Types of lawnmower engines.

Yes, they all cut your lawn but there are different kinds of engines that you will find on a lawnmower. 

  • A four-stroke 
  • A two-stroke

Both engines have their pros and cons but one engine is starting to dominate the market and the other is getting harder to find. 

So are all mowers four-strokes? – No, although most mowers are four strokes you can get two-stroke mowers. The newer the mower the more chance of it being a four-stroke, as two strokes lawn mowers are being phased out around the world due to their emissions and are now unavailable in a lot of countries. If in doubt as to what mower you have then look for an oil dipstick. If your machine has one it is a four-stroke. 

I remember as a kid watching my dad mow our lawns whit his own little ecosystem of blue smoke floating around him and the mower. He was using a two-stroke mower. 

Nowadays you are much more likely to see someone out with a four-stroke but what made them so popular?

So why are most lawn mower engines four-stroke?

There are a few simple reasons for this.

No need to mix fuel – This makes it easier to gas up your machine when you need it. You can just tip the gas in an go. Try that with a two-stroke and you will size the engine.

They use less fuel – Because the engine runs at half the RPM it uses less fuel so they are cheaper to run. 

A four-stroke is a quieter engine – The benefits of this are obvious. 

Fewer carbon emotions –  Due to the efficiency of the engine and the fact that it has no oil in the fuel a four-stroke engine runs a lot cleaner. 

Four strokes engines last longer – A four-stroke engine runs at a half the RPM (revolutions per minute)  than a two-stroke which equates to less wear and tear on the engine. 

This is the best explanation  I have seen of the difference between the RPM on both engines.

The 2-stroke at 3,600 rpm is firing 3,600 times a minute the 4-stroke at the same rpm is only firing 1,800 ties a minute. The 2 stroke sounds busier because it has twice as many power strokes at the same rpm. more power strokes more power.

Quote (Jonathan Tamm)

Before you go thinking that all two-strokes are bad, I should mention some of their good points.

Two-strokes are more powerful  – A faster blade does a faster cut. A two-stoke will do a better job on an overgrown lawn for the same reason.

They are easier to fix – less moving parts and because they have ports instead of valves. They also have fewer parts.

They are lighter than four-strokes – The produce the same power using half the weight. This is probably why most weed eaters, hedge cutters and blowers run two-stroke engines. (now modified to meet the new world emission standards) 

They are better mowers for slopes over 20 degrees – You are not going the have the same issues as a four-stroke, such as flooding the air filter or muffler with oil. You will also not get that lack of power when mowing up a hill that you would normally get with a four-stroke. 

You can flip a two-stroke on its side to clean underneath – This makes it super easy to clean your blades and is something you would not want to try with a four-stroke. 

Two strokes are cheaper – Normally they cost a little bit less than their four-stroke cousin. 

How does a four-stroke engine work? 

I will leave this to the experts at  Briggs and Stratton to explain. Here is an excellent video on four-stroke theory with a bit of history thrown in. 

Ways to spot the difference between a four-stroke and a two-stroke engine. 

Apart from the dipstick, there are a few more ways to tell what kind of mower you have.

A Four-stroke has a separate oil reservoir. 

A two-stroke sometimes has the oil mix written on the fuel cap. 

Look for a sticker on the engine saying “do not mix fuel” or “four-cycle”. This means you have a four-stroke

What is the difference between two-stroke and four-stroke fuel?

Two strokes need oil in the fuel in order to lubricate the engine this is one of the main reasons that they have such high emissions. 

Here is a Ratio chart from Briggs and Stratton that should help you work out your mix if you have a two-stroke. 

Four stokes take straight unleaded gas so they are easy and less messy to fill.

If in doubt and you really need to get a job done you can use two-stroke gas in a four-stroke mower. It will smoke a bit, but as a one-off, it shouldn’t do any damage to the engine. You cannot use straight gas in a two-stroke as it needs the oil to keep the engine lubricated. Running a two-stroke with straight gas will seize the engine.

A big mistake you can make when buying lawn mower fuel.  

While we are talking about lawnmower fuel, there is something that I should mention. A few years ago I became aware that some gas stations were starting to mix ethanol with their fuel. I had to actually tell my guys not to full up at certain gas stations. 

Techinecly you can use up to 10% ethanol but now some gas stations are starting to use 15% so its a case of reading the label carefully. 

I myself avoid any fuel with ethanol in it when it comes to my mowers. Better safe than sorry I say. 

Also, there is a limit of at least 87 Octane for a lawnmower engine so don’t go any lower than that. I tend to use 91 myself and I haven’t had any issues. 

I did at one point use a budget gas station and I had a lot of engine issues all of a sudden so do be aware that not all fuel brands are created equal.

I would stay away for budget brands. 

About the author lawnmowing101

Stuart Clifford is the owner of Gecko Lawns.
He has been building and selling lawn mowing business for the last thirty years. Last year he sold off most of his lawns and now earns a full-time income doing a 20 hours work week mowing lawns. Stuart has helped lawn mowing contractors grow and sell their businesses. He has also done lawn business evaluation for buyers. He now enjoys writing about lawn mowing much more than actually mowing lawns.
The Gecko Lawns website is https://www.geckolawns.co.nz/

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