Mercury 25 power head rebuild

[89Aluma]

Hi I'm new here and have been searching forums for a few days and thought It would be helpful to sign up. Here's my dilemma... About a month ago I got a free boat, 89 alumacraft lunker v14ltd with a Mercury 25hp, when I got the boat it hadn't been on the water for many years, so I did the tune up on the outboard, lower unit oil spark plugs fuel filter element new gas and oil mix 50:1 new impeller... The works! It started right up and we hit the water spent a lot of time on martins lake in Tripoli, then went to the cedar and topped the boat out 14 mph. Shut it off fished for about 20 minuets. But when we restarted the motor the top cylinder was making an awful screeching noise like the rings were grinding. So we got back to the dock and got home and the power head needs oversized Pistons and a rebuild but I'm having trouble finding parts and the info on whether or not the cylinders can be bored .20 over I know wiseco says they have pistons .20 over but is it even worth it? Or should I start looking for a different motor? Engine serial number is 0c179710 I would really appreciate some advise

 

[redneck joe]

welcome tot he forum. people way smarter than me will be along to help you.

 

[89Aluma]

Thank you very much! Hope they come soon lol

 

[MH Hawker]

it wont be long a day or 2 at most

 

[Chinewalker]

Depends on a few things - how mechanically able you are and how much money you want to throw at a nearly 30 year old motor. Also, many of those Merc 24-cube blocks are plated bores and are not bore-able. You may be able to have the bores sleeved, in which case you can go back to standard bore size. Or you can have the bore done and replated - I believe it was Nikasil at the time. You'd have to talk to a tech to confirm if it's doable.

A more practical solution might be to search around for a motor with a buggered lower unit and rob the powerhead, or search eBay for something.

Above all, find the CAUSE of the seizure. Whether it be a gummed up jet, clogged water passage, or whatever, if you don't find the cause, you might end up right back where you started...

 

[flyingscott]

Ok This may get a little confusing so bear with me gonna be lot of info. This info is for a 1989 motor which I am assuming yours is. Need a serial # to verify or look on the motor top jug see if it says Mercosil anywhere. This info is for a chrome bore only not a Mercosil block.

#1 you have a chrome bore cannot be bored out.
#2 Your motor can be sleeved by L.A. Sleeve or similar for about $300 a hole.
#3 If you sleeve you HAVE to use Wiseco pistons.
#4 advantage to sleeves is they can be bored in the future.

Option #2
#1 You can re-chrome the bore U.S Plating in Fon du lac WI. can Re-chrome a blind bore block.
#2 Last time I had one done was $225 a hole.
#3 With a re-chrome you MUST use Mercury factory pistons and rings.
#4 Chrome cannot be bored in the future.

That being said you may have gotten lucky the plating is pretty hard may just be some scuffing and you can get away with a re-ring or new pistons. You also MUST make sure the crank bearings are good one bearing alone is around $100. These are expensive motors to rebuild not like an evinrude. I agree with chinewalker try to find a good powerhead, but finding a parts motor with a good powerhead is tough. Most of the motors you will find will have smoked powerheads because people don't like to. change the waterpumps. There are also 2 different blocks made in those years one with a thermostat and one without.

 

[89Aluma]

Thank you everyone for your wisdom I would have replied sooner but had bass fever this morning pulled a necessary 24 inch largemouth out today the block I have has the thermostat on it and due to the fact it's not totally seized I think I may get away with new bearings Pistons rings and seals may tear it down on Sunday and get a better look at it, I've rebuilt a lot of 350's done some performance work and tuneing on drag cars took a new camero from 376 hp on the dyno to 685, if the bill for this is less that 600 I'll build it but more than 6 I'll probably get a used motor. Looking at 30 mariner oil injected but doesn't have tiller drive... So I guess we'll see I'll let you all know how it looks when I tear it down

 

[89Aluma]

Finally got it torn down, it hydro locked pretty viciously never found water in the bad cylinder but the rod bent pretty bad, the chuffing noise was the connecting rod needle bearing that got smashed the cylinders are a little worn due to the extra bits of metal Floating around should be able to hone it get a new crank shaft 1 new rod 1 new piston and a good cleaning and I think it'll be ready for spring

 

[89Aluma]

No Title

 

[89Aluma]

No Title

Cylinder the bent rod was in

 

[Faztbullet]

#3 If you sleeve you HAVE to use Wiseco pistons.

#3 With a re-chrome you MUST use Mercury factory pistons and rings

WSM makes replacements for both....cheaper than OEM and Seizco
Look on top of block and if it has the raised casting "MERCOSIL" it is a boreable block and only a special machine shop or motorcycle shop can do the work due to special tooling required.You can get a new block kit by shopping this part# on the web.(872-9533T40)

 

[Chinewalker]

Check your PM...

 

[flyingscott]

WSM makes replacements for both....cheaper than OEM and Seizco
Look on top of block and if it has the raised casting "MERCOSIL" it is a boreable block and only a special machine shop or motorcycle shop can do the work due to special tooling required.You can get a new block kit by shopping this part# on the web.(872-9533T40)

Do you have a part # for the chrome bore piston from WSM. When I go to their website all I can find is them selling is wiseco pistons and sleeves. I can't even cross reference the mercury #. I hope I am missing something as I would like to find a cheaper piston for them.

 

[89Aluma]

WSM makes replacements for both....cheaper than OEM and Seizco
Look on top of block and if it has the raised casting "MERCOSIL" it is a boreable block and only a special machine shop or motorcycle shop can do the work due to special tooling required.You can get a new block kit by shopping this part# on the web.(872-9533T40)

Thanks for the info on that, if can't save the cylinder block that will come in handy, but I think with a good honing the cylinders will be fine. The water jackets are good too no leaks I think it hydro locked because I was moving pretty quick and got stuck in some sand and that brought me to a pretty quick stop and that's when the power head started make the chuffing but it still ran

 

[racerone]

Not sure if " hydro locked " is the correct term here.----That would indicate that a fluid got into the cylinder that could not be compressed.---Nothing to do with hitting a sand bar.----Perhaps this motor was sumerged while running by previous owner.---That is why it was free !

 

[89Aluma]

When we hit the sand bar the water splashed against the transom pretty hard and I put a lot of hours on this since I got it, it was free because my wife's dad wasn't useing it anymore it always ran really well I think water backed up the exhaust and got just enough into the cylinder

 

[89Aluma]

Although I could be wrong, I be worked on cars for years but boats are a new animal to me what do you guys think happened so I can prevent it in the future