BMW 2002 Engine FAQ

Table of Contents

The BMW 2002 Engines

This section covers engine component specifications and designations. Throughout the production of the 2002, a variety of cylinder heads, induction, and and pistons were used. By enumerating these components, one can not only comprehend the lineage of the 2002 engine, but also conclude which components can be mixed and match to achieve the desired effects.

Engine Designations and Years


Engine Specifications


Cylinder Heads

Filippo's Motorsport Scheme Valve Cover

The 2002 engine was offered with four different cylinder heads during its 8 year production life. When building a high performance 2002, there are certain heads that may lend themselves to higher horsepower applications. Choosing among the various available options is dictated primarily by the intended application. All 2002 cylinder heads are designated by a number (either 121, 121TI, E12, or E21 2.0) which is cast into the head. The location of this number is on the intake side of the cylinder head, above the number four intake port. It is easily visible upon opening the hood.

Beginning in 1968, 2002's came with either the 121 or 121TI head. There is no real difference between these two types. They were referred to by BMW as having a "double-hemispherical combustion chamber." The valve diameters are 44mm intake, and 38mm exhaust. These heads were the standard heads on all 2-liter cars until mid 1972. Most 1972 2002tii's also used the 121/121TI head, but with larger, 46mm diameter intake valves. All else stayed the same. In mid 1972, ALL 2002's (tii's included) received a new head designated the E12. This is the so-called "smog" head. It featured a combustion chamber design taken from the big-six motors introduced 3 years earlier. It has 46mm intake, and 38mm exhaust valves. The major difference is in the combustion chamber shape. It features a "Tri-hemispherical" design, which attempts to provide a more complete burn of the air/fuel mixture. 1976 49-state 2002's came with a further revised E21 2.0 head, which also carried over to the 2-liter 320i's. It is basically an open-chamber modification of the old 121/121TI head, but with 46mm intake valves.

Over the years, the 121/121TI (early 2002 heads) have been the most popular with the performance and racer crowd, because of its smaller combustion chamber volume. Consequently, higher compression ratios are possible with this head, because of the availability of pistons. The E12 head also seems to work very well with few modifications. Since it already has the 46mm valves, it seems to flow well, and the revised combustion chambers seem to reduce detonation. As of date, there is little hard data regarding this subject. If you have a 121 or 121TI non-tii head, you probably still have the smaller intake valves. Luckily, it is not too hard to install larger ones (The larger valves can use the existing seats as long as they are enlarged.) Any competent automotive machine shop can perform this service.

The following piston options are available for the various 2002 cylinder heads:

121 Cylinder head:

8.5:1 CR U.S. "Spec" piston on 1968-1972 2002's
         42.3 mm pin-to-deck, flat top

9.0:1 CR U.S. "Spec" piston used on '72 US-model 2002tii's

9.3:1 CR European 2002TI (twin-carb model)
         42.1 pin-to-deck, 5.2mm dome

10:1 CR Early euro-spec 2002tii
        42.5 mm pin-to-deck, 4.4 mm dome

E12 Head:

6.9:1 CR Factory "Turbo" pistons (used on 1974 2002 Turbo)
         42.0 mm pin-to-deck, 3.7mm dish

8.1:1 CR flat-topped piston (much like the 8.5:1 CR used on the
         121 heads)  used on '75 US-model 2002's, also on most
         US-model 3-liter cars of the era. (keep in mind that
         the 2-liter 4-cylinder with the E12 head and 3-liter
         6-cylinder cars can interchange pistons)

8.3:1 CR U.S. "Spec" piston on mid 1972-1974 cars

9.0:1 CR U.S. tii pistons

9.5:1 CR European tii pistons

E21 2.0 Head:

8.3:1 CR flat-topped pistons (used on 49-state '76 2002's,
         US 2-liter 320i's)

9.3:1 CR domed pistons (used on european 4-cylinder 320i's)

Note: compression ratios given are with a stock head, and zero deck height.

