Page 1 of 2 1 2 LastLast
Results 1 to 10 of 15
  1. #1
    Flying Scotsman's Avatar
    Join Date
    May 2006
    Location
    IllINOIS
    Posts
    6,514
    +1
    4

    65U Group K cylinder/piston failure.

    Recently purchased pistons and cylinders borred by Group K and installed them on my 99 GP1200.

    Cylinders were 84.5mm non ported and #1 had been resleeved.

    I did not look them over because they came with receipt showing who had done the work.

    Motor ran good but started loosing rpm after 10-15 hours.

    I have only webcam pics I dont have a real camera but here are pistonwash pics
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Group K cyl 1.jpg 
Views:	106 
Size:	34.4 KB 
ID:	8775   Click image for larger version. 

Name:	Group K cylinder 2.jpg 
Views:	86 
Size:	33.9 KB 
ID:	8776   Click image for larger version. 

Name:	Group K cylinder 3.jpg 
Views:	79 
Size:	31.2 KB 
ID:	8777  


  2. #2
    Flying Scotsman's Avatar
    Join Date
    May 2006
    Location
    IllINOIS
    Posts
    6,514
    +1
    4
    I see a lack of wash on #1 and all 3 look a little lean #1 being the worst.

    Piston has the 4 corner seizure patern and cylinder has some deposits.

    After taking a look at the ports on #1 compared to #2 and #3 I see a noticeable lack of chamfering on the ports.

    Rings are intact and pins are still in place.

    I will be sending cylinders and pistons to Group K to see what they have to say.

    Not sure if the lack of chamfering contributed
    .
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	280920061807570798.jpg 
Views:	75 
Size:	23.4 KB 
ID:	8778   Click image for larger version. 

Name:	280920061807570648.jpg 
Views:	70 
Size:	26.4 KB 
ID:	8779   Click image for larger version. 

Name:	280920061807570518.jpg 
Views:	61 
Size:	27.6 KB 
ID:	8780   Click image for larger version. 

Name:	280920061832150264.jpg 
Views:	63 
Size:	27.4 KB 
ID:	8781   Click image for larger version. 

Name:	280920061832140823.jpg 
Views:	61 
Size:	27.0 KB 
ID:	8785   Click image for larger version. 

Name:	280920061832140743.jpg 
Views:	67 
Size:	24.3 KB 
ID:	8786  


  3. #3
    Flying Scotsman's Avatar
    Join Date
    May 2006
    Location
    IllINOIS
    Posts
    6,514
    +1
    4
    Looking for input prety sure ive got it worked out anyone care to comment.

  4. #4

    Join Date
    Dec 2005
    Location
    Beaufort, SC
    Posts
    119
    I thought that a 4 corner seizures happend when you ran lean?

    If you had snagged a ring, I thought that the lack of camfering might be a cause?

  5. #5
    Quote Originally Posted by Flying Scotsman
    Looking for input prety sure ive got it worked out anyone care to comment.
    I cant give any experienced input , but keep us posted i'd like to know end results !

  6. #6
    HopatcongGPR's Avatar
    Join Date
    Feb 2006
    Location
    New Jersey
    Posts
    1,114
    those crowns look lean to me.

    flip them pistons over and take a shot of the underside of the crown. i'll bet you have a big black spot under there.

    group k jetting or yours?

  7. #7
    jgustman's Avatar
    Join Date
    Apr 2006
    Location
    Cottonwood, Mn
    Posts
    133
    +1
    5
    When I had my 99 gp12 I ran stock staggered jetting lows one size bigger, 135 mains I believe, 1.5 n/s. and 35 psi. pop-off, v-force reeds, riva flame arrestors and riva pump gas head. At 1100 ft. altitude, Lows 3/4 turn out and highs around 1 1/4 and my piston wash was leaner than that and never seized or scored. Ran a best of 64.7 and always near or above 64 mph at 7,000 rpm.

  8. #8
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Location
    Mesa, AZ
    Posts
    16,712
    +1
    85
    Lean. Way lean. Way, way lean.

  9. #9
    cheatin' piston popper addicted's Avatar
    Join Date
    Jul 2006
    Location
    north jersey
    Posts
    6,188
    +1
    176
    I'm still learning about piston wash, but I would agree with Hydro. . .Way lean on pix 1&2. borderline on 3.
    But also, isn't a 4 coner seizure caused by overheating, or overexpanding pistons? Too tight bore/ piston clearance?
    Last edited by addicted; 09-28-2006 at 11:30 PM.

  10. #10
    Moderator OsideBill's Avatar
    Join Date
    Mar 2006
    Location
    United States
    Posts
    11,875
    +1
    30
    What brand pistons? GroupK used wisecos on my 65U 84.5 overbore Gerhard paid special attention to my chamfers as I had damaged the exhaust port. I then had a melt down on the #3 piston after about 10 hours of use and after switching over to an oring head I sent it back to them They cleaned up the cylinder for $35 I think it was more to ship back and forth. give them a call they are great to work with. as far as jetting goes they reccomended the stock jets with stock N&S change to 80 gram spring this is with their modified 91 oct pump gas head.

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. WTB Ltb 65u cylinder & pistons
    By cmherrera in forum Yamaha Classifieds
    Replies: 0
    Last Post: 06-01-2010, 12:58 AM
  2. 3rd Cylinder/Piston is Toast
    By howestek in forum Yamaha PWC Performance (2-stroke)
    Replies: 40
    Last Post: 04-17-2009, 02:15 PM
  3. cylinder & piston sizes
    By hedgehog in forum Polaris Open Discussion
    Replies: 5
    Last Post: 06-27-2007, 09:23 AM
  4. Cleaning case after piston failure? Best approach?
    By snowrunner in forum Yamaha PWC Performance (2-stroke)
    Replies: 2
    Last Post: 06-03-2007, 07:41 AM
  5. Piston Failure???
    By beerdart in forum Polaris Open Discussion
    Replies: 16
    Last Post: 03-13-2007, 08:04 AM

Posting Permissions

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