9.9 Outboard at WOT?
 

Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but what
about outboards?

The manual doesn't say: just describes break-in period. They say for the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12

9.9 Outboard at WOT?
 

Lloyd Sumpter wrote:

Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but what
about outboards?

The manual doesn't say: just describes break-in period. They say for the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12


The answer is no. No production outboards will have a long life if you
run them for long periods of time at WOT. For sustained operations, I'd
suggest no more than 70% or so of max RPMs. I run my 225 Yamaha
four-stroke at no more than 4500 rpm (redlined at 6000 rpm), and usually
at around 4100.

9.9 Outboard at WOT?
 

I would not run the engine at WOT for the first 10 hours period.
You also need to vary the throttle during the first 10 hours not keeping it
at a constant rpm.
As for wide open - No. You should never run an engine at wide open for long
periods of time. How long do you think your car engine would last running
at 5000 (or whatever your redline is) in say 2nd gear constantly.
Keep it at about 2/3 wide open or less for the most part. Wide open for
short periods is fine but I would not hold it for more than about 2 minutes
at a time.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Lloyd Sumpter" wrote in message
...
Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny
New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs
at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but
what
about outboards?

The manual doesn't say: just describes break-in period. They say for
the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12

9.9 Outboard at WOT?
 

Max Mustermann wrote:
On Sun, 13 Jun 2004, "Lloyd Sumpter" wrote:

Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny
New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but what
about outboards?

The manual doesn't say: just describes break-in period. They say for the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12


Both Harry and Tony are right on target concerning their thoughts on
running at WOT. Though I am running a diesel and expect a longer life, I do
not run at WOT for any length of time.

Consider the following from www.boats.com

In typical marine use, which involves considerable idling and medium speed
operation with relatively little full throttle use, a gas engine can
expect 2,000 hours before it needs an overhaul. A diesel used in a similar
fashion might go 5,000 to 7,000 hours before an overhaul is required. Even
at full throttle, a gas engine is going to need rings and crank bearings
in about 200 hours, while a diesel won't start burning rings or pistons
for 1,000 or more hours.

In a nutshell, continuous running at WOT will likely shorten your engine
life to a tenth of what might be expected under normal use.




I've run our Johnson 6 hp at WOT for hours on end for over thirty
years... the engine has never been apart and I've changed the points
once... do these engines last 300 years or more with more gentle use?

Rob

9.9 Outboard at WOT?
 

You are very lucky.
However, lets consider a few things. How many times have you actually run
this motor for hours straight at wide open. Where were you going? I can't
imagine riding in a boat w/ a 6hp engine running wide open for multiple
hours non stop.
Also, how many actual hours do you have on the engine given you have only
changed the points one time.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"trainfan1" wrote in message
...
Max Mustermann wrote:
On Sun, 13 Jun 2004, "Lloyd Sumpter" wrote:

Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny
New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs
at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but
what
about outboards?

The manual doesn't say: just describes break-in period. They say for
the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12


Both Harry and Tony are right on target concerning their thoughts on
running at WOT. Though I am running a diesel and expect a longer life, I
do
not run at WOT for any length of time.

Consider the following from www.boats.com

In typical marine use, which involves considerable idling and medium
speed
operation with relatively little full throttle use, a gas engine can
expect 2,000 hours before it needs an overhaul. A diesel used in a
similar
fashion might go 5,000 to 7,000 hours before an overhaul is required.
Even
at full throttle, a gas engine is going to need rings and crank bearings
in about 200 hours, while a diesel won't start burning rings or pistons
for 1,000 or more hours.

In a nutshell, continuous running at WOT will likely shorten your
engine
life to a tenth of what might be expected under normal use.




I've run our Johnson 6 hp at WOT for hours on end for over thirty
years... the engine has never been apart and I've changed the points
once... do these engines last 300 years or more with more gentle use?

