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 Bosch Fuel Injection System Trouble-Shooting Guide

SYMPTOM:	PROBABLE CAUSE:
No cold start	Fuel-pump fault or clogged fuel-filter
	Additional air-valve not opening correctly
	Start-valve not opening correctly
	Leak in fuel system
	Throttle-valve plate not opening correctly
	Temp.-sensor fault
	Diode-relay fault
Poor hot start	As above then:
	Leaking / faulty injector
	Heat/time switch fault
Poor idle	Baffle-plate stop wrongly adjusted
	Leak in Vacuum-system
	Fuel-filter clogged
	Mixture-adjustment incorrect
Backfire from engine	Weak fuel mixture
	Fuel pressure too low
	Starter-valve leaking
Engine runs on after shut-off	Leaking / faulty injector
	Stiff/stuck baffle-plate
	Stiff/stuck control-plunger
Excessive fuel consumption	Control pressure too low
	Starter-valve leaking
	Leak in fuel-system
	Fuel mixture too rich
	Heat/time switch fault
Idle-speed too high	Control pressure incorrect
	Additional air-valve stuck open
	Baffle-plate stop wrongly adjusted

Detailed maintenance guide / diagrams in this post [L-Jetronic] - https://www.beemerlab.org/2020/03/bmw-bosch-l-jetronic-fuel-injection.html

Bosch K-Jetronic injection-system overview / diagram here - https://www.beemerlab.org/2019/11/e21e12e28-bosch-k-jetronic-fuel.html

Bosch L-Jetronic injection-system overview / diagram here - https://www.beemerlab.org/2019/11/e30e28e34-bosch-l-jetronic-fuel.html

BMW UK Advertising Poster / Placard 1980 - M1, E21 320/6 + 6-cylinder engines

Nice 1980 placard from BMW UK advertising their family of 6-cylinder engines, from the later E21 320 to the M1's M88 and explaining the benefits of the. "Six cylinders where you'd expect to find four." in the compact 3-Series and "Six cylinders where you'd expect to find twelve." in the case of the supercar M1.

   BMW's dedication the six cylinder engine is not a recent phenomenon.

   It goes right back to BMW's original as a specialist engine-maker, rather than a car manufacturer.

   In fact, the first engines we ever built were six cylinder aircraft engines.

   Later, in the 1950's when conspicuous consumption was almost a status symbol, BMW preferred to stay with efficiency rather than extravagance and launched a six cylinder luxury car.

   Today, in the BMW 320, a car that's scarcely more than 14ft long, theres a sophisticated six cylinder power unit.

   And the BMW M1 on the right also needs no more than six cylinders. Even though in its most developed form, the engine can actually produce 800 bhp.

   It's not a blind dedication to six that makes us refuse the false economy of a four in the case of the 320. Or the wanton extravagence of a 12 in the case of the M1.

   Rather, we take our guidance from the laws of physics.

   According to those laws, it is not possible to build an engine that's perfectly balanced with less than six cylinders arranged in-line.

   Anything else, is a compromise that may help a car manufacturer balance its books. But won't help it balance its engines.

   Which is why every engine BMW make that's two litres or larger, is an in-line sic cylinder engine.

   Fortunately, there's no need for you to understand the laws of physics to discover the difference this makes.

   There's not a trace of roughness as you cruise. Or rawness as you accelerate.

   There's a smooth immediacy which motoring journalists normally describe as "turbine-like".

   And there's a flexibility which makes driving in traffic almost a pleasure. For with 85% of maximum torque at a mere 1900rpm you get a responsiveness in fourth gear that you might normally expect only in second gear.

   The BMW 320 costs £6,790.

   Which is scarcely more than cars whose manufacturers have chosen to compromise on their engines.

   And if they're prepared to compromise on the most important part of a car, where will those compromises stop?

