Page 1 of 2 1 2 LastLast
Results 1 to 10 of 13
  1. #1

    Whats wrong with this piston? 1994 Fuji 650

    Hi Guys,

    Thanks for all the previous responses to my questions...have learned alot from this site(...but obviously not enough yet....)

    My 94 polaris 650 is dead. I have done all the mentioned upgrades ie: triple fuel pump, lines, and complete carb kit, fuel filter. It seems to work quite well for a while, then shortly after the carb fix, it got very boggy, and died. At first I thought it was my high and low mixture, but it was twice verified with factory settings.
    It seemed like all the sudden, the sound of trying to start it was very different.....louded are rougher.


    Decided to take the heads off.... PTO piston is scratchy and marked had has the appearance of a dry rock. The other two pistons are slick and wet.
    Click image for larger version. 

Name:	2013-07-08_18-26-03_281.jpg 
Views:	109 
Size:	100.6 KB 
ID:	306164
    What now guys? New Piston? How do you know if the bearings are toast?

    Sheldon


  2. #2
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
    Join Date
    Jul 2007
    Location
    Cedar Rapids,Iowa
    Posts
    6,381
    +1
    23
    Piston is toast. Looks like it eat something, possible a piece of bearing or ring.

    One thing is the head gasket was installed wrong. the gasket has the word up stamped in it. you should be able to read it when installed correctly. As you can see most of the cooling openings are not showing thru the gasket. Could just be a burndown from too hot, but still looks like something got bounced around.

    Pull the jug and check the rod for slop (up and down and the cylinder walls.

    Also see all the chips around the top ring land? If one ring is installed wrong, the others may be too. pull all the heads and check.

  3. #3
    BlueFishCrisis's Avatar
    Join Date
    Aug 2011
    Location
    Medina, Ohio, United States
    Posts
    4,988
    +1
    140
    Quote Originally Posted by Keddano View Post
    One thing is the head gasket was installed wrong. the gasket has the word up stamped in it. you should be able to read it when installed correctly. As you can see most of the cooling openings are not showing thru the gasket.
    I can read the word "UP" in that photo. Also, the cooling holes on the 650 gaskets are MUCH smaller than the 750 and 780 holes, for whatever reason. But +1 to the rest of your statements...

  4. #4
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
    Join Date
    Jul 2007
    Location
    Cedar Rapids,Iowa
    Posts
    6,381
    +1
    23
    Quote Originally Posted by BlueFishCrisis View Post
    Quote Originally Posted by Keddano View Post
    One thing is the head gasket was installed wrong. the gasket has the word up stamped in it. you should be able to read it when installed correctly. As you can see most of the cooling openings are not showing thru the gasket.
    I can read the word "UP" in that photo. Also, the cooling holes on the 650 gaskets are MUCH smaller than the 750 and 780 holes, for whatever reason. But +1 to the rest of your statements...
    I stand corrected...LOL, My eyes must be upside down today or maybe my brain is in reverve. The head gasket is not indexed correctly.

  5. #5
    Man You are smart.

    It appears this is the only piston with a problem. Is it possible to fix this/replace piston, and not touch the other ones? Or do bearings need to be replaced by taking all three cylinders apart. I dont really know what you mean by " pull the jig and check the rod for slop"...lol. I'm not a mechanic.....but I have fixed everything on this machine so far( including a complete carb overhaul...first time ever). Do you think this machine is junk, or should I fix?

    Update....found two small metal pieces in the reed valves(PTO). One about dime size, the other very small. Is this relevant, or could it have been there from the start?

  6. #6
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
    Join Date
    Jul 2007
    Location
    Cedar Rapids,Iowa
    Posts
    6,381
    +1
    23
    Nope, that would be new damage, you need to remove the exhaust pipe and manifold then
    take the 4 nuts off the cylinder (jug) at the bottom of it and pull it off.

