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Ok I am rebuilding my powerhead (new rings and complete gasket set) on my Evinrude 15hp. Since I have it completely apart I am wondering what kind of gains I would see from boring it out? (they make .20, .30, and .40 over bore) Is this worth looking in to or just a complete waste? We used to bore out our dirtbikes back in the day and saw huge gains! But a boat engine?
 

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I Love microskiff.com!
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Discussion Starter #3
Mallory and Weisco both make them. I don't need pistons just rings, but since I have the power head off and apart.... Any one know of any gains I might get? 2-3hp?
 

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not really worth boring unless the cylinder is out of spec .

the shop doing the boring may not hold exacting tolerances and you would ending up worse off


optimize what you have ...
 

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Stripper in my own Mind!
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Unless your cylinder walls are in bad shape and you have seen a drastic drop in compression then I would just leave them alone. You wont see a big difference in boring them unless your dealing with a larger and more tolerant engine. Just my opinion..
 

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Cylinder walls and pistons are in great shape, surprising since the rings are completely shot! So I will just order new rings and call it a day.
 

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Follow the instructions on the new rings and you should do well. (break down the glaze with a hone) Often an engine gets hot from lack of coolant water and the rings lose their tension. This results in low compression and poor running. A new set of standard rings can help a lot. It would be much better to trade the 15 for a 25 than to bore it looking for power.

Frank_S
 

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Yeah Boring the cylinder, won't add performance without getting additional air into the combustion chamber. Which also will require additional fuel to keep from running lean.

If the walls are good then hone and replace the rings.

Tip: Any rebuild I do I always inspect the wrist pin carefully and Always replace the c-clips that hold the wrist pins in. The wrist pins are the most highly stressed part inside an internal combustion engine
 
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