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Discussion Starter #1
So i guess I blew a cylinder in my 2005 merc 25hp.i was running back to the dock and she locked up from full speed to nada in a few seconds.i wasnt able to pull the rope at all.....mechanic says its getting like 50 psi in the lower cylinder. Water pump was working when i started it that day. Oil has always been mixed at 50:1. What could have caused this?i guess im screwed into parting this out....any guesses would be great! Also whats worth trying to part out or just try to sell as a whole?thanks Rob
 

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Cert. Yamaha technician
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4,330 Posts
There actually is no "cylinder head" on a 25 merc.
But yes, you blowed it up.
Either it overheated and you didn't notice, or it was its time and it let loose
 

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Cert. Yamaha technician
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I'm not a merc guy so I'm not sure but if it has sleeves it can probably be bored out and rebuilt.
If its got chrome plasma cylinders it an anchor
 

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devilray snob
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Hopefully someone will chime in.thanks
There is a .030 piston kit you can get, I think boats.net has it.

Be prepared to spend ~$800 +- on the rebuild unless you do it yourself though.

I would just get a brand new powerhead off ebay:

like this:

http://www.ebay.com/itm/20HP-25HP-MERCURY-MARINER-POWERHEAD-CLEAN-FRESHWATER-135-LBS-COMPRESSION-/350907095335?pt=Boat_Parts_Accessories_Gear&hash=item51b3b15927&vxp=mtr

That's a GREAT DEAL.
 

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Discussion Starter #9
Mattyvac is that one on ebay a direct fit?that would be great if all the other parts just mount the same.is this an easy swapout?
 

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While I can't say for sure if that block would fit or not, I can say with certainty that it is not the same as the one on my 1999 Merc 25.

The guy gives the model and sn# in his listing, so you could pull up the schematics for both and compare the part #'s.
 

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devilray snob
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While I can't say for sure if that block would fit or not, I can say with certainty that it is not the same as the one on my 1999 Merc 25.

The guy gives the model and sn# in his listing, so you could pull up the schematics for both and compare the part #'s.
Your 99 is different than a 01-05 motor.

PCI is a great company and the owner is a great guy. I would recommend them but you need to tear down the block yourself anyway.

The one in the link 'should' fit. It looks exactly like the one I took off my 04 25 when I had it.

 

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Discussion Starter #12
Hey matty the guy replied and said he doesnt think it will fit.is there a certain range of years that are compatabale?
 

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devilray snob
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Hey matty the guy replied and said he doesnt think it will fit.is there a certain range of years that are compatabale?
Any 2000-2004 power head. I paid 500 for mine a few months ago.
 

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I'm not a merc guy so I'm not sure but if it has sleeves it can probably be bored out and rebuilt.
If its got chrome plasma cylinders it an anchor
You can bore those now, I have a couple machine shops doing them now.

That's not a brand new power head that is a used power head.

There are more than 2000-2004 years that are compatible.
 
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