Repair Mercury 90 Two-stroke or Re-power

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Hippo
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Repair Mercury 90 Two-stroke or Re-power

Postby Hippo » Sun Aug 19, 2018 5:58 pm

I have a 2001 90hp Mercury two-stroke on a Dauntless 160 (2001). A seal leak allowed seawater into the gear housing, and everything has locked up, so I am going to have to replace the lower unit. Also, the tilt-trim motor leaks. Otherwise, I have maintained the engine and it seems to be in good condition.

Does repair of this Mercury 90-HP engine make sense?

Or, should I just get a new engine?

If so, what engine would you recommend?

My old Mercury seemed a little underpowered for single ski starts or when I'm carrying a full load of people. Any help would be most appreciated.

jimh
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Re: Repair Mercury 90 Two-stroke or Re-power

Postby jimh » Sun Aug 19, 2018 8:28 pm

I suggest you look at an aftermarket replacement gear case. They are much less than a new OEM part—if those parts are even still available. A new gear case could be about $1,000 or more.

The failing power trim unit replacement could be expensive—another $1,000 perhaps.

As an alternative source for parts you might be able to find another Mercury 90 with a blown power head but good gear case and good power trim unit. What that might cost or if you could even find a seller is hard to say.

The classic two-stroke-power-cycle three-cylinder in-line engine by Mercury is a nice 90-HP engine. You might say that other than the poor reliability of the electrical components, the failing power trim unit, and the failed gear case, these are “bulletproof” engines, and that should give you some confidence in case anyone starts shooting at your boat.

There is a bit of nostalgic fun in having an outboard engine running on 1970-technology being still in service almost 50-years later, and if that is a source of pleasure for you then, by any and all means, do whatever it takes to keep it running and on the transom of your boat.

Otherwise, get a modern outboard with 115-HP rating.

Hippo
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Re: Repair Mercury 90 Two-stroke or Re-power

Postby Hippo » Mon Aug 20, 2018 10:23 am

Jim,

Thanks for the feedback. Does anyone know anything about SEI after-market lower units? They offer a new unit for $895, which is a lot cheaper than an OEM replacement. It comes with a three-year warranty too. Thanks again.

frontier
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Re: Repair Mercury 90 Two-stroke or Re-power

Postby frontier » Mon Aug 20, 2018 12:37 pm

You mentioned "My old Mercury seemed a little underpowered for single ski starts or when I'm carrying a full load of people."
Sounds like you need a 115 anyway, especially since your tilt and trim unit is bad also.
My advice is to try and find a good, used 115 HP V-4 Yamaha, Johnson or Evinrude 2-stroke. The 16 Dauntless is a heavy boat - 350 pounds heavier than the same year 17 Montauk. You may be disappointed even if you bought a new 115 HP 4-stroke - they are very heavy and low end torque is mediocre.

jimh
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Re: Repair Mercury 90 Two-stroke or Re-power

Postby jimh » Mon Aug 20, 2018 4:33 pm

The SEI gear cases for the Yamaha 200 have worked very well for John R on his boat HOLLY MARIE which has twin engines and both with SEI gear cases.

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Phil T
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Re: Repair Mercury 90 Two-stroke or Re-power

Postby Phil T » Tue Aug 21, 2018 9:35 am

If you replace the lower unit, to address the standing start, drop 2" of pitch in the same make and model of prop you have now. Make sure the engine is mounted 2 holes up (top bolt in the 3rd hole counting down from the top.)
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

Hippo
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Re: Repair Mercury 90 Two-stroke or Re-power

Postby Hippo » Wed Aug 22, 2018 9:07 am

Thanks for all the feedback. I have purchased an SEI lower unit rather than going for a new engine, and will be installing it this weekend. The three-year warranty made me feel more comfortable than buying an old unit off eBay. Phil, I will check the engine mounting and also try a new prop. Thanks for the advice.