OSD - Over Rev Safety Device

The OSD is designed to help prevent engine damage due to excessive RPMs. This device is intended as an aid to the driver when a broken drive chain or other failure causes the engine to over-rev. The OSD is not a RPM limiter and it is not recommended to be used for this purpose.

Racing is inherently hard on engine parts and potentially hazardous when engine parts fail. The OSD is not guaranteed to prevent engine damage and/or any resulting injury. It may only be used at your own risk.

The OSD comes pre-set from the factory at a selected Maximum RPM also known as the “Redline” mode. This setting will range between 5,000 and 10,000 RPM, depending on the model ordered.

The OSD also has a “Test” mode, factory pre-set at 2,500 RPM. This mode should be used whenever the OSD is installed on a new motor. Adjustments to the location of the OSD flywheel sensor will also require re-testing the OSD.

The OSD is a fully digital device designed to sense the rotation of the flywheel, by picking up the force of the flywheel magnet as it passes by the OSD sensor. The sensor should never touch the flywheel during operation, but it should be installed closely. The OSD cable should be installed about one-eighth of an inch from the flywheel for best results.

Installing the OSD

Mount the aluminum bracket, holding the OSD box, to the rear of the driver's seat or in another location close enough to the engine for the end of the OSD cable to reach the flywheel. Be sure the mounting location for the cable mounting bracket is taken into consideration when mounting the OSD box bracket.

Route the OSD cable away from the exhaust system and any other high-temperature parts.

Fasten the aluminum cable mount to the engine block, next to the flywheel.

Attach the OSD cable-end to the cable bracket with one hex nut on each side of the cable bracket. Adjust the distance from the cable-end to the flywheel to a gap of about one-eighth of an inch.

Install a 9-volt battery (not included) by removing the battery cover on the back of the OSD box. Replace the cover. Depending on the mounting location, it may be necessary to remove the OSD box from its aluminum mounting bracket in order to install and/or change the battery. Always have extra batteries on-hand.

Testing the OSD

Turn on the OSD using the toggle switch located on the bottom of the OSD box.

The version number will briefly display, like “0029”, followed by all zeros “0000”.

The engine can now be started.

Adjust the engine to around 3,000 RPM.

Press the “Mode” button on the faceplate of the OSD until the word “Test” appears. Release the button.

As soon as the “2500” appears on the display, you should notice the engine begin to “miss”, as the RPMs are dropped to 2,500.

Press the “Mode” button one more time and the “Curr”, Current Mode, will appear, followed by the current RPMs. At this point, the engine should have a noticeable increase in RPMs and the “miss” should have stopped.

Do Not go into Test Mode at high RPMs as the engine will backfire and damage is possible.

Operating the OSD

Normal operation of the OSD is to simply turn on the OSD, and then start the engine. There are a number of useful features which follow:

A low-battery indicator, “batt” will appear when the battery needs to be replaced. The OSD can be used to complete the current run down the track, but the battery should be replaced before the next heat.

By turning on the OSD and then immediately turning off the OSD toggle switch, the OSD will automatically turn itself off after 3 minutes. At that time, the High RPM, “Hi”, for the current session of the OSD will be recorded.

If you leave the OSD toggle switch in the “On” position (to the right), the OSD will not automatically shut off. However, it will still record the High RPM for the current session after 3 minutes.

Once pressed, the “Mode” button will automatically return to the Current RPM display, after a few seconds. When in “Test” mode, the Mode button must be pressed again after the display shows “2500”, in order to return to Current RPM mode.

The “Mode” button is used to:

View the “Hi”, High RPM, for the current session by pressing the Mode button one time. The Mode button may be pressed at any time during the current session to see the highest RPM the engine has reached. The High RPM recorded after 3 minutes can be viewed later, by turning the OSD back on and then pressing the Mode button, prior to re-starting the engine.

View the “Red”, Redline setting, of the OSD by pressing the Mode button two times. This value should be factory pre-set to the Redline RPMs of the product ordered.

Enter “Test” mode, by pressing the Mode button three times. See Testing the OSD for proper testing procedures.

The engine must reach 1,000 RPM before the OSD will begin displaying the Current RPM of the engine.

Once the Current RPM falls below 1,000 RPM, the OSD must re-cycle. This takes about 10 seconds. The OSD re-cycle is indicated by “0010” on the display.

NOTE: While care has been taken to avoid damage from liquids, the OSD should never be immersed in a liquid. Care should be taken to cover the OSD during rainstorms or while washing the vehicle.

IMPORTANT: The OSD begins to cause the engine to “miss” at about 300 RPM below the Redline RPM. This is to prevent the engine flywheel momentum from carrying the RPMs too far above the Redline RPM. Depending on the rate of acceleration of the flywheel, the actual RPM of the engine will likely exceed the Redline RPM by a few hundred RPM. Again, this is due to the momentum of the engine.