2-cycle vs. 4-cycle maintenance

Exactly Mr E, and that same part of the ring has to support the piston as it rides over circa 5% of the cylinder diameter. Id imagine that the rings end up with grooves in them from riding over the narrow bridges between ports... Not long before the seal is no good and the rings need replacement.

Another problem is uneven heat on the piston, as the hot gas escapes out the exhaust port. The inlet side of the piston is always cooler from the fresh fuel mixture entering so you end up with uneven piston expansion. Upon inspecting a siezed 2 stroke, i think everyone ive seen always has the scoring and piston wear on the exhaust side of the piston and cylinder.

 

What about 2-stroke diesels, doesn't seem to be a problem there with ring wear that I know of ?

 

"What about 2-stroke diesels, doesn't seem to be a problem there with ring wear that I know of ?"

Sure it is , a DD 6-71 as a prime gen set engine needs rings and cylinders every 20,000 .. 30,000 hours!

 

20-30,000 hours.......so 3-4 years of continous running, hell that is fast wear.

 

Never looked inside a 2 str diesel, but a quick google shows they're designed quite differently... Most show an exhaust valve in the cylinder head... Different beast by the looks of it, only the air inlet Is through the cylinder wall...

 

I worked on a AHTS with 2 7000hp 4 stroke Wartsilas, they needed rings at 15,000 hours, they were stuffed due to too much low load running

 

OK Lets get back to reality.

The older OMC, and Mercury outboard engines used to run in spite of being treated like crap by most of their owners. My dad swore by OMC and owned Johnson and Evinrude motors that would literally run with water in the bottom of their gas tanks. (He was a terrible mechanic, that's why I am a good one) They had a glass sight bowl filter on the side of the motor and you could see water in the glass, spin the nut on the bottom, throw away the water and get going again. Those motors were bullet proof, as was a properly maintained 2 cycle Mercury. I do not see how having to spend $1800 dollars for an injector pump for an outboard qualifies as moving forward. Now as far as replacing the rings goes, the rings were designed to take it, otherwise those old motors would not still be running. I have a 67 Merc 110 and a 72 Merc 200, and they still run like a watch, and have great compression. By the way, Marvel Mystery oil, and Seafoam are the best thing ever invented for a 2 cycle engine. I have been using both in ALL engines and especially Outboards since I was told about it as a kid, and I am now 66, and have never had one problem. The new outboards may be more fuel efficient, but sensors and computers do not give me a warm and fuzzy feeling out on the water.

 

It should more around 4 to 5 gallons an hour. I don't see a 50-hp outboard burning one gallon an hour. I looks quite impossible. In mixed usage outboard have a tendency to burn even more gasoline.

 

it would burn less than 5 us/gal/hour at WOT.

 

Yes at WOT can be 5.2 gallon under perfect condition. No sea, no wind, no current, perfect hull, perfect weight boat for the engine, clean, polished, two person on board, perfect propeller. In an other word, it is never the case in a boat. Very different than a car in fuel consumption.

 

For small craft I must admit that I like my little two stroke tender engines. 8hp to 25 hp. They never, ever, ever need maintence. Well, a rubber impellor every year or two. My two strokes have never been in a outboard shop. One of them..a Johnson is 19 years old.
The 4 strokes Ive used...40 50 hp needed substantial mantence. This maintence is so complex that I send them to a proper shop...then pay the bill. I must admit the 4 strokes are clean and quite...my two strokes belch out smoke and fuel is always dripping out of the carb when at rest.

 

"one gallon per hour in mixed usage." Concentrate on the "mixed usage" part of that sentence. The boat is used for exploring area lakes and reservoirs. In the Colorado mountains, the views of the pine forest, gushing waterfalls, and snow-capped mountains can be spectacular. If we used it for water skiing, I am sure that the fuel usage would be much higher. Instead, we cruise down the lake and explore any little inlets or canyons that we find, stopping for lunch. We always have short periods at top speed, but more often at 20-25 mph. Seriously, the boat has two six-gallon tanks, and I don't think that we have emptied one more than half way in 3-4 hours of boating.

 

When I outfitted the boat, I did not expect to get such good fuel efficiency. That is why I included two fuel tanks, but a single six-gallon tank seems to easily last for more than one outing. Now I don't even bother to fill the second tank for most outings. The dealer I worked with allowed me to experiment with different props to get the right one. I use two different props, one for lower altitude (5000-7000') and one for higher altitude. The hull has a relatively narrow beam with slight rocker and variable deadrise for better low speed efficiency. Wood/epoxy construction allows a significantly lighter weight than the usual fiberglass hull. Most of the time, just my wife and I are aboard. I have done some things to achieve efficiency, but the engine itself appears very efficient also.

 

Race outboards never use more then 1usgph/10hp so there's your worse case.
Modern DFI outboards are miles better than that.

 

Nothing will be efficient in fuel usage at WOT, I would think 2 gph would be quite realistic for a 50 e-tec at 3/4 of max rpm, but double that at WOT.