INSPECTION AND CLEANING

1. Inspect the crankshaft journals for scuffing, grooving or scoring. If crankshaft wear is uneven, the crankshaft should be turned on a lathe by a competent machine shop. Each journal will be undersize and new, undersize (thicker) bearings must be installed.
2. Make sure all the oil passages are clean, if necessary cleaning them with solvent and a stiff bristle brush.
3. It is recommended that crankpins and main bearing journals be measured with a micrometer to check for wear, out-of-roundness, and taper. Out-of-round is checked by measuring the journal across 2 diameters which are 90°apart (north–south and east–west) and comparing the two readings. The difference between the two readings gives the out-of-round specification.Taper is determined by measuring each journal at each end and comparing the numbers. If one reading is larger than the other, the journal tapers from large to small.
4. Inspect the bearing surfaces for burning, grooving, or scoring of any kind. Any but the slightest scratches disqualify a bearing from reuse; if there is any doubt, replace the bearings. (A good rule of thumb is to replace the bearing every time they are disassembled.) If the end-play, as measured above, is excessive, new bearings must be installed.

   NOTE: If new bearings fail to correct end-play problems, the crankshaft will have to be machined undersize and different bearings installed.

   Fig. 1: Checking the crankshaft for out-of-round and taper is extremely important

   Fig. 2: A dial gauge can also be used to check crankshaft runout — mount the gauge so that it reads off of the crankshaft main journals

   Fig. 3: Mount the gauge on all the different main bearing journals