Please note that Mahle is not the only OE piston manufacturer, Kolbenschmidt and Nural also supplied BMW with pistons. However, the majority of U.S. parts distributors usually supply Mahle products.

The pistons here are all high-silicon cast units. Mahle (one of the OE piston manufacturers for BMW) also offers a forged round top aluminum racing piston that yields a 12.5:1 compression ratio. These pistons, however, require clearance machining off ALL combustion chamber configurations to work. It should also be mentioned that along with these pistons available from Mahle, many American piston manufactures will make custom forged aluminum racing pistons for the 2002 with any compression ratio. Vendors such as Venolia, Arias, Ross and Wieseco have all produced excellent quality units at surprisingly reasonable cost. In addition, Cosworth also makes some excellent (though expensive) pistons for four cylinder BMW's.

On the Intake Side




Mechanical Fuel Injection

The 2002tii and 2002 Turbo were the two '02 models that were factory equipped with fuel injection. All of these cars were equipped with a Kugelfischer mechanical fuel injection system, which uses an engine driven injection pump to pressurize the fuel to extremely high pressures and inject it behind each intake valve, much like a diesel injection system.


The Kugelfischer Model PL O Mini Pump is the main component of the tii injection system. It utilizes 4 plungers which are actuated by a cam to pump fuel to each of the 4 cylinders. One way suction and pressure valves are installed on the inlet and outlet of the plunger chambers which control the flow of fuel. The amount of fuel that is injected is controlled inside the pump by regulating the stroke length of the plungers. This is done by controlling the rest position of the plungers. Less fuel = higher rest position = shorter plunger stroke. More fuel = lower rest position = longer plunger stroke. The rest position of the plungers is controlled by a regulating lever which is controlled in two ways. One side of the lever rides on an eccentric hinge which is connected to a lever which is rotated by the warm up transmitter or boost diaphragm (Turbo only). This side controls the enrichment for warm-up purposes or under boost conditions. The other side of the lever is mounted on a pin which rides on a three-dimensional cone. This cone controls the mixture over the speed/load range of the engine.

The surface of the cone describes the fuel requirements of the engine at each engine speed and throttle position. The cone is moved axially according to throttle position via the lever on the side of the pump. The cone is rotated radially by the shaft it is mounted on in relation to the engine speed. This is accomplished by a magnetic pick up mechanism, much like a speedometer, that takes the rotation of the pump camshaft (which rotates at half of the engine's crankshaft speed) and transfers it to the cam, rotating it much like a speedometer needle. This rotation is then proportional to engine speed, and each point on the cone along a circumference line varies the amount of fuel injected according to engine speed.

The injection system provides a richer mixture for engine warm up via the warm up runner mounted on the back of the injection pump. The warm up runner is connected to the lever on the back of the injection pump, which in turn is connected to the previously described eccentric hinge inside the pump. When the engine is cold, the warm up runner is fully retracted, rotating the eccentric hinge inside the pump to its lowest position, increasing the plunger stroke length and increasing the amount of fuel injected. This enrichment is linear across the entire speed/load range. As the engine and coolant passing through the warm up runner heats up, the warm up runner extends outward, allowing the eccentric hinge to rotate upward, leaning out the mixture until the linkage reaches it warm running stop. Extra air is also fed into the motor during warm up to provide a reasonable idle speed. This is accomplished by a hose from the intake manifold to the warm up runner and a cone mounted on the warm up runner rod. When the warm up runner is retracted, the cone is unseated and allows air to pass around it and into the warm up runner, which in turn flows to the intake manifold. As the warm up runner extends, the cone gradually reaches its seat, reducing the amount of air passing through until the cone seats and cuts off all additional air. Note that the additional air comes directly from the area above the warm up runner and is unfiltered.

