BMW M20 Engine: Front Timing Marks [Front Timing Cover]

Here is a great diagram someone (not me) has made to show the front timing marks for the M20 engine series. Handy. 

M40 engine timing marks HERE.

BMW Advert 1986 - 635CSi, M6, E9 3.0 CSL, M1 - 'The latest in a short line of supercars...'

Another great advert from BMW, this time from 1986, promoting the benefits of their tuned straight-six power plants and their innovative (for the time!) use of four valves per cylinder. 24-valves were first seen in the E9 3.0 CSL 'Batmobile' in 1974, again in the M1 supercar in 1977 and finally making its way to the general consumer in the 1986 635CSi model E24 6er. 

As BMW discovered years ago, when you need extra power from an engine - on the race track for instance - just double the valves per cylinder.

The extra valves mean the the cylinders can take in more air and fuel on each stroke, burn it more efficiently and expel it quicker. So much so that 6 cylinders with 4 valves can produce more power than 12 cylinder with 2.

Take the three cars above, developed by BMW Motorsport.

The 3.5 litre CSL, affectionately known as the Batmobile, won the first of many races at the Saltzburgring in 1974, beating a 7 litre Camaro in the process.

A 192 mph version of the M1 won its class at Le Mans for the last 3 years. (At the Nurburgring in 1981 it won the race outright.)

The M635CSi, however, is merely a luxury road going coupe. Although it's capable of 158mph, it hasn't won a thing.

Except praise.

E30/E28: Faulty AFM (Air Flow Meter) repairs, worn carbon-track quick fix

** FOR ADJUSTING AFM AIR/FUEL RATIO SEE THIS POST **

The AFM or Air Flow Meter uses a metal flap that is opened air entering the engine to move a brass arm up and down a carbon-track. The position of the arm along the carbon track alters the electrical resistance through the circuit and this lets the ECU know how much air is coming in, so it can deliver the right amount of fuel to the injectors. The E30 uses a BOSCH AFM unit, also used in many other BMWs with Motronic or Jetronic injection systems.

The analog electrics in the BOSCH AFMs rarely ever fail, but there are two areas that are failure prone after higher mileage - a worn carbon track and a faulty air-temperature sensor.

E30/E28: Adjusting AFM (Air-Flow Meter) - change air/fuel rich/lean mixture

 ** ADJUST YOUR AFM SETTINGS AT YOUR OWN RISK **

This is for BOSCH AFM units, fitted to most E30 and other BMWs fitted with Bosch Motronic or Jetronic injection systems.

The AFM, or Air Flow Meter, is a metal flap that is drawn open by air entering the engine and the position of the flap tells the ECU how much air is coming in so it can inject the right amount of fuel. The stock parameters for the AFM are set at the factory and unique to each car and BMW recommend that these settings should NEVER be adjusted... so do it at your own risk!!

Why would the AFM need adjusting??

• You have done a ‘gas-test’ and the results show your car is running rich (too much fuel for amount of air) or lean (too much air for the fuel being supplied) and wish to adjust for emissions / fine-tuning purposes.
• You have an air leak after the AFM, so more air is getting in than the ECU is supplying fuel for and the engine won’t run, especially when cold.
• You have an over-fuelling problem where too much fuel is being supplied for the amount of air and flooding the engine.

Adjusting the AFM in the second two instances is a quick and dirty way to get your car running well enough to drive it, but is not a long-term fix for an underlying problem, so bear this in mind before messing with the AFM.