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100hp merc what do you think

indy440

Member
"There is a 1971 mercury 100hp

"There is a 1971 mercury 100hp motor listed for sale locally for 600 dollars. Im thinking about buying it, what do you guys think of this motor? I think its an inline 6 but im not sure."
 
"run, run far away

1000 &#4


"run, run far away

1000 (100,0) 1518384 - 1665001 1963 6 cyl inline
1000 (100,0) 1665002 - 1755458 1964 6 cyl inline
1000 (100,0) 1755459 - 2318585 1965 6 cyl inline
1000 (100,0) 2318586 - 2484632 1968 6 cyl inline
1000 (100,0) 2484633 - 1969 "
 
"they made a 110, at least you

"they made a 110, at least you might find some spare parts, I would still run away, too old
110 2098352 - 2290662 1967
110 2290663 - 2508758 1968
110 2508759 - 2798056 1969
110 2798057 - 3002813 1970
110 3002814 - 3263262 1971
110 3263263 - 3482752 1972
110 3270367 - 9008003 1972 Belg.
110 3482753 - 3795657 1973
110 9008004 - 9041438 1973
110 3795658 - 4078999 1974
110 9041439 - 9068373 1974
110 4079000 - 4304784 1975
110 9068374 - 9101513 1975
110 4304785 - 4605111 1976
110 9101514 - 9126164 1976
110 4605112 - 4839253 1977
110 9126165 - 9165304 1977
soure=http://www.themarinedoctor.com/cgi-bin/YaBB.pl?num=1137539327"
 
thanks for the info!

Does t


thanks for the info!

Does that mean this probably has an old points ignition system? I hate points and have walked home because of them in the past (old snowmobiles)...
 
"One of the few positive thing

"One of the few positive things about points is that when they malfunction and cause a no start condition, they can usually be cleaned or adjusted allowing the engine to start and get you home. If an electronic ignition component malfunctions, there isn't very much you can do."
 
"Well you might get to them in

"Well you might get to them in a snowmobile, but hanging off the back of an early 60's Merc in a bouncing sea would not get you to the points on that motor. Those SOB's are hard to find when standing on the ground next to them, and to remove the distributor for service would at the least drop the cog wheel over board.

SO I echo the others- run and then RUN. These have a small value as a collector motor hanging off a mahogony runabout.

And $600. is about $500 to much."
 
"Awesome, thanks guys. I real

"Awesome, thanks guys. I really appreciate the info and I will not be buying the motor. I'll keep looking for something newer..."
 
I was waiting to get a serial

I was waiting to get a serial number from this guy to identify the engine. They told me they can't find the serial number but it has a "thunderbolt ignition" What does this mean?
 
"Merc has/had 4 different vers

"Merc has/had 4 different versions of the Thunderbolt ignition.

The earliest one T1 was also known as a Phelon ignition which was just a Magneto system with points/condenser.

The T2 was the one where they started putting "Thunderbolt" decals on the motor. This was also called a "Phasemaker" ignition and it still had points (but they renamed the condenser a capacitor - yipee)


The T3 was a modular CD ignition, so that the charge and ignition coils were mounted on a common base, but were still individual. And the system used a trigger, early switchbox with an external SCR (which took the pulse from the trigger and told the switchbox which plug coil should get the power).

The T4 started seeing service in the late 1970's and stayed as Merc's premier ignition system up until they moved to computer controlled ignitions (and is still used on the 50 and 90 horse two strokes sold outside of the US).

This ignition is the modern Stator (single component), Trigger, Switchbox and spark coils and basically after the late 70's, because it was near perfect, it was never changed.

Merc also horsed around with a CDM ignition system (mostly on 3 and 4 cylinder models) for a while, but it never really took hold.

If you are looking for an excellent motor in the 100 horse class you should set your eyes on a 3 cylinder 90 horse Merc, 1985'ish or newer.

The older 100 horse used a different rating system, so by todays standards only put out about 90 horses.

The earlier 90 models put out close to 100 (until the EPA made the mfgs tighten up their emmissions), and the best part is, as I stated above, the 2 stroke 90 is still in production - here in Canada I can walk into a Merc dealer and buy a "brand new" model - so parts support is 100%.

Merc has a few models that were very prolific and tended to be fairly trouble free (with regular maintenance) - in the size you are looking at, the 90 3 cyl and the 135 V6 come to mind immediately.