BMW E21 / E30 323i Engine Comparison [M20b23 2316cc]

Here's another quick engine comparison, this time the E21 and original E30 flagship models, the 323i. BMW introduced the E30 323i in 1983 using the same M20b23 2316cc injected 6-cylinder motor as the E21 had in its top model since 1977 and displacement was not increased until the better known 325i emerged in 1985. Even with sightly more weight, the E30 323i was still billed as a quicker car than its predecessor, but I have no idea what improvements were made to the engine, so lets see how the specs stack up:

M20 Engine	323i [E21]		323i [E30 <1987]
Bore	80.0mm (3.15")		80.0mm (3.15")
Stroke	76.8mm (3.02")		76.8mm (3.02")
Capacity	2316cc (141.3 cu in)		2316cc (141.3 cu in)
Comp. ratio	9.5 : 1		9.8 : 1
Power (BHP)	141 @ 5800rpm		148 @ 6000rpm
Power (PS)	142.8 @ 5800rpm		150.0 @ 6000rpm
Power (KW)	105 @ 5800rpm		110 @ 6000rpm
Torque (Lbs ft)	140 @ 4600rpm		151 @ 4000rpm
Torque (Nm)	190 @ 4600rpm		205 @ 4000rpm

A little more compression, along with a few extra horse power and a slightly higher redline make for a harder pulling engine in the high rev range, but the big difference seems to be in the torque figures. Not only does the E30 323i have a bit more, but peak-torque is delivered 600rpm lower down than the older engine and that is clearly what makes the E30 feel quicker.

BMW 1990cc [2L] Engines 4 and 6 Cylinder Comparison - M10b20 and M60/M20 [E21 320, 320i, E12]

Up to 1977 BMW used 4-cylinder engines for its original 320 and 520 models, evolving from the trusty M10 used in the 2002. After 1977 they began to use freer-revving 6-cylinder engines for all the 2 litre models, the M60 and after 1981 the M20, both still using the same 1990cc, the latter of which has evolved into all the modern BMW straight sixes we know today. The 2 litre four pot is still a very sought after power-plant though, with its light weight and torquey character making for a more responsive front-end, particularly in the smaller chassis models.

I have wanted to compare the specs of these two engines side by side for a while now to see how the bore/stroke and power outputs stack up, so here goes:

CARBURETTOR:

	M10 4-cyl.		M60/M20 6-cyl.
Bore	89.0mm (3.504")		80.0mm (3.15")
Stroke	80.0mm (3.15")		66.0mm (2.60")
Capacity	1990cc (121.4 cu in)		1990cc (121.4 cu in)
Comp. ratio	8.1 : 1		9.2 : 1
Power (BHP)	109 @ 5800rpm		120 @ 6000rpm
Power (PS)	110.5 @ 5800rpm		122.4 @ 6000rpm
Power (KW)	82.5 @ 5800rpm		90 @ 6000rpm
Torque (Lbs ft)	115.7 @ 3700rpm		118 @ 4000rpm
Torque (Nm)	157 @ 3700rpm		160 @ 4000rpm

The 6-cylinder looks to be the faster motor, making a good 10 bhp more, with the shorter stroke and higher compression ratio no doubt making for a peppier drive. However, with its longer stroke and bigger pistons, the 4-cylinder still makes very similar torque, so unless you are screaming it all the time, the lighter engine might still make a more balanced drive under normal use.

INJECTION:

	M10 4-cyl.		M60/M20 6-cyl.
Bore	89.0mm (3.504")		80.0mm (3.15")
Stroke	80.0mm (3.15")		66.0mm (2.60")
Capacity	1990cc (121.4 cu in)		1990cc (121.4 cu in)
Comp. ratio	9.3 : 1		9.8 : 1
Power (BHP)	125 @ 5700rpm		123 @ 5800rpm
Power (PS)	126.8 @ 5700rpm		125.1 @ 5800rpm
Power (KW)	94.6 @ 5700rpm		92 @ 5800rpm
Torque (Lbs ft)	126.6 @ 4350rpm		122 @ 4500rpm
Torque (Nm)	172 @ 4350rpm		165 @ 4500rpm

