What is the Crankshaft Nose (Snout)?

Crankshaft Nose Diagram

The crankshaft nose, or as is commonly referred to as the snout, is at the foremost portion of the crankshaft. In the image to the left, you will see a 350 cubic inch Chevy crankshaft nose pictured. Typically, the length of the nose is long enough to protrude out of the engine's timing cover and has a diameter that is large enough to accommodate a harmonic balancer over it. Though certain aspects of the crankshaft nose do vary by manufacturer, in principal they all serve the same core functions.


Purpose of the Nose

The nose of the crankshaft serves two primary purposes. First, the nose can accept a timing gear sprocket and secondly a harmonic balancer. To serve these functions, the nose has a keyway cut into it. Some crankshafts, like the one pictured above, have more than one keyway. When a key is installed, the timing gear sprocket can be properly located in the correct timing position. External balanced harmonic balancers also need the key as a location point on the crankshaft to perform as intended. In most cases, timing gear sprockets and harmonic balancers are installed as a slip fit over the nose though some aftermarket balancers prefer a press fit (interference) installation. A harmonic balancer bolt, or crank bolt depending on your terminology, secures the harmonic balancer in position and also limits the forward movement of the crankshaft timing gear sprocket.

Though the crankshaft nose is critical in maintaining an engine's ignition timing and balance, accessories often are powered off of the harmonic balancer. For example, a pulley may be installed onto the harmonic balancer so that a belt may be used to drive an alternator or air conditioning compressor.

Crankshaft Nose Damage and Repairs

Even though the crankshaft nose is not a wear surface, we still find a good number of noses damaged. In most cases a loose crank bolt is to blame. Once the bolt becomes loose, a slip fitted harmonic balancer is allowed to move about the nose. Initially, the balancer may move back and forth. After a period of time this movement causes the inside diameter of the harmonic balancer and outside diameter of the nose to wear. Once the wear on the nose becomes severe, a key may break or be sheared off by the balancer. Should the harmonic balancer bolt completely fall out, the harmonic balancer could become a very dangerous projectile or bend the nose of the crankshaft.

If the harmonic balancer bolt and washer have come loose, the threads inside the crankshaft nose are often damaged. In some cases the threads may be chased with a tap to perform a quick repair. In more severe cases, the nose of the crankshaft should be drilled and tapped to the next oversize thread. Damaged crank bolt holes may also be repaired with a helicoil. Whatever repair is performed on the crank bolt hole, it must be very precise so that the crank bolt and washer can properly fasten the harmonic balancer to the crankshaft’s nose.

Less common damage to a crankshaft's nose is the result of timing gear sprocket damage. A broken tooth from the crankshaft sprocket gear can wedge itself inside the remaining portion of the gear and cause it to shear the key right off. Fortunately this type of damage is lesson common because it does require extensive labor to fix.

Though harmonic balancer repair sleeves are available for the seal surface, there is no readily available solution available to make a harmonic balancer fit properly on a crankshaft nose. If the outside diameter of the nose is worn, the only safe and permanent repair option is to weld the nose of the crankshaft and grind it down to its original diameter. Such a repair requires that the crankshaft be removed from the vehicle so that it can be serviced. Although keyways are protected during the welding process using carbon inserts, it is quite common that the keyway(s) will need to be finish machined post weld.

In some cases a crankshaft nose is so badly damaged that it is more cost effective to replace the crankshaft. Such a determination is best performed at the automotive machine shop where tooling is available to measure the crankshaft's nose diameter and a thorough visual inspection may be performed to determine if the crankshaft’s nose is bent or if other damage is present.

 
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