Advice sought - overheated two-stroke outboard

[Lake-Effect]

The patient: 1983 Suzuki DT-5 two-cylinder, two-stroke 5hp longshaft outboard

The story: This is the propulsion for our 19' trailer sailor. Lightly used, mainly to get in and out of harbour; but occasionally some longer runs too. I've babied it for 16 years - fresh gas with good oil, regular cleaning and lubrication... and it's been dependable.

Sadly I did not check the impeller often enough, and failed to check for the pee stream each time i fired it up. This August, it started running a bit rough and occasional stall after about 10 min. First I thought water in the gas... then I thought sticking float in the carb... finally I noticed the lack of the stream, but by that time I'd maybe put another hour on it... and it had run, but didn't sound completely happy.

Last week I replaced the impeller. 3 of 6 blades broken, and all but some crumbs located and removed. But one of the blade ends had blocked the pump outlet, meaning zero water circulating.

The engine still starts and runs easily, and pees like a racehorse again. It doesn't sound as nice as it used to. I am going to take it for a short run today or tomorrow.


So, my questions:

• when a small two-stroke outboard gets overheated, what damage is likely or possible?
• has anyone experienced similar, and were they able to diagnose and repair such damage? or did they find that the repairs were uneconomic?

It's my hope that I can tear the engine down over the winter to repair it. I'm expecting that maybe the block "cover" with the sparkplugs may have warped, in which case I would get it machined flat again. And maybe inspect the cylinder walls and replace the rings.

Any and all suggestions appreciated.


The engine really owes me nothing, and I can afford to spring for a better used, or even a new, 5hp outboard next year. And it would be a 4-stroke, reducing my pollution footprint ... but it would also to fix the ole thing if its fixable.

[JPA Cate]

It "doesn't sound as nice" is really puzzling me. Is it louder? Is there a knocking sound? or clatter?

When you fire it up, is there more smoke? bluer or blacker? (that would point to rings)

Pretty sure you can get it running okay.

With luck you didn't run it hot long enough to do more than increase wear. Nothing seized.

Ann

[sailorboy1]

po I would running it as it sounds is running OK. If it makes it till end of year OK I would do nothing but flush it out. If it isn't working well I would become an off season take apart project to see if I find anything cheap and easy. If not I would just replace it.

[Lake-Effect]

Hi folks. Update:

We went out today for about 20 or so minutes of engine running (and a 90 minute sail too )

Scorecard:

• engine starts (and restarted later) easily as always, first or 2nd pull
• to me, it's a bit rougher-sounding generally (more later)
• drove the boat to 5kt (near hull speed) at about 60% throttle... this is about normal
• the piddle stream was warm
• engine cover was warmer than I remember it usually being

When you fire it up, is there more smoke? bluer or blacker? (that would point to rings)

When I bucket-tested it in the back yard after the impeller replacement, I thought the smoke was a touch darker now. I thought it was maybe just the oil-buildup in the leg when the water had stopped pumping.

It "doesn't sound as nice" is really puzzling me. Is it louder? Is there a knocking sound? or clatter?

I know, sorry. It's so subjective. Anyway both the Admiral and I agree that it sounds a little bit rougher than it used to. The engine was, for us, never silky smooth at all speeds, but it seemed that over 1/3 throttle or so, it just sounded... smooth and steady. Now, not quite as much.

Louder? Maybe, a little. Distinct knocking? No. Clatter? No.

"Rougher" remains the best adjective. Slight variations, little bobbles in the rpm. Seems like it's working a bit harder.

At this point, I'm thinking rings too. And maybe some gasket leak? A compression test might be the next logical step.

With all this being said, it was still as reliable as before, and it will serve to get us in and out of harbour till haulout in late October. And I can then overhaul it in the winter.

Thanks all for your interest and input.

[GreenWave]

Did you change the oil after the impeller work? Check the plugs?

[SailingHarmonie]

Originally Posted by JPA Cate

When you fire it up, is there more smoke? bluer or blacker? (that would point to rings)

Pretty sure that’s not true with a 2-stroke, which burns all the oil you put into it. Bad rings would lower compression, not increase oil consumption.

