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  1. #1

    Question 2003 Mercury 15 HP 4ST rebuild newbie questions

    Hi Guys,

    I recently purchased this 2003 Mercury 15ELH 4ST off craigslist non-running and intended on using it to learn how to work on, service, and possibly rebuild basic small engines. I purchased and am following the Seloc repair manual (1705) but still have a few questions.

    After repairing the recoil starter I did a compression test that resulted in ~85 PSI on the upper cylinder and ~60 PSI on the lower cylinder, so I decided to pull the powerhead off to take a peak. There is substantial salt in the head and there seemed to be a portion that clogged and lost it's flow and ate away at the head and I'm concerned. I also noticed a strange hole/window in the block, the shape of the hole looks intentional but the hole is rough making me think it's a problem. I've ordered a replacement powerhead gasket set after the low compression diagnosis but before noticing the damage.

    What do you think? Is this head & block salvageable?

    Questionable thin wall on cylinder head

    Cylinder head overall condition

    Questionable hole in cylinder block

    Thank you for any advice & guidance!

  2. #2

    Default Re: 2003 Mercury 15 HP 4ST rebuild newbie questions

    Well, after more digging and finding replacement powerheads on ebay that have the same wierd hole (3rd picture) I think i can safely rule that out as an issue, but i'm still questioning the integrity of the cylinder head.

    Any suggestions/questions/critiques/etc are welcome!


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