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Thread: Cylinder Head Question

  1. #1
    Senior Member DrTerrible's Avatar
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    Cylinder Head Question

    So I have two cylinder heads. One came off a rust bucket of a motor and is pitted from rust. I took it to the local shop and they said that I should have it bored to another size so oil doesn't get trapped in the pits and cause it to smoke. I have another head from my running motor that when it was dismantled, the piston was scratched so I'm assuming the cylinder wall is scratched also (would post pics but don't have any yet) which I am also assuming will need to get bored. Was hoping to get away with a hone as I ordered a stock piston and should be here in the next couple days. Since I will more likely have to return the stock piston...which oversize should I buy? was thinking of the 70mm so no other parts have to be purchased and wait another 3 weeks for the parts to arrive.

    What would you do?

    Cheers!
    Jim
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  2. #2
    Senior Member Bruce's's Avatar
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    Generally ,you don't bore any more than you have to ,because if you go too big ,the next time you have to do it you can't and you must replace the cylinder or sleeve it .What does the machine shop say ?
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  3. #3
    Senior Member scotti158's Avatar
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    Just for clarity sake, you are talking about the cylinder, not the head. As Bruce said, normally you don't bore any more than needed to clean up the cyl. Stock bore is 67mm. As an example, machine shop bores to 67.35mm to clean up score marks. Next oversize piston from Yamaha is 67.5mm. The shop would bore and finish hone to that size. (The actual measuring and fitting the piston to the cyl. with the proper clearance is a little more complex than that, but that 's the basic idea.)
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  5. #4
    Senior Member DrTerrible's Avatar
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    I haven't had time to take the other cylinder in. Shop said to bore the pitted one but never said what size to get
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  6. #5
    Senior Member DrTerrible's Avatar
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    I will see what they say but the pistons the sell are $80CAD more expensive then if I went with oemcycles. Made the mistake of ordering a stock size not thinking it might have to get bored. Live & learn, trial by error seems to be the theme of my project...all good though
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  7. #6
    Senior Member JerseyJeeper's Avatar
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    The shop needs to examine the cylinder closely to determine what size they need to bore it to in order to get past the pitting. They will need a list of available piston sizes from you so they know the different target sizes.
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  8. #7
    Senior Member elime's Avatar
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    One can get away with a lot less than perfection on a cylinder. Some glaze breaking and a new set of rings on the original piston and this engine ran like a champ as witnessed by the NorCal Nut Jobs. The bike was mine but Big D rode it for many trouble free non oil burning miles.

    P3080845.JPG

    If you are going with a new piston may I suggest a Wiseco. They come with new rings and wrist pin and clips. They are forged, therefore very strong, and are of higher compression than stock.

    I forgot to add that if you will settle for a really inexpensive 70mm cast piston and don't mind waiting the week or two it takes to get here this is a good choice.

    Piston Rings Pin Clips Kit For Yamaha XT225 XT 225 STD Standard Bore Size 70mm | eBay
    Last edited by elime; 05-03-2017 at 07:25 PM.
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  9. #8
    Senior Member DrTerrible's Avatar
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    Wow, thats an amazing price. I have a wiseco 67mm coming any day now but that was before the shop told me i need to bore because of the pitting and how oil can get in the pits to make it constantly smoke. The other cylinder i have, the guy that is working on the engine said i should get it ball honed because of the scratches. I will try and post pics here shortly.

  10. #9
    Senior Member DrTerrible's Avatar
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    Here is the scratched piston and cylinder of the rusty/pitted one

  11. #10
    Senior Member DrTerrible's Avatar
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    IMG_0189.JPG

    And here is the scratched one

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