How to degrease a motorcycle engine without damaging it

To degrease a motorcycle engine, let it cool, cover the air intake, electrical connectors and exhaust outlet, spray a degreaser made for engines onto the grimy areas, let it work for the time on the label, agitate with soft brushes, then rinse with a gentle stream of water and dry it thoroughly. Skip the pressure washer and keep degreaser off the brakes and tires. The job takes about an hour and leaves you with an engine where new leaks are easy to spot.

This guide covers choosing a product, what to protect, the full process, and how to tell when grime is actually a mechanical problem.

Why degrease a motorcycle engine

Oil mist, chain lube fling, road film and dust bake onto engine cases into a sticky brown crust. Beyond looks, that crust:

• Hides oil and coolant leaks until they're serious
• Traps moisture and salt against metal
• Makes it harder to see cracked hoses, loose fasteners or chafed wiring
• Gets on your boots and pants

A clean engine also makes any later repair easier. A mechanic who can see the gasket line can tell you much faster where a leak starts.

Choosing a degreaser

Type	Strength	Watch out for
Water-based / citrus degreaser	Mild to moderate	May need a second pass on heavy crust
Engine degreaser (aerosol foam)	Strong	Solvent fumes; keep off paint and rubber
Motorcycle-specific cleaner	Mild to moderate	Better for painted cases and plastics
Heavy-duty caustic degreaser	Very strong	Can stain or etch bare aluminum and magnesium
Brake/parts cleaner	Strong, fast-drying	Harsh on paint, plastic and rubber; not for whole engines

Many degreasers rely on solvents that release volatile organic compounds. King County's hazardous waste program lists ingredients worth avoiding where you can, including methylene chloride, methanol, MEK, perchloroethylene, trichloroethylene, toluene and xylene. Its suggestion is to look for lower-VOC or VOC-free, non-chlorinated or water-based products instead. For a home garage, a water-based or motorcycle-specific cleaner handles most bikes, and you can step up only for the worst spots.

Whatever you pick, read the label for surfaces it's safe on. Bare and polished aluminum, magnesium covers and clear-coated parts are the most likely to stain.

Safety first

• Wear nitrile gloves and eye protection
• Work outside, or with the garage door open and a fan moving air
• Keep solvent-based products away from flames, pilot lights and sparks
• Keep runoff out of storm drains. A drip pan and rags catch most of it, and many areas have rules about washing oily grime into the street

What you need

• Engine degreaser of your choice
• Soft detail brushes, an old toothbrush and a long-handled parts brush
• Plastic bags, painter's tape or rubber bands
• Garden hose with a gentle spray nozzle
• Microfiber towels and a leaf blower or air blower
• Drip pan and rags
• A stand to hold the bike upright

How to degrease a motorcycle engine: step by step

1. Let the engine cool

Never put degreaser on a hot engine. Berryman, which makes engine degreasers, says this plainly. On hot metal the product flashes off before it works and can leave stains, and cold water on a hot cylinder isn't kind to it either.

2. Cover what water and chemicals shouldn't reach

Wrap or tape plastic over:

• The air intake or airbox opening
• The exhaust outlet
• Exposed electrical connectors, the ignition switch, and any ECU or sensor connectors you can see
• The battery if it's accessible
• The alternator or stator cover seam on some bikes, if wiring exits there

Berryman's directions also call for covering the battery, alternator, air intake and electrical connectors with plastic.

3. Do a dry brush pass

Knock off loose dirt and any caked mud with a dry brush first. Less loose material means less degreaser and less runoff.

4. Apply the degreaser

Spray the dirtiest areas first: the lower crankcase, around the countershaft sprocket, and anywhere chain lube flings. Work bottom to top so drips don't streak cleaned areas. Keep it off the brake discs, calipers, pads and tires. If you're working near the rear brake, hold a rag behind the spray.

5. Let it dwell, but not dry

Give it time to break the grime down. Berryman's guidance is 10 to 15 minutes for its product, and to rinse within the recommended time rather than leaving it on longer. Follow your own product's label. Don't let it dry on the surface, which leaves spots that are harder to remove than the original grime. Work in the shade, and do one side at a time on a warm day.

6. Agitate with brushes

Brush between cooling fins, around bolt heads, and along gasket seams. A toothbrush gets into tight spots around the shifter and kickstand. For stubborn crust, apply a second light coat and brush again.

7. Rinse gently

Use a light stream of water from a hose, starting at the top and working down. Don't aim directly at the plastic-covered openings, and avoid pressure washers near wiring or sensors (see can you pressure wash a motorcycle). High pressure can force water past seals into connectors and bearings.

8. Dry it thoroughly

Pull off the plastic covers. Blow water out of fins, crevices, around spark plug wells and connectors with a leaf blower or compressed air, then wipe with microfiber. Water sitting in spark plug wells can cause misfires on some bikes.

9. Start the engine and check

Remove the exhaust plug first. Start the engine and let it idle for a few minutes to drive off moisture. Check that it idles normally and no warning lights stay on.

10. Protect and lube

Re-lube the chain, since degreaser strips it. Our chain maintenance guide covers the steps. If you want, apply a protectant made for engines to painted and bare metal surfaces once everything is dry. For the tank and bodywork, see how to wax a motorcycle.

What a clean engine tells you

Once the engine is clean, ride it for a few days and look again. Fresh wet spots show you exactly where oil or coolant is coming from.

Where the fresh grime appears	Likely source
Base of the cylinder or along the head gasket line	Head or base gasket seep
Around the countershaft sprocket	Output shaft seal or shift shaft seal
Bottom of the engine near the drain plug	Drain plug washer or filter
Around valve cover bolts	Valve cover gasket
Hoses and radiator area, sweet-smelling	Coolant leak

Our guides to a motorcycle leaking oil and a motorcycle coolant leak help you confirm the source and decide what to do.

Common mistakes

• Degreasing a hot engine
• Using a pressure washer up close
• Letting degreaser dry on the cases
• Spraying near brakes and tires
• Forgetting to remove the exhaust plug before starting
• Using caustic products on polished or bare aluminum
• Skipping chain lube afterward

When to see a mechanic

Get a shop involved if:

• The engine won't start, misfires, or shows a warning light after cleaning
• Degreaser or water got into the airbox
• You find oil or coolant leaking again within days
• Brakes feel weak after cleaning, even after you've cleaned the rotors
• A gasket, seal or cover is visibly cracked or weeping
• Corrosion or white powdery deposits are on aluminum parts

A shop can clean the engine properly during service and pinpoint a leak. See our maintenance services page, or browse the motorcycle repair directory.