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  1. #1
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    Default Seized 25hp 2-stroke

    My brother acquired a 25hp 2stroke mercury that is apparently only a few years old (don't have the year) and has very low hours on it. Someone ran straight gas in it and it's seized. I've tried dumping oil down the spark plug holes, still not freeing up with the pull rope.

    Question is should I try turning the crank with a wrench or just pull the head and see if the cylinder will come off the pistons??

    We are hoping that a bore and some new pistons will bring this motor back to life. Are we wasting our time? Lower end spins just fine.

  2. #2
    Petty Officer 1st Class Lubosleftboot's Avatar
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    Default Re: Seized 25hp 2-stroke

    You will have to tear down the power head to ascertain where the seizure is. It could well be in the bores as you say but it may also be at the crankshaft main shells..If it is seized at the crank and has any bad scores in the barrels you would be best off finding another motor tbh.

    LLB
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  3. #3
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    Default Re: Seized 25hp 2-stroke

    Quote Originally Posted by xjma View Post
    My brother acquired a 25hp 2stroke mercury that is apparently only a few years old (don't have the year) and has very low hours on it. Someone ran straight gas in it and it's seized. I've tried dumping oil down the spark plug holes, still not freeing up with the pull rope.

    Question is should I try turning the crank with a wrench or just pull the head and see if the cylinder will come off the pistons??

    We are hoping that a bore and some new pistons will bring this motor back to life. Are we wasting our time? Lower end spins just fine.
    Yeah plus the stopped making 2 strokes in 2006 or 2007, so it has to be at least 5 years old.....

  4. #4
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    Default Re: Seized 25hp 2-stroke

    Quote Originally Posted by Lubosleftboot View Post
    You will have to tear down the power head to ascertain where the seizure is. It could well be in the bores as you say but it may also be at the crankshaft main shells..If it is seized at the crank and has any bad scores in the barrels you would be best off finding another motor tbh.

    LLB

    How likely is it to have seized down on the crank bearings??? I'm hoping cylinders!!

  5. #5
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    Default Re: Seized 25hp 2-stroke

    What is the s/n of the engine and why not tear it down anyway? You own it and may get lucky. Nobody can say what the problem is until you get it apart.

    Gerry

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    Default Re: Seized 25hp 2-stroke

    RIght even if you part it out it will make you more $ than a parts motor.

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    Fleet Admiral Faztbullet's Avatar
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    Default Re: Seized 25hp 2-stroke

    Depending on the year it may be a scrap out motor. Only the blocks with the words Mercosil casted on the block is boreable if not it is a chrome bore and will need to be resleeved..
    When in doubt,Trim it out!!!
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  8. #8
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    Default Re: Seized 25hp 2-stroke

    where would I find the 'mercosil' cast?? Are sleeves available??

    I don't know much about the motor other than it's got low miles, merc 25 stroke outboard with electric start and some kid that temporarily worked at my brothers job ran straight gas in it and seized it. It's been sitting around since then and despite his work having tons of boats and motors of all shapes and sizes, nobody there knows how to tear into them, so they just buy a new one. When I saw it it was ofcourse dusty but I would guesstimate based on looks of the housing that it is early 2000s ish vintage. Apparently it was on a boat that nobody liked to use.

    I'll have to get the numbers off of it this weekend. I guess I'll just start tearing it apart and see what I find. Other than the lower end, what parts would be useful to people?? I guess if it's Fed the block could make a decent anchor for a jon boat or something, haha.

  9. #9
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    Default Re: Seized 25hp 2-stroke

    You can replace the powerhead, if you want to keep the motor, and use the needed parts from the old one. Check out the list of salvage yards listed on here, or ebay. If stright gas and no oil was used, the crank, bearings, pistons, and block are probley shot and can be sold along with the alluminim (SP) cans you collect while working on it. Isn't life grand Tee Hee. That way you will get some of your money back.Check out outboardexchange.com for a powerhead.
    Oldman570

  10. #10
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    Default Re: Seized 25hp 2-stroke

    Quote Originally Posted by oldman570 View Post
    You can replace the powerhead, if you want to keep the motor, and use the needed parts from the old one. Check out the list of salvage yards listed on here, or ebay. If stright gas and no oil was used, the crank, bearings, pistons, and block are probley shot and can be sold along with the alluminim (SP) cans you collect while working on it. Isn't life grand Tee Hee. That way you will get some of your money back.Check out outboardexchange.com for a powerhead.
    Oldman570
    With all due respect Oldman, I really do hope that you're wrong about the crank bearings, but I guess there is only one way to find out!! If the crank itself is fine (lower rod bearings OK) then it still shouldn't be too bad to fix.

