1987+ Merc 70/80/90hp variances?

[100333624]

Hello all,

I'm looking at purchasing a 1987-1990 Mercury 70 or 80 hp, these are the models where merc basically upped the displacement from 66.6 to 71.1 cu in and I was just looking through my manual and it shows the 70, 80 and 90hp models all are 71.1 cu in from 1987-1989, then in 1990-1992 they dropped the 70 and 80 and made 75 and 90hp models also at 71.1 cu in. What are the differences between these motors? Mainly I am looking at a 70 or 80hp to replace my 1978 merc 800 with power trim. I also want to know what the weight difference is (if any) compared to my current 800 with power trim? I believe my current motor is weighing in around 260 lbs but I'm not sure.... And I read somewhere that these later 70 and 80 hp models weigh in at 265 lbs? Can anyone verify this for me PLEASE as I am already slightly over powered and don't want to add too much extra power/weight...

The 70 and 80 are both the same in my book, same bore, stroke, 3 cylnders, rpm range, spark plugs, carbs and firing order... but one is 70 and one is 80, how is this possible??? My book also shows the 80 and 90 being the same except the rpm range for the 90 is 5000-5500 as apposed to the 4750-5250 for the 70 and 80hp models so something must be different on the 90...? But it also shows that the 80 and 90 hp models are both actually 80hp? I am so confused and don't understand why mercury did such a thing??? Are they trying to confuse or trick people or is there really a difference here because from what I see these motors are EXACTLY the same? So much confusion can anyone shed some light on this please???

THANK YOU!

 

[Laddies]

Re: 1987+ Merc 70/80/90hp variances?

Carbs, reed valves and tuner pipe, same weight

 

[Faztbullet]

Re: 1987+ Merc 70/80/90hp variances?

The 70/80 are the same motors only carbs are different, on the 90 the port timing and carbs are different same on the big bore motors..

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

Ok thanks guys!

What do you think of this?

Priced for quick sale, 1987 80 HP Mercury Outboard - Ontario Boats, Watercraft For Sale - Kijiji Ontario Canada.

I am interested in this one and have talked the owner down to $1500, but try renegotiating for $1400 when I go and check it out. It looks absolutely fantastic for what it is, practically new. Good deal? Anything I should pay attention to or check when I go see it? He will start it up for me on muffs....

Thanks!

Nick

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

Nick,
Had one just like it (actually 2) just parted out a 1987 70hp, and I once owned a 1987 90 hp. The motors are lightweight and offer some nice punch for a 3 cyl motor.

You guys are so lucky up north. Down here in Florida you would never find a good clean motor (of that Vintage) for the price. It would generally be a rust bucket. From my experience with those motors, I would check the stator wiring and trigger wiring for rot. Give all the electrical system an inspection checking for broken, cracked, or missing insulation from various wiring around the powerhead. I would perform a compression check if you can. Remember, repair parts for these motors are obsolete from the dealer generally. Some of the common parts are still available, but try finding an oil pump or something like that!

One final thing. Pop the lower unit screw on the lower unit and check for water intrusion by fluid color.

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

Nick,
Had one just like it (actually 2) just parted out a 1987 70hp, and I once owned a 1987 90 hp. The motors are lightweight and offer some nice punch for a 3 cyl motor.

You guys are so lucky up north. Down here in Florida you would never find a good clean motor (of that Vintage) for the price. It would generally be a rust bucket. From my experience with those motors, I would check the stator wiring and trigger wiring for rot. Give all the electrical system an inspection checking for broken, cracked, or missing insulation from various wiring around the powerhead. I would perform a compression check if you can. Remember, repair parts for these motors are obsolete from the dealer generally. Some of the common parts are still available, but try finding an oil pump or something like that!

One final thing. Pop the lower unit screw on the lower unit and check for water intrusion by fluid color.

Definitely! I come across very good condition motors often (1970s +) and I had an old 1969 9.8 merc that was in 10/10 condition that I bought from the original owner though I sold it few months ago, never seen one in that shape nor will I ever haha..

I appreciate your feedback, I will be sure to check the wiring as I have noticed cracks and whatnot all over my old 80 hp. I will also try to have a compression check done although I have never done one before, I know there is a guide on here somewhere that I read a few months back about how to go about doing one. From talking to the owner, it seems like he religiously takes care of his stuff so I'll see just how clean this motor is, hopefully its as nice inside as it is on the outside.

