Mariner/Mercury 20 hp 2002y 2 stroke

[raczekp1]

Hi.
I need some help.
Friend of mine overheated this motor. upper piston is badly scored.
I just looked at boats dot net and i se notice that oversize pistons is not avilabel.
Is there any source to find oversize pistons for this mtor

 

[flyingscott]

What is your serial#. A 2002 should have pistons available to .040 oversize.

 

[James R]

I think this is a Mercasil motor. Mercury says can do 30 over but dont waste your money. I have a 2000 motor on my bench now in reassembly. The first block could not be bored, too far out of round. Bored a second block to 30 over per Mercury's recommendation and the cylinders failed in a few days. I decided to salvage what money I can and had it sleeved. Nice job by my expert friend. All this cost a bunch of money. I now consider these Mercasil motors throw aways. Wont do anymore.
Interesting to note that I had a Mercasil 25HP Mariner in about 5 years ago. Had one cylinder bad. Bored to 30 over and the bore looked like crap and told the owner to not expect too much. It is still running.
how's your luck? I think sleeving is the right way to go or get a new block.

 

[Faztbullet]

You cannot bore it like a cast iron block as it takes a special bit and diamond honing stones to finish hone it . If bored by standard practices it will fail.

 

[raczekp1]

well, my friend is still thinking if invest any money with rebuilt or look for running powerhead.
machine shop says its hard to rebore becouse cylinder is open ony from one way.
how did you sleeve this cylinder block?how did you cut suction ports?

 

[flyingscott]

You need to find a shop that can do a blind-bore which is what it's called. Most of the Mercosil motors that have been bored and failed that I have seen, have done so because they put aftermarket pistons in. If you bore it you HAVE to use mercury pistons and rings. I would call a dealer and see who they recommend for machine work. Otherwise L.A. Sleeve makes a sleeve for it But you will have the same problem as the block will need to be bored out for the sleeve. L.A. sleeve can do the whole process but it is $300 a hole. I would call a dealer as boring would cost about a 1/3 of the price per hole.

And look at post #4 for more info

 

[Faztbullet]

You don't need to use OEM pistons as WSM makes pistons that have the alloy cast in them. Have used them in Mercoil blocks for years and no failures...As for block take it or call a motorcycle shop as a lot of the new bikes are using this process.

 

[flyingscott]

Sorry I got screwed up there in my post #7. That's why I shouldn't post when I am tired. Aftermarket pistons fit in the mercosil block, but double check with whoever you have sleeve it to find out whose pistons they recommend for their sleeve. Because you are changing the bore material from mercosil to a cast sleeve makes a difference.