I would stay away from the 115/125 inline four's that have the funky 2+2 CDM ignition, not because they are particularly bad, but they are a "quirky" motor that never (seem) to run "quite right"


And if you don't limit your options just to Merc's, there are others out there in the higher horsepower that were very decent engines. I'm pretty much a Merc guy, but my biggest motor is V4 OMC Looper (140 horse) - why? Couldn't find a 135 Merc for what I wanted to spend and considered that "the next best thing in that size"
"
 
"you are a wealth of informati

"you are a wealth of information.

I have not been limiting my options to merc only, its just what happened to pop up on craigslist... I will continue my hunt for a larger outboard...

I really appreciate you taking the time to explain all of this to me."
 
"In your search, I would stay

"In your search, I would stay away from older 4 strokes, used 4 strokes are a gamble at best, because if they are not maintained "exactly by the book" they quickly turn into junk.

The exception to that would be the Honda's. But Honda also discontinues parts when they discontinue a model, so an older one could be an issue.

If you stick to the big 3 - OMC/Merc/Yami, pretty much anything built from the mid 80's on is decent (although there are some exceptions).

You are definately going about it the right way. Find something and get an opinion. Even before I bought my OMC, I popped over to that board and asked Joe/Morten/JWB their opinion - it's best to ask the guys who know the problems/quirks for whatever you are looking at - could save you many a wasted dollar...

Good luck, and do stop by again.."
 
"I actually just bought the bo

"I actually just bought the boat last week. Its a 1981 Glastron 167 with a 1987 merc "classic fifty", which is apparently only rated for 45hp. Im already looking for a larger motor because im worried about being able to plane-out with more than two people in the boat. I havent even used the boat with the current motor yet, the first trip out is scheduled for tuesday night. There will only be two of us in the boat so it'll give me a good idea of how the 50 preforms. I went ahead and ordered a set of "smart-tabs" figuring they will help me plane more quickly. They wont be in until mid next week so the first trip out will be without them. I'll update this post after trying it out with the current setup."
 
"Good rule of thumb, power the

"Good rule of thumb, power the boat with 80% of the max horsepower rating.

That will give you optimal performance and the best fuel economy.

When you try it out with the 50 (40 with the reed restricter removed), consider another rule of thumb - a 50% increase in horsepower translates roughly into a 15% increase in top end performance.

So say you get 25 mph out of the 50 - moving up to 75 would give you an extra 3-4 mph.

More displacement gives you more low end torque (among other things), so if you are considering a family of motors (40/50/60 usually share a powerhead) the 75/90's would be the next largest displacement, so moving from a 40 to a 60 would produce a minimal gain, but moving up to a 75, while it wouldn't make an super top end difference, it would noticably improve the lower end, compared to the 40, 50 or 60.

I can't find a max hp listing for your boat, but it's dry weight is 850lbs, add the motor (200-350 depending on the hp), plus a couple adults, and associated "stuff" and you could be looking at a displacement weight of 1700 lbs - at that weight I would be looking at (min) 75 horses, or more probably a 90 which should allow the boat to perform as designed and maybe get you into the mid 30mph range at full throttle..."
 
"What do you mean 40 with the

"What do you mean 40 with the reed restricter removed?

The boat is rated for 120hp according to the tag.

I'd love to find a 90hp for it, I think that would be about ideal for the boat and how I intend to use it. I'd be quite happy with 35mph while loaded with 4 people..."
 
"This isnt my first boat BTW,

"This isnt my first boat BTW, I used to have a 1996 SeaRayder jetboat with the 3-cylinder 2-stroke 90hp mercury motor. That was an incredibly fun boat but it didnt get used much because of life at the time. Its been a few years so I figured I'd give boating another go and wanted to get started cheaply. As long as boating fits our family as well as I hope we'll spend some $$$ and get a bigger/nicer/newer boat."
 
"The difference between the 40

"The difference between the 40 and 50 Merc was simply the carbs and a reed retainer. When you remove the reed retainer from the 40 and replace it with the reed stop from a 50, you get a 45 horse motor (without changing the carbs).

Since guys were doing it anyhow, Merc simply did it themself and called the model a "Classic 50" - which produced the same horsepower (45 shaft horses) as earlier 50 horse models which were rated in BHP (Brake Horse Power).

So if you have a 3 cylinder 40, you can turn it into a "Classic 50" by replacing the three reed retainers with $3 reed stops (so for less than 10 bucks you gain 5 horses - not that you will notice any improvement, but you get that psycological rush from "upping" the horsepower)...."
 
Lost me on the 3- cylinder mer

Lost me on the 3- cylinder merc 40. And reeds are round the crank on those early ones. We used to jump those reeds by just bending the stops up about .010 inch. Had to watch the crank throw and how good the reed tips were.
 