The injected engines are a different story, with the compression ratio of the M10 not too far behind the 6-cylinder and both making the same power, though I would say the M20 is going to pull harder and smoother as you get up the revs and, ultimately have a higher redline. On the other hand, the 4-cylinder actually seems to be giving a bit more torque this time, obviously the higher compression and bigger bore contribute to this and it is all produced lower down the rev range. This could be why I have heard M10 enthusiasts saying it is more torquey, but either way it stands to reason that the lighter, more responsive handling and low-end grunt makes the 4-cylinder a better choice for round-town driving or even short-track racing.

I actually owned one of the rare 1990cc 4-cylinder M10 engines in 2012, having been given it with the '83 E21 316 I bought. The previous owner had intended to build it up and drop it into the E21, but never got round to the project and I decided not to pursue it given that the M10b18 1.8 litre unit was plenty quick enough for the car fitted with a twin-choke Weber carb, so I sold the 2 litre lump in bits, missing suitable con-rods, for £350!

More 1977 engine changes included the 1.6 litre engine used in the E21 316 now badged as the 315. The 316 now received a restricted-power version of the 1.8 litre M10 engine and a new model, the 318, was given a hotter version of the same engine. The 316 dropped back to 1.6 litres for economies sake with the newer M4x series of engines in the late E30 and E36.

BMW Tightening Torques [PDF]

Superb 136-page document from BMW showing the tightening torque for every different bolt / screw on your car. It covers generic torques for all BMWs, as well as model specific ones for petrol, diesel... even the V12.

https://drive.google.com/open?id=0B1JGYWCqjPsqSTBWRGZYdFBLS3c

CONTENTS:

• General Instructions
• Engine
• Engine Electrical
• Fuel System
• Radiator
• Exhaust
• Clutch
• Transmissions and Drivetrain
• General Electrical
• Instruments
• Equipment Accessories

GENERAL TORQUES:

M4 8.8 - 2.9 Nm M4 10.9 - 4.1 Nm M4 12.9 - 4.9 Nm	M8x1 8.8 - 26 Nm M8x1 10.9 - 36 Nm M8x1 12.9 - 44 Nm	M14 8.8 - 130 Nm M14 10.9 - 180 Nm M14 12.9 - 220 Nm
M5 8.8 - 5.9 Nm M5 10.9 - 8.3 Nm M5 12.9 - 10.0 Nm	M10 8.8 - 47 Nm M10 10.9 - 66 Nm M10 12.9 - 79 Nm	M14x1.5 8.8 - 143 Nm M14x1.5 10.9 - 200 Nm M14x1.5 12.9 - 240 Nm
M6 8.8 - 9.9 Nm M6 10.9 - 14.0 Nm M6 12.9 - 16.5 Nm	M10x1 8.8 - 54 Nm M10x1 10.9 - 75 Nm M10x1 12.9 - 91 Nm	M16 8.8 - 200 Nm M16 10.9 - 280 Nm M16 12.9 - 340 Nm
M7 8.8 - 14.8 Nm M7 10.9 - 21.3 Nm M7 12.9 - 25.5 Nm	M12 8.8 - 82 Nm M12 10.9 - 115 Nm M12 12.9 - 140 Nm	M16x1.5 8.8 - 216 Nm M16x1.5 10.9 - 303 Nm M16x1.5 12.9 - 364 Nm
M8 8.8 - 24 Nm M8 10.9 - 34 Nm M8 12.9 - 40 Nm	M12x1.5 8.8 - 87 Nm M12x1.5 10.9 - 123 Nm M12x1.5 12.9 - 147 Nm	M18 8.8 - 280 Nm M18 10.9 - 390 Nm M18 12.9 - 470 Nm
		M18x1.5 8.8 - 313 Nm M18x1.5 10.9 - 440 Nm M18x1.5 12.9 - 527 Nm