They may not be commercial engines, but Honda’s GC engines have proven to deliver reliable, efficient power in a wide range of mowers and home power equipment. Here’s everything you need to know to keep the horizontal shaft GC and vertical shaft GCV running reliably.

Maintenance Schedule

First 30 days or 5 hours of operation: Change the oil.
Every 90 days or 25 hours: Clean the engine air filter
Every 120 days or 50 hours: Change the oil. Check the flywheel brake (if equipped.)
Yearly or every 100 hours: Check the spark plug and spark arrester (if equipped.)
Every two years or 200 hours: Replace the spark plug and air filter element.

Oil

These engines are designed to use oil that meets SAE classification SJ or later. 5W30 and 10W30 are recommended. SAE 30 can be used at temperatures above 50ºF.

To check the oil, remove the dipstick from the filler neck. Wipe off any oil, then reinsert the dipstick without screwing it back into the engine.

To drain the oil on a GC engine, remove the dipstick followed by the drain bolt and washer on the base of the engine. Once the oil has drained, screw the drain bolt back in, using a new washer to get a tight seal.

To drain the oil on a GCV engine, remove the dipstick and tilt the engine, letting the old oil flow pour out of the oil filler neck.

Add oil via the filler neck. GC engines hold about 20 ounces of oil, while GCV engines hold about 12 ounces of oil. The oil level should come to the top mark on the dipstick.

Air Filter

To access the filter, push in the two tabs on the airbox cover and swing it out of the way. When reinstalling, the paper fins on the filter element should face out toward the cover.

To clean the filter, tap it against a hard surface or use compressed air to blow out any dirt between the pleats. Limit air pressure to 30 psi; higher pressures can force dirt into the filter medium.

Spark Plug

To remove the spark plug, disconnect the spark plug cap and clean out any surrounding dirt to keep it from getting into the engine. Use a spark plug wrench or socket to remove the plug from the cylinder head.

The spark plug gap should be 0.028-0.030 in. Replace the plug if it has signs of damage to the electrode or insulator.

When reinstalling the plug, tighten it by hand, then turn another 1/8-1/4 turn. If you’re putting in a new plug, turn the plug ½ of a turn to crush the washer and get a tight seal around the combustion chamber.

Flywheel Brake

This brake is included in some versions of the GCV. To check the brake, start the engine, set the throttle lever to “Fast” and release the brake lever. The engine should stop quickly. If it doesn’t, check the brake for wear:

1. Remove the three flange nuts from the top of the recoil starter. Remove the starter from the engine.
2. Remove the fuel tank and set aside. The fuel line does not need to be disconnected.
3. Check the thickness of the brake shoe, located next to the flywheel. If it’s under 3 mm, have the brake replaced by a service technician.
4. Reassemble the engine in reverse order.

Spark Arrester

This metal screen can be added to the exhaust pipe of any GC or GCV to comply with local fire codes.

To clean the arrester, wait at least 30 minutes after the engine has been on to ensure the exhaust is completely cool. Remove the three bolts holding the protector onto the muffler, then remove the bolt or screw holding the arrester inside the tailpipe.

To clean the arrester, scrub off any carbon with a wire brush. Replace the arrester if it is damaged or splitting. Reassemble the arrester and muffler in reverse order.

Storage

Wait until the engine has been off for at least half an hour to ensure it’s completely cool. Clean off any dirt using a moist rag. Do not use a pressure washer or garden hose: this can force water inside the engine.

Once clean, fix paint chips by adding a layer of touch-up paint and coat unpainted metal with a light oil. Remove the spark plug and pour one to two teaspoons of clean engine oil into the cylinder. Pull the starter several times to distribute the oil around the cylinder and piston, then reinstall the plug. It’s normal to have a smoky exhaust when the engine is first started. This is just the oil burning off.

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