"Just in the last 20 years, th

"Just in the last 20 years, the 40 Merc has come in a number of different designs.

After a few years with no 40 Mercs in production (the era of the Yami/Mariner 40's), in 1989 Merc began producing a 4 cylinder, 40 horse model.

There was a twin 40 that was introduced for the 1995 model year change that lasted for a bit.

After a couple years of producing the twin again, they scrapped that and went with a 3 cylinder model which shared a powerhead with the "new" 50, 55 and 60 horse models (which had been a 3 cylinder before, but now used the slightly larger displacement 59 cu in powerhead, instead of the 52 cu in which previously saw service).

It was that model that could be upped to 45 horse by removing the reed retainer that came on the 40 and replacing it with the reed stop from the 50 (could do the same with the 30 horse twin in the early 90's which shared the 40 twins powerhead).

All the models I'm referring to have the reeds directly behind the carbs. You have to go back prior to 1983 to find a 40 with the reeds on the dognut around the crank."
 
"And James, I meant you could

"And James, I meant you could make your own classic 50 for about 10 bucks if you had a 3 cylinder 40.

I was referring to the horsepower, not the specific model itself..."
 
"Heres another question unrela

"Heres another question unrelated to the original topic of this thread. My classic 50 is not charging the battery. I see there are three wires coming out of the motor (not going up to the controls) with a plug on the end that is just hanging out in the hull, not plugged into anything. I assume one of these is my charging wire. There is a black (or maybe brown), white, and purple wire, Im at work right now so those colors are just from memory... Anyone have a wiring diagram for it? Its a 1987 model."
 
"If it's not charging you

"If it's not charging you probably have either a bad rectifier or the battery is shot.

The battery is charged through it's own wires, you don't connect an extra one.

There will be a hot lead (red or sometimes yellow) going from the 3rd post on the rectifier over to the starter solenoid connected to the same post as the positive lead from the battery - thats how your battery gets charged.

This model originally came with "auto-blend" and believe the little harness you mention was for that. The purple is the lead for the warning horn, the black is a ground and can't remember what purpose the white wire served."
 
"I found a diagram online and

"I found a diagram online and you're right about the auto-blend, thats what that pigtail is for. I will take a look at the rectifier tonight and see if someone messed with the wiring.

I know the battery is good, its almost new and has only been used in my camper one weekend. I hooked everything up and also put a multimeter on the battery. It read about 12.50 volts, I started the motor (voltage dropped of course). Once it was running I expected the voltage to jump up over 13. BUT, now that im thinking about it... I never revved the motor, maybe at idle its not putting out enough power to bring the voltage up to a charging amount?

Im taking the boat out tonight and will bring the multimeter with me.

While we're on the subject, where should the idle be set? 1200rpms?"
 
"If the motor was ever run WIT

"If the motor was ever run WITHOUT a battery connected, the rectifier will fry in pretty short order.

A rectifier simply converts the AC produced by the charge coils to DC, it doesn't regulate it at all - that's the job of the battery (which is why a marine/rv battery should always be used - a normal auto battery will do the job but it's life will be short).

Anyhow, if it's doing what it should, you should see about 13.5-14.5 volts if it's charging right. You can see higher, upwards of 16, because it is unregulated power and that would not be considered a "problem" necessarily.

But also as you note, at idle it doesn't put out very much power at all - maybe an amp, so just a "trickle charge".

The 4 cylinders should idle at 600-700, in forward gear, under load. So if you have it on muffs or in a barrel, about 850 would be about right.

If you are just running on muffs however, don't rev it right up to check the charge circuit. A hose can't supply enough water for much more than a fast idle - you could smoke your impeller or even overheat the motor itself."
 
At least I can run it even wit

At least I can run it even without charging the battery. Its a fairly large deep cycle so Im sure I wont kill it in an hour long test run...

I'll bring the multimeter tonight and test it out in the water...
 
"ok, I got the boat out tonigh

"ok, I got the boat out tonight and it ran with no break downs. However, im not sure it ran properly. Two of us hit a whopping top speed of 21.5mph. My tach was not working properly, it would only go up to 4000 and I know the motor was spinning faster than that. It would seem to work fine, then hit 4k and stop even though the motor was still reving higher. I think max speed for the motor is 5500. I have no idea if it was going that high.

I also think maybe the carbs need to be cleaned because if you went wide open it almost felt like it was bogging. Max power was just back a little from wideopen. I checked the plugs and it was running on all 4 cylinders.

I also think a compression check is in order."
 
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