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Thread: Mercury 9.8

  1. #1
    Join Date
    Jun 2006
    Location
    Claremore, Oklahoma, USA
    Posts
    361

    Default Mercury 9.8

    What is the history of the Mercury 9.8HP motor? Years built, history of reliability, problem areas, etc.
    Bill

  2. #2
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    8,504

    Default Re: Mercury 9.8

    All 9.8's (whatever they were called) used Merc's 10.9 cubic inch block, and throughout it's life the block was never modernized. It was a "headless" split block with the reeds located in a (donut) around the lower portion of the crank - a real pain if you had a reed problem - had to crack the block to get at them.

    The 9.8 started it's model run in 1962 as the model 110 with Merc's Phelon ignition system.

    In 1970 it got the first "thunderbolt" ignition system - the "thunderbolt 2 - Phase Maker".

    In 1974, while still called the Model 110 it got Merc's Thunderbolt 4 ignition which stayed in production as Merc's near perfect ignition until 2005 when most 2 strokes were discontinued.

    In 1979 it simply became the 9.8.

    In 1985 both the block (which was shared with the 7.5 horse) and the 9.8 model were discontinued.

    1986 saw the launch of the 6/8/9.9 horse models with a new 12.8 cubic inch block (designed and built by Yamaha exclusively for Merc) which combined with the T4 ignition became the best and most reliable 2 stroke portables ever to hit the market.

    The 9.8, and it's little sister, the 7.5 built post-1974 were a relatively trouble free, generally reliable motor.

    However, you have to consider that the "newest" one out there is now 25 years old and some parts have been long discontinued.

    In the used market there is little price difference between an early 80's 9.8 and a later 80's 9.9 - with the 9.9, just from a parts support perspective, being the much more desireable motor.

    But if you have a 9.8 (or get one really cheap), it could be a viable motor for many more years...

  3. #3
    Join Date
    Jun 2006
    Location
    Claremore, Oklahoma, USA
    Posts
    361

    Default Re: Mercury 9.8

    Just the kind of information I was looking for. Very descriptive and informative!!
    Thank you,
    Bill

  4. #4
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    8,504

    Default Re: Mercury 9.8

    The key thing to keep in mind if you are looking at a used 9.8 and trying to determine a fair price compared to something a little younger is -

    A 1985, 9.8 model was designed in 1961 and was never technically advanced from that point (save the ignition system).

    A 1986 9.9 was designed in 1985 and still has full parts support - but the big plus is that is 24 years "newer" in terms of technology than 1985 model...

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,597

    Default Re: Mercury 9.8

    Gotta speak up here: The later, electronic ignition 7.5 and 9.8 hp motors are stone reliable, great running motors! I've had a half dozen in my shop this winter for tune ups and impeller changes (the LU is a dog to work with!) and every one ran great! The Phelon mag units also run great, but one needs to clean and reset the points every few years.

    Jeff

    PS: Anyone know why they are 9.8 hp? To beat the "under 10 hp" rule on many lakes. The 9.9 hp designation is to differentiate it from the 9.8 models.

  6. #6
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    8,504

    Default Re: Mercury 9.8

    Jeff, I absolutely agree that, in particular, later model 7.5/9.8's that had the T4 ignition are excellent little motors.

    My point was this - it's still a 1961 block that had a modern ignition put on it - so many of the parts are discontinued - plus they always used Tilloson carbs which are also tough to source some parts for.

    The 9.9 is still fully supported parts wise from Merc, so if you are paying the same money in the used market, why not go for the supported version.

    I'll do some guessing on why 9.8 (and this is just a guess).

    I think originally the model 110 was named that way because it was replacing the model 100 (10 horse) and since it wasn't really the same they just "upped the number by "10" to show they were a different model (rather than call it the model 98 which may have sounded weaker when trying to market against OMC)

    In the early 1960's there really wasn't restricted horsepower lakes around - so I suspect it's a 9.8 simply because that's what the dyno kicked out when they fired up their (new) 10.9 cube block.

    I don't remember exactly when the restricted horsepower lakes became "the thing", but the 10 horse cut-off was probably driven by the outboard industry as much as the tree huggers.

    If you look back, neither Merc nor OMC produced anything between 10 and 18/20 horses well into the middle of the 70's. You could have a 10 horse or next was a 20.

    By the time both companies launched their "new" line, there was a need to "keep it under 10" and the 9.9's were born - even if they did put out close to 11 horses...

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