    Keep in mind the total cost into this motor so far is zero, so throwing 500 bucks of parts at it is still a good deal to for us (my brother and I). I enjoy working on motors, when I have the time.... This is just a 'hey, we can get this otherwise mint motor that is seized up for free, think it's worth messing with?' deal.

  11. #11
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    Default Re: Seized 25hp 2-stroke

    Quote Originally Posted by xjma View Post
    With all due respect Oldman, I really do hope that you're wrong about the crank bearings, but I guess there is only one way to find out!! If the crank itself is fine (lower rod bearings OK) then it still shouldn't be too bad to fix.

    Keep in mind the total cost into this motor so far is zero, so throwing 500 bucks of parts at it is still a good deal to for us (my brother and I). I enjoy working on motors, when I have the time.... This is just a 'hey, we can get this otherwise mint motor that is seized up for free, think it's worth messing with?' deal.
    Well he is saying that if oil wasnt used, then your s.o.l. Hopefully someone just ran the motor with a blown waterpump and the pistons seized up, but the crank is fine.

  12. #12
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    Default Re: Seized 25hp 2-stroke

    My brother is pretty convinced that some 'summer help' didn't know the difference between 2 and 4 stroke and ran straight gas in it .

    I know that with other 2strokes, straight gas doesn't necessarily mean the crank will be toast....I'm hoping here!!!

    I really hate separate injection systems but in this case maybe it would have been better off....but then again, then I wouldn't be getting the whole outboard for nada.

  13. #13
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    Default Re: Seized 25hp 2-stroke

    Depending on what block you have, you could be in good shape. Blocks with chrome bores can not be bored out and have to be replaced if the bore is to scored real bad. You can sometimes lightly scrape the ammumin off a chrome bore and hone it and replace the pistons only if the crank and rod bearings are good. As for the oil injection, I would disconect it and use premix gas. That way you know it will get oil as the oil injection can and will go bad and you'll be back to square 1 again. Like I stated before, it is sometimes cheaper to just replace the power head with a good used one from one of the salvage yards. A good used powerhead shouldn't cost very much, as most dealers would rather sell new motors, rather than fix the older one and sell it, if the motor is 10 years old. At any rate the powerhead will have to come off and be split inorder to check the crank and bearings. Now you have a spring project, to keep you busy in your spare time, and you can end up with a motor that will last several years when done correctly.
    Best of luck and Boating,
    Oldman570

  14. #14
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    Default Re: Seized 25hp 2-stroke

    I think they were running pre-mix in this one...which is how the kid that didn't know ended up running straight gas. I prefer pre-mix too, except for on snowmobiles.....hard to mix at a gas station.

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    Default Re: Seized 25hp 2-stroke

    Quote Originally Posted by Faztbullet View Post
    Depending on the year it may be a scrap out motor. Only the blocks with the words Mercosil casted on the block is boreable if not it is a chrome bore and will need to be resleeved..
    So the motor is now in my back yard on a stand and ready for me to tackle it once I get the time. It's a 1998 model year, and the block says 'mercosil' so I guess it's boreable, which is a plus!!

    I would do pretty much all the work myself other than bore/hone and redoing the actual crank and rods if that is necessary I'd have an experienced machine shop do that and balance it, etc. but other than that I can work on motors. It is a little different than a dirt bike or ATV motor....some of the **** I'm like, what is that, but I'm sure I'll figure it out once I rip it apart. Speaking of which I think I'm going to go pull the head off of it right now, so wish me luck fellas!! Thanx for all the help so far!

