Introduction
This manual provides essential instructions for the installation, operation, and maintenance of the McCulloch 90658 Chain Bar Adjusting Screw. This component is designed to ensure precise chain tension for optimal performance of your chainsaw. Please read this manual thoroughly before attempting any installation or adjustment.
Product Overview
The McCulloch 90658 Chain Bar Adjusting Screw is a critical replacement part for maintaining the correct tension of the saw chain on compatible McCulloch chainsaw models. Proper chain tension is vital for safe and efficient cutting operations, preventing premature wear of the chain and bar, and reducing the risk of kickback.
Compatibility: This adjusting screw is specifically designed for McCulloch Mini Mac 25, Mac 110, and Mac 120 chainsaw models. It replaces MPNs 90685 and 90658.
Image 1: The McCulloch 90658 Chain Bar Adjusting Screw. This component is essential for setting and maintaining proper chain tension on compatible McCulloch chainsaws.
Installation Instructions
Safety First: Always ensure the chainsaw is turned off, the spark plug cap is disconnected, and the chain brake is engaged before performing any maintenance or installation. Wear appropriate safety gloves.
- Prepare the Chainsaw: Place the chainsaw on a stable, flat surface. Ensure the engine is cool.
- Remove Side Cover: Loosen and remove the nuts holding the clutch cover (side cover) in place. Carefully remove the cover.
- Locate Old Screw: Identify the existing chain bar adjusting screw. It is typically located near the base of the guide bar, often accessible through a small hole in the guide bar or clutch cover area.
- Remove Old Screw: If the old screw is damaged or broken, carefully extract any remaining pieces. You may need pliers or a screwdriver.
- Insert New Screw: Align the new McCulloch 90658 adjusting screw with its threaded housing. Gently thread the screw into place by hand until it catches.
- Reinstall Guide Bar and Chain: Ensure the guide bar is properly seated and the chain is correctly routed around the sprocket and guide bar.
- Reattach Side Cover: Place the clutch cover back onto the chainsaw, ensuring the adjusting screw's head aligns with the adjustment hole on the cover (if applicable). Hand-tighten the nuts.
Note: Specific steps may vary slightly depending on your exact McCulloch model. Refer to your chainsaw's primary user manual for detailed disassembly/assembly instructions.
Operating and Adjustment
After installation, the chain tension must be correctly set for safe and efficient operation.
- Initial Tensioning: With the clutch cover nuts still slightly loose, use a screwdriver to turn the adjusting screw. Turning clockwise typically tightens the chain, while counter-clockwise loosens it.
- Check Tension: The chain should be snug against the bottom of the guide bar, but still able to be pulled freely by hand. You should be able to pull the chain drive links up from the guide bar by about 1/8 to 1/4 inch (3-6 mm) at the center of the bar. The chain should not sag underneath the bar.
- Final Tightening: Once the correct tension is achieved, hold the tip of the guide bar up and fully tighten the clutch cover nuts. Re-check the chain tension after tightening to ensure it has not changed.
- Post-Adjustment Check: Run the chainsaw for a short period (e.g., 30 seconds) and then re-check the chain tension. Chains tend to stretch slightly when new or after initial use. Adjust as necessary.
Incorrect chain tension can lead to rapid wear of the chain and guide bar, increased fuel consumption, and dangerous operating conditions.
Maintenance
Regular maintenance of the chain bar adjusting screw ensures its longevity and reliable performance.
- Cleaning: Periodically clean the threads of the adjusting screw and its housing to remove sawdust, dirt, and old oil. A small brush or compressed air can be used.
- Lubrication: Apply a small amount of grease or chain oil to the threads of the adjusting screw to ensure smooth operation and prevent corrosion.
- Inspection: Regularly inspect the screw for signs of wear, bending, or stripped threads. If any damage is observed, replace the screw immediately to prevent issues with chain tensioning.
- Storage: When storing the chainsaw for extended periods, ensure the chain tension is slightly loosened to relieve stress on the components.
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| Chain tension cannot be adjusted. | Stripped threads on the adjusting screw or housing; bent screw. | Inspect the screw and housing. Replace the adjusting screw if damaged. If housing threads are stripped, professional repair may be needed. |
| Chain becomes loose quickly after adjustment. | New chain stretching; improper tightening of clutch cover nuts; worn guide bar or sprocket. | Re-tension the chain after initial use. Ensure clutch cover nuts are fully tightened. Inspect guide bar and sprocket for wear and replace if necessary. |
| Screw is stiff or difficult to turn. | Accumulation of dirt/sawdust; lack of lubrication; minor thread damage. | Clean the screw threads and housing. Apply lubricant. If still stiff, inspect for damage and replace if needed. |
Specifications
- Part Name: Chain Bar Adjusting Screw
- Model Number: 90658
- Compatible Models: McCulloch Mini Mac 25, Mac 110, Mac 120
- Replaces MPNs: 90685, 90658
- Material: Durable metal construction
- UPC: 670185986545
Warranty and Support
For information regarding warranty coverage or technical support for your McCulloch 90658 Chain Bar Adjusting Screw, please refer to the original purchase documentation or contact the seller directly. Ensure you have your purchase details and model information available when seeking support.
