[Rhodes22-list] 2 cycle vs 4 cycle

[Roger Pihlaja]

Ed,

What does the weight of one's outboard or whether it is 2-cycle or 4-cycle
have to do with the simple fact that gasoline & oil in the water tends to
embrittle & shorten the life of every outboard's water pump impellor?  My
views on 2-cycle vs. 4-cycle marine engines are well known on this list;
but, I was merely attempting to explain a common material of construction
failure mode.  There was no mention of any environmental issues.  You are
REALLY sensitive about this subject aren't you?

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Kroposki" <kroposki at innova.net>
To: "'The Rhodes 22 mail list'" <rhodes22-list at rhodes22.org>
Sent: Wednesday, February 11, 2004 9:12 AM
Subject: [Rhodes22-list] 2 cycle vs 4 cycle


> Rummy,
> Here we go again.  I know better than question the technical
> accuracy and efficacy of Roger's eloquent discussion, but I can lift my
> 2 cycle when I have to by myself.  Roger forgets that not everybody has
> two robust sons to help.  It is the old problem of being able to see a
> tree when you are in a forest.
> Ed K
>
> -----Original Message-----
> From: rhodes22-list-bounces at rhodes22.org
> [mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of Roger Pihlaja
> Sent: Wednesday, February 11, 2004 7:52 AM
> To: The Rhodes 22 mail list
> Subject: Re: [Rhodes22-list] Yamaha 9.9 Water Pump Replacement
>
> Jay,
>
> The usual problem with the water pump impellors on small outboards is
> that
> they are made from some sort of rubber.  It's really a rather clever
> design.
> At low speed & at start-up, the rubber vanes on the impellor touch the
> water
> pump housing, thus making the pump positive displacement & self-priming.
> At
> high speed, the rubber vanes deflect out of the way & ride on top of a
> boundary layer of water on the wetted surface of the water pump housing.
> At
> high speed, the vanes don't experience any wear because they are not
> touching the pump housing.  This design makes the water pump capable of
> automatically switching from positive displacement mode to centrifugal
> mode
> for delivering the high volume of cooling water required by high speed
> operation.
>
> So what goes wrong?  Well, if the water pump ever runs dry, the rubber
> impellor will lose the lubrication & cooling provided by the water,
> overheat, & destroy itself very quickly, like in a few seconds!
> Exposure to
> oil & gasoline in the water (like the oil film that laid down by 2-cycle
> outboards) will gradually break down the rubber polymer molecules in the
> impellor; leading to embrittlement, cracking, and failure.  This is
> probably
> the single biggest long-term failure mechanism.  Pump impellors should
> be
> routinely replaced every 4 years due to this cause alone.  There is also
> another common failure mechanism related to storage.  When the lower leg
> is
> lifted free of the water, the entire cooling system drains down.  This
> is
> why the water pump needs to be self-priming at start-up.  Even fresh
> water &
> especially ocean water, has a certain amount of dissolved mineral salts
> in
> it.  When the cooling system drains down, a small amount of water is
> left
> trapped in between the ends of the vanes on the water pump impellor &
> the
> aluminum pump housing.  When this water eventually evaporates in
> storage,
> the impellor vanes can be bonded by salt crystals to the pump housing.
> Depending upon how strong this bond is, the rubber impellor can be
> damaged
> the next time the engine is started when the vanes are ripped free of
> the
> salt crystals.  In addition, for the 1st few minutes of operation,
> before
> the salt crystals dissolve, they form a relatively rough surface on the
> water pump housing that the rubber vanes have to run over on every
> revolution.  Finally, there can be corrosion issues with moist salt
> crystals
> in long-term contact with the aluminum pump housing in this scenario.
> In
> salt water, it's considered good practice to fresh water flush the
> cooling
> system after every use & certainly before long-term storage.  After
> long-term storage, it wouldn't hurt to fresh water flush the cooling
> system
> prior to start-up.  As part of my outboard winterizing proceedure, I
> flush
> propylene gylcol potable antifreeze (RV "red pop") thru the cooling
> systems
> of my outboards.  propylene glycol will prevent the build-up of salt
> crystals in-between the vanes and the water pump housing.  During the
> boating season, on every start-up, I gently pull the outboard thru with
> the
> pull cord prior to starting it to break the water pump impellor free &
> give
> the engine several minutes of low speed warm-up.
>
> The result, the only water pump I've ever had fail on any of my
> outboards in
> 25+ years of boating was the time when my younger son Gary ran the
> inflatable dingy & Honda 9.9 hp outboard up on the beach with the engine
> at
> full throttle.  The water pump impellor was burnt to a crisp!
>
> Good luck!
>
> Roger Pihlaja
> S/V Dynamic Equilibrium
> ----- Original Message -----
> From: "Michael Meltzer" <mjm at michaelmeltzer.com>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Wednesday, February 11, 2004 2:25 AM
> Subject: Re: [Rhodes22-list] Yamaha 9.9 Water Pump Replacement
>
>
> > sounds like overkill and make work, maybe the impeller very 4 years,
> but
> the complete pump, nah. you are only putting 25-50 hours on
> > the motor every year, one thing you do have to watch is salt on the
> thermostat(and blow the pelages, clean the pee tub yearly), is
> > one of the few parts on the engine that is not rust proof, time will
> get
> it and they need to be replace every two years, luckily it
> > is also a simple job that you can do yourself.
> >
> > MJM
> >
> > ----- Original Message -----
> > From: "Jay Friedland" <a.jayf at verizon.net>
> > To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> > Sent: Tuesday, February 10, 2004 11:25 AM
> > Subject: [Rhodes22-list] Yamaha 9.9 Water Pump Replacement
> >
> >
> > > Folks,
> > > My ob service guy says Yam recommends replacing the water pump
> assembly
> > > every year. The motor is 2001 with this the first year in service.
> I'm
> > > in salt water 9-10 months, occasionally flush with ear muffs (once a
> > > month), and end of season run it in a barrel of fresh water for 1/2
> > > hour (alos to burn off deposits, etc.).
> > >
> > > Anybody offer best suggestions on proceeding with this replacement
> or
> > > any other winter routine?
> > >   Thanks, Jay
> > >
> > > __________________________________________________
> > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > >
> > >
> >
> > __________________________________________________
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> >
> >
>
>
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