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Excessive Smoke from 2-Strokes


Excessive Smoke from 2-Strokes

These RZ500 crank-cases are split horizontally. The seals are trapped between the upper and lower case halves. The seals have an outer circumferential ring to locate them.

John H Glimmerveen Licensed to About.com

2-strokes smoke at the best of times, but if a particular bike starts to show an appetite for gearbox oil, the chances are that the crank oil seals need replacing. If you own a twin, or any multi-cylinder 2-stroke, and the clutch side exhaust system begins to smoke more than the others, this is an indication that the crank oil seal on that side needs replacing.

Worn or damaged crankshaft oil seals on 2-stroke engines typically cause poor starting, as the damaged seals allow either oil from the gearbox to enter the crank cases, or air from the ignition side.

Engine Rebuild

Replacing crank oil seals on engines that have horizontally split crank cases requires a complete engine rebuild as the seals are trapped between the casing halves. This applies to the majority of Japanese multi-cylinder 2-strokes.

Vertically split crank cases have oil seals that can be replaced without completely disassembling the engine, in most cases. However, there is one very important point to remember when replacing seals: they must be placed in the cases clean and dry on their outer edges to avoid slippage under pressure (due to primary compression). However, the inner sealing ring should be lubricated with oil that the engine will run on.

Another cause of excessive engine smoking on 2-strokes with posi-lubrication systems is, of course, the oil pump settings. On many posi-lube systems adjustment is by way of a cable.

Pump adjustment is typically undertaken by: opening the throttle until a circle is seen through an inspection hole in the side of a carb (generally the right side carb). At this point, the marks on the rotating drum of the oil pump should align.

Oil Pump Setting

Another alternative for setting oil pumps on 2-strokes is to measure the flow rate of oil into the engine at a specific rpm. This is normally the factory recommended system for pump setting; however, a special flow rate meter is required.

Note: Under no circumstances should additional engine oil be added to the gasoline where a posi-lubrication system is fitted, as this will lean out the mixture (this can cause an engine seizure).

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