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  1. #1

    Yamaha power valve issue

    I'm rebuilding an 800 pv motor due to loss of oil to rear cylinder. After tear down i discovered that the front cylinders power valve is missing from it's stem and no where in the motor. I've run the ski for five years no no issues until the oil line came off. I know the ski since new and it has never been worked on. Just confused with what i found!
    I'm an old car engine guy and this is my first 2 stroke and looking for any advice on the rebuild.

    Thanks


  2. #2
    mudslanger's Avatar
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    Since the powervalve is missing go ahead and remove the cylinder to check for damage to the rings and piston. inspect the crank if it got hot from no oil to the crlinder.
    Good luck with the build

  3. #3
    Thanks mudslanger, i've have it completly torn apart, thats when i found the part of the PV missing. I just don't know if this could have been deliberate on just poor quality on Yamahas part, the guilitine part is missing for the stem . The cylinder that it's missing from is the front and both cylinder and piston look fine.
    If it had broke off while it was running it seams that would have caused a lot of damage!
    Here's my plan
    I found a place in Auburn Al (Langcount) that can repair a recoat the rear cylinder so I'm sending both in case they have to bore out the damaged rear.
    Order new pistons after i get the cylinders back
    Send crank off to rebuild, I've talked to company (crankworks) in Arizona, but would prefer somewhere closer to Atlanta.
    Any recomendations would be appreciated.

  4. #4
    smacota1's Avatar
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    You will need to send a piston with each cylinder that needs a replate. They replate and hone the cylinder to match the piston for clearance.

  5. #5
    pv might be in the exhaust, did you check there

  6. #6
    Can't find it anywhere in the exhaust system. Guess i just got lucky and it some how spit the thing thru and out.
    Does anybody have any experience with the aftermarket Billet Power valves. I won't be lucky twice!

    Thanks for the repies.

  7. #7

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    Quote Originally Posted by Grandaddy View Post
    Can't find it anywhere in the exhaust system. Guess i just got lucky and it some how spit the thing thru and out.
    Does anybody have any experience with the aftermarket Billet Power valves. I won't be lucky twice!

    Thanks for the repies.
    The aftermarket power valves work fine, but do not expect any performance gains.... just piece of mind. The gas valves are much easier to work with than the mechanical power valves. I do not know if the Riva gas valves also apply to the 800 models.

    Crankworks is an excellent builder... you would be wise to go with them.

    Renicasil your cylinders back to stock using the stocker piston for a guide. Remember ask for the pistons that match the cylinders based on the stamped number on top of each cylinder when you order them

  8. #8
    Does anyone recommend a particular Gasket set and seals for the yamaha 800.

  9. #9

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    Quote Originally Posted by Grandaddy View Post
    Does anyone recommend a particular Gasket set and seals for the yamaha 800.
    Go with the OE. The head gasket should be reuseable if there are no bends in the aluminum and no signs of communication between the water jackets and cylinder. The base gaskets and seals are a must though. The crank builder may also send new front and rear seals. Check with them before you buy.

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