[Kettlewell]

My two cents is to just keep running it and don't worry about it. There shouldn't be any smoke once the engine is warmed up and running at normal throttle. If you're seeing smoke it could just be the oil mixture is off kilter. An old 2-stroke engine that size is not worth making major repairs on. Get a 4-stroke replacement and burn half the gas, which at today's prices will save you some bucks helping to ease the pain of a new motor. I like Yamaha 4-strokes. I got a used 4HP this year that looked like new for $700 and just sips gas. I thought I would have to get a gas tank, but after using the puny internal tank for days and days of running ashore and such I realized that I no longer need to deal with the separate tank. Also, the 4 stroke has lots of push at lower throttle settings, making it very easy to maneuver at low speeds.

[Jammer]

Choices for overheating damage are: Head, reed valves, block and rings.



Old 5-6hp outboards are inexpensive and plentiful if that's what you want.


As pointed out upthread, 4 strokes use half the fuel so it becomes feasible to use an internal tank so that you don't have the external fuel tank bouncing around the cockpit. On the other hand they have more vibration and are harder to start.


My advice would be to run it until it dies. It might outlast the boat.

[Lake-Effect]

Originally Posted by GreenWave

Did you change the oil after the impeller work? Check the plugs?

You mean the gear oil? No; that hasn't usually been a problem on this outboard. When I've done a change, the oil I dump always looks almost new. I will check & change it after the boat's out of the water for the season.

The plugs were a bit oilier than usual but were fine otherwise. I cleaned them, checked the gaps; they still seem to work well. They get cleaned, checked and gapped every spring.

Kettlewell, Jammer - yeah, it's 40 yrs old, has given us 16 years of service... It owes me nothing and it still runs... It's just fine for short runs from/to the slip.

Originally Posted by Jammer

Choices for overheating damage are: Head, reed valves, block and rings.

Reed valves, rings... I would tackle that. If it's head or block, and more than just getting a machinist friend to mill a face flat again... it's toast. Done.

If I have the time on my hands this winter, and a better idea of what needs doing, I might tear into it just for the learning. I have most of the required tools except for the ring sleeves. Or, as you suggest, I will just keep using it as-is, while watching for a score in a more recent 4-stroke.


Thanks all.

[Khaos13]

All outboards go thru various "doesn't sound quite right" phases. Often, the only moving part is the guy pulling the string. Run it 'til it quits. Oh yeah... you CAN sail it to the dock, right?

[Kettlewell]

The #1 problem with most outboard issues is crummy gas and/or crud in the fuel system somewhere, and with 2-strokes you can add incorrect fuel/oil mixture. I add StaBil 360 to every can of gasoline used on my boat, and with a 2-stroke just add it when you put the oil in. I would just replace those plugs if they looked oily--a cheap fix possibly. I once had an outboard that wasn't running the best and I discovered one of the plugs was just loose. The typical places to check on a 2-stroke: clean fuel with the proper oil ratio (use quality oil), clean plugs and tight clean connections, clean carb jets, check float and needle valve for sticking.

[Lake-Effect]

Originally Posted by Khaos13

All outboards go thru various "doesn't sound quite right" phases. Often, the only moving part is the guy pulling the string. Run it 'til it quits. Oh yeah... you CAN sail it to the dock, right?

Oh yeah. I can and have sailed back to my slip, up to a mooring, etc. When my wife lets me.

Originally Posted by Kettlewell

The #1 problem with most outboard issues is crummy gas and/or crud in the fuel system somewhere, and with 2-strokes you can add incorrect fuel/oil mixture. I add StaBil 360 to every can of gasoline used on my boat, and with a 2-stroke just add it when you put the oil in. I would just replace those plugs if they looked oily--a cheap fix possibly. I once had an outboard that wasn't running the best and I discovered one of the plugs was just loose. The typical places to check on a 2-stroke: clean fuel with the proper oil ratio (use quality oil), clean plugs and tight clean connections, clean carb jets, check float and needle valve for sticking.

Appreciated. I was an early convert to only using fresh ethanol-free gas in our boat and small engines. Good 2-stroke oil, measured correctly, and a shot of stabilizer or Seafoam. So I'm with you there. Being fussy about gas is maybe the main reason the engine has remained dependable for all these years.

I spray cleaner through the carb annually, and this spring I took the carb off for better cleaning, and poked the idle jet, which made a small improvement. I also examined and backwashed the fuel strainer/filter, and did it again a few weeks ago when looking for problems.

I thought my plugs looked ok after cleaning, but they are several years old. So yes, new plugs would be a cheap thing to try.