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0.250" compression height w/shim

Powaton said:
With 4 strokes the game is to get squish as small as you dare. Independent of timing or any other variables. In some more extreme cases the piston will "kiss" the combustion chamber at max RPM. But the head gets a longer cool down period in a 4 stroke. The gain is from provoking maximum turbulence in the chamber, allowing higher compression before detonation and pushing as much combustIble material to the center as fast as possible.
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this is the first that I have ever heard anyone use the word squish in a four stroke application before, interesting ..
 
I just got off the phone with C V tech and according to the person I spoke to (not very understandable english on that end) the Woosner p/n for 08-10 800 CFI 4 Dragon and the 11-15 PRO RMK 800 CFI 2 piston is K 7044 DA-2 and they do not have a replacement for 16-17 AXYS RMK 800 but I suspect that if the 16-17 Polaris AXYS piston will fit the 11- 15 PRO, then the Woosner replacement PRO piston will work in the AXYS ( my thoughts only and I have been wrong before)! My thoughts here is to get away from the repair with the fix kit plates and taller Compression Height pistons in order to get more longevity. Another question here, when did Polaris offset the piston pin in the piston .020 and is the offset to the forward side or to the rear?
gtwitch in wyoming
 
Goerge, I'll look into the piston for you as I have a good contact there and deal with them a lot .

Polaris off set the pin 0.020" back in 08 if I remember correctly. Many piston kits have followed this too because it just plain works .
 
Talked to Kelsey and I'm going to try out his pistons as it's the same height as Polaris (which I like).

Lighter , tighter tolerances and less taper. All good .

Going to spec it before install and after a season of hard hard riding/racing
 
Another thing that I have discovered about some of the aftermarket pistons is that some of the other manufacturers Wiesco and at least a couple of others to include first gen of Snow-X used or still use the ring end closure that tapers under the ring end pin which is not exactly in the center of the ring groove (Snow-X has changed this to match Cat now as it cost them plenty of rebuilds because of failures) instead of having the pin in the middle of the ring groove and having the ring end closure nearly cover the pin at the ring end gap. I have had some problems caused by this type of ring end closure. The Polaris and Cat pistons both have the ring closure pin centered in the ring groove! I have pictures of some of the piston failures and I asked Snow-X about this and of course the "did not really answer" .
Do you have the Woosner number for the PRO 800 and AXYS Pro replacement piston?? I will probably do my son's 12 PRO 800 this summer/fall because it has about 3500 miles on it and probably needs top end freshened and have a new set of Boysen reeds to go in it also.
 
Brock said:
Talked to Kelsey and I'm going to try out his pistons as it's the same height as Polaris (which I like).

Lighter , tighter tolerances and less taper. All good .

Going to spec it before install and after a season of hard hard riding/racing
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What brand of pistons is Kelsey selling these days ?
 
George A Twitchell said:
Another thing that I have discovered about some of the aftermarket pistons is that some of the other manufacturers Wiesco and at least a couple of others to include first gen of Snow-X used or still use the ring end closure that tapers under the ring end pin which is not exactly in the center of the ring groove (Snow-X has changed this to match Cat now as it cost them plenty of rebuilds because of failures) instead of having the pin in the middle of the ring groove and having the ring end closure nearly cover the pin at the ring end gap. I have had some problems caused by this type of ring end closure. The Polaris and Cat pistons both have the ring closure pin centered in the ring groove! I have pictures of some of the piston failures and I asked Snow-X about this and of course the "did not really answer" .
Do you have the Woosner number for the PRO 800 and AXYS Pro replacement piston?? I will probably do my son's 12 PRO 800 this summer/fall because it has about 3500 miles on it and probably needs top end freshened and have a new set of Boysen reeds to go in it also.
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I'll get you that number soon as Vincent hasn't returned my call yet.
Also? Can you post pics of the piston failures you talk about? Thanks
TPRO8 said:
What brand of pistons is Kelsey selling these days ?
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Kelsey is selling wiscoe.
 
Dr. What kind of really good (secret) stuff are we waiting to see comming down the pike?? Back to my ring end gap comments, I had 2 weisco sets with this ring end closure issues, ie. there were scuffs on the cyls in line with the ring end gaps and the ring ends show some rolling or tilting wear in the first .2 in on either side of the ring end pin and two sets of Snow-x (first gen) pistons were the same ring end closure type and showed similar marks in the cyl and also show a mark on the piston from the ring end gap down the side of the pistons. After I went back to Polaris stock for non-fis kit rebuilds or Arctic and Sno-x ( 2nd gen) for fix kit rebuilds, that ring end area scuffing problem went away. My observations and opinions only.
 
