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Author Topic:   Classic Mercury 115/125 HP
buddy79 posted 03-25-2004 12:20 AM ET (US)   Profile for buddy79   Send Email to buddy79  
Had question in marketplace about my 4-stroke 90 on my Monauk since I was thinking of doing the 115 4-stroke. Somebody mentioned the 115 mercury 2-stroke and I noticed the mercury 125 2-stoke classic was still inside the weight and was actually less money at edsmarine online. Would it be difficult to change to 2-stroke? Anybody know about the 125 classic mercury? I'm not worried about overpowering the boat, my dad had 19' Allison with Black Max modded mercury that was clocked over 100 and was every bit as scary as you might think. I'll just take off the decals. Thanks for your opinions :)What kind of speed do you think I could get with 125 2-stroke?
jimh posted 03-25-2004 08:51 AM ET (US)     Profile for jimh  Send Email to jimh     
The 115/125 HP Mercury "Classic Carbureted Two-Stroke" outboard is a 113 cubic-inch displacement in-line 4-cylinder engine.

It uses the same bore and stroke as the 90-HP, 3-cylinder engine. It weighs about 45-lbs more than the 90-HP, has a taller cowling, and is otherwise quite similar. There are two significant differences, however.

The 115/125 engine is designed to run only on two cylinders at lower speeds, and shifts to four cylinder operation when the crankshaft speed gets above about 1800 RPM. The engine will be running on just two cylinders at idle or trolling speeds, so it may not be quite as smooth as one would anticipate. I really don't know precisely how it idles; I don't have one.

The low speed operation on only two cylinders probably saves gasoline if you are doing a lot of fishing or trolling.

The shift from 2-cylinder to 4-cylinder operation is accomplished in a rather crafty manner, and does not rely on anything exotic. The two cylinders that are cut off are fed with carburetors that do not have idle jets. At low speeds the venturi effect does not have enough force to pull fuel from the high-speed jet, so those cylinders do not get fuel. Once the engine spins up to higher speeds these cylinders come alive and start getting fuel. The engine shifts from 2-cylinder to 4-cylinder operation. I believe that when this happens you could say it really "kicks in."

The other difference from the 90-HP 3-cylinder engine is that the 115/125 HP engine has a lower maximum speed. Mercury recommends holding the wide open throttle (WOT) speed to 5250 RPM maximum. This may be in part to the inherent in-line 4-cylinder design. My understanding of engine design is limited, but I believe that there are certain problems in vibration with any in-line 4-cylinder engine. To counteract these vibrations some engines employ balancing weights on the crankshaft. I do not know for certain if the 115/125 has or does not have these weights, but inasmuch as they are not mentioned and the engine has a rather low maximum speed, my inference is that these models to not have balancing weights on the crankshaft. Or, if they do, it is still advised not to run the engine over 5250. You could conclude that perhaps there are balancing weights and they are the reason not to rev the engine too high!

As for the general reputation of this engine, I will add this anecdotal data:

My local Mercury dealership is owned (in partnership) by a fellow who began in the marine business as a mechanic. I mention this so that when later I tell you that "my dealer said..." you understand that this dealer did not get into the marine engine business after his coin-operated laundry business failed, or his bowling center burned down. This dealership is owned by a guy who is also an experienced outboard mechanic and has all the Mercury "master mechanic ratings."

I have been talking with him lately about buying some engines, and I have been leaning toward buying a pair of the 90-HP Mercury "classics." He keeps trying to talk me into the 115-HP versions. He says they are very good engines and would be a real "rocket ship" on my boat. And his current master mechanic out in the shop agrees. He likes them, too.

So there you have it, a description of the engine, and an endorsement with some background on the endorsers.

I am sure others will have some comments on these engines, too. I think Clark Roberts has had one of these.

jimh posted 03-25-2004 08:56 AM ET (US)     Profile for jimh  Send Email to jimh     
Also, a colleague has one of these engines (115 Mariner) on a 17-foot fiberglass fishing boat. He reports WOT speeds of 50-MPH and is generally enthusiastic about the engine, although he did have to replace a stator on it a couple of years ago. The stator assembly was about $275 and he did the installation himself.

I am certain that on a 170 MONTAUK this engine would be quite fast, and might approach 50-MPH also.

jimh posted 03-25-2004 08:59 AM ET (US)     Profile for jimh  Send Email to jimh     
I don't know how the controls and gauges would match up with your current set up, but I would guess that if you currently have Mercury controls and wiring harness, it should be a simple job to switch to a different Mercury engine.
bwmenemsha posted 03-25-2004 09:31 AM ET (US)     Profile for bwmenemsha    
Hi...don't mean to jump in on your conversation but my ears could not help but perk up at Jimh explanation of the merc115 classic. l am strongly considering repowering the SHA from the 90 h/p johnny and tho never having been a big fan of the merc's l wonder if l have cut myself out of large corner of the market. Jimh certainly seems to consistently present a valid presentation and probably could convince me that donkeys could fly...well, not really, but you know what l mean.Now l geuss l am willing to expand my horizon's and look at them...the 1st place l went was this similar to what you were talking about or could you point me in right direction.....(1991 Mercury 115 HP, 2-stoke outboard like new Item number: 2469666624 )...sorry l don't know how to hot link it. Thank you Buddy and Jimh.

