Mercosill block boring

[perfmarine1]

Have any of you guys bored these blocks and do you need special cutter/honing stones?

[25XS]

Short answer: Yes. Mercosil can be bored & honed. Mercury sells 0.030" oversize pistons only. Aftermarket sells 0.020", 0.030", & 0.040" oversize pistons. Yes. Special tooling is required to do it correctly. Extra hard cutters & a diamond hone and "Profilometer" is recommended by the machining industry to test the machined surface profile when done. However, Mercury Marine states that a diamond bore to 20 micron Ra works fine for production engines and a bore followed by Osborn brush is even better.

U.S. Chrome in Fond du Lac, Wisconsin can & will "skim bore" Mercosil blocks and then plate the bores with their NiCom plating process and they report excellent results on 20/25hp Mercosil engine rebuilds.

I found this document online written in the year 2000, and for you guys who like technical articles, you're in for a treat. Based on the conclusions of Dr. Raymond Donahue, Mercury Marine, and his co-writer, I am a little surprised that ALL Mercury engines don't have Mercosil blocks & specifically, cylinder bores, but I'm pretty sure it has to do with the added tooling cost to do it right as well as the constantly pushed myth that Mercosil is a plating, liner, or coating on a cylinder wall (it's not; it's the entire block casting made of Mercosil aluminum alloy).

Enjoy, the good stuff starts on page 2, the conclusions are on page 10. Seems they shared the technology with Mercedes & Porsche and it was good enough for their cars to incorporate.

http://www.ncccoat.com/PDF/MercuryNCCSA ... papers.pdf

Here are some of the paragraphs that made me really concentrate!

In the mid-1980’s, Mercury Marine started its largest and
most systematic field study in its die cast Merc 25hp block to
evaluate a family of copper-free hypereutectic aluminumsilicon
alloys called Mercosil technology. Mercosil is an
acronym for Materials Engineered for Resistance: Corrosion
(copper free) and Wear (silicon). After accumulating
1,000,000 field hours with test fleet of engines with no
failures attributed to the alloy, the decision was made to go
into full production in 1994 with Mercosil for the Merc 25
block.
The Mercosil Merc 25 engine replaced a very successful
engine block that had chrome plated bores, and was in
production for over 20 years. The only flaw inherent in the
previous Merc 25 with chrome plate bores (besides cost of
manufacture) was its susceptibility to fatal damage when large
debris was ingested by the engine. The Mercosil Merc 25 is
tolerant of ingested debris
Mercosil engine has a clear advantage because low emission
2-cycle engines that have to conduct heat out of the
combustion chamber through a cast iron liner will be
penalized in performance and durability over the all-aluminum
Mercosil engine that has a high conductivity path for the
combustion heat.

And this couple paragraphs... WOW! No honing necessary. Now I see the comparison to SeaDoo blocks!

Cylinder Bore and Surface Finish

Based on six years of production experience, honing is not
necessary for the Mercosil 2-cycle application with a
thermostat when TCW-3 oil is used with a regular unleaded
gasoline. Diamond boring Mercosil to a 20 microns RA maximum
surface finish is sufficient.

The absence for the need to hone a
pattern into the bore is significant because it is the general
practice to hone a pattern into the bore to hold the lubricant.
However after 1000 hours of running the “as bored” surface,
it has the topography of a honed and etched bore.

Significantly, when the as-bored Mercosil bore is honed and
Osborn brushed, the Mercosil bore outperforms the chrome
plated bore in the 30% kerosene test and the 4-Stroke oil test.

Here is another great article. http://www.sunnen.com/NewsDetails.aspx?NewsID=11

Another great article... Especially good near the end! http://www.mmsonline.com/articles/new-h ... nder-bores

[FUJIMO]

Thanx for posting this 25XS... Mercury developed Mercosil years ago, and uses it more & more these days, and licenses this product/processes to other manufacturers as well.

[perfmarine1]

Thanks 25XS, I know they can be bored as book says so,but dose not specify tooling.

[25XS]

Thanks 25XS, I know they can be bored as book says so,but does not specify tooling.

I've never seen tooling specified in any outboard manufacturers' service manual... The article does provide a final finish specification that you can take to your machinist. 20 micron RA I personally would finish hone it at home with a Brush Research Manufacturing "Ball Hone". I have a new one that I have only used in Mercosil blocks and nothing else.

Here is an example of the Nicom plated work from U.S. Chrome in Fond du Lac, Wisconsin on a "pre-Mercosil" block.

http://www.ebay.com/itm/321733172712

[perfmarine1]

So does anyone actually do the boring on these blocks?