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Old 07-21-2011, 01:56 AM   #1
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Hi Folks!

Our 4 year old Yamaha 15 two stroke is now becoming "frozen" within two weeks of non use and I'm baffled as to the cause... and the solution.

The engine is mounted on our RIB tender and has served us well for the past three years across the Pacific.

We've stopped for work in Australia and have moved into a marina and thus no longer use the dinghy on a daily basis... but we try to get out for a weekend once a month.

The last two trips required me to remove the spark plugs & pull starter assy and put a wrench on the flywheel nut and tap it with a mallet in order to move the engine. It was pretty stiff but slowly loosened-up enough to reassemble. The engine started right up (as Yamaha's always seem to do) and off we went to the beach! And it started & ran perfectly all weekend... at high & low speeds and certainly long enough to warm-up to operating temperature.

Upon return to the marina I began to give the engine starter a pull every few days while hanging on the boat in the davits, well above the water.

BUT - ten days have now passed - and the engine is frozen once again!

I intend to launch the dink this afternoon and get in with the required tools AGAIN... but I thought I'd write and see if anyone here may know why this problem persists and be so kind to offer a possible solution.

We're berthed just within the warmer side of the Tropic of Capricorn and it's winter now... but it's not THAT cold!

Suggestions?

Thanks,

Kirk
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Old 07-21-2011, 03:05 AM   #2
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All kinds of things might do this but I vote for a spun bearing. No real hope, for any of the list of problems, other than a complete tear down.

Assumptions are you have kept up with the oil.
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Old 07-21-2011, 04:15 AM   #3
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She started right up after the usual starter removal & socket wrench routine. I'm pretty sure a bearing is at the heart of the problem because there was a high-pitched squeeking sound for about the first ten seconds when it ran.

Not savoring the idea of breaking the engine apart.

To Life!

Kirk
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Old 07-21-2011, 06:10 AM   #4
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Quote:
Originally Posted by Gallivanters View Post

She started right up after the usual starter removal & socket wrench routine. I'm pretty sure a bearing is at the heart of the problem because there was a high-pitched squeeking sound for about the first ten seconds when it ran.

Not savoring the idea of breaking the engine apart.

To Life!

Kirk
Kirk,

When removing plugs can you turn engine with starter cord? OR/and By putting in gear and turning prop?

Before stripping, suggest drain lube oil, then replace with kerosine(paraffin)turn engine by hand. Drain, add SAE 10 - run engine for couple of minutes. Drain SAE 10 and replace with 10 <> 40 multigrade -- run the engine normally.

Kirk, the Yamaha 15 has a problem with latter day gasoline, eventually causing piston rings to jam open tight - they have a fuel additive called "Ring Free Fuel Additive"

If that does not cure, then if she partially seizes again, you will have to strip completely - the symptoms are also pointing to poor lubrication (blocked oil gallery ??)

Richard
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Old 07-22-2011, 02:09 AM   #5
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No - I cannot budge the engine with the starter cord or prop in gear after the engine sits for a few weeks.

I ran it for 20 min yesterday at idle speed. It's stiff today... but loosens with each pull of the starter. Once it starts - it runs fine.

She's a 2 stroke so I have to assume you're recommending a drain & flush of the lower end unit progressively bringing it up to 90 wt gear oil?

Don't know if it has anything to do with this but the temp drops to between 5 & 10 deg C. at night.

I really don't want to tear this engine apart. It's winter now and I have no bench to work on.

Thanks for your help! I certainly do appreciate it!

To Life!

Kirk
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Old 07-22-2011, 08:15 AM   #6
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Just got back from an hour-long dinghy cruise at all speeds. The engine runs great and doesn't miss a beat - as always.

I've been offered the use of a nearby work bench. First thing I'm gonna do is separate the top & lower ends and take it from there. I suspect the lower end. Stay tuned.

To Life!

Kirk
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Old 07-22-2011, 09:58 AM   #7
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Quote:
Originally Posted by Gallivanters View Post

No - I cannot budge the engine with the starter cord or prop in gear after the engine sits for a few weeks.

I ran it for 20 min yesterday at idle speed. It's stiff today... but loosens with each pull of the starter. Once it starts - it runs fine.

She's a 2 stroke so I have to assume you're recommending a drain & flush of the lower end unit progressively bringing it up to 90 wt gear oil?

Don't know if it has anything to do with this but the temp drops to between 5 & 10 deg C. at night.

I really don't want to tear this engine apart. It's winter now and I have no bench to work on.

Thanks for your help! I certainly do appreciate it!

To Life!

Kirk
I believe the Gear oil can just be replaced 90 >> 90

I did a search of my Yamaha Manuals regarding the Piston rings seizing as a result of the long term use of modern day gasoline, but they don't cover 2 stroke fuel (eg. 1 oil : 50 gasoline)

I have spoken to a friend who has had 5 Yamaha 15s - nec

ver a problem

He suggests take plug out and squirt WD40 onto cylinder- then see if that eazez the problem. If that does not help take the Head off first to check the cylinder wall for any sign of seizing.
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Old 07-25-2011, 03:07 AM   #8
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If the prop spins freely (in neutral), by hand, then the problem, most likely, isn't in the lower unit.

You need to tear this down and are malingering. You will be very surprised at how easy a job this is on a 2 stroke.
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Old 08-02-2011, 10:51 PM   #9
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Thanks for all the suggestions, Folks!

It's been ten days since I lugged my outboard to the bench.

I removed & serviced the lower end. The only thing I found wrong was the oil was contaminated.

New impeller, oil, drain-plug gaskets and lubed all threads & shaft spline.

It's been running like a new outboard ever since! Perhaps the lower shaft bearing was seizing in the seawater that had entered the lower gears?

Only time will tell if I've actually cured the problem... but the ol' Yamaha starts on the first pull again and there's no hint of stiffness after 72 hrs. between runs.

And I'm glad I didn't jump to the worst conclusion and tear the engine apart.

To Life!

Kirk
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Old 08-03-2011, 11:14 PM   #10
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Originally Posted by Gallivanters View Post

Thanks for all the suggestions, Folks!

It's been ten days since I lugged my outboard to the bench.

I removed & serviced the lower end. The only thing I found wrong was the oil was contaminated.

New impeller, oil, drain-plug gaskets and lubed all threads & shaft spline.

It's been running like a new outboard ever since! Perhaps the lower shaft bearing was seizing in the seawater that had entered the lower gears?

Only time will tell if I've actually cured the problem... but the ol' Yamaha starts on the first pull again and there's no hint of stiffness after 72 hrs. between runs.

And I'm glad I didn't jump to the worst conclusion and tear the engine apart.

To Life!

Kirk
I guess you will make sure to fresh water flush after use ?
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Old 09-02-2011, 04:05 AM   #11
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Hi Folks!

It's been well over a month since I "cured" my outboard problem by simply changing the oil in the lower end.

Our dinghy has been hanging by the davits more than two weeks now and it just sprang to life with only a quarter pull on the starter cord!

When I removed the lower unit I did notice a bit of crust on the shift rod where it entered a rubber seal at the transmission... which may have allowed the ingress of seawater... as evidenced by the contaminated oil. It had been a year since the last oil change.

But the difficulty in starting the outboard has gone away... and simply changing the lower end oil is what did the trick.

To Life!

Kirk
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