CONTINUOUSWAVE

Guys--[I may buy] a Boston Whaler boat with [a 1989 Yamaha 70-HP two-stroke-power-cycle] engine. [Please] share your thoughts about reliability and known problems. Thanks--John

Reliable.

No problems.

During several years of owning a pair the only malfunctions were:

--stator coils for battery charging alternator failed, but this was caused by external wiring error; once external wiring error was remedied all problems with stator coils ceased;

--a spark plug wire came loose at a spark plug due to apparent stiffness in the rubber boot; remedy was to increase friction of boot onto plug with nylon cable tie;

--replaced propeller shaft seals on advice of my mechanic: one engine had frozen retaining collar which had to be cut to remove it: engines had some earlier use in saltwater which probably contributed to the corrosion of the aluminum collar retainer.

Other than those minor problems my c.1987 engines started and ran flawlessly.

One thing to note: these engines will not start if the safety lanyard is not properly installed in the lanyard switch.

Thank you very much. I ended up buying it. I do believe it was in salt water once or twice...I am going to take your advice regarding the propeller shaft seals. Thanks Again.

Jim--one more thing: this [1989 Yamaha 70-HP engine] has a oil pump in it for the mixture.

Do you know if the engine has a safety shut-off built in if the pump goes bad or runs out of oil (as opposed to frying itself)?

Thanks

Waterfun wrote:[does] the engine [have] a safety shut-off built-in if the pump goes bad or runs out of oil ...?

I do not recall any outboard engine that has an automatic shut-off feature which autonomously stops the engine from running if some parameter of normal operation is exceeded. That would be extremely unusual in my opinion. Generally any engine used for propulsion won't arbitrarily shut off on its own if it detects a problem. A more typical behavior would be to alert the operator. The operator would decide if the condition necessitates the propulsion engine being shut off. So on that basis, I would reply, NO, I very highly doubt the 1989 Yamaha 70-HP will shut itself off if it detects that the oil mixing pump fails or the oil for it has been exhausted.

The engine itself has no alerting system for the operator. This is typical for outboard engines. Any sort of alerting system would be provided by the electrical or electronic rigging associated with the engine, by the particular gauges installed, how they were installed, and if the proper rigging procedures were followed. It is impossible to know the exact state of the engine installation or rigging on your particular boat.

I don't have the owner's manual for the Yamaha 70-HP engines any longer; I included it with the engines when I sold them. I cannot look up any information about them. I recommend you carefully read the owner's manual. It will inform you of what sorts of features the engine has with regard to alerting you to operating parameters that are out of tolerance.

The typical two-stroke-power-cycle engine will let you know:

--if the engine block temperature is above normal
--if the oil level in an associated oil reservoir tank is below normal

In well-designed engines, you will also get an alert:

--if there is a failure of the oil pump to operate

In really well-designed engines you will further get an alert:

--if the actual low of oil into the fuel-oil mixing system is not detected
--if the vacuum suction in the fuel hose providing engine fuel is excessive

I cannot say exactly what set of those alerts will be provided in your particular engine, but the owner's manual should inform you of that.

The only form of propulsion engine shut-off provided with outboard engines is typically the safety lanyard. Removal of the safety lanyard from its holder-switch will cause the engine to immediately stop.

Waterfun wrote:...I am going to take your advice regarding the propeller shaft seals.

I did not offer advice that you should replace the seals; I only gave an account of a repair that was performed on my engines.

The seal I had replaced was the rear propeller shaft seal. The cost was about $100 or so, but was that maybe 15-years ago, at an off-the-water service shop, with whom I had been a customer for many years.

Before replacing the seal, you should consider having the gear case tested with a positive pressure test. This is a simple test. A slight positive pressure is applied to the gear case, perhaps just a few PSI. The pressure is monitored over a brief period, ten minutes or so, so see if there is any change. If the pressure is lost, the inference is there may be a leak in a seal.

In addition to the propeller shaft seal, the gear case is also sealed where the engine drive shaft enters and where the shift shaft enters.

When choosing a dealer or service shop to provide service, carefully evaluate their credentials and reputation. Look for a service provided who has a long history with the brand and model of engine you want serviced, has a good reputation, and seems like someone you will be comfortable working with.