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  1. #1

    Yamaha 25hp CV to bore or resleeve?

    Hey guys i rebuilt a yammie on here a year or two ago we got it running but she had a slight knock at idle, now shes ny motor im going to repair it

    I think i over honed one cylinder, would it be cheaper to bore,hone, new os pistons or just resleeve to std size?

  2. #2

    Re: Yamaha 25hp CV to bore or resleeve?

    I doubt you over honed it unless you had rasps on your cylinder hone. Bore it out and fit oversize pistons would be my guess.

  3. #3

    Re: Yamaha 25hp CV to bore or resleeve?

    Do u think the lower main crankshaft bearing is the problem we had a shop install a non oem bearing that had to get a locating pin installed in the outer race, we ran the motor max 5mins tore it down and that one bearing is loud and lose

  4. #4

    Re: Yamaha 25hp CV to bore or resleeve?

    The main crank bearing probably won't cause a knock (but it could of course) but it needs to be replaced! more likely a rod big end or small end bearing, not too sure you can put a sleeve in those! and I also doubt you honed it too much, unless it was very badly worn in the first place

  5. #5

    Re: Yamaha 25hp CV to bore or resleeve?

    Noelm we had the who crank disassembled inspected than reassembled by a engineering company mate after i tore the motor apart i took the crank back and had it inspected and the guy swears its ok

    i don't know weather to take it to a shop a Yamaha dealer and have a mechanic inspect it or invest the money in tools of my own to measure it

    there is no play in the rods or main crank bearings only that one bottom bearing this is why i thought i may have over honed the cylinders

    i will take another squiz now i will use the calipers to check the little end rod roundness brb just measured the one new piston and old piston

    new piston around the top measures 71.42mm around the bottom measures 71.90mm

    old piston around the top measures 71.38mm around the bottom measures 71.86mm

    the reason i replaced one piston was the rings were seized in the piston ring gap, do u think the above measurements are ok? i might have to pay for a workshop manual just hard to find for the CV models

  6. #6

    Re: Yamaha 25hp CV to bore or resleeve?

    if you say the crank and big ends are good, then just replace the non genuine bottom bearing. if it's just piston slap, i wouldn't worry, just do a compression check and make sure they are even. they will go forever!

  7. #7

    Re: Yamaha 25hp CV to bore or resleeve?

    Yeah it has to be piston slap the old piston measures 71.86mm the manual states 71.94-71.96mm so it is fairly off i will replace the bearing and the piston

    cheers for the replies guys i seriously thought i over honed the cylinders because this was my first ever hone job

  8. #8

    Re: Yamaha 25hp CV to bore or resleeve?

    You need to measure the piston to bore clearance with a dial bore gauge and micrometer and hone to spec and check ring gap in bore

  9. #9

    Re: Yamaha 25hp CV to bore or resleeve?

    I only have vernier calipers mate i do need to invest in a set of bore gauges however the manual does give measurements for piston and for the cylinder which both would need to be calculated together but they are not on the same service page in the manual

    i will remeasure the ring gap today just to check again and be sure

  10. #10

    Re: Yamaha 25hp CV to bore or resleeve?

    Cannot believe it, Ordered the gasket kit on ebay on Thrusday and it arrived Monday from Taiwan to Australia for AUD$80 total including shipping, Yamaha Australia wanted $170 and its a 2 day wait

    They wonder why we shop overseas
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