Two Stroke Engine Timing Diagram

Learn How to Set Up 2-Stroke Ignition Timing on Your Motorcycle

Avoid Having an Engine That Runs Backward

Andreas Schlegel/Getty Images

Imagine watching a motorcycle reverse into a car at a stop light. It can happen even if the rider goes through the normal start procedure (check fuel, ignition on, out of gear, kick the start lever, put the bike in first gear). The bike may fire up and sound normal, but it can actually go backward!

Why Ignition Timing Is So Important for 2-Stroke Engines

The cause of this unique problem with 2-stroke engines is the ignition timing. If the timing is close to TDC (top-dead-center) it is possible to catch the piston just at the wrong time with the result that the engine runs backward.

This problem can only happen on a 2-stroke because there are no valves to be operated in a set sequence, as in a 4-stroke engine. Typically, this problem happens when the contact points become worn, or more precisely when the contact point's heel becomes worn. The net effect of a worn contact point heel is that the ignition timing progressively slows.

Checking the ignition timing on an early motorcycle is best done monthly if the bike is ridden daily (for example, if it's used as a commuter bike). Not only will the potential for running backward be avoided, but the engine's entire performance range will be optimized too.

How to Set Ignition Timing

Setting 2-stroke ignition timing is fairly simple. The majority of classic 2-strokes have ignition systems that fall into one of two types: contact points inside a flywheel magneto (Villiers and early Japanese engines) and external contact points mounted on an adjustable plate with an internal flywheel.

Flywheel type ignitions with the contact points mounted internally are more difficult to set up. That's because the mechanic must complete the task through small inspection and adjustment holes in the flywheel which has magnets around its perimeter. The difficulty is simply getting a feeler gauge into the contact points without too much interference from the magnets.

To Complete the Ignition Timing Process, Follow These Steps

To begin the ignition setting sequence, the mechanic should remove the spark plug as this will make it easier to turn the engine over for piston positioning.
Next, the crankshaft must be rotated to give the largest opening of the contact points — typically around TDC.
With the points open at their widest, the mechanic should set the required gap. However, if the points are badly pitted the mechanic should replace the points; a flywheel extractor will be required for this job.
With the contact points' gap set, the mechanic can turn his attention to the ignition timing. On all internal combustion engines, the ignition timing is set BTDC. This early ignition of the compressed gases inside the cylinder allows for the time it takes for the ignited gases to reach their fullest pressure.
To find the correct timing position, the mechanic should rotate the flywheel in the normal direction of travel when the engine is running. To find the direction of travel, the mechanic can use the kick-starter, or by rotating the rear wheel with the bike in gear. After locating TDC, the mechanic should rotate the flywheel backward (typically around 2.0-mm vertically of the piston) until marks on the flywheel align, this is the timing mark and the point at which the contact points should begin to open.

To get an indication of when the contact points are opening (ignition point) the mechanic can use a piece of paper. A strip of paper fed between the points' contact faces should have gentle pulling pressure applied as the flywheel is rotated toward the timing mark. As the points open, the paper will suddenly become loose. If the paper comes out before the flywheel mark for ignition (sometimes marked with an 'F' for fire), the internal mounting plate should be moved slightly in the direction of travel.

On some engines (most of the early Japanese multi-cylinder bikes), the contact points were mounted externally on a plate. The ignition setting procedure on this type of ignition is the same for the most part as that of the flywheel type. The biggest difference is that the timing marks are located on an internal flywheel; these marks become visible through an inspection window as the engine is rotated.

Tips

Use a plastic drinking straw in the plug hole to ease finding the piston position. Metallic objects such as screwdrivers should not be used for this procedure as it is possible to get them jammed against the plug threads.
To allow for the thickness of a piece of paper, the contact points' gap should be adjusted. For example, if the paper is 0.005" thick, the points' gap should be reduced accordingly.

Posted by: katharinakatharinacierse0268167.blogspot.com

Source: https://www.liveabout.com/2-stroke-ignition-timing-3971677