Marlin posted 03-25-2004 12:21 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Jim, your description of how the 115 2-stroke runs on 2 cylinders is interesting. Excuse me if this has been discussed at length before, but wouldn't this bring up oiling issues? If there's no fuel drawn from the carb, then there's no oil in the cylinders, and yet they're still moving at normal speeds. Seems like long periods of idling might not be a good thing for this engine design?


LHG posted 03-25-2004 12:37 PM ET (US)     Profile for LHG    
In this 4 cylinder Mercury 2-stroke design, I would go with the 125 HP version. For some reason, it is disproportionally stronger than the 10 HP indication over the 115 model. The 3 cylinder Merc 90 can almost run with the 115 on lighter boats, but not with the 125. At 348#, it's 11# lighter than the Suzuki 4-stroke 60, and 40# lighter than the Merc 90 4-stroke!

As mentioned, on the 190 Nantucket tests by BW, this engine is 4 mph faster than either the Merc-aha 115 4-stroke or the new 115 Optimax, much to my surprise, I've got to say. A 170 should be screamer with the 125. Be sure to mount in 3 rd hole and run a Laser II prop. The fact that it puts out this HP at much lower RPM (5250 vs 6000) means a lot less running noise and piston travel, which should translate into incresed life.

It's simple to rig, needing no additional oil tank, so a conversion from 4-stroke to this should be simple and clean.

Clark Roberts posted 03-25-2004 09:34 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Bob, there is a small orifice which allows enough fuel to the disabled cyls. to sufficient oil. Also the idle of these engines (on two cyls) is amazingly smooth and quiet. Like LHG said, the 125 is very strong and the 115 is not quite as fast on a light boat as the 90hp 3 cyl running at 5500-5600 rpm. and properly propped. The current 75,90,115 and 125hp engines share most mechanicals and differ only in no. of cyls, gear ratios , timing and jetting. These are very rugged and dependable engines and I have had a few 90's and a 115 and know others who have the 75 and 125 variants. My favorite of the bunch is the 3 cyl 90 which does everything very well. Happy Whalin'... Clark... Spruce Creek Navy
Marlin posted 03-25-2004 10:55 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Clark, thanks for that info. My last 2-stroke outboard was an ancient Evinrude 9.9, and I'm quite at home with my new 115 4-stroke with its crankcase oil, dual overhead cams, EFI, etc. Just like all those cars I've been working on, though someday I'll have to figure out how they handle the connecting rod journal oiling...


buddy79 posted 03-25-2004 11:32 PM ET (US)     Profile for buddy79  Send Email to buddy79     
Thanks for the help. Could someone help me understand this whole EPA thing? Someone told me if I were to buy a new '04 Mercury 125 classic I would have to remove it by '05 or '06 since it is non-emission compliant. Surely this is not the case. Thanks.
jimh posted 03-26-2004 09:31 AM ET (US)     Profile for jimh  Send Email to jimh     

The manufacture and sale of "high-emission" outboards is prohibited on a schedule beginning in 2005 or 2006. The use of "high-emission" outboards is not generally regulated by any federal law.

There are many local laws which regulate use of outboard motors on particular bodies of water. For example, certain lakes may ban motors above a certain horsepower.

You should check with local authorities about the bodies of water you plan to use to see if there are any restrictions on them. In general, only a few lakes in the state of California have restrictions in place or planned which would affect use of engines not meeting certain low-emission standards.

When you complete your research into this topic you may wish to post your findings in a separate article, as this current thread is focused on the design, construction, and performance of a particular outboard engine, and a complete discussion of EPA air and water pollution is really beyond its scope.

jimh posted 03-26-2004 09:34 AM ET (US)     Profile for jimh  Send Email to jimh     
This is funny, but on recollection my dealer has been trying to talk me into the 125-HP engines (not the 115-HP engines I mentioned above). In light of the recent comments, perhaps there is more to that recommendation of the 125-HP than I first understood.

Thanks Clark and LHG for your comments.

bwmenemsha posted 03-26-2004 09:36 AM ET (US)     Profile for bwmenemsha    
Was my question was to dumb to get an answer? Or not formated correctly?
LHG posted 03-26-2004 01:09 PM ET (US)     Profile for LHG    
BW - Yes, be sure to look at Mercury for your re-power options. I think the 90's, 115's and 125's are great 2-stroke products. I remember someone at BW saying how amazed they were at the performance of the 115 on the new Nantucket. See JimH's article on BW's performance comparisons on the boat.

As for your e-bay question, I would try to find a used one with the one piece bucket cowling as opposed to the earlier split cowling models, first brought out in 1989. I think the 1991 still had the split model. Somewhere in this period, the cubes were increased on the 75/90's also.

bwmenemsha posted 03-29-2004 07:23 AM ET (US)     Profile for bwmenemsha    
Larry...thanks for your response...felt like l was in a roomfull of people talking but was apparently invisible or my lips were moving but no words were coming out. Anyway at risk of sounding redundant,l may have overlooked a great deal of the market by ignoring the merc's till just now.l am trying to figure out which one are the "classics" as you all were referring to.That one l pointed out to you in calif looked good but geuss that is not a you like mercs so much and l am thinking of repowering with them (if l do have to repower)check this arrangement out on ebay....looks like something l could get real interested in at the right time and place/cost ****Sorry l did not get back to you right away l was transporting a prisoner from out of state back to Fla over weekend....thank you Larry....Bob

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