2002 Mercury 25 EH Low compression. Runs.

[lineman22]

Bought off Craigslist as a parts motor.
Owner had replaced starter and prop. Took to local shop for poor performance and 410.00 later had impeller replaced, carb and fuel pump rebuilt. Took home and still ran poorly. Took back to shop where they were told poor compression, junk motor. Has set for 7 months.
I felt a soft tank bulb and thought I had a keeper. New gas and I got it running with my hand on throttle linkage. Water from pee hole gets very warm/hot. Checked compression. 70 on top and 55 on bottom. Water jacket cover by spark plugs does leak a little. I have heard all kind of stories but I ask, is there any hope?
JB, I did try to keep it short.

 

[saumon]

Re: 2002 Mercury 25 EH Low compression. Runs.

It is shot.

 

[Bondo]

Re: 2002 Mercury 25 EH Low compression. Runs.

Checked compression. 70 on top and 55 on bottom.

Ayuh,... It might qualify as a rebuildable core, but it Ain't a running motor with those #s...

 

[JB]

Re: 2002 Mercury 25 EH Low compression. Runs.

I would do a thorough decarb on her, then recheck compression.

Worst case, you got the parts you wanted. Best case, you have an outboard with years of use left in her.

Let us know what you find.

Good luck.

 

[Faztbullet]

Re: 2002 Mercury 25 EH Low compression. Runs.

You should have the Mercosil block on that year engine and it is boreable!!! I myself would tear it down and inspect cylinders, if not to bad have bored and install new pistons as you can get from a .010 to a .040 oversize and turn it into a $1500 sellable engine or use it yourself.

 

[lineman22]

Re: 2002 Mercury 25 EH Low compression. Runs.

I did soak with Seafoam and run through the carbs. Engine sounded like it wanted to run and accelerate with no hesitation the next day. I tried several different compression gauges and the new numbers were 100 and 75 psi. Bottom spark plug still comes out with a little wet.
I had read here about a Seafoam/ PB Blaster mix and soaked the cylinders. Yesterday I wanted to start and run engine a little to see if it had healed itself. Never started again and the solenoid finally died. Tried to rebuild the solenoid tonight and had just a little luck. Will buy a new one now. Could I have hurt the reeds with excess mix running backwards through intake. I am still on the fence about the disposition of this motor and wanted magic to remove carb and make all like new. Hasn't happened yet. This doesn't have a removable head and I can see where the dealer removed the water jacket to check condition of cylinders. He didn't know. How do I know if this is a Mercosil and rebuildable? I see 2 pistons with rings an easy $400, then whatever the machine cost are for bore.

 

[Faztbullet]

Re: 2002 Mercury 25 EH Low compression. Runs.

The block will have the word Mercosil embossed on it and pistons are $122ea. You will need to tear it down to check the bores or borrow a borescope and look thru the spark plug holes in jugs to get a idea if you want to fool with it. If you want to fix it quick order a block kit from Promarine, it comes with NEW block,pistons,bolts and bleed lines.

 

[lineman22]

Re: 2002 Mercury 25 EH Low compression. Runs.

Laid off a week on this motor. Went out tonight and ran it for a while. Compression is around 80+ on the bottom and around 90+ on the top. Starts and sounds pretty good. Borescope on the way. Considered exhaust cover removal to take a look but that just means more parts to put back. Planning to put on a boat and in the river to see how it does. I did find a used powerhead that was on a good motor when the lower unit left. Most of the parts have been stripped but this may be an option. Parting out the whole thing isn't off the table yet.
Thanks to everyone for the comments.

 

[saumon]

Re: 2002 Mercury 25 EH Low compression. Runs.

Took to local shop for poor performance and 410.00 later had impeller replaced, carb and fuel pump rebuilt. Took home and still ran poorly. Took back to shop where they were told poor compression, junk motor.

As a side note, never go to this shop again. From what you said, they rip you of 400$ for fixing a ?poor performance? problem without even checking the compression the first time. Or worst, they do and they didn't tell you.

 

[lineman22]

Re: 2002 Mercury 25 EH Low compression. Runs.

Borescoped cylinders today. Walls are certainly affected with deep marks. I think a borescope or other visual inspection of the cylinders should be as important as a compession test do determine condion of engine components. Even with what I know now I am sure I would have bought this engine. Maybe find the block I need and be good to go or it goes for sale soon to someone that thinks they ae ready for a project.
I looked in my 88 Evinrude and can still see the cross hatching from the hones. Maybe different metals or an easier life but expected to see something besides carbon buildup on the high crown pistons. All of this could have been done through an intake or exhaust inspection plate but the boresope was easier.