Rob

9.9 Outboard at WOT?
 

Tony Thomas wrote:

You are very lucky.
However, lets consider a few things. How many times have you actually run
this motor for hours straight at wide open. Where were you going? I can't
imagine riding in a boat w/ a 6hp engine running wide open for multiple
hours non stop.
Also, how many actual hours do you have on the engine given you have only
changed the points one time.


This boat is used for everything - diving, fishing, tender, touring,
camping, picnicking, social visits, etc., it is an exceptional engine -
1972 & well cared for. It is probably due for an ignition tune-up again
- last time was about 1985! We have toured the upper & lower Fulton
Chain, Raquette Lake(99 miles of shoreline), the Eckford Chain, Long
Lake, Stillwater Reservoir countless times, and probably about 2000-2200
hrs total time on the engine, based on use compared to the ski boats
which we do know how many hours they have on them.

At WOT, we go just about the right speed - 9-10MPH loaded, to take in
the sights and cover some ground(water). I don't think I would do this
with a 7.5 or 9.8 Merc, or 9.5/9.9/15 OMCs, they are too high strung to
put out power for this long a time.

The 6 has never whimpered, though.

Rob

9.9 Outboard at WOT?
 

I think 4 strokes are going to end up being 80% engines (run them at 80% WOT
80% of the time for long life). It is simply the number of moving parts you are
dealing with.
I know small 2 strokes will run WOT all the time, I suppose they are designed
that way but you don't hae that many moving parts. We have guys here with 20'
pontoon boats and decades old ~20hp motors who use the throttle like a switch.

9.9 Outboard at WOT?
 

"Lloyd Sumpter" wrote in message
...
Hi,



Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but
what
about outboards?


There are two issues when running at WOT: High RPM and heat.

It is common to have the propeller pitch selected such that WOT results in
the fastest possible speed, which is usually at the maximum RPM. Maximum
RPM is often stressing internal engine parts in such a way that they will
not survive long. It is also typical to get an excessive amount of blow by
and resultant loss of oil at high RPMs.

If the load on the engine is sufficient to keep the RPMs in check then the
next concern is heat build up. Even with an infinite amount of cooling
water (the lake) the engine may not be able to draw the heat away from the
hottest areas, specifically the piston tops and cylinder head. Prolonged
running at such conditions could burn a piston or a valve.

Rod

9.9 Outboard at WOT?
 

were talking small outboards. Over the last 30 years I have had a 5hp
Johnson, a 9.9 rude, 4hp rude, 2hp Suzuki. There was only 2 throttle
positions, troll and WOT. I still use 3 of the motors, the old 5HP was a
victim of a relative not adding any oil to the gas. All work fine. Now 4
stroke I know nothing about but seems they would be more susceptible to
damage at WOT because of the valve train.

Trainfan1 sounds like my area. I run up a lot of steams and small lakes in
the western Adirondacks. Got a Camp in the Pieseco area.

"Lloyd Sumpter" wrote in message
...
Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny
New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs
at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but
what
about outboards?

The manual doesn't say: just describes break-in period. They say for
the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12

9.9 Outboard at WOT?
 

On Sun, 13 Jun 2004 09:30:14 -0700, "Lloyd Sumpter"
wrote:

Hi,

I just gave up trying to find a used 9.9 4-stroke and bought a Shiny New Merc
9.9 4-stroke. It's LIGHT!

Anyway, I've always run older 2-strokes and often ran them WOT for hrs at a
time. Now that I have a new one, I'm more concerned. Are outboards (esp.
4-strokes) designed to run WOT full-time? I know inboards are not, but what
about outboards?

The manual doesn't say: just describes break-in period. They say for the
first 10 hrs do not run WOT for more than 5 minutes. After that...?

Lloyd Sumpter
"Skeeder" Mirrocraft 12

I don't know if this is the case with your motor, but many 9.9 HP
motors (2 Stroke) were/are, de-tuned 15 HP motors. Basically smaller
jets & inlet throats. If this is the case, isn't running a 9.9 at WOT
is the same as running a 15 HP at 66% of what it was designed for
......(in theory)?