  16. #16
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    Default Re: Seized 25hp 2-stroke

    think I'm going to go pull the head off of it right now
    That a water jacket.....
    When in doubt,Trim it out!!!
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  17. #17
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    Default Re: Seized 25hp 2-stroke

    Good news, the crank turns!! I'm about to go get a compression gauge, but from my thumb the top cylinder seems to have a little more than the bottom....hopefully the gauge will tell a different story. Going to pull the exhaust cover and see what I can see and use an actual gauge to get numbers, it could just be the way I'm holding my thumb. Either way, seems to have enough compression to run, so we will do a test run soon. Woo hoo!!

  18. #18
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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    So, maybe I shouldn't have taken the water jacket cover off at night after a few drinks?? Too late now, I just realized that I broke two of the SS screws holding the water jacket on, and a third had already been broken, one that holds the water return fitting on there. It was somewhat drilled out and held on with a larger screw, so only holding that fitting on and not clamping it to the block A few of the screws that I didn't break came out with varying amounts of aluminum in the threads....hello thread chaser and anti-seize!! Wonder if the potential seize had anything to do with the stuck bolts??? Why SS on aluminum, because of the potential marine aplication?? This was to my knowledge only ever used in ponds and maybe a little brackish, but never out in the actual ocean. Oh well. I'm better at taking steel screws out of aluminum on say dirt bike/ATV motors....live and learn, again.

    I was planning on popping off the exhaust cover (or what I assume covers the exhaust, large cover plate covering side of both cylinders on port/tiller side of motor) so that I could get a look see at the pistons and the rings, but the two middle screws are pretty stuck and I don't want to be extracting any more!! All of the outside screws were way loose. This doesn't appear to have been messed with since factory assembly as the SS screws had the factory black paint on them with no scratches or indication of being worked.


    SO, what's the best procedure for extracting stuck SS screws from aluminum block?? Apply heat (I have MAP gas, no oxy/acet, but could borrow some), cool with PB/WD, and give er a try?? Luckily there is enough of each screw protruding that I can get them with a vise grips. It would REALLY suck to have to try to drill these SS screws out!!! Would I be even more screwed if they were steel fasteners instead of stainless??

    Should I replace with SS fasteners or mild steel?? I'll use the good anti-seize during re-assembly!!

    My brother was hoping to come over today with the gas can and see if we could fire this puppy up....hopefully we can get the jacket on good enough so that we can at least get a test run in...with water leaking all over the place. I'm sure that will be fine, no??

    Will chasing threads with a tap and using anti-seize be fine, or do I need to heli-coil some of these?? Is this normal for so many stuck screws??


    thanx for all the help!!

  19. #19
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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    Way back when I asked you for the s/n it was for a reason, so we could get you the service manual online and the parts listing. We don't even know if it is a 2/3 cylinder.

    There is a difference between being a bull in a china shop and being patient enough to try and salvage the engine. I still can't believe that you are so anxious to run this thing. At least getting the exhaust off you can have a look and feel to see if the rings are frozen or broken.

    Have you at least dropped the LU to see the condition of the impeller before running it?

    The wisdom of others on here would have shown you to soak, heat and tap the screws, gently working them to avoid breaking as many as possible.

    However, if you must run it, go ahead, maybe you can succeed in damaging it even further!

    Gerry

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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    Chasing threads often works fine. You can send pics if you'd like. If the head is not down tight, with a fresh headgasket, water will not only squirt all over the place, it will find its way into the cylinders. Just do it the right way and wait until you get the head back on before trying to fire it up.

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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    Quote Originally Posted by carholme View Post
    Way back when I asked you for the s/n it was for a reason, so we could get you the service manual online and the parts listing. We don't even know if it is a 2/3 cylinder.

    There is a difference between being a bull in a china shop and being patient enough to try and salvage the engine. I still can't believe that you are so anxious to run this thing. At least getting the exhaust off you can have a look and feel to see if the rings are frozen or broken.

    Have you at least dropped the LU to see the condition of the impeller before running it?

    The wisdom of others on here would have shown you to soak, heat and tap the screws, gently working them to avoid breaking as many as possible.

    However, if you must run it, go ahead, maybe you can succeed in damaging it even further!

