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  1. Default 1987 Honda CR80 oversized piston

    Hello everybody, I am new to the forum and would like some questions answered. I bought an 87 cr80 for $100 yesterday. I tore it down to the top end and found that the ring snapped and got lodged into the piston and made a scratch in the cylinder wall. I took the cylinder to a machinist who said I would have to get a .050 oversized piston for it so he could begin to bore it. Anyone know where I could get a .050 piston? Already checked ebay and the only one available is new-old stock for a 1985 model but I have no idea if it will fit my engine. Also, This engine is intended to be mounted to a race kart. (hence my name)

    Thanks in advance!

  2. #2
    Join Date
    Oct 2010
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    Illinois
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    Default

    I would try RJATV.
    Last edited by bansheekx; 08-17-2012 at 05:58 PM.

    1992 banshee
    2000kx250
    1999 polaris 400 sport

  3. Default

    Quote Originally Posted by cr80shifter View Post
    Anyone know where I could get a .050 piston?
    The guy said standard bore was 47mm and I should get a .050 piston. I have no idea what that is. Help?

  4. #4
    Join Date
    Nov 2009
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    Alabama
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    .050 over would make it 48.25

    edit:

    according to wiseco's website your motor is a 46mm bore stock. here is the part number for the one you want.

    http://www.wiseco.com/ProductDetail....987&AppID=4428
    Last edited by volfan537240; 08-17-2012 at 08:56 PM.




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  5. Default

    Quote Originally Posted by volfan537240 View Post
    .050 over would make it 48.25

    edit:

    according to wiseco's website your motor is a 46mm bore stock. here is the part number for the one you want.

    http://www.wiseco.com/ProductDetail....987&AppID=4428
    Thanks man.

  6. #6
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    Alabama
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    no problem boblem




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  7. #7

    Question Confusing Piston Measurements

    Piston oversize’s are a little confusing since they are in Metric MM and SAE Standard Thousant’s of an inch. A metric oversized piston would be stamped on the dome, .25, .5, .75, 1.00. Each .25mm = .010” of an inch. With me so far?
    Metric pistons
    Std
    .25 = .010"
    .50 = .020"
    .75 = .030"
    1.00 = .040"
    2.00 = .080"
    3.00 = .125" or 1/8" 3mm oversize is about as large as most Japanese engines can
    be bored without a new liner installed.

    You might give you cylinder boring bar operator a polite nudge and inform him that no one makes .050 oversized cycle or ATV pistons. If you find one let us know, we always need another piston supplier. Maybe you should check around for a more knowledgeable person to bore your cylinder.
    For the first oversized bore job you are usually faced with the decision, do I bore .25mm or .5mm, since both piston sizes are usually available. Many shops may not be able to do a .25mm overbore since it’s such a small amount of stock removal. Know your machinist; the lowest price may not be the very best deal.

    JT
    Last edited by John Tice; 08-18-2012 at 10:37 AM.

  8. #8

    Default

    I don't know who was nice enough to put my old comment in here. I wrote something like it again since I didn't see this first.
    Keep Learnin Man

    Hello CR80 Man: A quick piston primer. Honda pistons are not supplied in a +.050” over size.
    You have metric sizes and standard SAE sizes.
    A Quickie First over. +.25mm +.010”
    Second over +.50mm +.020”
    Third over +.75mm +.030”
    Fourth over +1.00mm +.040”
    Sometimes you can get a +2mm +.080”
    +3mm +.125” or 1/8”

    The standard big bore pistons for Honda and other 4-strokers is 3mm. 1/8” is about as far as a standard OEM Japanese cylinder liner can be bored safely. One other thing to keep in mind. There are Cast & Forged pistons available for your engine. Either one will work just fine for you. The forged piston will usually cost twice as much as a cast piston. Your engine boring man needs to be familiar with cycle engines. Their tricky little devils’ to set up properly.
    Any engine man in your area who is an E2S member is the kind of person you should probably think of first. Their a great bunch of people to know. Sorry for running off at the mouth. Just stuff a newbie should be familiar with.
    “Old Dog”

  9. #9
    Join Date
    Oct 2004
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    pennsylvania
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    You can get .050 over sized forged pistons for many Atv engines
    Don't think you'll find one for that bike though
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  10. #10

    Default

    Dennis is correct. You can get any piston you want, all you gotta do is fork over the BUX.