# Mercury 150 black max rebuild



## tilefish (Aug 6, 2012)

Anyone know how to rebuild mercury outboards? My 89 150 Black Max lost compression on 1 cylinder. Pulled head and there isn't any major damage to the cylinder wall but I can see where what I am assuming is the ring is smeared against the cylinder wall. The metal that is on the cylinder wall flakes off when lightly scraped. I'm mechanically inclined and was thinking about tackling the rebuild myself. Any thoughts or advice would be appreciated.


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## bountyhunter (Apr 28, 2004)

never done it but I,d watch a lot of U TUBE before I did it ,and take lots a pic.


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## fastwater (Apr 1, 2014)

Yep...pics will be your friend. Especially on wiring. Take plenty before and during tear down.
The good thing is if after you have the cyl. honed, if you find that that didn't clean the cyl. up and cyl. wall is still scuffed, you can get it bored out and get oversized piston/rings to install. Don't have to sleeve it unless it can't be honed within specs.

I would also be looking very hard for the reason for the failure.
You may want to take a good look at #1 spark plug and compare it to the rest of the plugs to see if it looks like #1 plug was running lean. If so, I'd be looking at either the carb for #1 or the oil injector(if still equipped).

You may wait for firemanmike2127 to respond or shoot him a pm as he most likely has a bunch of experience on this mtr.


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## bustedrod (May 13, 2015)

make sure ya have a good shop manual for that serial # motor, was just looking at rings and gasket kits and power heads oh my lol


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## tilefish (Aug 6, 2012)

Thanks for the responses guys! I don't have the money to buy another motor so a self rebuild is my only option. If I do it I will get a full rebuild kit and will delete the oiler system. Also will have the carbs re done. If i cn get this done for less than $2000 i will do it. Otherwise I'm selling everything and taking up knitting.


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## crappiedude (Mar 12, 2006)

tilefish said:


> Otherwise I'm selling everything and taking up knitting.


Look for something else, my wife does a lot of knitting and $2k won't cover it either


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## UFM82 (Apr 6, 2004)

The metal coming off the wall is probably aluminum from the piston. They tend to melt before the cylinder wall does. Did the engine go lean? Overheat? Need to find the cause before running the rebuilt engine to prevent the same occurrence.
I'd love to help but I barely have time to work on my own stuff.


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## tilefish (Aug 6, 2012)

I appreciate your thoughts. I will check into the exact cause. I was running WOT and it shut down. I was able to start it but could tell it wasn't running right so I used my bow mount to get home.


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## Skip99 (Jul 29, 2017)

I have the same motor, and that oiler system has always bothered me, i believe it still works, but ive always put some oil in the gas just in case. Im interested in what you do..
Pm sent


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## Cajunsaugeye (Apr 9, 2013)

My xr4's oiler was unhooked the day I bought it. Manual mixing is my choice but it will never break!


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## fastwater (Apr 1, 2014)

Skip99 said:


> I have the same motor, and that oiler system has always bothered me, i believe it still works, but ive always put some oil in the gas just in case. Im interested in what you do..
> Pm sent


If you are counting on the AOS to do the oiling, I hope you are also performing the required maintenance on the AOS system. Up to and including periodically draining, cleaning and refilling the oil tank, inspecting oil delivery lines and cleaning/replacing filter(if applicable on your system).

If you are doubting( but not knowing) whether your AOS is working and adding oil to your gas as well, and your AOS is working, then you are running rich on your oil. Which can create its own set of problems. 
While the purpose of two stroke oil is to 'lube' while the gas 'cools' ,some believe continuously running rich on oil in a two stroke can even make the eng. run in a 'lean burn' condition causing the engine to run at hotter temperatures eventually causing piston scuffing/piston meltdown. This topic has been debated extensively.
One thing thats known about running to rich on oil is doing so creates premature plug fouling and builds excessive carbon. Which could include carbon on the piston rings. To much carbon buildup on piston rings could cause rings to seize, break and cause serious issues.

