new to forum...seized mercury 25

[altrocker1]

hello all!

well to be honest i'm a newbie to the site and soon to be a newbie to the world of outboard repair. since i'm a glutton for punishment, i am in the process of picking up a few used outboards with the hopes of getting one or two decent working ones...and by a few i mean 6. fortunately the final price for everything will be a whopping $200. 5 are johnsons, but the one i'm most interested in is a "seized" 2000 mercury 25 horse 2 stroke electric start. i don't have it in my posession yet, but my brother is picking it up for me in the morning. after talking with the owner, it is still unclear as to how or why it is seized.

now i have done my own wrenching on cars and small lawnmowers, but this will be my first time working on a 2 stroke. i apologize if i ask any stupid newbie questions and feel free to point me to a google search or forum search at any time, but is there a simple way to diagnose the cause of the seize without tearing this motor down? i've downloaded the factory service manual for the motor and i have done a fair amount of searching so it looks like disassebly is fairly straightforward, but what are the odds that it is a piston/sleeve and not the crank? am i better off looking for a new powerhead? from what i know about the motor everything is in working order, the powerhead is just seized...so from what i figure, the worth of the working parts certainly outweighs the cost of all six motors.

any advice?

 

[Willyclay]

Re: new to forum...seized mercury 25

Welcome to the iboats.com forum! The members here are great and the experts, which I am not, can help you solve any problem. I also bought a seized motor once that the PO said, "It just stopped in the middle of the lake". The first alternative to a complete teardown of the powerhead would be to remove the lower unit to determine if the seizure is in gearcase or, if not, by default the powerhead. If the powerhead, start investigating by pulling the head and exhaust cover which may give you a clearer picture of the problem. Mine was connecting rod bearings so it required a complete teardown and rebuild. I am just an old geezer who has never worked a day as a professional in the marine industry. Hopefully, one of the experts will post in your thread and help us both. Good luck!

 

[altrocker1]

Re: new to forum...seized mercury 25

so before i started taking things apart i wanted to see if the motor would come unseized. i still plan on pulling the powerhead and opening the exhaust cover to take a peek, but after putting some oil in the cylinders and letting it sit vertical last night, it easily unseized by rocking the flywheel gently a few times. i sat the motor upright and did a cold compression test using the electric start...now i know its not really that accurate since the engine isn't heated up, but i was able to get 115 on the top cylinder and 100 on the bottom at wot. now i know the bottom is definitely not right, but i was expecting it to be a lot lower. i didn't have very much time today and i got some of the motor stripped down. i'm going to finish taking it apart tomorrow, but is this any reason to be optomistic that i might get this back in spec with a hone job and new rings? or am i still looking at a bore job? i will get the rest apart, and hopefully have some more to report tomorrow

 

[Willyclay]

Re: new to forum...seized mercury 25

but is this any reason to be optomistic that i might get this back in spec with a hone job and new rings?

Absolutely! Hopefully it was just light rust on the cylinder walls and not an overheat or no-oil seizure. When you fully open it up, everything should be right in front of you. Good Luck!

 

[Faztbullet]

Re: new to forum...seized mercury 25

is this any reason to be optomistic that i might get this back in spec with a hone job and new rings? or am i still looking at a bore job?

Sorry but no, you are looking at boring it. The motor does not have a sleeve so it cannot rust as it is a Mercoisil block,sort of like a B&S lawn engine. It take a special boring bit and diamond hone to repair these blocks and the pistons are a special hardened aluminum. These engine do not like to be overheated or they will sieze as the silica will breakdown in the cylinder walls and it will look like a handful of sand has been thrown into it.

 

[Willyclay]

Re: new to forum...seized mercury 25

Hopefully, one of the experts will post in your thread and help us both. Good luck!

Faztbullet is one of those experts I mentioned. He will steer you straight. Me also. Good luck!

 

[altrocker1]

Re: new to forum...seized mercury 25

so here is what i am looking at...just what i suspected. cylinder is going to need a hone/bore job and i'm going to need at least 1 new piston. faztbullet, i pmed you the other day, did you get it? here are pics of the scoring that was done. top cylinder is fine here is the bottom piston and cylinder head from 2 angles.


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