Best Mercury Outboard Ever Made - 1984 50hp 4cyl

[CaptainDinghy]

Hey guys,

I've heard it said a few times before that the 1984(ish) model 50hp engine was one of the best outboards that Mercury ever made. Is there truth to this?

The reason I'm asking, is that I am considering repowering my boat with a larger outboard (boat is rated to 90hp) and I want to know what used motors to look for? If there is truth to the 50hp being a great motor, is it dumb of me to strap something else on in its place? Are the larger Mercury's of that vintage also a great engine or are there some to stay away from? Ideally, I would like to reuse all of my controls and wiring, so it's just a simple bolt on installation.

I saw a 1970's 85hp Mercury on craigslist recently, but I don't know enough history about the motors to feel good about it.

Does anyone have a historical breakdown of what Mercury outboards are "compatible" with one another?

Oh, and by the way... here's the gem I'm floatin' in!



Thanks!

 

[jimmbo]

How are you defining 'Best'? If you are by means of length of production, then yes. This engine goes back a long way, 1958 was the first year for the 44 cubic inch block, an enlargement of the 1949 40 cubic inch 'Lightning' engine, which was made of two 20 cubic inch 'Thunderbolt' engine blocks.

Mercury has made many engines of 2, 3, 4, and 6 cylinders based on common parameters of Bore and Strokes

The 1973 - 1977 85 hp used a 66.6 cu in 4 cylinder block utilizing the power ported pistons. this engine used the same pistons as the 6 cylinder 150 hp and the 3 cylinder 70hp of the era.

 

[Georgesalmon]

I have owned the "classic 50" and the mariner 45. Same engine. I'm one that will say it is one of the best motors ever made. For its time it was the quietest, best idling motor you could buy. For us fisherman it would troll all day with never a miss a beat and when time to go home it jumped up and took you there. Based on friends outfits I think it was pretty good on gas too.

 

[fishin98]

I had two of those POS motors, One on a flats boat and one on a 15ft Slyvan Sea Monster. Those motors had the early thunderbolt electronic systems. It wasn't if it is going to breakdown it was when. Was not until the late 80's until Merc got it right. I finally replaced the 50hp on the Sea Monster in 1999 with a NEW 40hp 4cyl Merc. It would run circles around the 50hp. Do yourself a favor look for a 1999-up 90hp 3cyl Merc, Great Motor,easy to do simple work on, easy on fuel. Had one on the back of my 2000 Bayliner, never spent a day in the shop, only down time was impellor replacement. Those 1980's Merc's gave Mercury a BAD rep.

 

[Scott Danforth]

It all comes down to maintenance. Yes, the 84/85 50 hp motors were good motors. Updated versions of the motors from the 60's and 70's Had a few of them in the family. Wouldn't call it the best. That may be a mark 7 hurricane.... Or maybe the mark 20b.....

 

[jimmbo]

I had two of those POS motors, Those motors had the early thunderbolt electronic systems. Was not until the late 80's until Merc got it right. I finally replaced the 50hp on the Sea Monster in 1999 with a NEW 40hp 4cyl Merc. It would run circles around the 50hp.

You had a 1967 or 68 engine? They were one of the most reliable engines back then. As for your 4 cylinder 40hp, I'll bet it was IDENTICAL to a 50hp from the 80s. Just a decal to allow for 'prop rating'

 

[fishin98]

The NEW 40 I had, was equiped with the NEW electronic package and the oil injection tank under the cowl. Both of my 50's were 83' and a 85' year groups both had those flimsy metal wrap around shrouds...say what you want...If you have a good one that works....be thrilled. As far as purchasing ANY 70's or 80's Merc...RUN FORREST RUN!!!! Just my opinion.

 

[flyingscott]

There is no best outboard made, only the one that you took care of and got you home most every time.

 

[roscoe]

Go ahead and replace it.

Yes its a good motor, but adding 20, 30, or 40 hp will make you Sylvan come alive.

A mid 90's motor won't set you back too much.
I would probably stick with 2 stroke, as your boat is extremely weight sensitive, try to keep the new motor weight below 300#.

270-303# motors would include all Mercury or Mariner 75, 80, and 90 hp 2 stroke models, from 1987 and newer.

The Yamaha 2 stroke 90 hp were only 260#.

 

[flyingscott]

This is mine, the hull is identical to yours but the Starcrafts for some reason are rated at 85 hp instead of 90 like the sylvans. I run a 1986 70 hp Evinrude I don't feel the need to put a 85/90 hp on this boat. With this set-up I get 39 MPH with a 15 hp kicker 3 batteries and 15 gallons of gas, me and the dog. By the way you have a beautiful boat that is great condition. I have always felt that hull and the 3 cylinder evinrudes were a perfect match JMO

 

[Chris1956]

Gee, how about a vote for the OMC Big Twin? There were probably more of those sold than any other motor in history.

 

[xxtavixx]

I have the mid 80's 50 hp - been great. Easy enough to work on, been very reliable so far and this is the second boat I'd have it on in ~15 years

 

[JimS123]

Gee, how about a vote for the OMC Big Twin? There were probably more of those sold than any other motor in history.

Now ain't that the truth. Second only to any OMC 3 cyl model.

Mercury never made a best motor. The old saying "Buy a Merc if you want to get there fast, but buy an Evinrude if you want to get back" held a lot of truth.

The best Mercs are the ones they sell now, since they started making them in Japan...