Water intrusion in the lower unit would usually turn out murky yellowish, like a creamy color right? As far as I know he only had one problem with the motor when he bought it brand new, some wiring problem on cyl 1 spark and mercury replaced the wiring under warranty. When I asked him how long it sat and when the last time it was used, this is what he told me in our last email conversation:

"I’ve run it every year including last fall, no leaks, fuel lines disconnected before shutting off and fuel run dry, carbs fogged as gas is run out. I also changed the bottom end oil every couple of years including last fall. No gunk in carbs as no gas was allowed to sit in them. I also pulled the spark plugs and sprayed WD 40 into the cylinders. The wire was replaced under warranty (factory defect) and I haven’t had any problem since. No fuel pump to worry about."

Do you think this is a good price is everything works fine?? I am debating between the motor discussed here, and a completely rebuilt 1986 Mercury 75hp 4 cyl, which is basically the exact same motor I got now (1978 80hp). But the owner of this one buys and rebuilds motors so I kind of trust him a bit more. He has about 30 motors currently at his house for sale! This 75hp he rebuilt he spent about 50 hours rebuilding and working on it. Its got oversized pistons in it, and is in great shape but hes asking $1800 because he put $1500 just in parts into it. So it all comes down to which is the better motor/deal.

What do you think??

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

One thing I forgot to add:

How is the oil injection system on these motors? I hear a lot of people removing them due to failure... Is it recommended to remove it and just use premix?

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

I like the price of the motor if everything is cool. I was looking at a cherry 1989 75 Mariner in Virginia for $2500, so your is a great deal if it is solid. The mid-range 2 stroke engines are getting hard to find because of high demand (from guys like us)

The 3 Cyl Merc/Mariners were a powerhouse considering their weight. I think they weigh in at about 275 Lbs with the oil tank. My Johnson 90 (V-4) weighs in at 350 lbs, so there is quite a difference. A lot of people started mixing their gas when repair parts became obsolete for this motor. Truthfully, I never had an oil pump failure with my motors, but it does not mean it can't happen. Pre-Mixing your fuel takes out the guesswork or worry. Like I said, some NEW repair parts are impossible to find with this series of motor. The everyday stuff is still readily available.

Mercury/Mariner still had wiring issues during this time. Some people blame it on the HEAT of the engine, some people blame it on WD-40 (or something) people use to spray down their engines.....but wiring rot is very common. Again....not a deal breaker (to me) because all these parts are still available in the aftermarket. Be sure to check all the wiring coming from the stator and trigger.

Just pop the bottom lower unit screw and check for water. Milky or Grey is no good. BLACK is OK because it just means the fluid is dirty and needs to be changed.

One final issue with this series of motors. Does it have trim and tilt? Tilt the motor up and look at the trim cylinders. Are they leaking? Is the motor "leaking down" as you watch? Do the motors and pumps sound smooth as the motor travels up and down? T&T units on this series are difficult because NO ONE want to work on them, and parts are obsolete.

Man I hope I don't sound too negative on a $1500 motor. I loved my old Mercs, but I did learn quite a few lessons as I tried to service them over the years. Hopefully you will get a good one. Good Luck.

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

Oh, by the way. The first outboard motor does indeed have an engine mounted fuel pump.

The second motor (86 75 hp) is a real screamer too. This was the last year for Mercury to make this 4cyl design, because the redesigned 3 Cyl motors came out in 1987. This is a Mercury "Band" motor, and it is a little harder (for me) to work on. The whole design seems to be more cramped up; however, there are Mercury guys on the forum who love the old towers of power. Personal choice I guess.

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

Oh, by the way. The first outboard motor does indeed have an engine mounted fuel pump.

The second motor (86 75 hp) is a real screamer too. This was the last year for Mercury to make this 4cyl design, because the redesigned 3 Cyl motors came out in 1987. This is a Mercury "Band" motor, and it is a little harder (for me) to work on. The whole design seems to be more cramped up; however, there are Mercury guys on the forum who love the old towers of power. Personal choice I guess.

Ya I know, and that 1986 75hp is the last year of 75/80hp in 66.6 cu in displacement also because the 3 cyl version that took over was 71.1 cu in right. This is such a hard decision I like both of these motors, and I dont know what I'm gonna do.... With the 1986 I wouldn't notice too much of a difference since its the same motor as my current 78 80hp 4 cyl, but it sure looks and sounds nice, not to mention the self contained trim unit in the transom assembly! I like that fact that both motors have newer trim than mine so I don't have to mount the trim motor inside the boat, and no messy leaking lines anywhere....

