MTD 8Q78HU engine Parts

For your MTD engine model 8Q78HU, the fastest way to get the right replacement parts is to use the full model number and serial number from the engine label, then match those numbers to the parts list and diagrams in the 8Q78HU operator’s manual.

• Locate the model number and serial number on the engine’s ID label.
• Write them down exactly; one character off can change the parts list.
• Use the model number 8Q78HU to look up the parts manual/parts list.
• Identify the part by component name (spark plug, air filter, oil filter) and confirm it on the diagram.
• Order using the part number listed for that component.

The manual for this MTD engine lists these common service parts:

MTD engines often have multiple versions that look similar. Using the exact model and serial number helps you avoid ordering a part that fits a different production run, which can cause hard starting, poor performance, or installation problems.

Last updated: February 2026

A 547cc 4-stroke lawn and garden engine typically falls in the 18 to 25 HP range when governed for mower use. For the MTD 8Q78HU specifically, the operator documentation identifies it as a 679 cc OHV vertical shaft engine, so use the rated power listed in the 8Q78HU operator’s manual for the correct horsepower.

Displacement (cc) is only one piece of the power rating; the same 547cc can be tuned for different torque and RPM.

• Governed RPM setting (often 3,000 to 3,600 RPM on mowers)
• Torque curve and cam timing
• Compression ratio and ignition timing
• Intake and exhaust flow (air filter, muffler design)
• Emissions calibration and carburetor jetting
• Operating conditions (altitude, temperature, fuel quality)

Use this as a comparison tool; always match by the manufacturer’s rated output for your exact engine model.

Because the 8Q78HU is documented as 679 cc, the right approach is to use the engine’s published rating, not a cc-to-HP conversion.

• Find the engine model and serial on the model plate
• In the manual, look for the specifications section (HP, torque, governed speed)
• Compare engines using the same rating type (gross vs net) and the same RPM

Using the correct rated horsepower helps you avoid underpowering or overloading equipment, which affects mowing performance, belt life, and engine longevity.

Last updated: February 2026

If you cannot find a part for your MTD engine model 8Q78HU on Sears PartsDirect, use your full model number and serial number to confirm the exact engine version, then order by phone or through MTD Customer Support using the part list in the 8Q78HU operator’s manual.

• Recheck the model plate on the engine and write down the model number and serial number (both matter for correct parts).
• Search again using only 8Q78HU (no spaces) and try common part names like spark plug, air filter, or oil filter.
• Use the manual’s replacement parts list to match the component name to the correct part number.
• If the part still does not appear online, order by phone with your model and serial number ready.
• If you are unsure which maintenance part you need, compare what is installed on your engine to the manual’s descriptions.

These are frequently requested items for this engine; matching by part number helps when search results are incomplete.

Use the option that best fits what you need.

• Sears PartsDirect parts help: best when you want to purchase through us and need help locating the correct listing.
• MTD Customer Support: best when you want the official parts manual, engine-specific guidance, or MTD ordering options.
• Local service technician: best when you cannot identify the installed part or the engine has multiple variations.

Lawn and garden engines can have multiple builds under the same model family; the serial number narrows the exact configuration so you get the correct air filter, spark plug, or oil filter the first time.

Last updated: February 2026