Polish piston crown



  • Hi guys , got the mitaka piston , std size and was reading the post about porting and polishing here. Wondering if its any good to polish my piston as its different from the one like wossner, this is like rough material I think from casting .

    0_1491052686902_s-l300.jpg

    It might should be there so better ask here haha. What you think? And also my kit was supplied with a spring which going under one piston ring and dont know which one. Nothing about it in haynes bible.



  • Polish the combustion chamber, leave the piston crown alone!

    Basically, the performance of an engine drops slightly when installing a new piston, when the piston crown is covered in carbon the performance goes back up.

    The science is because Ally dissapates heat better. When you polish the crown you effectively build a resistance to carbon build up. When the carbon builds up it adds a layer. The layer of carbon is not very conductive, so heat takes longer to go through to the piston, and then to the cylinder walls.

    In extreme cases this is bad, but when matched appropriately, the higher combustion tempertures causes higher combustion pressure, more pressure is then exerting on the piston, forcing it down and producing power.

    However since the power is made in the combustion chamber, this wants be polished to resist carbon build up.

    There is more science, if you're interested then I suggest you read Graham Bell's Two Stroke Performance Tuning.



  • @Calum yeah , working on the combustion chamber atm and Im asking because I was reading your older post where you said to polish it. Have that book from Mr. Bell in watchlist on eBay for months but always had more important parts to buy



  • https://c1.staticflickr.com/3/2816/33775090465_8825e16fdb_c.jpg

    You shouldn't be polishing either really,

    but here is a used MITAKA vs a New WOSSNER to illustrate. Carbon does help to a point. The Wossner is a CNC finish, but if your hunting power there wont be any difference.

    Problem with forged is the difference in thermal expansion to a cast alloy. MITAKA is a good choice for the DT.

    https://c1.staticflickr.com/1/548/31277391110_2d27cd8549_c.jpg

    Smooth yes, but a rough surface lends itself to optimising fuel atomisation, that is more important.