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brettzilla
  • Rank:Silver Member
  • Posts:94
  • From:Canada

Date Posted:09/12/2016 1:51 AMCopy HTML

can someone please clarify the oversize info for me? i've read that you can buy oversize pistons and rings in .25, .50 .75 and 1.00 sizes. but i don't know what those sizes mean. i don't think they're measurements, are they?  .25 of an inch is too big of a jump. and even if it were in millimeters, that's still a big jump, although a little more believable.

or are those numbers meant to represent something else?

also, the piston i took out of my engine has a "2" stamped on it. it seems to measure larger than what the manual allows for. does this "2" mean that its an oversize?

any help would be greatly appreciated.

thanks.
dmoh #1
  • Rank:Bronze Member
  • Posts:22
  • From:Australia

Re:oversize piston info

Date Posted:09/13/2016 7:11 AMCopy HTML

 .25 is 0.25mm, etc
Cheers,
Dennis
100258 #2
  • Rank:Bronze Member
  • Posts:37
  • From:USA

Re:oversize piston info

Date Posted:09/14/2016 2:17 AMCopy HTML

 brettzilla,

THE "2" ON THE PISTON INDICATES THAT IT IS A SECOND OVERSIZED PISTON AND SHOULD MEASURE 0.50 MM LARGER THAN A STOCK PISTON. 

0.25 MM MAY SEEM TO BE "BIG": TAKE A LOOK AT A METRIC RULE AND VISUALIZE THE SMALLEST DISTANCE BETWEEN TWO LINES BEING DIVIDED INTO QUARTERS (1/4'S).  NOW TAKE THAT DISTANCE AND DIVIDE IT IN HALF (1/2) AND THAT IS HOW MUCH METAL IS REMOVED FROM THE STOCK CYLINDER WALL WHEN IT IS RE-BORED FOR A 1ST OVERSIZED PISTON. IT'S LIKE REMOVING A COATING OF DUST.

MARK



brettzilla #3
  • Rank:Silver Member
  • Posts:94
  • From:Canada

Re:oversize piston info

Date Posted:09/14/2016 11:16 AMCopy HTML

 thanks guys.  That resolves things nicely.

Mark, since the metal removed from the cylinder is so small, can it be done with only a hone?

Also, what is the optimum clearance between cylinder wall ID and piston OD?
100258 #4
  • Rank:Bronze Member
  • Posts:37
  • From:USA

Re:oversize piston info

Date Posted:09/14/2016 11:19 PMCopy HTML

brettzilla:

TO REMOVE THE NECESSARY AMOUNT OF METAL BY HONEING WOULD REQUIRE A LOT OF TIME AND WOULD NOT GIVE NECESSARY, CONSISTANT RESULTS.  SINCE IT IS USUALLY DONE BY HAND WITH AN ELECTRIC DRILL FOR A SHORT TIME; IT REMOVES SO LITTLE METAL THAT IT DOESN'T AFFECT THE ACCURACY OF THE BOREING OPERATION.  I'M AFRAID MY DISCRIPTION OF HOW LITTLE METAL IS REMOVED WAS AN EXAGERATION TO EMPHASIS THE SMALL AMOUNT THAT IS REMOVED IN THE BOREING  OF THE CYLINDER FOR A 0.25 mm OVERSIZE PISTON. SOMETIMES, AS COULD BE WHAT HAPPENED TO YOUR BIKE WITH A 2ND OVERSIZE PISTON, A DAMAGED CYLINDER CANNOT BE CLEANED-UP WITH JUST A ONE STEP CHANGE IN THE SIZE OF THE CYLINDER BORE.

A REPUTABLE, EXPERIENCED BUSINESS THAT BORES MOTORCYCLE CYLINDERS SHOULD KNOW THE CLEARENCES BETWEEN THE NEW PISTON AND THE CYLINDER.  XLINT PERFORMANCE OFFERS A CYLINDER BOREING SERVICE, PISTONS AND RINGS ON THERE SITE.  http://www.xlintperformance.com/

DON'T FORGET TO CHECK AND ADJUST THE RING GAP OF THE NEW RINGS BEFORE INSTALLING. THE SPECS AND WEAR LIMITS ARE IN THE FACTORY SERVICE MANUAL.

MARK




Go soothingly on the grease mud ... as there lies the skid demon! ...






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