Last in the area of mixture control is the Start Enrichment System. This is a completely seperate system from the injection pump and serves only to provide extra fuel when starting the engine. This system consists of the start injector mounted in the throttle body, the thermo-time switch mounted in the coolant flange at the front of the cylinder head, and the control relay, mounted on the firewall behind the air filter. The thermo-time switch controls the length of injection depending on coolant temperature. This is done by a bi-metallic strip which is heated by the coolant and by a electric heater connected to the starter current. The relay keeps the injector powered until the thermo-time switch shuts off the current, and also allows the injector to spray for one second, even on a warm motor.

The injection pump is lubricated by the engine oiling system, taking a pressurized oil feed from the oil filter head and returning the used oil into a fitting on the side of the engine block. The throttle linkage on the injection system is critical is maintaining the correct relationship between the throttle position and the injection pump lever position. All linkages must be tight and of the proper length, and the throttle body must also be tight in order for the system to work properly. The injection pump is mounted on an extension of the engine's lower timing chain cover, and is driven by a toothed timing belt off of the crankshaft pulley. Fuel is supplied to the injection pump at moderate pressure by an electric fuel pump at the rear of the car and excess fuel is returned to the tank. One interesting note about the fuel curve: the injection pump has an overrun fuel cut off. This means that when the acclerator linkage is in the idle position and the engine speed is above idle (i.e. when coasting), the pump cuts off fuel injection, much like a newer EFI equipped car.

System Differences:

All 2002tii models use the same basic Kugelfischer system. Two versions of the injection pump were used. All european and the '72-'73 US models used pumps equipped with the V7 fuel control cone, and the '74 US only tii used a pump with the V6 fuel control cone. Both pumps are identical in appearance and function other than the mixture curves.

There were two different styles of intake manifolds used. All cars equipped with the 121 or 121TI cylinder head used a manifold with the rubber/plastic intake runners. All later cars equipped with the E12 head used a manifold with aluminum intake runners. The plastic runners were prone to cracking and poor sealing, hence the switch to the more reliable aluminum runners.

Two different, but completely interchangeable throttle bodies were also used. The later version used a redesigned CO adjustment screw location that made mixture adjustment easier and less touchy.

Adjustments/System set up:

Basic setup of the injection system is relatively simple. First of all, insure that the valve clearances are correct, and that the ignition timing and ignition advance curve is correct. Incorrect ignition timing will cause difficult tuning, and poor power. As a guideline, the timing should be around TDC at idle, and max out at 32-34degs BTDC at over 3800rpms. Compression should be good, and plug gaps, dwell, etc. should be set to spec.

  • Pump timing:

    Remove the upper cover for the pump belt. With the engine set at TDC compression stroke on cylinder #1, the notch on the belt pulley should line up with the cast in line on the top of the timing cover. Don't worry if the timing is off by less than 1 tooth. Correct as necessary by slipping the belt off and turning the pump pulley to the correct position and reinstalling the belt.

  • Warm-up runner:

    The engine needs to be cold to perform this check/adjustment. Pry up the warm up runner with a screwdriver until the groove in the air cone is above the edge of the warm up runner housing. Insert the retaining plate (BMW p/n 88 88 6 135 140) to hold the runner in position, or alternatively use a thin piece of metal to do the same. The distance between the screw on the pump's enrichment lever should be 2.6mm. This distance can be adjusted if it is incorrect by loosening the lock nut and turning the plate nut up or down as needed to correct the distance. DO NOT adjust the screw on the enrichement lever -- this is preset at the factory.

  • Accelerator linkage:

    The first part of the linkage to check is the short link from the throttle bell crank to the injection pump itself. This link must be 85mm long, from the center of one ball end socket to the other. There is a special BMW tool to measure this linkage (p/n 88 88 6 135 040), but it isn't really necessary. If the linkage you have still has the plastic end pieces, be very careful with them -- the plastic ends are prone to breaking off.