    Then you can see if you feel any up and down play in the connecting rod, and also get a better look at the inside of the cylinder and piston.

    take some pictures of what you find.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    Location
    near Toronto, Canada
    Posts
    36,591
    +1
    1,275
    Quote Originally Posted by Spoulin View Post
    ... It appears this is the only piston with a problem. Is it possible to fix this/replace piston, and not touch the other ones?

    Or do bearings need to be replaced by taking all three cylinders apart.

    I dont really know what you mean by " pull the jig and check the rod for slop"...lol. I'm not a mechanic.....but I have fixed everything on this machine so far( including a complete carb overhaul...first time ever).

    Do you think this machine is junk, or should I fix?

    Update....found two small metal pieces in the reed valves(PTO). One about dime size, the other very small. Is this relevant, or could it have been there from the start?
    Danno is just typing too fast

    What you need to do is incrementally open up the engine to inspect and evaluate the condition of the internal parts.

    Removing the cylinder with the damaged piston inside will allow you to more clearly view the piston sides and the cylinder walls. It will also allow you to peer into the crank case itself.

    The main thing to be looking for is any signs of damage to the bearing where the connecting rod rides on the crank shaft. If that bearing is in any way loose in the up and down directions, or has excess play side to side, then the entire crank shaft must be rebuilt.

    That you found metal pieces in the lower crankcase, just behind the reeds, suggests that either a crank bearing is coming apart or the metal came from the piston itself or the small 'wrist' bearing attached to the piston.

    The piston can be easily replaced, as can the upper wrist pin and bearing. The cylinder can be rebored slightly larger (by a machine shop) if needed to restore a serviceable and smooth finish.

    One advantage of these Polaris 2-stroke watercraft engines is that even a complete engine rebuild is much, much less expensive than a rebuild on a newer 4-stroke watercraft engine. To get a rough idea what the worst case cost might be, have a look at the rebuilt Polaris engines from SBT.

    I am not saying that SBT rebuild is the best option for you, just a useful reference point regarding cost.

  8. #8
    Ok thanks for the replies guys...I guess I'll dig in even deeper...then post some pics.

    Any ideas why this has happened?
    I tried to do everything right with the upgrades so this WOULDn't happen.
    F my life!


    Sheldon

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    Location
    near Toronto, Canada
    Posts
    36,591
    +1
    1,275
    Quote Originally Posted by Spoulin View Post
    Ok thanks for the replies guys...I guess I'll dig in even deeper...then post some pics.

    Any ideas why this has happened?
    I tried to do everything right with the upgrades so this WOULDn't happen.
    F my life!


    Sheldon
    The engine is nineteen years old!

    If this is the first time the engine has failed since new, that's not so bad.

  10. #10
    BlueFishCrisis's Avatar
    Join Date
    Aug 2011
    Location
    Medina, Ohio, United States
    Posts
    4,988
    +1
    140
    Quote Originally Posted by Spoulin View Post
    Any ideas why this has happened?
    Did you check your crank index? An out of phase crank can cause issues. Did you perform a leak down test. A leaky crank seal at the PTO or MAG location can lean out the cylinder and cause it to fail. Are there any air leaks in your fuel system / lines? Air bubbles can cause a lean condition as well....

Page 1 of 2 1 2 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Whats wrong with this???
    By Duke in forum 4-Tec Performance
    Replies: 59
    Last Post: 01-24-2010, 11:23 PM
  2. whats wrong with this picture?
    By RHeller1 in forum Yamaha Open Discussion
    Replies: 12
    Last Post: 10-26-2009, 05:24 PM
  3. Whats wrong with this vid?
    By ou812 in forum Videos & Pictures
    Replies: 1
    Last Post: 04-21-2008, 10:36 AM
  4. Whats wrong with this picture?
    By ou812 in forum 4-Tec Performance
    Replies: 20
    Last Post: 05-21-2007, 09:22 AM
  5. Whats Wrong With This Pic??????
    By WATER WOODY in forum Yamaha Open Discussion
    Replies: 9
    Last Post: 12-13-2006, 11:11 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •