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Since the fuel does not pass through the crankcase, a separate source of lubrication is needed.
==Diesel==
{{Main article|Two-stroke diesel engine}}
{{Unreferenced section|date=September 2010}}
[[File:BronsV8.jpg|thumb|left|[[Brons]] two-stroke V8 diesel engine driving an [[:nl:Heemaf|N.V. Heemaf]] [[Electrical generator|generator]]]]
Diesel engines rely solely on the heat of compression for ignition. In the case of [[Schnuerle porting|Schnuerle-ported]] and loop-scavenged engines, intake and exhaust happen via piston-controlled ports. A uniflow diesel engine takes in air via [[Scavenging (automotive)|scavenge ports]], and exhaust gases exit through an overhead [[poppet valve]]. Two-stroke diesels are all scavenged by [[forced induction]]. Some designs use a mechanically driven Roots blower, whilst marine diesel engines normally use exhaust-driven turbochargers, with electrically driven auxiliary blowers for low-speed operation when exhaust turbochargers are unable to deliver enough air.
Marine two-stroke diesel engines directly coupled to the propeller are able to start and run in either direction as required. The fuel injection and valve timing are mechanically readjusted by using a different set of cams on the camshaft. Thus, the engine can be run in reverse to move the vessel backwards.
==Lubrication==
{{Unreferenced section|date=September 2010}}
Many two-stroke engines use their [[crankcase]] to pressurize the air-fuel mixture before transfer to the cylinder. Unlike [[four-stroke engines]], they cannot be lubricated by oil contained in the crankcase and sump: [[lubricating oil]] would be swept up and burnt with the fuel. Fuels supplied to two-stroke engines are mixed with oil so that it can coat the cylinders and bearing surfaces along its path. The ratio of gasoline to oil ranges from 25:1 to 50:1 by volume.
Oil remaining in the mixture is burnt with the fuel and results in a familiar blue smoke and odor. Two-stroke oils, which became available in the 1970s, are specifically designed to mix with petrol and be burnt with minimal unburnt oil or ash. This led to a marked reduction in spark plug fouling, which had previously been a problem in two-stroke engines.
Other two-stroke engines might pump lubrication from a separate tank of two-stroke oil. The supply of this oil is controlled by the throttle position and engine speed. Examples are found in Yamaha's PW80 (Pee-wee), and many two-stroke snowmobiles. The technology is referred to as [[Automatic lubrication|auto-lube]]. This is still a total-loss system with the oil being burnt the same as in the premix system. Given that the oil is not properly mixed with the fuel when burned in the combustion chamber, it provides slightly more efficient lubrication. This lubrication method eliminates the user's need to mix the gasoline at every refill, makes the motor much less susceptible to atmospheric conditions (ambient temperature, elevation), and ensures proper engine lubrication, with less oil at light loads (such as idle) and more oil at high loads (full throttle). Some companies, such as Bombardier, had some oil-pump designs have no oil injected at idle to reduce smoke levels, as the loading on the engine parts was light enough to not require additional lubrication beyond the low levels that the fuel provides.<ref>{{cite web|url=http://www.klemmvintage.com/oils.htm |title=About Two Stroke Oils and Premixes|access-date=2016-08-21}}</ref> Ultimately, oil injection is still the same as premixed gasoline in that the oil is burnt in the combustion chamber (albeit not as completely as premix) and the gas is still mixed with the oil, although not as thoroughly as in premix. This method requires extra mechanical parts to pump the oil from the separate tank, to the carburetor or throttle body. In applications where performance, simplicity, and/or dry weight are significant considerations, the premix lubrication method is almost always used. For example, a two-stroke engine in a motocross bike pays major consideration to performance, simplicity, and weight. Chainsaws and brush cutters must be as lightweight as possible to reduce user fatigue and hazard.
Crankcase compression two-stroke engines suffer oil starvation if rotated at speed with the throttle closed. Motorcycles descending long hills and perhaps when decelerating gradually from high speed by changing down through the gears are examples. Two-stroke cars (such as those that were popular in Eastern Europe in the mid-20th century) were usually fitted with [[freewheel]] mechanisms in the [[powertrain]], allowing the engine to idle when the throttle was closed and requiring using brakes to slow down.
Large two-stroke engines, including diesels, normally use a sump lubrication system similar to four-stroke engines. The cylinder must be pressurized, but this is not done from the crankcase, but by an ancillary Roots-type blower or a specialized [[Turbocharger#Marine and land-based diesel turbochargers|turbocharger]] (usually a turbo-compressor system) which has a "locked" compressor for starting (and during which it is powered by the engine's crankshaft), but which is "unlocked" for running (and during which it is powered by the engine's exhaust gases flowing through the turbine).
{{See also|API-TC}}
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