Two Stroke / Four Stroke Outboards

[Cloud IX]

Highlander,

Roger that. I certainly would, except that the dink is rated for 10hp max and the Admiral is a stickler.
Don

[Canibul]

Down here a lot of the fishing charter guys go through outboards every couple of years. When we first moved here, over four years ago, they were all running Yamaha two strokes. Then some of them tried the E-tecs, and i was in the market for a power boat then and was really paying attention. I was trying to decide which outboard to spec for a new 22 ft. panga hybrid from Andros. I talked to one of the charter guys here who had just sold six E-tecs and was going to Yamaha four strokes, at that time. He told me that they frequently hit sand with their outboards on charters, and when the intakes got clogged on an E-tec the motor would shut down and he would have to call a service guy with a computer to come straighten it out. With the Yamahas, you just clear the clogs and start it back up. There is one E-tec dealer here.

Lately, they have been going back to Commercial Yamaha two strokes in the 200-250 HP range. Which you cannot buy in the US. They come here from Japan directly. I asked why, and was told that the reliability, cost, and cost to operate were much lower for the two strokes than anything else out there. One guy told me he could take a commercial Yamaha two stroke all the way down to the crankshaft and rebuild it all the way back up in one day using about ten common tools.

If you ignore the marketing hype, and just consider the motors, it's pretty obvious what the differences are going to be. Four strokes are quieter, and more expensive.
Two strokes have a better power-to-weight ratio. All of them together probably pollute as much as Al Gore's jet. If it were not for the US government and regulations, everyone in the US would still be running two strokes. Other than the regs, there's no good reason not to. Engineering wise, they are pushing fewer parts around. Any engineer will tell you this is a good thing. If you know anything about Milspec, and have ever done a MTBF calculation based upon parts count, that pretty much says it.

One thing I have heard a few times is that you want to be careful how you store four strokes. Some of them do NOT like being stored horizontally.

[Cheechako]

Take a 250cc Yamaha motorcycle taxi ride into the city in the Dominican Republic some afternoon and you will realize just how bad polluters 2 stroke engines can be. It pretty much resembles fog it's so bad..... they are almost all Yamaha 200-250cc's...

[Canibul]

you reckon that's the way they were designed, or is it that they will still run though badly out of tune?

[Cheechako]

Good point, I'm sure they have a lot of miles on them... but still.... would 500 well worn 4strokes in the same situation produce the same cloud...? Not sure I guess...

[Highlander40]

Who knows what they put in the gas for lube. Could be old motor oil.
I don't think they spring for synthetic 2 stroke oil.

[forsailbyowner]

As to longevity and the supposed lower maintenance and mtbf of less parts, I don't think your taking into account the fact that all the lubrication takes the form of a fog of fuel/air/oil that passes by and around the rotating assembly in a two stroke. Four strokes bearings run with oil forced under pressure through a gap as small as .001 where the metal surfaces ride on the pressurized oil not each other. Rebuilding a two stroke with ten hand tools? This includes straightening cylinder walls, chamfering intake and exhaust ports?
How are crankshaft clearances met? If a new jug,rotating assembly are purchased every time is this more cost efficient than a four stroke rebuild where the clearances are restored without throwing out major components? I'm not up on the large outboards. Are the big fours using computer controlled fuel injection? Or are they still carbureted? Might be the Etec is going way sophisticated and complicated to make up for the inherent ineffieciency of the two stroke design.

[Canibul]

I don't think that the lower maintenance and rebuild costs of two strokes is "supposed". If four strokes were cheaper, you can bet the third world would be using them. I am not sure what you mean by "straightening" a cylinder. If you are talking about a cylinder hone, yeah, that's a pretty common tool. rebuilding a motor doesn't require chamfering ports. That's something you do when you are building a racing engine, and it's a modification. Not a rebuild of a stock engine. Called 'porting'. You smooth the radius where gasses make turns. And yeah, it could be done with common hand tools.

As for the pollution...I wonder how much of the visible smoke actually makes it higher than say a hundred feet before settling back to earth? I sincerely doubt that two stroke oil is making it to the ozone layer. The gases that are are of concern are common to any motor that burns gasoline, which includes two and four stroke. The torque and power curves of two strokes is a direct result of the fact that they have more power strokes and fewer parts to spin.

The desired result of an outboard motor is to spin a shaft and turn a prop. To think that using two or three times as many moving parts to do that is somehow more efficient is naive. Also, the new two strokes are competitive with the four strokes for fuel consumption. A lot of what people think they know about two strokes is actually obsolete information, based upon what two stroke technology was forty years ago.

I run a 300 hp two stroke outboard. It has five fuel pumps, and the injectors are at 800 psi. This makes for very efficient atomization of fuel.

As for how clearances for crankshafts and connecting rods are met...same as four strokes. Insert main bearings and connecting rod bearings. You don't purchase a new piston ( not a jug. A jug is the cylinder) every time you rebuild an engine, two or four stroke. You buy new bearings and piston rings. Same for both. You don't throw major components away if they ain't broken. Again, if four strokes were cheaper to run and maintain, those taxi's in DR would be four strokes.

The reason the USA is awash with four stroke motors is because Uncle Sam said so. It's fair to establish pollution guidelines. And if a two stroke can meet them, it's a good choice for a simple, lighter, less expensive motor.

Four strokes are a lot quieter, I like that about them. A shame they are so heavy.

[Cheechako]

"I wonder how much of the visible smoke actually makes it higher than say a hundred feet before settling back to earth? " I dont know about you, but I breathe in the lower 100 feet! :>)

[Canibul]

I'm a Texan. We're taller than that......

ha ha.

But seriously, in the US we take all this environmental stuff so seriously, and act like we are making a big difference. How many two stroke motorbikes you figure there are in China?