Results 1 to 4 of 4
  1. #1
    Tony's Avatar
    Join Date
    May 2007
    Location
    North Carolina
    Posts
    1,760
    +1
    38

    Lost the PTO on the 780

    I'd been riding for about 2 hours when the ski died. Fired right back up but wouldn't idle. We headed back to the ramp (3-4 miles) and I was down 100 rpm.

    I pulled the plugs, they looked good but the PTO has a tint of silver/ash color to it. Redneck compression test (thumb over hole) told me it was low on the PTO.

    A little background...topend .50 OS WSM rebuild about 28 hours ago. Carbs were cleaned and rejetted for good wash,new fuel lines,filters,selector,sending unit,etc. Case passed leak check.

    I expected to find a holed piston but instead found this. There's small pieces embedded in the head. The cylinder walls are smooth, the marks in the picture are undetectable with your fingernail and mostly oil streaks. The piece embedded in the piston near the exhaust port is more squared off the round. The piston has no detectable up and down motion when at TDC.

    I'm thinking crank seal failed and leaned it out but what is the debris?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	DSC00161.JPG 
Views:	42 
Size:	573.2 KB 
ID:	83006   Click image for larger version. 

Name:	DSC00160.JPG 
Views:	35 
Size:	628.2 KB 
ID:	83007   Click image for larger version. 

Name:	DSC00159.JPG 
Views:	36 
Size:	627.7 KB 
ID:	83008   Click image for larger version. 

Name:	DSC00158.JPG 
Views:	32 
Size:	576.2 KB 
ID:	83009   Click image for larger version. 

Name:	DSC00157.JPG 
Views:	32 
Size:	472.8 KB 
ID:	83010   Click image for larger version. 

Name:	DSC00156.JPG 
Views:	34 
Size:	521.4 KB 
ID:	83011  

    Click image for larger version. 

Name:	DSC00155.JPG 
Views:	34 
Size:	594.1 KB 
ID:	83012   Click image for larger version. 

Name:	DSC00154.JPG 
Views:	39 
Size:	342.5 KB 
ID:	83013  


  2. #2
    Tony's Avatar
    Join Date
    May 2007
    Location
    North Carolina
    Posts
    1,760
    +1
    38
    All gawk,no talk?

  3. #3
    Quote Originally Posted by Tony View Post
    All gawk,no talk?
    You had some detonation happening but not at a large amount.
    My guess is that you have a rod pin, thrust washer gone or blued.
    It also could have been a circlip and that it went out the exhaust. thats kind of what the dent above the exhaust port shows

    Crank seals just dont FAIL. They have a reason for it and I dont see that anywhere on your piston. Did the piston seize in the bore?? You pics dont show the side of the cylinders


  4. #4
    Tony's Avatar
    Join Date
    May 2007
    Location
    North Carolina
    Posts
    1,760
    +1
    38
    Quote Originally Posted by prochamp View Post
    You had some detonation happening but not at a large amount.
    eize in the bore?? You pics dont show the side of the cylinders

    What leads you to believe this?, Not doubting you, just trying to learn.

    Quote Originally Posted by prochamp View Post
    My guess is that you have a rod pin, thrust washer gone or blued.


    Haven't pulled the jug yet. Would this cause an audible noise? What about eventual crank seizure. I rode for atleast 3-4 miles back to the ramp at WOT after the problem first became apparent.

    Quote Originally Posted by prochamp View Post
    It also could have been a circlip and that it went out the exhaust. thats kind of what the dent above the exhaust port shows



    I wondered about the circlip but I thought it would do more damage. The cylinder walls are smooth. There's a mark on the cylinder wall that would correspond with the forward clip but it's undetectable to the fingernail. After I took the pictures I realized the mark was 90% oil streak. I would think a light hone would take care of it.

    Quote Originally Posted by prochamp View Post

    Crank seals just dont FAIL. They have a reason for it and I dont see that anywhere on your piston. Did the piston seize in the bore?? You pics dont show the side of the cylinders

    Really? I assumed they could fail over time just like automotive crank seals. I don't think it seized, it cut off while cruising about 20-25 mph. I thought WTF? check my fuel guage, hit the start button and jumped right up on plane. Then I notice loss of 100 rpm at WOT. The cylinder walls are all but mark free.

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Replies: 3
    Last Post: 11-17-2012, 03:09 PM
  2. the 780 build is on
    By freemandino25 in forum Polaris Open Discussion
    Replies: 12
    Last Post: 07-07-2011, 10:17 PM
  3. Lost a nut on the steering nozzle linkage
    By bex in forum Yamaha PWC Performance (2-stroke)
    Replies: 4
    Last Post: 01-27-2010, 10:35 PM
  4. Lost the PTO again
    By Feral in forum Polaris Open Discussion
    Replies: 32
    Last Post: 07-06-2008, 11:57 PM
  5. Thought I lost the Clutch Sunday???
    By 1 FAST VE in forum 4-Tec Performance
    Replies: 4
    Last Post: 08-16-2005, 01:05 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
  •