2 stroke vs 4 stroke

We might be approaching a point with outboard engines where, as has been the case for a while with big diesels (DD vs Cat, etc), the argument of "2 vs 4" is becoming secondary to other considerations. The modern direct-injected 2-stroke and the modern 4-stroke are now roughly comparable in power, reliability, fuel consumption, cost and weight. The differences between the two types, based on these factors (which are really all the average boater cares about, in the end) are at present miniscule (on the order of 10%), and the categories overlap more than they are distinct.
My advice is, you can't base your decision solely on number of piston strokes anymore. Look at how the engine's power curves compare to what you want to do with it, look at where the dealers are and how honest/sleazy their mechanics, look at the tradeoffs between price and power, or between reliability and weight. List the criteria you need your engine to fulfill, figure out how you'll weight them, and buy the engine that fits them best.

 

I am a marine mechanic here in Fla. Typically, a four stroke outboard will cost you more in maintenace than a two stroke couter part, but not much more. with a four stroke, you have these items to do once a year (or every 100 hours):
1) Oil change . 3 - 5 qts oil and filter.
2) Gear oil change 2 - 3 qts of gear oil.
3) Thermostat replacement.
4) Water pump impeller replacement.
5) Spark plug replacement / compression test.
6) Fuel and air filter replacement.
7) Check / adjust all linkages.
8) Grease all fitting.
9) R&R prop, grease splines.
10) Decarbon.
11) Sea trial.

Two stroke:

1) Replace head gaskets.
2) Gear oil change 2 - 3 qts of gear oil.
3) Thermostat replacement.
4) Water pump impeller replacement.
5) Spark plug replacement / compression test.
6) Fuel and air filter replacement.
7) Check / adjust all linkages.
8) Grease all fitting.
9) R&R prop, grease splines.
10) Decarbon.
11) Sea trial.

Engine manufacturers have their own guidelines, but from experience, the list above is highly recommended.


As far as operating cost, the two strokes will burn far more fuel and you have to buy oil at a gallon for every 75 - 100 gallons of fuel.

Over all, four strokes will cost you less, but they are heavier and slower than a two stroke..... the choice is yours.

 

On the 4stroke list you made no mention of valve adjustment or checking clearances. There has to be a check somewhere on its life, unless they are hydraulic?

On the 2 stroke list I disagree with changing head gaskets ever 100 hours. Unless you mean re torque after first 100 hours.

Changing a thermostat every 100hours?
Changing impeller every 100hours?

I dont think youve cleared the confusion between the 2 but certainly helped to clear the confusion of why does proffesional maintenance cost so much.

I think 100 hours on the gear oil is exessive too. AND spark plug replacement.

Errr --no mention of the cam belt then?

 

Obviously, you don't think a rubber impeller should be changed at least every 100 hours or once a year (which ever comes first)?

Thermostats...... they clog up, if you pull them to inspect them, replace them.

Head gaskets on 2-strokes..... all the boats I work on down here are in salt water, a lot od corrosion. Also, there is a lot of movement due to the heads being so flimsy allowing the gasket to weep. Just look at any outboard used in salt water, if you see corrosion at the head/block joint, that is water weeping out......... and in. The only way to keep that in check is an annual inspection and replacement.

Gear oil..... why neglect the part that takes the most stress and beating.

To you it may be excessive, but to me, it's you being cheap on how you take care of your stuff. You will pay me now or later.......much more later.

Valve adjustment is not necessary on almost all 4 strokes... they are either hydraulic or shimmed on assembly or rebuild. the only time the adjustment goes out is if you warp a head or wipe out a cam.

As far as the cam belt... check and adjust evry 100 hours, replace every 200 hours. ....you lose a belt, you trash your heads. Most outboards only live to about 1500 - 2000 hours..... only the ones that are pudently taken care of make it to 3000 hours and more.


P.S..... The cost of prfessional mechanics are so high due to the training we must go through to work on these hi-tech machines, not to mention all the EPA, DERM, Dispoasal, Permit, License and insurance costs and the cost of living. The average marine mechanic only makes $30,000........... not even enough to buy a house down here. Oh yeah....... we also have to buy our tools...... I have $350,000 in tools right now, so don't get me started on how much we charge.

 

Yes I do think that changing the water pump impeller ever 4 days of constant use is exessive.

Dont you fresh water flush?

You didnt mention anodes?

Dont 4 strokes suffer from head gasket/water absorbtion too.

You never ever check valve adjustment? even on shimmed vales?

Change Cam belt 200hours?? Do you ever get to use the engine? What egines are these?

I removed an impellor from one of my engines last month --they are original supplied with the motor 4 years ago. It was as new.

 

forget it

 

Sorry RMSOSF I was looking forward to a good debate on 4 stroke motors, Oh well!!

 

maintenance on two and four stroke engines do very some i do agree i've only ben wrenching 16year now on outboards and if you differant techs they will all say something differant
i myself don't agree with rmsosf's list 100% but can't knock it if asked personally about maintenance i do give customers copies of the maintenance schedule right out of the service guides this does end a lot of agruments about the work to be done
as far as water pump impellers this is the second most neglected and miss understood part of a boat (four years will not look new if you know what to look for)
trying hard not to say to much but everyone has one and nobody listens to another!!!!

 

Pehaps I should have said --sevicable--Full water pressure no overheat at all.

I do not think that as I have spares on board anyway that I should replace an impellor because a book says so.

A technician should be able to tell if it is servicable -- ie all blades intact with no cracking around the base of each blade. Blades not distorted beyond servicability.

In the old days workshop mauals did not say replace,- it said remove and check for sericability.

 

The old outboard engines used to have impellors that were not centered in the housing so one blade was always left bent against the housing when the engine was not running. All newer outboards have centered impellors so unless they have overheated due to starvation, they should easily last 600 hours +. Now days, the most important reason to change the impellor at less than 600 hours is to be able to separate the lower unit before it freezes up.

I recomment you install a water pressure gage, it takes all the guesswork out of your impellor performance~

 

Yeah, try replacing that outboard impeller 10 miles out to sea in 800 feet of water

 

How does the ETEC engine work? Does it need oil injection? Or is it gas only, with a pump to inject the fuel instead of the crankcase-as-pump?

Alan

 

Fair point and one that I was going to mention . Engines do have different roles and if it just pushes a dinghy to shore and back then you can row home but I still maintain 100hours ie exessive.

 

the e-tec works by injecting the oil it needs to the crankcase so yes oil does enter the crankcase and then to the combustion chamber kind of like two stroke motorcycles have bin for years
as for fuel it has an electric fuel pump that feeds the injectors then the injectors are not a conventional injector but (bottle cap injectors) they are a high-pressure pump as well controlling the pintal three ways and these injectors are mounted in yhe cylinder not the intake

 

Thanks! And going on-----------How does this engine do in terms of emissions? I know that common two-stroke engines fail miserably to meet even the most lax standards. If the oil is being burned, is it done in such a way as to limit emissions to levels competitive with four stroke outboards?
Because I would see emissions as a factor in choosing this engine, along with all the other variables. In fact, if it produced (in circumstance in which I would use the engine, i.e., all things considered) pollutants above the average four stroke, that alone would outweigh any other factors.

Alan