Trojan Boat Forum

Hello all:

For the past 6 years I have been using a 1976 9.8 Mercury 110, 2 stroke in my high pressure air floor roll up dinghy.

It’s a 10.5’ hypalon dink and the air floor has an inflatable keel so she will plane nicely.

I bought the Merc from a retired Mercury mechanic who built it to 12 hp specs.

The motor performs well and gets us up to over 20 kts – fine when smooth but unsafe when rough.

The motor always starts, however for whatever reason the drive shaft housing (the big cast piece between the lower unit and powerhead) is broken in a spot that cannot be effectively permanently repaired. Used housings are available but the question now is do I put another $100-$200 into this unit and who knows how much time plus what broken/rusted fasteners will I encounter in tearing down the entire unit to replace the driveshaft housing.

I love the power from this unit, but the weight is an issue as this unit is 65 lbs. I store it in the lazarette of my 33’ Trojan and use a St Croix mini crane to get it out and over the transom as the damn thing is heavy and bulky and I am afraid of losing it over the side when setting it on the dink.

For weight, storage on it’s side and maintenance reasons, I want to stay with a 2 stroke.

Even though I flush and rinse after each use, the Merc was not designed for salt water and when I drop the lower unit to replace the impeller, I can see how rusty the drive shaft is. Also in my partial disassembly I can see that there may be an issue with some fasteners

Don’t know if I have or need a long vs short shaft for the dinghy

Fix or replace, I want to stay with the 2 stroke so I realize new is not an option.

Reliability and weight are the most important factors a used 2stroke Yamaha 8 is about 60 lbs

A newer outboard will have the advantage of electronic ignition – I still have points/condenser

While a 3.3 will move it fine there is zero chance to plane and the current power combination is really fun to chase around in.

Can you please provide your advice and opinions regarding the correct shaft length/horsepower and repair or replace opinions?

THANKS !

RWS

Been down this road ( and still going ) First short shaft is what you need . longer shafts are for tall transoms or sail boats .the can be used but more drag and draft ( =slower ) and a little heavier

I have a 9’ hypalon and a 10.5’ PVC both ribs the engine I have used are a 5 hp 2 stroke sears a 6 hp 4 stroke merc 2 Nissan 2 strokes a 8 hp and a 9.9 all but the 9.9 were less then 60 lbs But the 9.9 Nissan was 87 lbs . ( BTW a 9.8 Nissan is 56 ) . The 5hp just moved them , with the 6 hp 4 stroke it would barley plane on the rib ( I am not light weght ( 250 ) The new owner of it with a soft bottom inflatable Can fly with it . With 8hp both boats fly with just myself with both of us it struggles ( like I said I am not light and she is not skinny )( I am a dead man now) The 9.9 with boat of us on it will run 22 knots and even fast when I put the kit on (15hp) The problem with the 9.9 its to dam heavy. and the 8 is just slightly under powered for us heavy weights a 9.8 would be great '

bottom line

A friend with the same 8 hp Nissan and a inflatable bottom like yours , has no issue planing ( there not heavy weights like us ) so unless your going to caring a heavy load the a 8hp 2 stroke should work fine , heavy load that around 9.8

To fix or not ? there are a ton of parts for sale on E-Bay for the 110 (9.8 ) merc , take a look .

hope this helps some , good luck

I am currently going through the same process. I'm going to buy a new soft bottom (high pressure floor) 11' dinghy. I had a 10 foot hypalon and used a 7.5 2 stroke merc.....it worked OK with just me in the boat (225lb), planed nicely but I always thought a couple more HP would be good.

I still have the merc but am looking for a good used 8-9.9hp.........problem is finding one in good condition for reasonable $$. I don't want to buy somebody's problems. I think I'd consider rebuilding yours....while keeping an eye out for an alternative. Small short shaft outboards sell good so if you ended up with 2 it should be easy to sell one....

The dinghy I'm considering has what they call a "drop stitched high pressure air deck floor", they say it is extremely ridge and can be stood on like a wood floor.....is yours by chance like that? Can you stand in it? Thanks..........John

I say keep the Merc though I know weight is a huge consideration. But parts are easy to get, they were built pretty robust, if looked after will last for years to come, and may even outlast anything you could buy now I'm not a big outboard guy but one need only tear down some of this new stuff to see what I'm talking about. I know they're trying to make them lighter but there is plastic where there simply shouldn't be IMO.

I would get a new one, or atleast a newer one.

I have a Merc 15hp 2 stroke, (02) on my caribe 10' RIB She does pretty good. I like the motor, fast, easy to start, and shift, and I dont feel its too heavy to lift off the boat in the water.