    Gerry
    Hey, I wouldn't say I'm a bull in china shop!! I just didn't expect to encounter broke bolts....one was already broken, I did two myself. Once I realized that bolts were breaking, I decided not to remove any other parts!! Maybe it was used in salt water, or maybe the stuck bolts are just bad luck?? I'm not overly anxious, I just find time to work on it here and there between all the other honey do things and then my other toys that I probably should sell anyways . I hadn't been able to spend any time on it and last weekend in the evening I was left alone to do whatever I liked and was a little over zealous, oops. I won't wreck the motor...one can always heli-coil if necessary!! I'm way more experienced with broken bolt extraction than I'd like to be....although not with SS fasteners in alloy block, but I'll manage with a little help I'm sure!!

    Serial is 0G63xxxx, 2 cylinder, 1998 model 25ELH, 6000 max rph, 25hp, 115#. Here is a website with parts listings and really crappy quality diagram scans http://www.mercruiserparts.com/selec...c_nbr=18583+94
    Service manual would be much appreciated!! Thanx!!

    I would like to get that exhaust off, but those two bolts that I can feel will break scare me...probably going to be doing so heli-coils already!!! Not looking to do a bunch of them though!! I'm trying to find my map torch.....

    I think I'll go grab a compression gauge and check the cylinders. If they're good, do you think it's worth dealing with the stuck bolts to check on the pistons/rings?? I guess it would be bad to try to start it if there was a broken ring, but other than that, no harm if the rings were just worn. The thing is turning nice and smooth, which I can't believe, so I'm not worried that any bearings are bad...I can't hear any noise at all or feel anything grinding, but then again, I did put a good amount of pre-mix oil down the cylinders!!

    I wish I could find my map gas torch!! I'll soak everything in PB in the meantime.

    Thanx for the continued help!!!!

  22. #22
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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    If the compression is good then no, leave the exhaust plate on. Why search for a problem (and make more) that isn't even there.

  23. #23
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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    Oh and you will need to check compression when the new head gasket is on (obviously).

  24. #24
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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    Quote Originally Posted by sutor623 View Post
    Chasing threads often works fine. You can send pics if you'd like. If the head is not down tight, with a fresh headgasket, water will not only squirt all over the place, it will find its way into the cylinders. Just do it the right way and wait until you get the head back on before trying to fire it up.
    Doesn't look like there is a head gasket to me, only a water jacket. Looks like the heads are cast into the cylinders themselves....so no way for water to get in from this end. But I take it people generally don't think that this is a good idea, so I'll tell my bro no, we won't start it yet. We do want to see if it will start, but I guess it will have to wait until I can find the time to get everything in tip top shape.

    Here are some pics, just because. Pic of the cylinder where it says mercosil from last week, before I had done anything other than pour tons of pre-mix into the spark plug holes.


    Here you can see the exhaust manifold. All of the outside bolts were actually loose, almost 1/4 of a turn. they would all come out no problem, but I tightened them down. The two middle ones you can see where I had the socket on there....I loosened a tad, tightened a tad, and said F it, I don't want to deal with breaking off any more bolts!! The paint was untouched prior to me just doing this.


    and here it is, the cylinder with the water jacket removed. Top left you can see the broken bolt from someone else...there was a wood screw holding the water pisser housing on....I guess it must have worked??? No wonder the previous owner didn't bother to check to see how seized this motor really was!! Then the other two broken bolts are me .
    Last edited by xjma; April 10th, 2012 at 09:30 PM. Reason: to fix pic links that I moved

  25. #25
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    Default Re: Seized 25hp 2-stroke *Update* not seized up!!

    Here is the parts listing:

    http://www.crowleymarine.com/mercury-outboard/368.cfm

    Here is the service manual, P/N: 90-826883

    http://1manual.com/Mercury%20manuals...83r2/cover.pdf

    You must have Adobe Acrobat reader installed to use this manual. If you scroll down to the lower part of the opening page, you will see the various engine components in red. Click on the one you want and when the first page opens, click on the "Save As" icon at the top LH corner of the page and you can save it to your computer.

    Gerry

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