Whether you already own and actively use one or have spent any time looking into buying one, “2 stroke” and “4 stroke” are terms you’ve most likely run into when it comes to lawn mowers. Both of these terms relate to the same vital component of a mower; the engine.
The differences between a 2 stroke vs 4 stroke lawn mower are numerous, including how they are lubricated (oil mixed in fuel vs separate in crankcase), the emissions they produce (2 stroke mowers are being phased out because of this), and the better size to power ratio that 2 stroke engines offer.
We’re going to discuss all of these differences and more in this post.
How a Lawn Mower Engine Works
Whether it’s 2 stroke or 4 stroke, a lawn mower engine works by mixing air and fuel (compression stroke), before igniting it (via the spark plug) to generate an “explosion” (power stroke) that drives the piston downward, which powers the engine.
So What’s the Difference Between 2 Stroke and 4 Stroke Lawn Mower Engines?
Following on from the explanation of the basic functioning of a lawn mower engine above, there are some differences between how a 2 stroke works vs a 4 stroke.
As the name suggests, with a 2 stroke engine each cycle only contains the 2 strokes we just mentioned – a compression stroke and a power stroke. The key point is that each cycle contains both of these strokes, and the piston only goes around the engine once per cycle.
With a 4 stroke engine, there are 4 strokes (not exactly surprising!) instead of just 2. In addition to the compression stroke and the power stroke, there’s also an exhaust stroke and an intake stroke. The other difference between the two is that in a 4 stroke mower engine, the piston goes around the engine twice per cycle vs once in the 2 stroke engine.
Related Article: How to Drain Gas from Lawn Mower Without a Siphon
2 Stroke vs 4 Stroke Lawn Mower Engines: How Do They Compare
Now we’ve got the technical stuff out the way, I’m going to run through the differences between the two from a user perspective. The stuff you’ll actually notice when using one to mow your lawn.
As the owner of either of these machines, this is one difference that you’ll notice right away. You see a 2 stroke machine doesn’t have a reservoir in the crankcase where the oil is stored, and valves to discharge it through as needed. A 2 stroke engine’s design is far simpler. For that reason, to keep the various engine parts lubricated, the oil needs to be mixed with the gas in a very precise ratio, which is a bit more of a hassle. With a 4 stroke lawn mower, you just need to keep the reservoir in the crankcase topped up with oil to the recommended level.
If you like your peace and quiet, you probably don’t enjoy mowing with a gas mower. But you’ll enjoy it even less with a 2 stroke lawn mower, as they run noticeably louder than a 4 stroke mower. I’m not 100% sure why this is, but as explained earlier, 2 stroke engines are firing on every cycle (twice as often as a 4 stroke engine), which could have something to do with it.
The fact that the design of a 4 stroke mower is more complex in nature, and contains more parts, means that they cost quite a bit more to manufacture. And that added cost is passed on to you when you buy your mower.
Because a 2 stroke engine has fewer parts (no oil reservoir and valves, for starters) and is smaller in its design, they are often significantly lighter (I’m talking almost 50% lighter in some cases) than a 4 stroke engine. And given then the engine is one, if not the heaviest part of a lawn mower, this can have a big impact on the overall weight of your mower.
I had a 2 stroke lawn mower in the past and comparing it vs a 4 stroke lawn mower in terms of starting it up and reliability, it’s night and day. I rarely have an issue with my 4 stroke, but with the 2 stroke, it was a lot more common.
There’s only one winner in the 2 stroke vs 4 stroke lawn mower debate if we’re talking about fuel efficiency. 2 stroke mowers guzzle far more gas as they consume fuel every two strokes as opposed to every 4 strokes for a 4 stroke engine.
The simple design of a 2 stroke lawn mower engine means that when things go wrong and a repair is needed, it’s almost always cheaper with a 4 stroke. It can get incredibly expensive to repair a 4 stroke engine and I’ve had more than one buddy that has just opted to buy a whole new mower rather than try to salvage an aging 4 stroke engine due to cost.
Emissions + Environmental Impact
A 2 stroke lawn mower is less environmentally friendly. There’s no getting away from it. This is because of the fact that the oil is mixed with the fuel, and so burnt oil is also released into the air along with the other exhaust fumes. These emissions are the reason why 2 stroke lawn mowers are being gradually phased out, as they do not meet modern emission standards.