Tom

FWIW, I stuck a grand into my 15hp Yamaha from 1983 that I have owned since new just this past spring. It was either that or buck up 3 or 4 times that for a new one.

jddens wrote:I am currently going through the same process. I'm going to buy a new soft bottom (high pressure floor) 11' dinghy. I had a 10 foot hypalon and used a 7.5 2 stroke merc.....it worked OK with just me in the boat (225lb), planed nicely but I always thought a couple more HP would be good.

I still have the merc but am looking for a good used 8-9.9hp.........problem is finding one in good condition for reasonable $$. I don't want to buy somebody's problems. I think I'd consider rebuilding yours....while keeping an eye out for an alternative. Small short shaft outboards sell good so if you ended up with 2 it should be easy to sell one....

The dinghy I'm considering has what they call a "drop stitched high pressure air deck floor", they say it is extremely ridge and can be stood on like a wood floor.....is yours by chance like that? Can you stand in it? Thanks..........John

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Yes, it's a high pressure air floor with a seperate inflatable keel under the floor.

Yes, you can stand on it. It is extremely firm.

Planes nicely with the Merc.

RWS
RWS

Commissionpoint wrote:FWIW, I stuck a grand into my 5hp Yamaha from 1983 that I have owned since new just this past spring. It was either that or buck up 3 or 4 times that for a new one.

3 to 4 grand for a New one ???

The current Mercury outboard is a 9.8 110 series from 1976.

points - condenser - carburetor(s)

I was told but cannot confirm that the carb jets and reed valves have been changed out for 12 HP

I purchased this motor used in 2006

It weighs right at 65 lbs.

The driveshaft is rusty and the casting that connects the lower unity to the powerhead is broken where the shifter shaft comes through. This is NOT repairable and I am finding boneyard parts on line for approx $100 - $175 with shipping.

Perhaps I need to first put her back together and make sure it runs first. Then tear it down to see if it will even come apart before moving ahead.

The question is . . . . . is this engine worth all this time, cost and trouble or should I just bail and get something like a used 1990's Yamaha 8 HP 2 stroke with electronic ignition running a 100:1 ratio fuel mix at about 60 lbs....

The Merc has in my opinion, poorly designed manual tilt trim brackets with springs and the 50:1 oil ratio makes for an oily mess at the base of the unit. Additionally when servicing the unit I found almost no gear lube in the bottom unit and the top bearing, just below the impeller unit appears to be rusty.

I find the idea of the Yamaha 8 2 stroke to be appealing from a reliability standpoint and although less powerful, we should still get on plane with a hard air floor with keel dink hauling 2 people and an adult Lab or 3 people.

If the motor in question was a 90's Yamaha with the same problems, the answer would be yes, of course, do the repairs.

That is why I am seeking yoiur input here.

THANKS !

RWS

prowlersfish wrote:

Commissionpoint wrote:FWIW, I stuck a grand into my 5hp Yamaha from 1983 that I have owned since new just this past spring. It was either that or buck up 3 or 4 times that for a new one.

3 to 4 grand for a New one ???

That should say 15hp Yamaha. But, yes, the list price on a new unit with a 15 inch shaft was just under 3500. I figured 600 in parts plus labor and tax was a reasonable investment compared to the cost of replacement.

perhaps I should start looking for a used Yamaha 15 2 stroke?

Wonder what that weighs in at ?

RWS

I have an aircooled 2 HP Honda on my outboard so I'm at the other end of the spectrum

Surprise, it's slow but it just needs gas and only weighs 26 lbs. You know what you have, I would probably fix it if you could do it for a few hundred dollars.

Plus, this is something you can bring home and do at your leisure....

Bob

Fix a boat at your leisure ? Never ! all else goes on the back burner . Its not like he is snow bound .

I have a Johnson 6 hp 2 smoke I used to use on my Zodiac 310 zoom. It would get me and two golden retrievers on plane.

I have a 10' achilles hypalon with the high pressure floor that I purchased off Ebay it is a 1999 that looks brand new, gave $860.00 for it. I run a 2003 Johnson 8hp 2 stroke short shaft i bought off ebay last year for $740.00 that was only run in fresh water looks brand new. It will plane the dinghy with my wife, 16 year old grandson and me ( 460 lbs ), plus gear ( life jackets, 6 gallon gas tank, oars ), runs 14mph on the hand held gps and is very stable, when I run just myself it is scary fast, I am not sure what the motor ways ( I can lift it with one hand barely, would guess 60lbs ), Some times you can get good deals off ebay but you have to becareful, I purchased locally and drove to the persons location to pick items up so I could look at there condition. I am very happy with my johnson.