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.