4 stroke explanation, please

[Btuvi]

I'm not a mechanic nor am I particularly familiar with outboards. I'd like to have a better understanding of 2 stroke/4 stroke differences. One question in particular - Am I correct that 4 strokes, unlike 2 strokes, do not require that oil be mixed with gas - that in that respect they are like inboard/outboards?

If that is the case it seems that eliminating the frequent purchase of oil would cut down on the usuage expense considerably.

What are the most important considerations in deciding between the two?

Thanks

 

[JB]

Re: 4 stroke explanation, please

You are correct that 4 stroke outboards operate similarly to I/Os and inboards, Btuvi. They are lubricated from a sump, rather than by oil in the fuel.

Like I/Os, 4 stroke outboards require regular oil changes. Modern DFI 2 strokes use very little oil compared to old tech 2 strokes, so the purchase of oil, even the purchase of fuel is comparable between the 2 and 4 stroke outboards.

 

[jay_merrill]

Re: 4 stroke explanation, please

Four stroke outboards are lubricated the same way that your automobile is - via oil in the "pan." There is a pump in the motor that circulates oil in order to provide lubrication the the internal, moving parts. A four stroke outboard motor requires periodic oil and filter changes, also just like your car.

Lubrication in a two stroke motor is provided oil mixed with the gasoline. Modern two stroke motors usually have oil injection units that do this automatically, at a predetermined ratio of oil to gas. In older two stoke motors, the oil is mixed with the gasoline in the tank at ratios varying from abiut 18:1 (gasoline to oil) to about 100:1.

As to which system is less expensive, it really depneds on the motor, how often it is used, and whether or not the owner services the engine himself or herself.

 

[Silvertip]

Re: 4 stroke explanation, please

The engine in your car or truck is a four cycle engine. It is exactly the same engine that appears in I/O and inboard boats -- except for marinized accessories like starters, alternators, distributors and cam is profiled more like a truck than a car. Whatever you do for your car or truck you do for a four stroke outboard with the exception of the cooling system. Cars and trucks have closed systems and outboards have an unlimited supply of lake water so they are open systems. Because of the extra parts (valves, camshafts, timing chains or belts, etc) four strokes tend to be a little heavier than an equivalent two stroke.

 

[steelespike]

Re: 4 stroke explanation, please

If you go to the library and have a look at an outboards service manual most have 4 stroke and 2 stroke illustrations in the front of the manual.
to keep it simple a 4 stroke uses 2 or more valves per cylinder to intake
fuel air mix and to exhaust the burnt mixture 4 stroke has intake,compression,power,exhaust strokes.(each cylinder)The valves open and close in correct time.One power stroke each 4 strokes thus (4 stroke)each cylinder has many moving parts.piston,rod,crank,up to 4 valves,each with at least one spring,one follower,up to 2 cams with a timing chain or belt for each cam timing gears,base with oil pump, etc.4 stroke needs less refinement to be clean and relatively efficient.
The 2 stroke has exhaust and intake ports that are opened and closed
by the movement of the piston.Fuel air mixture is drawn in through the crankcase as the piston goes up (oil in the gas lubes the motor.the piston fires, as it goes down it compress the mixture in the crankcase and exhaust goes out the exhaust ports as they are uncoverd by the piston intake ports are uncovered and the compressed fuel is pushed into the cylinder, piston moves up compresses the mixture and fires.motor fires every 2 strokes one down one up thus "2 stroke".fires everytime piston comes up.Each cylinder has 3 moving parts,piston,rod and crank.The unrefined 2 stroke is dirty and inefficient.Todays refined 2 stroke (Etec) and some others are every bit as clean and efficient as the refined 4 stroke.
4 stroke is generally smoother and some what quieter,said to be more efficient in certain specific areas over all the 2 designs are very close in efficiency.Generally the 4 stroke is heavier and more complicated,the 2 stroke has better low end power, top end is very close.The, 2 stroke generally has fewer,less complicated service intervals.the 2 modern designs
oil cost is a wash 4 strokes require oil changes 2 stroke oil fuel mix.
Most modern day motors are very good. A buyer should give each design a close look and lots of test drives and make their decision based on their preferences and the location of a qualified full service dealer.
This is keeping it simple??

 

[Btuvi]

Re: 4 stroke explanation, please

Wow! I'm glad that I was able to view simple explanations before getting to steelespike. I tend to understand things a little at a time so by the time I got to steelespike's reply I found myself able to understand it - after several readings.

Thanks to all of you. Further question.

What year did most manufacturers stop making engines that require gas and oil mixture in the gas tank. Those are the engines I have used.

I see designations such as DFI, Etec, etc that are meaningless to me. Are there simple explanations. I can only take in so much and my mind is filled to the brim with steelespike stuff at the moment.

Thanks again. Very helpful.

 

[Silvertip]

Re: 4 stroke explanation, please

Yamaha, Mercury and Evinrude still build two stroke motors. They are DFI (direct fuel injection) motors. A DFI motor has the fuel injected directly into the cylinder. EFI is Electronic Fuel Injection which operates in a similar manner but the fuel is injected into the intake rather than directly into the cylinder. E-Tec is simply an Evinrude trade name but it is a high-tech, stratified charge motor that can best be explained by going to the Evinrude web site. All of these two stroke motors still require oil but the oil and fuel are not mixed as it was in carbureted two stroke motors of years gone by.

 

[jay_merrill]

Re: 4 stroke explanation, please

The answer to your question bout when oil injection became the norm depends on which brand of motor you are considering. The specific model/hp will also make a difference. I just surfed around shop.eviinrude.com and found that 1984, seems to be the year that VRO oil injection started showing up, in some models.