Re: Wiseco Piston Break In Process
WELL, My 2 cents: I have rebuilt a number of different brands of 2 cycle outboards and if possible, I always use Wiseco. They are amazingly well made and worth every buck you pay for them.
NOW: from necessity, when the owner picks-up his rig, I take it out on the water with him. With only about 5 minutes running time, It is necessary for me to use full throttle to set timing. HOWEVER: Once timing is checked and confirmed as correct, the engine no longer sees full throttle. I caution the owner to not exceed 3/4 throttle or 3500 RPM until at least two 6 gal tanks of double oil mix has been run through the engine. On the larger engines, this works out to somewhere around 4 hours. Say, 1,000,000 cycles
I have never had a return or complaint, and all my personal engines run "like a top."
ALL outboard engine pistons are cam ground because the cooling water cools the cylinder unevenly. This also causes the piston skirt to heat and expand unevenly. Thus, when the engine warms up, the piston becomes more nearly circular and it and the cylinder now match in shape. Engine tolerances vary from manufacturer to manufacturer. For example, while OMC uses .005 clearance, Force uses .002. AND total wear allowed in the cylinder for taper, out of round, or oversize is .005 on OMC and .002 on Force. THUS if your Force engine has only .002 wear, it is necessary to bore .010 over. AND- the listed clearance is hot clearance--wiggle a cold piston in a cold cylinder--amazing how much slop there is, especially at the crown which gets way more heat than the skirt.
Since racing applications or higher power modifications usually result in more cylinder pressure and higher temperatures, and since the aluminum piston expands to a greater degree than the steel cylinder liner, these applications require a bit more clearance. Engine runs like crap until it warms up but racing engines are not meant to run cool or slow.
NOW: My personal opinion--- 3000 RPM works out to 180,000 cycles per hour. If rings aint seated and it aint broke in by then, it aint never gunna be.