    The throttle and pump can now be synchronized. Two pins are needed for this operation -- a short, straight 4mm pin (p/n 88 88 6 135 080) and a 5mm hook (p/n 88 88 6 135 050), although properly sized rods can be used. Remove the cap on the throttle body. Back off the idle adjustment screw on the throttle body so that it no longer touches the throttle cam. Insert the 5mm hook into the top hole on the injection pump lever so that it locks into the pump housing. This locks the pump into the idle position. With the pump locked in this position, insert the 4mm pin into the hole next to the cam inside of the throttle body housing. The backside of the cam should touch the pin. If it doesn't, loosen the 10mm bolt(s) on the clamp on the vertical throttle linkage piece, right next to the throttle body. Push the cam against the pin, and retighten the clamp bolt(s). Remove the 5mm hook and work the linkage several times. The hook should reenter the holes on the pump easily with the cam resting against the 4mm pin.

  • Full load stop:

    Fully open the throttle and insert the 5mm hook into the last slot on the pump lever so that it locks into the hole on the pump housing. The lever should just touch the stop screw at this position. Adjust the stop screw if this is not the case. Removing the #1 intake runner will ease access to the screw.

    Check that the long linkage rod between the firewall bell crank and the engine block bell crank is 289mm long between end centers. Adjust as necessary.

    With the throttle still fully open, adjust the pin on the vertical lever coming up from the pedal lever so that the acclerator pedal hits it's stop (check for carpet interference) before the pump hits its stop.

  • Idle adjustments:

    The final adjustments to make are for idle speed and mixture. Set the idle speed to 850-1000rpms using the adjustment screw, and set idle CO to 2-3% with the small adjustment screw inside of the throttle housing. Turning the screw in decreases CO, turning it out increases CO. Make sure the engine is fully warm when performing the final adjustment.

    System Specifications:

    Injection pump: Kugelfischer PLO 4 4-piston injection pump
    Injectors: Kugelfischer type DLO, opening pressure 30-38 bar (435-550 psi)
    Electric feed pump: Bosch roller cell, pressure 1.5-2.0 bar (22-29 psi), flow rate max. 120L/h



    Vacuum Advance Distributor


    Mechanical Advance Distributor



    All '02 models use the same basic cooling system with a couple of exceptions. All models use an engine driven water pump and cooling fan with a vertical flow radiator and dual action thermostat.


    We'll provide a quick discussion on the coolant flow in an '02 motor for familiarization. Starting at the water pump, the coolant is pumped into the engine block and up through the cylinder head. Most of the coolant exits the engine at the top of the cylinder head, at the hose flange next to the intake manifold. From here, the coolant flows either to the thermostat or to the radiator. If the engine is below the thermostat opening temperature, the coolant flows to the thermostat to warm it up, and from the thermostat it flows back to the water pump and into the engine. If the engine is hot, the thermostat shuts off the flow from the top of the head back into the engine, instead forcing the coolant to flow to and through the radiator. The coolant is cooled as it flows through the radiator and emerges from the bottom hose of the radiator to the bottom half of the thermostat. This cooled coolant then flows to the water pump and into the engine. By using this system, the thermostat controls the temperature of the coolant entering the engine, instead of the temperature of the coolant exiting the engine. This allows for better temperature control and prevents having ice cold coolant from a radiator on a cold day hitting a hot motor when the thermostat opens.

    The heater takes hot coolant from a fitting on the back of the cylinder head, passes it through the heater core, and returns it through a pipe or through the bottom of the intake manifold to the water pump, where it is cycled back through the engine. The automatic choke on carburetted cars so equipped takes hot coolant from the back of the block and returns it into the manifold to go back to the water pump. The warm-up device on the tii and the manifold heater on a downdraft carburetted car takes hot coolant from the flange on the head and returns it to the water pump as well.

    System Differences:

    All '02s use the same basic cooling system with a few component differences.


