External small engine repairs such as spark plugs and belts require basic hand tools, such as ratchets, a socket set, wrenches and pliers, a mallet and screwdrivers. Internal work requires specialized tools, such as pullers, feeler gauges and a torque wrench.
Begin with a basic mechanic's tool set, which is available at any store's hardware section. If working on something that rotates, such as the flywheel, get a tool to hold the part in place while you loosen and tighten the bolts. Look over your engine for special fasteners such as star-shaped Torx bolts, tamper-resistant bolts and square-head bolts. Most tool kits don't include tools for these bolts. Determine whether your engine uses metric bolts or SAE bolts, as the tools are different sizes.
For internal work, the first tool to buy is a torque wrench; it lets you tighten bolts to an exact torque measurement and is vital for parts such as cylinder heads that need even torque on all bolts. Although they're not tools, consumables such as thread sealer, anti-seize and penetrating oil are vital when working on an engine. Thread sealer gives bolts more gripping power; many engines come with it from the factory, so have some on hand to reapply when you replace bolts. If a bolt isn't turning, spray it with penetrating oil to loosen it. A small amount of anti-seize during reassembly may make the bolt easier to remove in the future.