The 3 cyl 1987 80hp must perform better since it is a bit bigger in displacement ya? Are they are smooth as the 4 cylinder ones?

Also what do you mean by the 1986 4cyl being a Mercury "band" motor? Heres some pictures of the 1986 motor...

 

[emckelvy]

Re: 1987+ Merc 70/80/90hp variances?

The 3-cyl won't idle as smoothly as the 4-cyl, but the 3's aren't that bad. A buddy of mine had a 90hp triple on a 16' Tahiti-style hull, and it ran just about as strong as my old Merc 100hp Six, but used a lot less gas. A little shaky at idle but smoothed right out under way. Very, Very quiet compared to the older motors.

Both motors are rated at the prop, so yeah the 3-cyl should have a bit more guts but should still be pretty easy on gas. The oil injection system has it's pros & cons, the problem areas I've seen are not necessarily with the pump but the external bits. The oil alarm float in the tank has a magnet glued to it, which triggers a magnetic reed switch. Very common to see the magnet separate from the float & fall to the bottom of the tank, causing a constant alarm. Only fix is to replace the tank. The alarm module can be troublesome as well, I've replaced more than a few of those.

The 4-cyl is an older, less-sophisticated, but proven design. Almost Stone-Age but the last year's production run did benefit from all the refinements Merc made over the years.

The biggest caveat on the 66-c.i. Four is that there is no thermostat, so it tends to run cool. This will wear the cylinder walls unevenly over time. Thus the oversize pistons in the rebuilt 75hp.

So, if you're fishing and using the big motor to idle all the time, it's probably not the best one for that application. If you're cruising or doing watersports, no problems there, she'll get warm enough at speed and under load.

The 3-cyl does have a "modern" thermostat design with spring-loaded poppet relief valve. So it'll get nice and toasty for a "cleaner" idle.

The biggest issue I see is that you're looking at a 26-yr-old motor whose internal condition is unknown, vs. a 27-yr-old motor which has been rebuilt.

That, rather then the sophisticated design or lack thereof, might be the deciding factor, since both motors are pretty close in price.

You might get lucky with the 3-cyl and find it totally reliable, but spending good money on a used motor is pretty dicey if you can't do more than just run it on a rack. It would be far better to be able to test it underway, any faults become evident pretty quickly.

If you take a hard look at the 3-cyl, definitely do a compression check and if it's not perfect, I'd think twice about it. Certain models of the Big Threes and Fours had a problem with the pressed-in cylinder sleeves rotating, this is a very expensive repair. Any compression readings significantly higher than the others should be suspect, a friend of mind had a 135hp V6 with very hi compression in one cylinder, turned out the sleeve shifted. Very Strange Indeed!

BTW the "band" comment probably refers to the fact that there was very little difference in the old Fours and Sixes except for the color of the stripe or "band" around the cowling. Thus, my old 1350 Merc (what a Screamer it was!) was a "Red Band" model, which made the year pretty easy to pinpoint.

HTH & let us know which one you decide on........ed

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

Thanks Ed. That is a lot more information than I could give him.

By "Band" motor, I was refering to the metal band which surrounds the motor. The 1987-1990 models had a clam shell type cowling which opened to allow access to the motor itself. And you are correct. The 70-80 90 3cyl models had a a completely self contained oiling system, and the 86 75 had a seperate oil tank design.

Both motors are close in price, so it may be a toss-up. Personally I like the rebuilt idea as long as it was done correctly.

 

[emckelvy]

Re: 1987+ Merc 70/80/90hp variances?

If the '86 75hp has the auto-oil mixing 6-gal inboard tank, I'd throw it away! Those are notoriously unreliable.

Far better to just do pre-mix.......ed

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

Thanks for all your help guys but the deal for the 3 cyl 80hp is off...

I wasn't aware that the 1986 4 cyl 75hp motors had internal oil tanks??? I thought it was the 3 cyl models that had that 1987+ no??? I didn't see any oil tank in it when I checked it out, it looks exactly the same as my 80hp merc, but with newer wiring, coils etc.. Newer power/ignition plug in the motor (internal) and not the big old external plug on mine. Self contained trim unit and not the big old external trim motor that mounts in the boat with 4 hydraulic lines...