 

[jimmbo]

Mercury never made a best motor. QUOTE]

In the 50s and 60s they were far ahead of OMC engineering wise. OMC didn't get on par with them until the 70s, and that was only after Mercury's Chief engineer Charles Strang changed companies. Jump to 2016, I would buy and Evinrude E-tec before I would buy a 4 stroke Merc. But in the 70s, 80s and 90s, the best engines I owned were Mercs

 

[CaptainDinghy]

Thanks for all of the comments. What I'm struggling with is that I know this 50hp has been taken care of and I don't want to risk losing that maintenance history for a something with more HP, only to have problems with it. Are the larger HP 4cyl Mercury's of this vintage basically the same design just a larger block and/or bore? What is the largest HP 4cyl they made in these years?

I've heard that the 6cyl (tower of power) Mercury's had some cooling issues on the top cylinders. Is that true? I also don't want to add so much weight either, so I'm not too keen on the 6cyl.

I would love to repower it with something bigger, but maybe it's just not worth it on an old rig like this... maybe I just need to try some different prop and/or hydrofoil combinations to get better hole shot when loaded.

 

[CaptainDinghy]

This is mine, the hull is identical to yours but the Starcrafts for some reason are rated at 85 hp instead of 90 like the sylvans. I run a 1986 70 hp Evinrude I don't feel the need to put a 85/90 hp on this boat. With this set-up I get 39 MPH with a 15 hp kicker 3 batteries and 15 gallons of gas, me and the dog. By the way you have a beautiful boat that is great condition. I have always felt that hull and the 3 cylinder evinrudes were a perfect match JMO

Nice setup you got there! I'll get 29mph out of mine with 1 or 2 people and about 27mph with 4-5. I really have no complaints about my 50hp when its just two of us fishing. It's when we do a day cruise with 4-5 people that it really struggles. I'm finding that the 4 person day cruise is happening more often, so I'm just looking for ways to improve performance without having to spend a bunch of money on a new boat (that probably won't fit in the 3rd stall of my garage...haha).

 

[CaptainDinghy]

How are you defining 'Best'? If you are by means of length of production, then yes. This engine goes back a long way, 1958 was the first year for the 44 cubic inch block, an enlargement of the 1949 40 cubic inch 'Lightning' engine, which was made of two 20 cubic inch 'Thunderbolt' engine blocks.

Mercury has made many engines of 2, 3, 4, and 6 cylinders based on common parameters of Bore and Strokes

The 1973 - 1977 85 hp used a 66.6 cu in 4 cylinder block utilizing the power ported pistons. this engine used the same pistons as the 6 cylinder 150 hp and the 3 cylinder 70hp of the era.

I'm defining it by a reliable motor that doesn't have a lot of common issues. And also like Georgesalmon said above - a smooth idling motor that's fairly quiet for it's year. I've been very happy with mine, starts quick and easy, idles smoothly - I don't even have a trolling motor on my boat yet. Fuel consumption has been ok for me... So, I don't want to lose those characteristics if I would repower my boat.

 

[flyingscott]

Nice setup you got there! I'll get 29mph out of mine with 1 or 2 people and about 27mph with 4-5. I really have no complaints about my 50hp when its just two of us fishing. It's when we do a day cruise with 4-5 people that it really struggles. I'm finding that the 4 person day cruise is happening more often, so I'm just looking for ways to improve performance without having to spend a bunch of money on a new boat (that probably won't fit in the 3rd stall of my garage...haha).

I can sympathize looking for more power my boat originally had a 1993 yamaha 50 hp 3 cylinder on it. It was a wonderful motor one of the best I ever had but it was low on the power side when I loaded the boat up for fun. Best thing I ever did was putting the 70 hp on made a huge difference and good on gas. The only mercury I would say don't get is any of the 3 cylinder mercs in the 65/70 range from the 70s and 80s. I think they are cranky under powered outboards and the OMCs 3 cyl are heads and tails above them. I think the 80/85 hp 4 cylinders would be a good choice for your motor they are relatively smooth and reliable. The 6 cylinder mercs really only had a problem with cooling the upper cylinders cooling was mainly when the waterpump was neglected and not replaced.

 

[jimmbo]

The largest old style merc was the 66.6 cu. in. engine it was an 80 hp 1968 - 1972. In 1973 with the addition of the 'power ported' piston and block, became and 85hp. Then in 1978 it was relabeled 80hp, and in 1984 it was 'prop rated' as a 75 hp until its discontinuation in the late 80s.

In 1987 a 105 cu. in. block was introduced and eventually was made as a 100 hp, 115 hp, 120, and 125 hp. Totally different engine with loop charging and on some models a feature that leaned out one of the carbs so much that below approx. 1700 rpm, the engine was running on 2 out of 4 cylinders. These engines did not like being revved over 5500 rpm.

As for the 'tower of power'... In my eyes, with the exception of the 'dockbuster', Mercury did not make a bad 6 cylinder. Very smooth engine, good fuel economy, very wide powerband(courtesy of it being easier to tune the exhaust on a 3 cylinder engine than a 4. A 6 cylinder 2 stroke can be treated as two 3 cylinder engines on the exhaust side). The only times there were 'cooling issues' on the top cylinders were a very worn water pump, or the engine was being starved for water by too high transom height or overtrimming. The inline six usually weighed between 275 and 315 lbs.

In 1978 Mercury offered a 66.6 cubic inch 4 cylinder rated @ 80 hp, the also offered a 99.9 cubic inch 6 cylinder rated @ 90 hp. A 50% increase in displacement for only 10 hp. On the same boat the top speeds were only about 2 - 3 mph different, but the acceleration difference was very noticeable.

 

[jimmbo]

My last comment should have started out as The largest old style 4 cylinder merc...