# Mercury 25 HP Rebuild Options



## flyclimber (May 22, 2016)

Pics for reference


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## Guest (Jan 13, 2019)

Dang brother, at 30 over already I think she is toast. But let the machinest look anyway to be sure. Maybe he can sleeve her with some iron!


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## flyclimber (May 22, 2016)

Let's hope my measurement device is inaccurate! It has been pretty beat up.


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## RunningOnEmpty (Jun 20, 2015)

My local machine shop won't touch those blocks. If you can bore it and find pistons, Why not? Maybe open up those intake and exhaust ports a little too


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## devrep (Feb 22, 2009)

can it be sleeved?


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## Guest (Jan 13, 2019)

RunningOnEmpty said:


> My local machine shop won't touch those blocks. If you can bore it and find pistons, Why not? Maybe open up those intake and exhaust ports a little too


Maybe some CC block stuffers and fiber reeds? Might as well do some tuner work too!


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## RunningOnEmpty (Jun 20, 2015)

Those things use an aluminum with a very high silica content that allows them to run without sleeves. I've never heard of someone re sleeving one?


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## flyclimber (May 22, 2016)

I see an outboard machinist here in town. Supposedly ~30 years of experience. Will post up results tomorrow. 

I am not opposed to any mods. Reliability is still #1. Thankfully no downtime from fishing from a motor that is torn apart!


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## fishnpreacher (Jul 28, 2018)

The scoring may clean up with some honing. The major culprit is a cylinder usually gets ovaled, or egg shaped. It's not noticeable with the eye, but you will see it when you mic the cylinders. I'm not very familiar with marine engines, so the actual alloy of the block may disallow sleeves. Definitely see a marine specialist.


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## devrep (Feb 22, 2009)

I've had nikosil mx bike cylinders sleeved. not all can be done cause over boring for the sleeve can conflict with the power valves but not an issue on an old merc.


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## devrep (Feb 22, 2009)

_here's a kit that goes to .40.

https://obparts.com/mercury-mariner...mercosil-block-powerhead-1994-up-rebuild-kit/


_


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## No Bait / Lures Only (Apr 10, 2011)

Boatbrains said:


> Maybe some CC block stuffers and fiber reeds? Might as well do some tuner work too!


Now ya talking!


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## flyclimber (May 22, 2016)

I think the machinist is flaking... Any one know of a machinist near Jax?


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## No Bait / Lures Only (Apr 10, 2011)

freeclimber said:


> I think the machinist is flaking... Any one know of a machinist near Jax?


Call Jon Wolfe @ hydro tec


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## flyclimber (May 22, 2016)

No Bait / Lures Only said:


> Call Jon Wolfe @ hydro tec


I thought they only worked on Yamahas?


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## No Bait / Lures Only (Apr 10, 2011)

No not true, a machine shop as well n sell mercury parts too....
Sign into scream n fly many people knowledgeable mercury people. Chris Carson does mercury motors...


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## flyclimber (May 22, 2016)

No Bait / Lures Only said:


> No not true, a machine shop as well n sell mercury parts too....
> Sign into scream n fly many people knowledgeable mercury people. Chris Carson does mercury motors...


Yep I reached out to the guys over there and they are split. One guy did say that there is a .040" over piston for my engine! So there is hope!

I just put the new axle on the trailer. I think I can swing by the machine shop tomorrow. The shop was supposedly closed for the last couple of days due to meetings...


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## flyclimber (May 22, 2016)

Alright here the story. The machinist is old school and has been refinishing blocks for about 30 years. REAL DEAL!

The block I have... Cylinder #1 is near perfect only out .0005 in one spot, cylinder #2 needs a sleeve. It would be about $400 to throw the sleeve in there or more. 

Can you run different sized bores in the same block? I may just try to find another powerhead that hasn't had any work done on it and rebuild that one.

Very random thought, While talking to the machinist a gentleman walked in, turns out to be an descendant 8th generation of the Davey Crockett.


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## Guest (Jan 18, 2019)

I’ve seen different bores on cylinders but don’t reccomend it. It will throw the balance off.


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## flyclimber (May 22, 2016)

Boatbrains said:


> I’ve seen different bores on cylinders but don’t reccomend it. It will throw the balance off.


I think I will be looking for a powerhead for a little bit or decent outboard to get it done right the first time.


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## Guest (Jan 18, 2019)

What year model is yours?


