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Old 03-22-2021, 06:45 PM   #1
SV72
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Default A little advice from the boat mechanics

Looking for a little advice from the boat mechanics on the green screen regarding my outboard motor. The motor is a 2 stroke 1996 Nissan 40HP (NS40C). I have had the boat (17 foot Tracker) and the motor for 3 years or so now. Initially, I had issues with the motor, however, I found that removing the old gas tank and replacing it with a brand new 6 gallon portable eliminated the issues I was having. (would not run at high speed) Last year, I ran the boat all summer (10 or 11 trips) and had no issues. The first trip this year, it ran great until I got back to the dock and put it in reverse and it died. I got it started using the throttle (which is not normal) and got it on the trailer, but the next day, it was really hard starting and did not seem right when it did start. Normally, when cold, it will start right away after choking it.

That said, I went back to square one and did a quick compression test today and I am showing 130 in cylinder 1 and 50 in cylinder. Back in 2018, they both were showing 130.

Any advice on fixing this motor vs buying another used motor?

Any help is greatly appreciated.
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Old 03-22-2021, 07:15 PM   #2
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Try this, and don't skip any steps. First tear down the carbs and clean them good. Make sure every passage and orifice is clean. Put them back on the motor but don't hook up the gas lines. Get rid of all the gas in your gas can and get fresh gas and oil mix. Squeeze the bulb til good clean gas comes out. Hook line up to carbs.. Now go the the auto parts store and get a can of aerosol sea foam. Start your engine, let it warm up, and spray 3 or so seconds into each carb one at a time. Try not to let the engine die. Up the idle if you need to. Use about half the can of spray. Then really flood the bad cylinder. If the motor doesn't die, shut it off and let it sit for about 30 minutes. Fire her back up and run it til it stops smoking. Do another compression test. Either be better or needs a rebuild.
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Old 03-22-2021, 08:08 PM   #3
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Are you running oil mixed in the fuel or counting on the VRO, or whatever Nissan called it? Or is this a four stroke? I would think most engines back in 96 would still be 2 strokes. It's pretty common for the VRO system to crap out and burn up a piston. It kind of sounds like that's where you are.

If so, that cylinder will need to be cleaned up, honed, then the piston and rings replaced. But doing another compression test, make sure the adaptor is screwed all the way in and that the o-ring is sealing to the head properly. I have done compression tests a few times where the hose was not screwed into the head far enough and got low readings. Then after panicking went back and did another compression test and got the adaptor on the hose screwed all the way in, and got good readings.
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Old 03-22-2021, 08:35 PM   #4
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[quote=RifleBowPistol;15533775]Are you running oil mixed in the fuel or counting on the VRO, or whatever Nissan called it? Or is this a four stroke? I would think most engines back in 96 would still be 2 strokes. It's pretty common for the VRO system to crap out and burn up a piston. It kind of sounds like that's where you are.

If so, that cylinder will need to be cleaned up, honed, then the piston and rings replaced. But doing another compression test, make sure the adaptor is screwed all the way in and that the o-ring is sealing to the head properly. I have done compression tests a few times where the hose was not screwed into the head far enough and got low readings. Then after panicking went back and did another compression test and got the adaptor on the hose screwed all the way in, and got good readings.[/quote

The motor is a 2 stroke and I mix the oil with gas. With regard to the process you describe (new piston and ring, honing, etc.).......how expensive is that normally? will try the test again and make sure the hose is all the way in, but I am pretty sure it was seated correctly.

Last edited by SV72; 03-22-2021 at 08:40 PM.
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Old 03-22-2021, 09:09 PM   #5
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I would not put much money in a 20+ year old outboard. It's already outlived it's life expectancy.
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Old 03-22-2021, 09:20 PM   #6
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dang the luck!
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Old 03-22-2021, 09:28 PM   #7
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Quote:
Originally Posted by Capt Glenn View Post
I would not put much money in a 20+ year old outboard. It's already outlived it's life expectancy.


Shhhhh! Donít tell my 2000 OX66 that!
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Old 03-22-2021, 09:31 PM   #8
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The back cylinder is the PTO and take the load its always the first one to go
Just based off the comp chk its going to need a rebuild.
A Reman power head is likely the best route for ya. The bottom ends will come back to bite you. If this was a dirt bike I'd say pop cylinder off and go one over but these are usually easier just to get a reman powerhead and move forward bc of the extra work
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Old 03-22-2021, 10:26 PM   #9
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Quote:
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Shhhhh! Donít tell my 2000 OX66 that!
I had an 03 200hp VMax ox66, it was a very good motor.
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Old 03-23-2021, 06:22 AM   #10
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Full rebuild on 2/3 cylinder outboards usually cost less than $1000 depending what all is needed. A lot cheaper than buying a newer 40-60hp these days
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Old 03-23-2021, 08:02 AM   #11
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Thanks for all of the replies. I would much rather rebuild this one, knowing the work I have in it, than to go buy a brand new one. Any recommendations for a good shop in the San Antonio area? I live in Bulverde.
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Old 03-23-2021, 08:22 AM   #12
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If you have 130 and 50 for compression you'll have to have the the top end rebuilt. Don't waste time on all the carb stuff until you get the power head right even though they may need to be cleaned/rebuilt. Good luck finding anyone to work on one this old especially this time of year.

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Old 03-23-2021, 08:37 AM   #13
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Quote:
Originally Posted by SV72 View Post
Thanks for all of the replies. I would much rather rebuild this one, knowing the work I have in it, than to go buy a brand new one. Any recommendations for a good shop in the San Antonio area? I live in Bulverde.
I would get online and look for a piston, rings and head gasket for that thing, probably no more than $150. The two stroke mechanic trick I learned years ago, is you get some boric acid and clean the aluminum off of the cylinder wall, with the acid. It will clean it up very well, then you just run a hone down the cylinder and install the new piston and rings.

I can't say for sure, that the piston will be cheap, but after seeing what I saw for my 4 wheeler. I would bet you could probably buy the piston online for $20 to $40 with rings. Then a gasket kit for probably $45.

There is not much to a old two stroke, should not be hard to get it running again.
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Old 03-23-2021, 09:23 AM   #14
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A Plus Cash is the only place I can think of that will even look at that old motor.
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Old 03-23-2021, 09:32 AM   #15
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Bummer. sounds bad, slim chance but doubt the piston ring is just temporarily stuck.

I agree with post #13 above. You can pull the head and inspect it. Replacing a piston and ring is fairly easy (with a few new tools) and using a simple drill attachment hone to clean and smooth the cylinder walls if in good shape.

the pain of it is there are so few places that even work on these things anymore.

i've got a 1997 Merc and only a few places will touch it.
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Old 03-23-2021, 10:19 AM   #16
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Sounds like you will need to have it bored out and oversize pistons. That's what I done with a 50 Merc. Hope that's not the case.
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