Book Excerpt: Scooter Repair Manual: 50 to 250cc with Carburetor Engine Twist-and-Go Scooters
To assess the condition of the big-end bearing, hold the crankshaft assembly firmly and push and pull on the connecting rod, checking for any up-and-down freeplay between the two (see illustration). If any freeplay is noted, the bearing is worn and either the bearing or the crankshaft assembly will have to be renewed. Note: A small amount of big-end side clearance (side-to-side movement) is acceptable on the connecting rod. Consult a scooter dealer about the availability of parts. Note: If a new bearing is available, fitting it is a specialist task which should be left to a scooter dealer or automotive engineer.
Inspect the crankshaft where it passes through the main bearings for wear and scoring. The shaft should be a press fit in the bearings; if it is worn or damaged a new assembly will have to be fitted. Evidence of extreme heat, such as discoloration or blueing, indicates that lubrication failure has occurred. Be sure to check the oil pump and bearing oil ways before reassembling the engine.
If available, place the crankshaft assembly on V-blocks and check the runout at the main bearing journals (B and C) and at either end (A and D) using a dial gauge (see illustration). If the crankshaft is out-of-true it will cause excessive engine vibration. If there is any doubt about the condition of the crankshaft have it checked by a scooter dealer or automotive engineer. Note: The crankshaft assembly is pressed together and is easily damaged if dropped.
Inspect the threads on each end of the crankshaft and ensure that the retaining nuts for the alternator rotor and the variator are a good fit (see illustration). Inspect the splines for the variator pulley on the left-hand end of the shaft. Inspect the taper and the slot in the right-hand end of the shaft for the alternator Woodruff key (see illustration). Damage or wear that prevents the rotor from being fitted securely will require a new crankshaft assembly.
Where applicable, inspect the oil pump drivegear teeth on the crankshaft and on the pump driveshaft for damage or wear (see illustration). Inspect the ends of pump driveshaft where it runs in its bearings. Renew any components that are worn or damaged.
Subject: Scooters 50 to 250cc with Carburetor Engine Twist-and-Go Scooters service, maintenance, repair. ISBN-10: 184425920X ISBN-13: 9781844259205 | Haynes 4082
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