Noise management: Lawn mowers

• Rotary lawn mower
• Reel mower
• Ride on mowers

Introduction

Rotary mowers range in noise levels from 84 to 94 dB(A) depending on engine type (4-stroke or 2-stroke) and condition and operating speed. Because the noise levels of a rotary mower can exceed 85 dB(A), personal hearing protection is normally used. 

Maintenance

• Ensure all covers are securely fastened. 
• Ensure the muffler is in good condition (no holes) and is bolted firmly to the side of the engine. 
• Ensure throttle control is in good working order and regulates the revs of the machine in a smooth manner. Some mowers (mostly 2-stroke) have a plastic carburettor body and if not serviced regularly, can suffer from the cam and lifter assembly within the carburettor sticking. 
• Ensure that blades are free running (not hitting against guards) and not worn down. 
• Maintain lawnmower to ensure efficient running and easy starting. 
• Machines that do not operate efficiently require higher revs and make more noise.  

Noise control

The noise level of a four stroke  lawnmower can be reduced by fitting a 'Low Tone' muffler to the engine. These mufflers reduce noise levels by approximately 3dB(A) more than the standard mufflers and are available from most mowing equipment suppliers.  

Operator control

• Do not 'over rev' machine. Use only enough power to perform the work. 
• Mark normal operating revs on throttle control. 
• With 2-stroke powered mowers, ensure that the correct petrol/oil mixture is used. Lack of oil in the mixture will cause the engine to "rattle" more due to insufficient lubrication of the main and big end bearings. 
• Ensure staff are adequately trained in correct use of the lawnmower.  

Alternatives

• On replacement, specify and purchase a four-stroke mower (these tend to be quieter) fitted with a low tone muffler. Test run several different types of mower and take the noise levels into consideration when making your final choice. 
• There are two types of blade holders found on rotary mowers, the straight bar type and the disc blade holder. Most Australian manufacturers use the blade disc, which is the quieter of the two. Some imported mowers are fitted with the cheaper and noisier straight bar type. 

Maintenance

• Check all chain and belt drives for correct tension. A slack chain can rub against its cover creating noise. 
• Ensure all covers are securely fastened. Check the "gear lever" for rattling in its selector plate. 
• Adhesive gaffer tape may be applied to the area on the lever that produces the noise. 
• Ensure the muffler is in good condition (no holes) and is bolted firmly to the side of the engine. 
• Ensure throttle control is in good working order and regulates the revs of the machine in a smooth manner. 
• Maintain lawnmower to ensure efficient running and easy starting. 
• Machines that do not operate efficiently require higher revs and make more noise. 

Noise control

• The noise level of a four stroke lawnmower can be reduced by fitting a 'Low Tone' muffler to the engine. These mufflers reduce the noise level by approximately 3 dB(A) more than the standard muffler and are available from most mowing equipment suppliers. 
• Reel mowers do not normally exceed 92 dB(A). Sometimes high noise levels may be emitted from the blades. If this is the case check the following points: 
  • The cutting height may be too low causing the fixed blade to be forced against the cylinder.
  • The adjustments to the fixed blade may be incorrect. The blade may be set too close to the cylinder (this can cause damage to the cylinder called scalloping) and should be backed off. If this results in loss of cutting ability then the cylinder and fixed blade should be reground professionally and set back in the machine. 

Operator control

• Do not 'over rev' the machine. Use only enough power to perform the work. 
• Mark normal operating revs on throttle control. 
• Ensure staff are adequately trained in correct use of the lawnmower. 

Alternatives

• On replacement, specify and purchase a mower fitted with a 'low tone' low noise level muffler. Test run several different types of mower and take the noise levels into consideration when making your final choice. 

Maintenance

• Ensure engine is kept in a good state of tuning with regular changes of air and oil filters. 
• Examine condition of the muffler, making sure it is in good condition (no holes) and bolted firmly to the side of the engine. 
• Tighten all loose and vibrating parts, making sure that all covers are securely fastened. Vibrating covers can be silenced with silicone sealant. Loose and rattling gear levers can be quietened by mechanical adjustment or application of 'gaffer tape' to parts of gearshift rattling in selector plate. 
• Check belts and chain drives for correct tension and lubricate bearing heads. 
• Check blades for wear and replace if necessary. 

Noise control

• Fit 'low tone' muffler to Briggs and Stratton type engines. These mufflers reduce the noise level by approximately 3dB(A) more than the standard mufflers. With some rear engine types the muffler may be directed towards the operator. If possible orientate exhaust away from operator's seated position. 
• Heavy-duty rubber matting placed on the blade guard will reduce vibration. 
• If engine is rear mounted, place 15 mm plywood cover with 50 mm fibreglass insulation faced with perforated foil behind operator's seat separating the operator from the engine noise. 
• Alternatively enclose the engine under a hood lined with fibreglass insulation faced with perforated metal foil and take the exhaust through a modified high efficiency exhaust system. Care must be taken not to obstruct cooling air.  

Operator control

• Don't over rev engine. Use RPM range suitable to work being performed. 

Alternatives

• When replacing ride-on mower select a quieter model.