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Can you use a 4 stroke lawn mower on a slope?

Customers often ask us if they need to purchase a 2 stroke mower to a mow a steep slope?  There seems to be a general misconception that a 4 stroke mower will seize or will suffer severe engine damage if used to mow a steep slope sideways or in a top to bottom direction.  Lawn mower shops are in part to blame for this misconception.  Many Victa dealers who sell Victa 2 stroke mowers advise customers that a two stroke engine is better than a four stroke engine for mowing slopes.  It is important to note that Victa is the only remaining manufacturer of 2 stroke lawn mower engines.  Suzuki no longer manufacture 2 stroke engines for lawnmowers.  Before we disprove the theory that 2 stroke lawn mowers are better for mowing slopes we need to consider the following:

Two stroke vs 4 stroke engine

The most important difference between a 2 stroke and 4 stroke engine is the mixing of oil and fuel.  2 stroke engines do not have a sump and therefore require oil to be mixed with petrol to ensure proper lubrication of the engine’s cylinder, piston and bearings.  4 stroke engines have a sump and require oil in the sump to ensure proper lubrication of the engine’s internal components.

This difference is often used in the argument that 2 stroke mowers are better for mowing steep slopes.  People arguing for the latter will state that when a 4 stroke mower is on an angle, the oil level will fluctuate in the sump, being higher on the side of the sump facing down the slope.  They will argue that this change in oil level will cause a lack of lubrication to the required parts in the engine.  Unfortunately, this argument is simply not true.  Whilst the oil level will change in the mower’s sump, depending on the degree of the slope, the change is not enough to result in a lack of lubrication to the 4 stroke’s cylinder, piston, crankshaft or crankshaft bearings.

Splash feed vs pressure lubrication

Another myth is that you need to purchase a lawn mower with a full pressure fed engine like a Kohler or Kawasaki.  Whilst the aforementioned engines are good quality engines and do have an oil filter to filter oil, they are much more expensive than Briggs & Stratton or Honda engines and are not an essential requirement to mow a steep slope.

The evidence

People have been mowing steep slopes with splash fed, 4 stroke lawn mowers for years.  Allot of commercial lawn mowing contractors and landscapers use Honda mowers with 4 stroke, splash fed Honda engines without any problems.  In Europe and the USA the use of 2 stroke lawn mowers is prohibited under emission laws and 4 stroke mowers have been sold to mow steep slopes for years. We have been selling and repairing mowers for 20 years and have never had a 4 stroke mower seize after mowing a slope.  Having said that, please make sure your 4 stroke mower’s engine oil is topped up prior to mowing.

In conclusion, using a 4 stroke mower on a slope will not damage the engine provided your oil is at the correct level.  We recommend that you consider purchasing a self propelled mower if you intend mowing a steep slope. This will help propel the mower up the slope.


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