George A Twitchell said:
Dr. What kind of really good (secret) stuff are we waiting to see comming down the pike?? Back to my ring end gap comments, I had 2 weisco sets with this ring end closure issues, ie. there were scuffs on the cyls in line with the ring end gaps and the ring ends show some rolling or tilting wear in the first .2 in on either side of the ring end pin and two sets of Snow-x (first gen) pistons were the same ring end closure type and showed similar marks in the cyl and also show a mark on the piston from the ring end gap down the side of the pistons. After I went back to Polaris stock for non-fis kit rebuilds or Arctic and Sno-x ( 2nd gen) for fix kit rebuilds, that ring end area scuffing problem went away. My observations and opinions only.
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Goerge , what year were these pistons made and for what model ?

As for cylinder, there's lots of improvement and has been since Polaris came out with a 800cc twin. Intake was and is always a major improvement along with porting .

Keeping the same compression height as Polaris stock pistons is proper. Just lighten the pistons with better tighter tolerances and titanium wrist pins.

I'm working on a new kit along with richy. Both will be good with tq and hp . Just wait for us to put it together and off to Dyno.

We're trying to make great packages at good value Div20
 
Brock, I have pistons from old Gen 2 2000 and up and they were no problems and never used aftermarket on them. I just went out to the shop (12 mi west of town) and picked up the pistons to photo and will post them when I can and these are the ones that had (IMO) the problems with the wrong design ring end and pin closure. These are 2009,10 CFI-4 - 2011-2012 CFI-2 800 and I think that those engines today will all run the 16 AXYS RMK pistons and I also think that Polaris has improved these pistons to the present design but have not lightened them much or none at all, so, that being said, we need to try and find a lighter design with the polaris design ring end closure and stock height "Compression Height" with tighter Cyl-piston specs!
gtwitch in wyoming
 
George A Twitchell said:
Brock, I have pistons from old Gen 2 2000 and up and they were no problems and never used aftermarket on them. I just went out to the shop (12 mi west of town) and picked up the pistons to photo and will post them when I can and these are the ones that had (IMO) the problems with the wrong design ring end and pin closure. These are 2009,10 CFI-4 - 2011-2012 CFI-2 800 and I think that those engines today will all run the 16 AXYS RMK pistons and I also think that Polaris has improved these pistons to the present design but have not lightened them much or none at all, so, that being said, we need to try and find a lighter design with the polaris design ring end closure and stock height "Compression Height" with tighter Cyl-piston specs!
gtwitch in wyoming
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The first 800's up to the dragon years were lighter pistons but about 0.080" higher compression height vs axys pistons and the dome was different.

I'm looking into wossner but have wiscoe on order to try . I like the skirt support, tighter tolerances, less taper and lighter piston so I'm going to try it in one engine .
 
Brock said:
Goerge, I'll look into the piston for you as I have a good contact there and deal with them a lot .

Polaris off set the pin 0.020" back in 08 if I remember correctly. Many piston kits have followed this too because it just plain works .
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I may be wrong but I don't think it was until the '13 or '14 model year that they offset their pistons.
 
Neal@BMP said:
I may be wrong but I don't think it was until the '13 or '14 model year that they offset their pistons.
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I'll look into that Neal as I may be wrong but I thought it was model year 2008 ?
 
Dr.Notadoo said:
There are a couple other ways to fix the issues that plague the HO cylinder and piston..stay tuned, good stuff coming...
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You had better deliver! :)
Brock said:
Goerge , what year were these pistons made and for what model ?

As for cylinder, there's lots of improvement and has been since Polaris came out with a 800cc twin. Intake was and is always a major improvement along with porting .

Keeping the same compression height as Polaris stock pistons is proper(no shim!!!!!!) Just lighten the pistons with better tighter tolerances and titanium wrist pins.

I'm working on a new kit along with richy. Both will be good with tq and hp . Just wait for us to put it together and off to Dyno.

We're trying to make great packages at good value Div20
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Sounds good!
 
I'm not against" the shim " ,and I'm not against different pin heights.. what needs to be considered here is proper piston support in the cylinder,there are pistons out there that will do that. Also you can have the "proper pin height"as quoted by Brock and use a shim..hint ,hint..
 
Dr.Notadoo said:
I'm not against" the shim " ,and I'm not against different pin heights.. what needs to be considered here is proper piston support in the cylinder,there are pistons out there that will do that. Also you can have the "proper pin height"as quoted by Brock and use a shim..hint ,hint..
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Working towards the same compression height as stock Polaris with shim and without yes yes :D
 
IMG_2023.JPG

Axys 800 piston vs 2002 800 piston.
Just to show compression height changes over the years .

The smaller the compression height the better .
 
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