Naval History and Heritage Command

Use of the Clutch on the Gray Marine Diesel Engine

Most of the Gray Marine diesels which you are likely to use are equipped with one of two clutches. The first of these is a friction-type clutch which makes use of two clutch plates for which it is called the twin-disc clutch.

When shifting it is absolutely necessary that the engine be run at idling speed. Also, the shift lever should either be in the full forward or full reverse position. If the clutch is not fully engaged the clutch plate will slip between the flywheel and the pressure plate causing destructive and unnecessary wear. Also, the screw shaft and screw will not respond normally if the clutch is not fully engaged and boat handling is difficult.

When the clutch is engaged while the engine is running at high speed the same kind of damage occurs to the clutch. Great friction is caused and wear and warping results. Finally, when the clutch is engaged at an excessive speed the sudden overload throws a great strain on the engine and may require repair work on the diesel.

The twin-disc clutch has no manual adjustment. This is an additional reason for proper, careful shifting. Remember, haste may cause a delaying breakdown or leave you helpless in the surf, so go easy on that shift lever.

The Borg-Warner clutch is the second type commonly found on the Gray Marine Diesel. It works on the same principle as an automobile transmission, transmitting engine power to the propeller shaft by means of gears.

The coxswain must pause for a moment in neutral while shifting with a Borg-Warner clutch. This is due to the fact that gears cannot be meshed safely while one or the other is revolving without chipping or breaking gear teeth. When the shift lever is in neutral it releases the plate from the flywheel, thus permitting the transmission gear to stop spinning and engage smoothly after about two seconds.

With the Borg-Warner clutch it also is necessary that the shift lever be in full forward or full reverse position. Otherwise a partially engaged gear may slip and strip the gear teeth. If the engine is speeded up when shifting, the gears will spin longer and make it necessary for the coxswain to leave the shift lever in neutral for several additional seconds when shifting to another position.

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[End of Appendix E]