09-28-2006, 03:02 PM #1
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
09-28-2006, 03:16 PM #2
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
09-28-2006, 06:29 PM #3
Looking for input prety sure ive got it worked out anyone care to comment.
09-28-2006, 06:55 PM #4
- Join Date
- Dec 2005
- Beaufort, SC
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?
09-28-2006, 06:56 PM #5
Originally Posted by Flying Scotsman
- Join Date
- Sep 2006
09-28-2006, 09:17 PM #6
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?
09-28-2006, 10:41 PM #7
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.
09-28-2006, 10:42 PM #8
09-28-2006, 11:27 PM #9
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.
09-29-2006, 01:46 AM #10
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.
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