At any rate, gas/oil mixtures are set for engines for obvious specific reasons. And the engines running on mixtures within specs., run better, last longer and have less issues over the long haul.

In your situation with doubting, or not knowing whether the AOS is working...and especially if you haven't and don't want to perform the required maintenance on the system, IMO, rather then dumping extra oil in your gas, I would have the AOS bypassed and manually mix my oil. I think you will be much happier in the long run...and so will your engine.


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## tilefish (Aug 6, 2012)

Yes if I do the rebuild the oiler will be deleted!


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## Skip99 (Jul 29, 2017)

When i boght the boat 3 monthes ago, he saidthe aos wasnt working, and had been mixing his gas, motor was hard to start, i had a mercury mechanic come look it over and channge lower oil, i changed the plugs and motor was 100 % better, i ordered the aos bypass kit, and meanwhile, just added pure gas to the tank, since i dont run the motor at wot, i figurd it safe until i figure it all out.there were couple other issues, just took a bit to straighten it all out, such as bad stator, i thought the motor ran great, but now its charging as it should, starts as soon as you touch the key, and smooth as glass. Im monitoring the oil level in the tank, while im keeping about a 100-1 in the tank, so its only slightly rich. Ive heard it both ways from mercury mechanics and they all have diff opinions, one says remove the aos and premix, another says its a good system, worked well in thousands of motors, so leave it, unless im running 6k rpm all the time...so, i compromised, for now, im pretty sure the oiler is working, it just takes time to see a level change, and ive premixed lightly, im at the point where i thnk its safe to quit premixing, so, assuming the oiler is working...whats your opinion, premix, or install the bypass kit?


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## Skip99 (Jul 29, 2017)

tilefish said:


> Yes if I do the rebuild the oiler will be deleted!


Iread where the issue in the motors was not the oiler to begin with, but was actually something causing the bushing in the oiler to get hot and seize on the shaft which , looks like an oiler fail, but was actually over heat related, but then again, its all just hearsay....like they say, you hear about a few failures, but you dont think about the 10s of thousands that are stillrunning great..


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## Cajunsaugeye (Apr 9, 2013)

That's why I stated "my choice" in my reply. I KNOW it's always getting oil by pre-mixing. Mine may have worked fine for years but pre-mixing mixing worked for decades. JMO.


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## fastwater (Apr 1, 2014)

IMO, especially with what a new eng. costs, I want to know, not assume or hope my eng. is oiling properly.
My thoughts on whether you should bypass the AOS is, yes I think you should.
Though I may be a cert. mechanic by trade, I am NOT a cert. outboard mechanic. But can assure you that with whatever application there is, if it's 'mechanical' it's subject to fail. Especially if the proper maintenance on the mechanical device isn't kept up. Then, in this case, insuring the safety features(alarms) in case of failure to the oiler are in and remain in working order.
Would also like to add that whether you are running the eng. at WOT or not, if that engine is not getting lubed properly, you are damaging that engine and asking for big issues that will be high $ in repairs. And it's just a matter of time before those issues happen.
If you chose to keep the AOS, that's your choice. But I'd surely take it to a cert. Mercury tech. and have the system tested to insure it's working properly and have the regular maintenance that's required done on the system. Would also have the safety system checked out in case of failure to the AOS.
Granted, there are a lot of AOS's out there that have run just fine for years. Have a 1994 60hp Rude in my drive right now that belongs to a buddy of mine that I'm doing some work on. It's ran great but he's tired of the maintenance on the system and one of the things I'll do is bypass the AOS before it leaves here.

Lastly, there's one thing you need to think about when reading or listening to anyone talk about the reasons the EOS fails...do you really care 'why' it failed? Fact is, some do....some don't.
One thing for certain...if it does fail, whether due to mechanical failure or lack of maintenance to the system or whatever, and you do damage to your eng. those guys telling you to keep it aren't gonna pay for the repairs.
So the choice is obviously yours. Again, especially since you've been forewarned there may be an issue with the AOS, if nothing else, just for peace of mind, I'd bypass, mix my oil and be done with it.


