Piston scoring on a fresh rebuild. Cause?

[odoggak]

Just did a rebuild on a 08 D7 and can see some light scoring on the sides of the pistons. Really stumped on the cause of this. I have only put 50 miles on the sled. Things were well oiled when it was put together, oil pump was bleed and richened up, and oil was added to the fuel. Just was breaking it in, so never even hit full throttle and always keep an eye on the temp gauge. Sled was always brought to temp before riding. The pistons i replaced also had the same light scoring on them, but being the 3rd owner, i figured that someone had let it get hot and they squeaked a little. I didnt measure piston clearance or ring gap, which i should have, just figured OEM pistons, shouldnt be a problem and its not like I really got a choice on size. Anyone experience this, or have an idea for the cause? Thanks

 

[ttreewalkerr]

Just did a rebuild on a 08 D7 and can see some light scoring on the sides of the pistons. Really stumped on the cause of this. I have only put 50 miles on the sled. Things were well oiled when it was put together, oil pump was bleed and richened up, and oil was added to the fuel. Just was breaking it in, so never even hit full throttle and always keep an eye on the temp gauge. Sled was always brought to temp before riding. The pistons i replaced also had the same light scoring on them, but being the 3rd owner, i figured that someone had let it get hot and they squeaked a little. I didnt measure piston clearance or ring gap, which i should have, just figured OEM pistons, shouldnt be a problem and its not like I really got a choice on size. Anyone experience this, or have an idea for the cause? Thanks

This doesn't answer your question, but.. My fall work on sled i looked in my exhaust port and saw my walls had some aluminum staining from piston on it,,, and piston had some verticle score lines that their is no feel to the touch. i put Y pipe back on,,, and had hard 250 trail mile shakedown ride this past weekend,, and screams like it should,, so,, i think there is some acceptable levels of scuff.

But yes, i attribute my marks to some high temps that took place... But im not worried from it,, and yes i have 05' pistons still in,,,,, 1600 miles now.

 

[theshadowrider]

Just did a rebuild on a 08 D7 and can see some light scoring on the sides of the pistons. Really stumped on the cause of this. I have only put 50 miles on the sled. Things were well oiled when it was put together, oil pump was bleed and richened up, and oil was added to the fuel. Just was breaking it in, so never even hit full throttle and always keep an eye on the temp gauge. Sled was always brought to temp before riding. The pistons i replaced also had the same light scoring on them, but being the 3rd owner, i figured that someone had let it get hot and they squeaked a little. I didnt measure piston clearance or ring gap, which i should have, just figured OEM pistons, shouldnt be a problem and its not like I really got a choice on size. Anyone experience this, or have an idea for the cause? Thanks

Can you post some pictures? Are they scored, or is it wear marks in the coating? Are both pistons the same? Can you post pictures of your old piston also? Have you checked the compression and compared each cylinder?

 

[diamonddave]

Are the locating pins facing the exhaust or the intake?

It may just be the wonderful world of loose tolerances in Polaris motors for the last 4 or 5 years syndrome wearing off the coating.

 

[ragingwong]

the coating they put on the skirts is not very thick,so it doesn't take much to rub thru it

 

[Pownar]

X2 on the typical Polaris scuffing. You didn't mention any honing? If you did, was it the Polaris one?

 

[skibreeze]

the coating they put on the skirts is not very thick,so it doesn't take much to rub thru it

I have been told that these coatings are for break in only, not a permanent coating like others.

 

[thefullmonte]

I have been told that these coatings are for break in only, not a permanent coating like others.

I think it's a myth skibreeze. I know that is the story we keep hearing in the Polaris section. And maybe that really is the story with the OEM pistons????

However, a properly toleranced motor will keep the coating on the pistons indefinitaly. Polaris are the only motors that I've seen wear that stuff off. It is a friction reducer and more of a failsafe. For break in Polaris already recommends an additional pint of oil in the gas. If they need to use the piston coating for break in as well then there are even more problems than I've found. The rings are supposed to do the wearing, not the piston skirts.

It is common to see scoring on these motors on either side of the exhaust port. I even found it on the old 800s. I'm lead to believe much of the problem lies in the design of the guilitine style exhaust valve. Although functional, the design doesn't allow for a proper cooling passage around the exhaust port. There is theory that the head doesn't allow for enough coolant exchange to this area either.

 

[skibreeze]

I dunno, I sent my last set of new pistons to Swain Tech for their coatings and so far so good on no scoring. I also took the turbo off before the start of the season.

 

[crh_repair]

08 700 RMK

I rebuilt my sled at the end of the season last year after it broke a ring and gouged up the cylinder, got it running for one last ride to the cabin and noticed a lose in power after 40 miles. I parked it for the summer and now that it's riding season again I'm pulling it apart to find the piston scared up again and not ready to run, and idea on what would cause that?

 

[jeffwmc54]

I rebuilt my sled at the end of the season last year after it broke a ring and gouged up the cylinder, got it running for one last ride to the cabin and noticed a lose in power after 40 miles. I parked it for the summer and now that it's riding season again I'm pulling it apart to find the piston scared up again and not ready to run, and idea on what would cause that?

You need to make sure that there is nothing plugging the coolant galleys in the cylinder! This was a problem when Polaris started recalling the 8's and dealers were slamming em together and not cleaning parts properly... After an engineer from slp told me of these problems I put on about ah dozen of there coolant bypass kits for all my buds and the scoreing problems went way down! It is normal though that you will get alittle just as long as you can't drag ur nail or feel it with a ballpoint pen. I remove the power valves and checked them last year after every ride because of this kind of crap!!!

 

[Pownar]

Where is the scoring, exhaust or intake side? The reason I ask is because those air boxes were designed by the mentally challenged! Tons of chit in mine till it was all sealed up. Now I never have problems. I really babied my last top end and freaked out after opening it up after the first ride because the pistons and cylinders were really scuffed up. Thought they were scored then yanked the cylinders to find they were just scuffed and looked worse than it was. Put it back together and put 2000 miles on it and opened it up 3 days ago and looked way better than the first ride. Getting it re-niked and new pistons just because the compression went down a little. Could of easily just of thrown new rings in it.