Pro-800 Cylinder skirts breaking?
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R
Rally2
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two things as I understand 1) tighter fit reduces rocking motion and 2) lighter piston weight reduces forces overall
edit: above applies to straight piston replacement. Kits like PMS take it one step further by using taller pistons and a spacer plate under the cylinder. The taller piston distributes side forces more evenly along the cylinder bore.
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theshadowrider
Well-known member
IMO the first thing I do to my pro when I get it is get rid of the cast pistons. Warranty does me no good when you are in the back-country. Forged pistons are far superior in many ways. For one they fit. I have yet to hear someone pull there motor apart an have the clearances in spec. Some are seeing .008" or more clearances. They seem to have tightened up the clearances over the CFI4 engines but, but still to loose. Forged are lighter and stronger. Many nay sayers when it comes to forged, but if you do your homework you will see they are far superior to cast and expansion is not a problem in a aluminum nicasil cylinder. On my dragon I have run up to 14 lbs boost and temps 1300+ and forged will give you the confidence back!
http://www.snowestonline.com/forum/showthread.php?t=269999
http://www.snowestonline.com/forum/showthread.php?t=269999
If you own a 2011 or 2012 800 Pro, you will have ring damage around 1000 miles. Just like the pictures. I have that same set of pictures in real life sitting in my garage in a plastic tub. Lets open this up for discusion and see where it goes.
I was told, and it makes sense to me, that the semi-direct placement of the injectors is actually washing the piston of lubrication when they fire. Since oil/gas are not mixed before the injectors fire, the fuel hits the piston and ring at the transfer port and you do the science from there. No lube, lot's of friction, pieces of rings and pistons is the end result. That is why it is so crucial to run oil in your tank not just turn up the pump. Anybody else want to chime in? It all makes sense to me and after I convinced my dealer to tear my motor apart and quit chasing gremlins, we found pitted/chipped rings and damaged pistons....exactly where we were told it would be. Where is that? Transfer ports right where the incoming charge washes the lubrication from the piston. Maybe I am the only one this happened to and it's because I have an "SLP "sticker on my hood, or maybe it's the "Holz" bumper or whatever. Probably all my fault though I am sure.
I was told, and it makes sense to me, that the semi-direct placement of the injectors is actually washing the piston of lubrication when they fire. Since oil/gas are not mixed before the injectors fire, the fuel hits the piston and ring at the transfer port and you do the science from there. No lube, lot's of friction, pieces of rings and pistons is the end result. That is why it is so crucial to run oil in your tank not just turn up the pump. Anybody else want to chime in? It all makes sense to me and after I convinced my dealer to tear my motor apart and quit chasing gremlins, we found pitted/chipped rings and damaged pistons....exactly where we were told it would be. Where is that? Transfer ports right where the incoming charge washes the lubrication from the piston. Maybe I am the only one this happened to and it's because I have an "SLP "sticker on my hood, or maybe it's the "Holz" bumper or whatever. Probably all my fault though I am sure.
PV, did you do a leak down test? I thought my rings were fine until I was told to run my finger nail around them. Piston had some knifing on the same side of piston also. Looked as if the rings were "rocking" back and forth or up and down as it would be.
no blow by on piston rings,carbon under rings?replaced my pistons on 2800 km.were severe blow by,flaking on rings.PTW clearance was 0.25 mm.pistons were not damaged,but i was down on power and i excepted skirts would break soon.bought and installed RKT drop in kit.have 650 km on it now.recomend this if your gonna replace pistons.nice power upgrade too
Well I would consider yourself pretty lucky. Most of the people with about 1000 miles or so on the motors are going to find ring damage like I and PUS1100 did. EPA mandates are killing these motors.
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pura vida
Well-known member
i would definitely agree this is having a significant effect on the all two stroke motors.
pv
Yep, and comparable 800's; Zuke uses relatively ancient THROTTLE BODY injection, still, and Doo DI or carbs, only Poo has been hitting the transfers and washing down pistons directly with high flow injectors (doo's SDI in 2000 doesn't count). I believe it has played a significant role in failures since the CFI-4 came out on 8's. This is seldom mentioned when comparing design dimensions and failure rates.
It may not be the only issue, e.g., the 6 and 7 CFI's don't have the same failure rates, but they also have different skirt thicknesses and dynamics. Multiple design issues have conspired to affect the Liberty 800. In pure reality - WE ARE PAYING Poo to R&D their motor designs. Poo rushed the 8 into the market based on the raw 7 in early 2008, after killing the 855 (another motor tested by the customer). They couldn't even deliver non-RMK 800's in 2008. They have never been able to get in front of it again. It was all about the Rush/Pro chassis. The motor is a trail sled motor at best, and their mountain chassis geniuses worked with what they had.
Not too different than the DPF tech pushed out on 2007 and later diesels mfg by Dodge, Ford, and GM. Another reason I still have my LBZ... But sleds are not 6k anymore, either. We do deserve better motors. If it wasn't for the Pro chassis, the RMK brand would be nursing the hind teet, behind the Nytro.
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Well said. They did the same thing after Doo came out with the Rev. Polaris put out the Fusion and we all know what happend there. I was told by a person within the Polaris loop that Roseau warned Medina back then that the fusion was not ready for production, but they went ahead anyway. Just as you say, tested by the customer. (Kind of reminds me of Microsoft.)
Thanks again, you know a lot more about sleds than I do but I think were both on the same page.
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