How to Fix the Pull String on a Lawn Mower: Step-by-Step Repair Guide
To fix a broken pull string on a lawn mower, you must access the recoil starter assembly, remove the old cord, properly wind the new recoil spring, and install a new starter cord. The process involves removing the starter cover, releasing tension from the old spring, winding the new spring correctly, threading the new cord through the pulley and handle, and reassembling the unit. Always ensure the recoil spring is properly tensioned and consider consulting your model’s manual for specific configurations.
Understanding the Lawn Mower Recoil Starter System
The pull-start mechanism on a lawn mower is a simple but crucial system that allows you to manually crank the engine. Understanding its basic components will make the repair process much clearer.
The main parts of a typical pull-start mechanism include:
- Starter Cover: The outer housing that protects the internal components and is bolted to the mower’s engine shroud.
- Recoil Spring: A coiled, flat spring that provides the tension to retract the starter cord after you pull it.
- Starter Pulley: A wheel or disc that the starter cord wraps around. It is connected to the recoil spring.
- Starter Cord: The rope you pull, which is attached to the pulley and runs through a handle.
- Starter Dogs or Pawls: Small, spring-loaded levers on the pulley that engage with the engine’s flywheel when you pull the cord.
When you pull the starter cord, it unwinds from the pulley, causing the starter dogs to extend and catch the notches on the engine’s flywheel. This action cranks the engine. When you release the cord, the recoil spring winds the pulley back up, retracting the cord and disengaging the dogs from the flywheel.
Diagnosing the Problem with Your Pull String
Before you begin disassembly, it’s important to confirm that the pull string itself is the issue. Common signs of a broken or worn pull string include:
- The cord is frayed, snapped, or has come untied from the pulley.
- The cord pulls out but does not retract, indicating a broken recoil spring or a tangled cord inside the housing.
- The cord retracts very slowly or feels slack.
You should also check the recoil spring and starter pulley. If the cord is intact but won’t retract, the spring is likely broken or has lost its tension. If the cord pulls out but the engine doesn’t crank, the starter dogs may be worn or the flywheel may be damaged.
Tools and Materials Needed for the Repair
Having the right tools and materials on hand will make the job smoother. For most walk-behind lawn mowers, you will need:
- Basic Tools: A socket set or wrench to remove the starter cover bolts, a screwdriver (Phillips or flat-head), and pliers.
- Replacement Starter Cord: A high-quality, braided nylon cord. The diameter is typically 3/16 inch (4.8 mm) for most walk-behind mowers, but check your manual.
- Replacement Starter Handle: If your old handle is cracked or damaged.
- Light Lubricant: A light machine oil or silicone spray for the pulley and spring.
- Work Gloves: To protect your hands from sharp edges and the tensioned spring.
Step-by-Step Guide to Replacing the Pull String
Follow these steps carefully. The process can vary slightly by model, so having your mower’s manual is helpful.
Step 1: Remove the Starter Assembly Cover
First, ensure the mower is off and the spark plug wire is disconnected for safety. The starter cover is usually held on by 3-5 bolts or screws around its perimeter. Use your socket set or screwdriver to remove them. Carefully lift the entire starter assembly cover off the mower. You may need to gently tap it with a rubber mallet if it’s stuck.
Step 2: Remove the Old Cord and Release Spring Tension
With the assembly removed, you can access the pulley and cord. If the old cord is still attached, untie the knot at the pulley or cut it off. To safely release the tension from the old recoil spring, you need to let the pulley unwind slowly. Hold the pulley firmly and allow it to spin in the direction that unwinds the spring until all tension is gone. Caution: The spring is under tension and can cause injury if it releases suddenly.
Step 3: Wind the New Recoil Spring (If Replacing)
If you are only replacing the cord and the spring is in good condition, skip to Step 4. If the spring is broken or needs re-tensioning, you must wind it correctly. Place the spring into its housing in the cover. Wind it clockwise (for most models) by turning the pulley, ensuring it seats properly in the grooves. Wind it until it has moderate tension—typically 4-5 full turns. This step is critical for proper cord retraction.
Step 4: Thread and Secure the New Starter Cord
Cut your new cord to length (usually 60-70 inches for walk-behind mowers). Tie a secure knot at one end. Thread the other end through the hole in the starter pulley from the inside out, then pull it through until the knot seats firmly against the pulley. Now, wind the cord onto the pulley in the direction it will naturally wrap (usually clockwise). Leave about 1-2 inches of cord on the pulley.
Step 5: Reassemble the Starter Unit
Place the pulley back onto the post in the starter cover, ensuring the starter dogs are oriented correctly. Pull the free end of the cord through the eyelet in the starter cover and attach the starter handle. Tie a secure knot in the handle. Now, carefully re-tension the spring by pulling the cord out about 12 inches and then letting it retract slowly, winding the cord neatly onto the pulley. Repeat this until the cord retracts fully and automatically with good tension.
Step 6: Reinstall the Starter Cover and Test
Place the entire starter assembly back onto the mower, aligning it with the mounting holes. Reinstall and tighten all the bolts or screws. Reconnect the spark plug wire. Give the pull cord a few test pulls. It should retract smoothly and completely after each pull. When you pull it, you should feel the engine turning over.
Troubleshooting Common Issues After Repair
If you encounter problems after reassembly, here are some common fixes:
- Cord Won’t Retract: The recoil spring is likely not wound tightly enough. You may need to remove the cover again and add a few more turns of tension to the spring.
- Cord Feels Excessively Tight: The spring may be over-wound. Release some tension by carefully letting the pulley unwind a few turns.
- Cord Pulls but Engine Doesn’t Crank: The starter dogs may not be engaging the flywheel. Ensure they are not worn and that the flywheel teeth are clean and undamaged.
- Cord Retracts Too Slowly: The pulley may be binding. Apply a small amount of light lubricant to the pulley post and the spring housing.
Frequently Asked Questions
Can I replace just the pull cord without touching the spring?
Yes, if the recoil spring is functioning properly and still has tension, you can replace just the cord. The key is to not fully unwind the spring during the process. Carefully remove the old cord, wind the new one onto the pulley while maintaining the spring’s existing tension, and then reassemble.
What type of cord should I use for my lawn mower?
Use a high-quality, braided nylon starter cord. The most common diameter for walk-behind mowers is 3/16 inch (4.8 mm). Avoid using hardware store twine or thin rope, as they will fray and break quickly. Check your owner’s manual for the exact specification for your model.
How do I know if my recoil spring needs to be replaced?
You should replace the recoil spring if it is visibly broken, cracked, or has lost its ability to retract the cord. If the cord hangs loose and doesn’t pull back in at all, the spring is the likely culprit. If it retracts slowly or sluggishly, the spring may just need cleaning and lubrication, but replacement is often more reliable.
Is this repair safe to do at home?
Yes, this is a common and generally safe DIY repair. The most important safety precaution is to disconnect the spark plug wire before starting to prevent accidental engine starts. Also, be cautious when handling the recoil spring, as it is under tension and can cause cuts if it releases unexpectedly. Wear work gloves for protection.
