[Fig. 7] shows a counter balanced crank shaft. This type of crank-shaft is provided with weights which balance the shaft and carry the momentum gathered in the revolution.
| Rear Main Bearing | Weight | Center Main Bearing | Front Main Bearing |
| Fly Wheel Attached to this Ring | Timing Gear Attached Here | ||
| Crank Pin | Crank Pins | ||
Fig. 7. Counter-Balanced Crank Shaft
Main Bearings
Fig. 8. 5-M-B Crank Shaft
[Fig. 8] shows the plain type of crank shaft with the timing gear attached to the front end and the fly-wheel attached to the rear end. The crank shaft shown is carried or held by five main bearings, which is an exception, as the majority of motor manufacturers use only three main bearings to support the crank shaft, while in some of the smaller motors only two are used. These bearings are always of the split type, the seat for the upper half is cast into the upper part of the crank-case, and the lower half is usually attached to the upper half by four bolts which pass through the flange at each side of the bearing. Small shims of different sizes are employed between the flanges of each half of the bearing in order to secure a perfect adjustment which is very essential, as these bearings are subjected to heavy strains and severe duty. A shim may be removed occasionally as the bearing begins to show wear. A worn main bearing can be detected by placing the metal end of a screw-driver or hammer on the crank-case opposite the bearing and the other end to the ear. If the bearing is loose or worn a dull bump or thud will be heard. This looseness should be taken up by removing a shim of the proper thickness.
| Cam Gear | Bearings | Cams |
| Cams |