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## Skip99 (Jul 29, 2017)

I might as well, i already bought the block off kit...


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## steelneyes2 (Jul 19, 2011)

tilefish said:


> Anyone know how to rebuild mercury outboards? My 89 150 Black Max lost compression on 1 cylinder. Pulled head and there isn't any major damage to the cylinder wall but I can see where what I am assuming is the ring is smeared against the cylinder wall. The metal that is on the cylinder wall flakes off when lightly scraped. I'm mechanically inclined and was thinking about tackling the rebuild myself. Any thoughts or advice would be appreciated.


You may be able to find a good used powerhead if your budget is under $2k to get it done. It doesn't take long to get there in terms of parts if you have to have boring and sleeving done, plus start replacing pistons and rings. Even though it only wiped out 1 cylinder, you certainly want to make sure everything is in top shape before investing significant money into the motor and having another issue shortly thereafter. Also keep in mind you still have a 30 year old motor other than the powerhead at that point. I admire the desire to rebuild, but just like to encourage people to step back and consider when it comes to motors that are of that age. I had trouble finding carburetor parts for a 1986 tower of power last year. The carbs have been discontinued and I had to pay a premium after hunting around for them and finding them new.


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## tilefish (Aug 6, 2012)

After pricing out the rebuild kit at about $950. I am figuring on $500 in machine work as I will have all cylinders bored and sleeved. And I will pay to have the carbs rebuilt at a quoted cost of $300. This will give me a basically new engine. All pistons will be new and the oiler will be removed. I have rebuilt car motors before so I am motivated to try my hand at this. Plus it will give me the knowledge for future use if I need to fix anything else on the engine. I definitely appreciate everyone's input though!!! I was quoted a cost of $1,400 to install a new power head. That combined with the cost of the power head will put me well over my budget and really at that point I would just spend $3500 on a newer motor if I was to go that route.


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## fastwater (Apr 1, 2014)

Heck...go ahead and knock out those carbs yourself.


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## ssv1761982 (Jun 2, 2004)

The carbs are simple compare to a Qjet. The rebuild is not hard, just a little different that a car motor.


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## steelneyes2 (Jul 19, 2011)

I 3rd. the rebuilding the carbs yourself. They are probably the "easiest" part of the project here. That's if there's even a problem in them to start with. With damage to only one cylinder the most probable cause is either just age, old stuff breaks eventually, or a problem in the ignition system. Specifically, the bias circuit in the switchboxes. Just finished up a 200 Merc. last week that simply quit running. Still had spark on all 6 cylinders and was "guaranteed" by a local shop over the phone to need a $600 carb. rebuild. Thankfully, the fellow didn't trust someone willing to diagnose a motor without even looking at it. After proper diagnostics testing, the bias circuit was malfunctioning in the packs and thankfully the motor quit running before causing any damage to any of the cylinders. It's running like new now and there were zero issues in the fuel system. 
If you do a complete rebuild and don't run thorough diagnostics on the ignition system, you can quickly wipe out all of your hard work.


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## tilefish (Aug 6, 2012)

Yeah I guess that makes sense. Probably not nearly as difficult as the rebuild.


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## UFM82 (Apr 6, 2004)

Bear in mind that an oil failure would have resulted in damage to entire engine, not just one cylinder. I just learned that the hard way when #4 died on my 150 XRi. So all this talk about the oiling system is probably off base as far as a cause. Lean is the problem so probably a carb issue. I think I must have lost an injector or something because #2 and #6 look great. I will be going the rebuild route as well so I'm joining the crowd. DAMN!


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## tilefish (Aug 6, 2012)

Yeah I saw your post. Sorry to hear. I will be going the premix route as well.


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