Owner’s manual
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How old is my mower by serial number?
On Craftsman gas walk-behind lawn mower model 917378920, the serial number is on a decal on the rear of the mower housing; that serial number identifies your unit, but the build date is typically determined by matching the serial to the manufacturer’s date-code format and your recorded purchase date in the 917378920 owner's manual.
Where to find the serial number on model 917378920
We use the serial number from the decal on the rear of the lawn mower housing.
- Look on the rear housing for the model and serial decal
- Write down the full serial number exactly as shown
- Record the date of purchase (if known) next to the serial number
- Keep the information with your maintenance records for oil changes and blade service
How to estimate the mower’s age from the serial number
Most walk-behind mowers use a serial number that includes a date code or a manufacturing sequence that the engine or mower manufacturer can decode.
- Check the first 4 to 6 characters for a date-style pattern (common formats include YYMMDD or MMDDYY)
- If there is no obvious date code, treat the serial as a production sequence and use the purchase date as your best “in-service” date
- If your mower has a Briggs and Stratton or other engine brand, the engine model/type/code can also indicate engine build date (engine date is not always the same as mower assembly date)
- Compare your findings to the maintenance schedule in the manual to judge service intervals
Quick guide: what “age” can mean
| What you’re trying to date | Best identifier to use | What it tells you |
|---|---|---|
| Mower assembly age | Mower serial number | When the mower was manufactured (if date-coded) |
| Time in service | Purchase date | How long you have been using it |
| Engine build date | Engine code/model | When the engine was produced |
Why it matters
Knowing the approximate age helps us choose the right replacement parts and maintenance timing, especially for wear items like the blade, drive belt, wheels, and control cables.
If you are servicing cutting performance while you’re checking age, our how to sharpen a lawn mower blade guide pairs well with the manual’s blade safety and torque guidance.
Last updated: January 2026
How to find Craftsman model number?
For Craftsman gas walk-behind lawn mower model 917378920, the model and serial numbers are printed on a decal on the rear of the mower deck (rear housing). We use that exact model number to match the correct parts list and owner documentation.
Where to look on the mower
Check these common spots on the rear of the deck:
- Rear of the mower housing, near the back edge of the deck
- Between the lower handle mounts (where the handle brackets attach)
- On a sticker or metal decal facing outward (easy to read when standing behind the mower)
If the decal is dirty or faded, wipe it with a damp rag first; avoid scraping so you do not remove the print.
What to write down (and why)
Record both numbers exactly as shown:
- Model number (example format: 917.378920)
- Serial number (unique to your mower)
- Date of purchase (helpful for maintenance and parts history)
Why it matters
The model number identifies the exact Craftsman configuration (deck, drive system, handle hardware). The serial number helps confirm production details when there are multiple versions of similar mowers.
Quick check: model number vs. part number
| Item | What it identifies | Example |
|---|---|---|
| Model number | The mower | 917378920 |
| Part ID | The Sears PartsDirect part listing | 532169778 |
| Part number | The manufacturer number printed in diagrams | 169778 |
If you are replacing a drive component, the model number ensures you get the correct belt and controls, such as the lawn mower ground drive belt, 3/8 x 33-9/16-in 532169778.
If the decal is missing or unreadable
Use the mower’s owner documentation to confirm identification details and diagrams, then match parts by illustration and key number.
- Check the 917378920 owner's manual for the model/serial decal location and parts diagrams
- Compare your mower’s handle, wheels, and drive setup to the diagram views
- Match the diagram key number to the part listing before ordering
Last updated: January 2026
Should I use 87 or 91 gas for lawn mower?
For the Craftsman 917378920 gas walk-behind lawn mower, use fresh, clean, regular unleaded gasoline with a minimum of 87 octane. Using 91 octane is not required for normal operation; it will not add power or improve mowing performance in this mower. See the fuel guidance in the 917378920 owner's manual.
What to use (and what to avoid)
- Use 87 octane (regular unleaded) or higher if that is what is available.
- Buy fuel in small amounts you can use within 30 days to keep it fresh.
- Do not mix oil with gasoline (this is a 4-cycle mower).
- Avoid long-term storage with fuel in the tank; stale fuel causes hard starting.
- Be cautious with alcohol-blended fuels; they can attract moisture during storage.
Quick comparison: 87 vs 91 for this mower
| Fuel choice | OK to use? | What it changes | Best use case |
|---|---|---|---|
| 87 octane (regular) | Yes (recommended minimum) | Normal starting and power | Everyday mowing |
| 91 octane (premium) | Yes | Typically no performance benefit | Only if regular is unavailable |
If the mower will sit for 30 days or longer
The manual guidance for storage is to prevent fuel system damage from stale fuel.
- Empty the gas tank.
- Start the engine and let it run until the fuel lines and carburetor are empty.
- Refill with fresh fuel next season.
Why it matters
Using the right fuel helps the engine start easily, run smoothly, and reduces carburetor and fuel-system issues caused by stale gas or moisture. Octane is mainly about preventing knock; this mower is designed to run correctly on regular unleaded.
Last updated: January 2026
