in a fooling device. That way there would be no fault on the dash of the later models and no faults showing in the ECU’s of any models. Downside is there would be no Exhaust Flap Update 3.

Please don’t get too excited and fall off the edge of your seat. The next task is to re-assemble the scrap valve and if that goes well persuade a willing member to let me loose on their complete system.


Author: bobmack70