My only other question and concern about the rebuilt motor is that its the 2nd rebuild. Does that make a difference? He said it had oversized pistons in it already, and they were in good condition including the cylinder walls... But I haven't asked why hes rebuilt it in the first place.... I will be sure to find out, what else should I ask to find out about this? I trust him as someone who rebuilds these things as hes been doing it for a while. How could I tell if its been "properly" rebuilt or not? What are the signs to look for? The motor has only been started once or twice since the rebuild, then the carbs were removed and rebuilt as well and hasn't been started since they were installed so when I go check it out before I buy it, it will be basically the first run on muffs. What should I be checking for as this is a completely rebuilt motor and I am not at all familiar with diagnostics for rebuilt/new engines. I will be sure to check the above mentioned things but anything else additional to this as it looks like this is the motor I'm gonna be getting since the other deal failed..

Nick

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

Nick, the 1986 75 had a remote oil tank...not built in. The design change came in 1987 with the 70-80-90 models.

 

[Faztbullet]

Re: 1987+ Merc 70/80/90hp variances?

How is the oil injection system on these motors? I hear a lot of people removing them due to failure

The oil injection rarely fails on these engines, it the V-6 motors that the most problem....

He said it had oversized pistons in it already,what else should I ask to find out about this?

What size was it bored to?,was main jets increased?was impeller and t-stat replaced? what failed on originally taht required it to be bored? was it a ignition /electrically problem and was it addressed/repaired?

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

Thanks for all the great info guys! I will try to find out the rest of the info on the rebuilt motor as far as what had failed and why it needed a rebuild... I am not sure if this motor has an oil tank, nonetheless I'd rather not take chances with the oil tank and premix instead, no headache to deal with.

The motor is going to be used for fishing/boating basically but I don't idle a lot when I fish. I start, go and stop. I have an electric trolling motor to do the rest... As for the rebuilt motor, how do I know it was rebuilt PROPERLY? What do I look for when I go to test it out? It's going to be tested on a stand with muffs so its not like its going to be on a boat.... Since its rebuilt I guess theres no point in doing a compression check, or is there? Check for spark? Check lower unit oil and check for water? Anything else I need to know??? What if it leaks dark oil and water from the prop like my current one does after it rests for a few hours? Is that normal for oil to come out of the exhaust at the prop as well as with water?

He has a video of it so you guys can check it out on youtube at:

75 hp Merc 1986 with power trim rebuilt - YouTube

the video was taken when it was just rebuilt. He has now rebuilt the carbs after the video was taken and it has not been started since. The video was recorded this past December so it was a very cold start! What do you guys think? I have my heart set on this motor!!! hahhaha....

Nick

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

You guys up North are so lucky. A nice, clean older motor like this one are extremely rare down here in Rust/Corrosion country. Plus, I guess your motors are only used a few months of the entire year....which means are they probably low-time motors. I went all the way to Kentucky (where my Dad lives) to purchase my motor....extremely clean.

 

[100333624]

Re: 1987+ Merc 70/80/90hp variances?

Yes we can only really use our boats from april/may to about october/november. I find a lot of motors roughed up more so from people neglecting them more than water/weather wear. It isn't difficult to come across a very nice condition motor with barely any rust or corrosion. This 75hp has no rust on it from what I saw when I checked it out, it is surprisingly super clean for a 1986. My 1978 on the other hand.... don't even get me started! I had to change a swivel pin assembly and yoke because it was so corroded the teeth were completely stripped off!

There are quite a few people around here who rebuild these old motors, including stripping them down and repainting/re-decal them. They go for around $2500 and that usually includes rebuilt trim pumps with SS hydraulic lines. I saw some last year and I couldn't believe how pretty they were, just like they came out of the factory!

 

[TD_Maker]

Re: 1987+ Merc 70/80/90hp variances?

Yeah, good two stroke motors are getting hard to find...especially in the mid range. Good news is that more and more people are going to 4 Strokes, so motors are coming on the market slowly. Hopefully you will learn how to work on your older motor, because it is getting very difficult to find a mechanic who actually knows how, or WANTS to work on these old motors.

Your motor looks and sounds good. I would mix your fuel 50/1 and call it a wrap, plus your existing controls should hook right up...another big plus.

Good Luck