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## flyclimber (May 22, 2016)

04


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## yobata (Jul 14, 2015)

At some point in this process, it may become cheaper to purchase a working Merc 25HP 2 stroke than to do all this machine work and repair?

The link below is from a guy in Central Florida who sells these from Wisconsin - a few members have bought from him and the motors are in excellent shape...

https://orlando.craigslist.org/bpo/d/clermont-2003-mercury-25-tiller-short/6793052782.html


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## Gatorgrizz27 (Apr 4, 2015)

Boatbrains said:


> I’ve seen different bores on cylinders but don’t reccomend it. It will throw the balance off.


Couldn’t you machine a bit off the skirt of the larger piston to make them the same weight? I agree it isn’t ideal, but it would probably run fine for years.


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## Guest (Jan 19, 2019)

Gatorgrizz27 said:


> Couldn’t you machine a bit off the skirt of the larger piston to make them the same weight? I agree it isn’t ideal, but it would probably run fine for years.


I believe you could, I am no machinist but have seen it and they’ve ran fine honestly.


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## RunningOnEmpty (Jun 20, 2015)

yobata said:


> At some point in this process, it may become cheaper to purchase a working Merc 25HP 2 stroke than to do all this machine work and repair?
> 
> The link below is from a guy in Central Florida who sells these from Wisconsin - a few members have bought from him and the motors are in excellent shape...
> 
> https://orlando.craigslist.org/bpo/d/clermont-2003-mercury-25-tiller-short/6793052782.html


That's close to what I paid for a new 25hp Merc back in the early 2000's. I do love those little Mercs though! I couldn't kill mine and I abused it every weekend for years.


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## flyclimber (May 22, 2016)

yobata said:


> At some point in this process, it may become cheaper to purchase a working Merc 25HP 2 stroke than to do all this machine work and repair?
> 
> The link below is from a guy in Central Florida who sells these from Wisconsin - a few members have bought from him and the motors are in excellent shape...
> 
> https://orlando.craigslist.org/bpo/d/clermont-2003-mercury-25-tiller-short/6793052782.html


I did see that one while digging earlier. The problem I have is that, on more than several occasions I have been burned by getting a "good" or "great" condition anything. I would rather put the money down and know without a doubt it is good. 

I would pull the trigger on the new one but the power-to-weight ratio, simplicity, and cost of running are in my mind in favor of the old two strokes. 

I got a quote for the new Yamaha it was almost $4k. :O


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## devrep (Feb 22, 2009)

I've rebuilt a lot of 2 stroke dirt bike engines and my son and I completely rebuilt the 4 cyl merc 50 2 stroke on the StarCraft rebuild we did (I had a machinist bore the block but we did the assembly and I have a set of bore gauges and was able to check his work). I would NEVER do one with mixed bore sizes. Also, personally I would never have someone else do a rebuild for me, there are too many shortcuts they can be tempted to take that you will never know about. I have read too many posts about newly rebuilt engines taking a crap and the rebuilder not taking responsibility. The post of our rebuild is on this website.


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## flyclimber (May 22, 2016)

I will have to check it out! I very much agree. I just need a good powerhead to start on.


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## devrep (Feb 22, 2009)

here's the post, the engine work starts on page 3.
https://www.microskiff.com/threads/rebuilding-my-1st-skiff-for-son-and-grandson.40413/page-3


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## RunningOnEmpty (Jun 20, 2015)

devrep said:


> I've rebuilt a lot of 2 stroke dirt bike engines and my son and I completely rebuilt the 4 cyl merc 50 2 stroke on the StarCraft rebuild we did (I had a machinist bore the block but we did the assembly and I have a set of bore gauges and was able to check his work). I would NEVER do one with mixed bore sizes. Also, personally I would never have someone else do a rebuild for me, there are too many shortcuts they can be tempted to take that you will never know about. I have read too many posts about newly rebuilt engines taking a crap and the rebuilder not taking responsibility. The post of our rebuild is on this website.


Re boring every other cylinder is half assed in my opinion. I would only do that if I was really hard up.


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## noeettica (Sep 23, 2007)

I have a block scored but standard PM me with an offer


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## devrep (Feb 22, 2009)

this is the guy who bored and honed my merc 50 block. he also has decent prices on rebuild kits. He's been in the same shop for about 30 years.

http://precisioncycleinc.com/servic...oring-services/cylinder-boring-pricing-sheet/


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## flyclimber (May 22, 2016)

Bumping my old thread. What components are needed for the charging circuit? Just the auxiliary stator and Voltage conditioner/regulator right?


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