New member - difference between 2 stroke and 4 stroke lawn mowers

2strokevs4stroke · Feb 6, 2012

Hello everyone,
I was wondering if someone could please explain the differences between the 2 stroke and 4 stroke mowers?
Also, is there any chance someone might have or can reccommend where I can find images/pictures/animations showing the difference?
I thank you all in advance.

Cheers!

Two-Stroke · Feb 6, 2012

The basic difference is that a two-stroke engine fires every time the piston reaches the top of the cylinder while a four-stroke fires every other time.

Two-Stroke: (1) Compression and Exhaust; (2) Power and Intake.

Four-Stroke: (1) Intake; (2) Compression; (3) Power; (4) Exhaust.

That's it in nutshell. But why did you choose this question as your username?

KennyV · Feb 7, 2012

Two-Stroke said:
why did you choose this question as your username?

I'm also wondering that same thing... Why a ? type for your username... Hope to see you a lot in the future... WELCOME to LMF...

For an illustrated view...
Here is a 4 cycle.. Four Stroke Engine Animation - YouTube

Here is a 2 cycle... Two Stroke Engine Animation - YouTube

Both very short but very easy to follow. you can pause the sequence if you like. :smile:KennyV

reynoldston · Feb 7, 2012

I see you have a lot of information how they run and operate. I see a lot of people say 2 or 4 stroke and I have been brought up with the term 2 or 4 cycle I guess just the neighbor hood we were brought up in?

A 2 stroke engine runs at higher RPM to get its power and has fewer parts making the engine lighter. It is used on hand held equipment like chain saws and trimmers. It doesn't run as efficient and pollutes the air and larger equipment like lawnmowers they are doing away with them.

A 4 stroke engine gets it power from lower RPM with a lot more parts making it heaver. Runs a lot more efficient, quieter and less pollution. This is the reason that a lot more manufactures are going to the 4 stroke engines like outboard boat motors, motorcycles, push lawn mowers etc.

Grass ala Mowed · Feb 7, 2012

Technically, it is 2 stroke cycle and 4 stroke cycle. A stroke is the movement of the piston from bottom dead center to top dead center or visa versa and a cycle is a complete evolution of exhausting, getting a fresh intake charge, compressing the mixture and extracting power from the combustion. A 2 stroke engine does this in one crankshaft revolution, the 4 stroke takes 2 crankshaft revolutions. A 2 stroke also has lubricating oil mxed into the gas and the 4 stroke has the oil retained in the crankcase, necessitating periodic oil changes. Not having the oil in the crankcase also helps the 2 stroke run at any angle, even upside down, a nice feature in a chainsaw or trimmer.

2strokevs4stroke · Feb 9, 2012

Thanks so much everyone! This is def helpful information and it's much appreciated.:smile:
Since you're being this helpful, I have one more quick question for you all:
what would you say is the easiest way to differentiate the two mowers just by looking at them. For instance, I go to a Home Depot store and see 10 mowers displayed. Without looking at the product description, how would you know which ones are 2 stroke and which ones are 4 stroke?

BKBrown · Feb 9, 2012

Nearly all will be 4 stroke (4 cycle) now -EPA does not like 2 stroke.

I don't know of any NEW 2 stroke mowers - someone else might know.

Grass ala Mowed · Feb 9, 2012

Exactly, due to emissions requirement, very few if any new mowers are 2 stokes. One of the problems is that the pre-mixed oil must be enough for worst case engine loading, which results in too much oil 90% of the time. Two-stroke outboard motors and snowmobiles have gone to variable ratio oiling, where the oil is carried in a separate tank and metered into the engine based on rpm and throttle position. This is too expensive for a lawnmower. If there is a 2 stroke mower on the shelf, it should say something on one of the warning labels (if they're not mssing) about needing oil mixed into the gas. A 4-stroke will usually have a prominent place to add oil to the crankcase with a warning label to add oil before starting the engine.

jerye · Feb 16, 2012

A good read over here:

2 stroke and 4 stroke engines

oldyellr · Feb 19, 2012

Grass ala Mowed said:
Exactly, due to emissions requirement, very few if any new mowers are 2 stokes. One of the problems is that the pre-mixed oil must be enough for worst case engine loading, which results in too much oil 90% of the time. Two-stroke outboard motors and snowmobiles have gone to variable ratio oiling, where the oil is carried in a separate tank and metered into the engine based on rpm and throttle position. This is too expensive for a lawnmower. If there is a 2 stroke mower on the shelf, it should say something on one of the warning labels (if they're not mssing) about needing oil mixed into the gas. A 4-stroke will usually have a prominent place to add oil to the crankcase with a warning label to add oil before starting the engine.

Unfortunately, with the ever increasing amount of information and skills people have to learn each day, everything gets dumbed down so make it idiotproof. E.g., automatic transmissions, ABS brakes, traction control, electrinic stability control, you name it. I predict, in a couple of generations, the word "skill" will be irrelevant. So much for Darwin! As far as 2-stroke vs. 4-stroke for lawnmowers, any additional lubrication technology for a 2-stroke is far less complicated, expensive or heavy, than a 4-stroke valve train. I bet most old 4-stroke mowers running today generate more pollution than a modern 2-stroke would.

New member - difference between 2 stroke and 4 stroke lawn mowers

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