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Old 29 April 2019, 10:52   #1
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Mariner 25 power head replacement

Hi, I picked up a boat that had a blown 2 stroke Mariner 25 on it. I have another motor to run on this boat, but am considering doing something with the Mercury since it was effectively free.

I'm new to outboards but reasonably mechanically inclined. The motor is definitely blown, it looks like connecting rod hardware for the bottom cylinder has broken out of both sides of the case. Visually, the engine seems to be in pretty good shape otherwise and getting a reasonable 25hp engine for the price of a good used power head and some labor on the weekend seems like a win.

The S/N is bleached out and unreadable on the label, but I understand I should be able to find something on one of the freeze plugs. Hopefully this is the case.

If I decide to move forward with a new power head, how should I approach this? Do I need to get something close to the same serial number? Or does it even matter since it's a whole new power head?

Thanks, this is new territory for me.
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Old 29 April 2019, 11:30   #2
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Watch “Dangar marine” YouTube channel videos. Even though they probably don’t have your exact motor they helped me a lot on knowing what your in for with the problems you have with metal equipment that lives it’s life in salt water. A good manual will give you the other information.
I did pivot bushing on mercury 40 efi. The aftermarket manual on CD I bought off eBay reversed torque pounds of two different sets of head bolts. It cost me double what a official mercury manual would have and saved me grief.
And I’ve never worked on a motor before so the experience was a valuable one.
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Old 30 April 2019, 08:45   #3
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Good tips, thanks. Yes, Youtube is definitely a help. If this is the guy down in Aus/NZ I think I've seen his videos.
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Old 30 April 2019, 10:50   #4
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That’s him. He worked on a Yamaha 50 for the same problem as my 40 mercury. It was almost the same design. I think/know the motor designs are very similar and generally the process is almost the same. Danger marine really does a great job explaining the process.
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Old 30 April 2019, 19:52   #5
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One last question if you don't mind... what book did you get that gave the bad info? I'm looking for a factory manual that matches my year and it doesn't seem to be available. It's either Clymer or Seloc from what I can see.
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Old 30 April 2019, 22:46   #6
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Quote:
Originally Posted by potshot View Post
One last question if you don't mind... what book did you get that gave the bad info? I'm looking for a factory manual that matches my year and it doesn't seem to be available. It's either Clymer or Seloc from what I can see.
I bought on eBay a cd of a manual. It must have been a aftermarket manual because on the power head bolts mine have two different bolt sizes. With very different torque settings. I snapped a long head bolt. So the other 7 had been over torqued and I opted to replace all 8 at $10 each. As far as I know that was the only wrong information. The factory manual had the numbers right.
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