Owner’s manual
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Does it matter what spark plugs you use in a lawn mower?
Yes, it matters; your Craftsman lawn mower model 247377870 needs the correct spark plug type for the engine’s thread size, reach, and heat range so it starts easily, runs smoothly, and avoids misfires or overheating. Use the plug specified in the 247377870 owner's manual and the engine manual that came with the mower.
What “correct spark plug” means
A spark plug is not one-size-fits-all. The right plug matches your engine’s design and operating temperature.
- Thread size and reach: Must match the cylinder head so the plug seats correctly.
- Heat range: Too hot can cause pre-ignition; too cold can foul with carbon.
- Terminal style: Some use a threaded stud, others a snap-on terminal.
- Gap specification: The engine requires a specific gap for reliable ignition.
- Electrode material (copper, platinum, iridium): Can affect service life, but fit and heat range come first.
Quick selection checklist (what we recommend)
Use this order of operations to get the right plug every time:
- Check the spark plug spec in the 247377870 owner's manual.
- Match the plug to the engine model (often listed on the engine shroud or valve cover).
- Set the gap to the engine spec using a wire gauge.
- Replace the plug annually as part of routine maintenance (the mower’s maintenance schedule calls for annual spark plug replacement).
- If the mower ran poorly right after a plug change, reinstall the correct plug and recheck the gap.
Common symptoms of the wrong plug
| Symptom | What it often points to |
|---|---|
| Hard starting or no start | Wrong gap, wrong heat range, wrong reach |
| Surging or misfiring | Incorrect heat range, poor connection at boot |
| Plug tip sooty/black | Plug too cold, rich fuel mix, dirty air filter |
| Plug tip blistered/white | Plug too hot, overheating, lean condition |
Why it matters
Your mower’s manual emphasizes safe, reliable operation and routine maintenance (including spark plug replacement). Using the specified plug helps protect performance and reduces the chance of ignition problems during the season.
Last updated: February 2026
What model number is the Craftsman 247377870?
The model number for this Craftsman walk-behind mower is 247.37787* (the last digit varies by version); 247377870 is one of those versions. You can confirm the exact full model shown on your mower’s ID label and in the 247377870 operator’s manual.
How to confirm the exact model on your mower
We recommend matching the number in two places so you order the right parts (blade, belt, wheels, bagger):
- Check the product ID label on the mower deck or rear housing
- Match it to the model list shown in the manual (it’s listed as 247.37787*)
- Write down the full model including the last digit (example: 247377870)
- Use that exact model when searching parts diagrams and part numbers
- If the label is dirty, wipe it clean so every digit is readable
What “247.37787*” means
The asterisk (*) indicates a model family where the final digit changes by configuration or production run. Your mower’s full model (such as 247377870) is the specific version within that family.
| What you see | What it indicates | What to use for parts |
|---|---|---|
| 247.37787* | Model family | Use your full model from the ID label |
| 247377870 | Specific version | Use this exact number |
Why it matters
Parts can vary between close model versions, especially for drive components and controls. Using the exact model helps ensure correct fit for common replacements like the lawn mower ground drive belt 954-04259A and the 21-in deck mulching blade 942-0741A.
Last updated: February 2026
What year did Craftsman make the 247377870?
Craftsman walk-behind mower model 247377870 aligns with the 247.37787* mower family covered by the operator documentation dated November 17, 2017, so this model line was current around 2017. Use the mower serial number and the engine date code to pinpoint the exact build year; see the 247377870 owner's manual.
How to find the exact build year on your mower
Use the mower ID tag and the engine label together; that combination identifies the production run more precisely than the model number alone.
- Locate the mower model and serial tag (commonly on the rear housing or deck)
- Write down the full model number and serial number exactly as shown
- Find the engine label (often on the blower housing) and record the engine model and date code
- Compare your configuration (bagging, side discharge, mulching) to the manual sections
- Match replacement parts by the full model number first, then by part number
What the manual date means
The date printed on the operator documentation indicates when that manual version was published for the 247.37787* series. It is a reliable way to place the mower family in time, but the serial number and engine date code identify your specific unit.
| Identifier | Where to look | What it tells you |
|---|---|---|
| Manual publication date | Manual cover page | Model-family timeframe (around 2017) |
| Mower serial number | Mower ID tag | Production run tracking |
| Engine date code | Engine label | Engine build date (often closest to mower build year) |
Why it matters
Knowing the correct year helps us match the right blade, drive belt, wheels, and control cable for your exact Craftsman 21-inch platform. Small mid-series changes can affect fit and performance.
Last updated: February 2026
Where is Craftsman's model number?
On a Craftsman walk-behind mower like model 247377870, the model number is typically printed on a product ID label on the mower deck (near the rear discharge area) or on the rear of the deck housing. We recommend matching the full model number on the label to the model list in the 247377870 operator’s manual before ordering parts.
Where to look on the mower
Check these common label locations first:
- Top of the mower deck, usually near the rear discharge opening or bagging area
- Rear of the deck housing, behind the engine
- Side of the deck near the height-adjustment levers
- Handle support area where the lower handle mounts to the deck
- Under the grass bag door or near the side chute opening
What the model number looks like
For this series, the model number is a 247.xxxxx format. Your mower’s label may show a family format where the last digit varies.
| What you see on the label | What it means | What to do |
|---|---|---|
| 247.37787* | Model family; last digit varies | Use the full number on your label when selecting parts |
| 247377870 | Full model number (no dot shown) | Use this exact number for the best parts match |
Tips to avoid ordering the wrong part
- Write down the full model number exactly as shown (including any dots)
- If the label is dirty, wipe it clean and use a flashlight to read stamped or faded print
- Use the model number to confirm key assemblies like the drive system and deck components
- When replacing wear items, verify fit by comparing your old part to the listing (shape, mounting holes, size)
Why it matters
Craftsman mower model numbers identify the exact deck, drive, and handle configuration. Using the correct model number helps ensure parts like a grass bag, wheel, blade adapter, or ground drive belt match your mower’s build.
Last updated: February 2026