    All '02s except for the Turbo use the same sized radiator. All early models and most non-US models use a radiator with a bottom hose fitting that extends straight back from the bottom tank and connects to a simple 90 degree bend lower hose. This lower hose setup does not clear air conditioning compressors. Most US models and all others equipped with air conditioning use a radiator with a bottom hose fitting that protrudes from the right side of the bottom tank and curves towards the back and upwards. This allows the lower hose to clear an A/C compressor.

    Some 2002A's have a transmission oil cooler built into the bottom tank of the radiator. '75-'76 2002 radiators also have mounting ears for a fan shroud. There are also variations in core structure and thickness depending on the year and version of the radiator.

    The 2002 Turbo came with a wider radiator for extra cooling capacity. The left side of the radiator is extended approximately 2 inches such that the edge of the radiator is next to the battery tray. This radiator can be fitted into any other '02, but the radiator support opening needs to be enlarged and the mounting holes redrilled.

    Water Pumps:

    There are only 2 types of water pumps used on the '02. All non-tii and non-Turbo models use one pump, with the heater/manifold return pipe offset 180 degrees from the thermostat inlet fitting. The tii models and the Turbo have a water pump with the heater return pipe fitting offset 90 degrees from the thermostat inlet fitting. This was done because the location of the injection pump does not allow the use of the standard pump.

    Cooling Fan/Fan Shroud/Pulley:

    There were three types of cooling fans used. Very early US cars and most pre-'71 non-US cars came with a 4-blade fan. '71-up non-US cars and '75-'76 US cars came with a 5-blade 360mm diameter fan. '69-'74 US cars and available as special equipment on non-US cars was the 5-blade 400mm diameter "tropical" fan.

    A fan shroud was installed on '75-'76 US 2002s. This shroud only works with a radiator equipped with mounting ears and the 360mm fan.

    Most 2002s use the same sized pulleys, but the '75-'76 US 2002 had an overdriven water pump/cooling fan. The crankshaft pulley was larger than standard, and the water pump pulley was smaller than standard. This was done, in addition to the fan shroud, in an attempt to keep the engine cool with the addition of major emissions controls. This is also why '75-'76 US 2002s tend to have more fan noise than the earlier cars.


    The stock thermostat is an 80 deg C unit. 71 and 75 deg C units are available from the aftermaket. These can help the engine run cooler in extremely hot weather and help marginal cooling systems.


    The main component in an '02 cooling system that is worthy of upgrading is the radiator. While a fresh, clean stock radiator will typically be adequate for most circumstances, extremely hot climates, lots of stop and go driving, the use of air conditioning, or a hopped-up engine may overwhelm the stock radiator. Several upgrades are available.

    1. Recore the stock radiator using a thicker, high-efficiency core with a greater tube and fin count. This keeps the stock look yet is sufficient for just about every situation.

    2. Retrofit a 320i radiator. The 320i radiator is larger, and the use of a plastic/aluminum or plastic/brass unit reduces weight. This is also sufficient for most setups. The drawbacks to this installation is the need for custom brackets or the drilling of extra holes in the body, and the need for different hoses.

    3. Install a Ford Pinto or Volvo 240 radiator. These installations will work, and improve cooling capacity, but involve modifications to the body. Other similar-sized radiators can also be installed with modifications.

    Other cooling system tips:

    The 400mm cooling fan theoretically moves more air, and can help if you have overheating problems in traffic, but more often than not, the 360mm fan works better, as it is quieter, uses less power, and is typically adequate in most circumstances. The same applies to the overdriven pulley setup.

    Removing the engine driven cooling fan entirely and replacing it with an electric fan improves engine performance, reduces engine noise, and can reduce engine temps in traffic, given an adequately sized fan. The drawbacks to this setup are the need to drill holes in the car to mount the fan, installing wiring to operate the fan, and the reliability of an electric fan vs. the engine driven fan.



    Standard 2002 Exhaust


    2002tii Exhaust


    2002 Turbo Exhaust


    Erik Frank
    Ben Thongsai

    Last updated 02/19/97 © Copyright 1997., Inc.