Meaning of Bubbles, Yachtwin 4hp

[yachtwin]

My new old (1973) yachtwin 4hp bubbles eventhough propellor isn't spinning (needs a shearpin).

It is in a trash can with water and the air bubbling is increases eneormously with increased throttle. Thought the exhaust ports above water line is where air would come out. Lots of smoke and oil comes out of water with huge bubbles. Whats going on?

Noticed exhaust does seem to come from the ports above waterline (4 small holes on either side of rear shaft), but no water "spits" onto my hand from these. So the impellar or pump must be out? Connection with bubbles?

 

[F_R]

Re: Meaning of Bubbles, Yachtwin 4hp

Well, of course it bubbles under water. After all, it is underwater exhaust, y'know. The holes above the water line are merely exhaust relief holes tomake it start and idle better.

Yes, water should spray out the exhaust relief holes. Not a lot, just a spray, with a bit of exhaust.

 

[Daviet]

Re: Meaning of Bubbles, Yachtwin 4hp

I think what you are seeing is exhaust from the outlet in the lower unit. The higher the RPM the more the bubbles. The smoke is from the oil/fuel mixture burning in the cyliners and coming out of the exhaust.
Sometimes there is not much water coming out of the small holes, remove the cover and touch the cylinder head. You should be able to hold you hand on the cylinder head for 2-3 seconds.
If the pump has not been replaced in the last couple of years, it should be replaced anyway.

 

[yachtwin]

Re: Meaning of Bubbles, Yachtwin 4hp

Thanks daviet and FR.

I could not hold my finger to cylinder head for 2-3 seconds, just touch and have to remove. Very hot.

Is there a positive or more objective way to check for cooling water flow and for engine temperature? -Thanks

 

[Rick.]

Re: Meaning of Bubbles, Yachtwin 4hp

You can buy a little laser (infra red) temp. reader for cheap. You just point and shoot it at the head (or what ever you fancy) and it will tell you the temp. But at first try this. Add way more water to your trash can. The water needs to be well up the leg in order for the pump to prime and then pump. Many times folks simply don't put enough water in the barrel for the cooling to work. Even if this works, I would still put a new impeller in it just to be certain. Best of luck.

 

[Fuzzytbay]

Re: Meaning of Bubbles, Yachtwin 4hp

Replace the impeller, its cheap, easy and that way your "new" old motor doesn't become "parts"

 

[yachtwin]

Re: Meaning of Bubbles, Yachtwin 4hp

Thanks. If I buy a laser temp reader, what temp range should the engine cylinder read? Is there a way to check for cooling water flow, perhaps a hose or tube could be loosened to see if water is being pumped up to engine?

I need to use this engine day after tommrow, but live on an island and no parts for it that fast. If I am wrong and it is operating in right temp range and/or I see that water being pumped through engine, then I can use and overhauls water, points etc later.

 

[Rick.]

Re: Meaning of Bubbles, Yachtwin 4hp

There are some small holes in the back of the leg. If you have a fine mist coming out those holes your motor is cooling. If not then don't use it. Rick.

 

[F_R]

Re: Meaning of Bubbles, Yachtwin 4hp

That motor has a couple of areas that are not water cooled, and they get hot as blazes in those areas. One is the flat plate on the side of the cylinder block. The other is the area right around the spark plugs. There is fire on the other side of those two areas, and if you touch them you are going to have a hot hide on your finger.

There is only one way to be secure against overheating, and that is to know that you have a good water pump. Old impellers sometimes disintegrate suddenly. So, you may have a good cooling spray right now, but five minutes later be cooking your pistons. All the tell-tales and thermometers in the world won't prevent that. Or even warn you unless you are constantly looking at them.

 

[Chinewalker]

Re: Meaning of Bubbles, Yachtwin 4hp

Is the lower unit deep enough in your barrel? The water level must be above the pump bulge to prime it.

Regardless of whether you have a new impeller onhand, I would inspect the old one. Four bolts, drop the unit and take a peek.

 

[yachtwin]

Re: Meaning of Bubbles, Yachtwin 4hp

Thanks a lot all. There simply is no "mist" coming out of the above-water holes on shaft. So I have to assume its no being cooled. I will later break it down and replace whats needed. Hope it is not already burned up by me or previouse owner.

Thanks everyone. I am sure after I start work on it I will have questions. I sure like the size of this engine and how it looks (1973 4336C) and I like that it has two pistons, its cool.