Anyone check their compression after runing their turbo for a bit??
- Thread starter cr187
- Start date
F.c. told me I had around 100 at start of the year
im at 90 psi on each cylinder. shes running strong!
Yes, when i bought my 11 pro, it had been turboed for a good bit of its life and had 900 miles on it. The pistons on top looked perfect I. E. no heat in ring lands, no det signs etc.. However, pistons and rings were sacked. Compression with a stock 12 head was 105 pounds and idle was rough. Rings were extraordinarily worn and misshapen. I replaced pistons and rings and compression immediately was back to a reasonable 123 pounds. Idles perfectly even when cold.
I still theorize that stock cooling on the Pro may have contributed to wear. Stock cooling without the front heat exchanger found on the rmk is lacking in poor cooling conditions even when scratchers are down. I added 100 square inches in the rear and it now works really well.
Sorry for long post. Hope it helped
I still theorize that stock cooling on the Pro may have contributed to wear. Stock cooling without the front heat exchanger found on the rmk is lacking in poor cooling conditions even when scratchers are down. I added 100 square inches in the rear and it now works really well.
Sorry for long post. Hope it helped
s$#t,,, so i should probably do mine then eh? i only have about 600 miles on it now i think, and only around 300 were boosted. 98% of the time arount 5 - 6 pounds of boost.... ?
It might be a good idea. Mine were really hammered and the fresh parts had a really dramatic effect. The wear was really strange on the rings but consistent from side to side both in appearance and on the compression gauge. As poor as the compression was on a cold engine it is hard to imagine how bad they might have been with some heat applied to them.
When have folks done a top end?
Stock it had 580 miles, I am now 350 more or so with Boost (5-6lbs).
I haven't checked the compression, but it appears to be running strong still.
What's the cost too? Are the 2012 pistons a different part number?
Stock it had 580 miles, I am now 350 more or so with Boost (5-6lbs).
I haven't checked the compression, but it appears to be running strong still.
What's the cost too? Are the 2012 pistons a different part number?
I have 1800 miles on mine with the last 300 or so turboed and I'm about 85psi on both cylinders. Bout time to rebuild I think
i was a 90 on both, two rides later im now at 85 on both. i have a big sled trip planned this weekend, f it, rider till she blows i guess?? im now at 644 kms not miles. 300 boosted.
Did you have any problems with poor starting and also a poor quality idle like it's running on about 1-1/2 cyls when you had the low compression? Just wondering if the low oil usage has something to do with it?
Yes, i had very poor quality idle before I rebuilt it. It now starts and idles perfectly. I turned up my oil pump and have been adding one ounce of oil to the gas in addition. Iam told this is very important for pto crank bearing life as well. Good luck. Hope this helps.
I meant one ounce of oil per gallon of gas. Friends who operate rental fleets say crank life is dramatically improved. This was also confirmed by a crank rebuilder. Good luck.
K
Kestrel2126
Well-known member
Maybe I'm misunderstanding here, but did you say that you got your compression back up to 123 PSI, after you put in new pistons? If thats the case, I think something is wrong. Cold compression on the 2011 and 2012 Polaris Pro 800 motor, is only supposed to be 102-107PSI. That is stock, and brand new, other than the rings seated with break in. Polaris does not give out an exact compression number on the motor anymore, but I'm pretty sure that it should never be as high as 123.
Stock compression
By historical standards, 105 to107 pounds would indicate an extremely worn motor in all but a few snowmobile 2 strokes over the last 25 years. Finding cranking compression of 85 to 90 pounds would certainly indicate extremely worn parts, a burn down or something having gone through the motor. The day I checked my 2011 with 2012 stock head on it, I used a brand new digital snap on gauge. I was at 4200 feet of elevation with an ambient temperature of 60 degrees. The motor was cold i.e. had not been warmed up. My business partners sled was parked 25 feet away, is a 2012 rmk 800 and his compression on the same gauge was identical at 123 pounds. Squish clearance between piston and head at the outside was 63 1000ths if anyone is interested.
Again, I have substantially turned up my oil pump from stock and when measured carefully it still only uses enough oil to equal a 43 to 1 mixture. What is the stock mixture, 60 to 1. I don't know. Might be worth considering. Again, I am told by guys who operate rental fleets and crank repair shops that an extra ounce of oil per gallon is a real help for crank life. Hope this helps.
By historical standards, 105 to107 pounds would indicate an extremely worn motor in all but a few snowmobile 2 strokes over the last 25 years. Finding cranking compression of 85 to 90 pounds would certainly indicate extremely worn parts, a burn down or something having gone through the motor. The day I checked my 2011 with 2012 stock head on it, I used a brand new digital snap on gauge. I was at 4200 feet of elevation with an ambient temperature of 60 degrees. The motor was cold i.e. had not been warmed up. My business partners sled was parked 25 feet away, is a 2012 rmk 800 and his compression on the same gauge was identical at 123 pounds. Squish clearance between piston and head at the outside was 63 1000ths if anyone is interested.
Again, I have substantially turned up my oil pump from stock and when measured carefully it still only uses enough oil to equal a 43 to 1 mixture. What is the stock mixture, 60 to 1. I don't know. Might be worth considering. Again, I am told by guys who operate rental fleets and crank repair shops that an extra ounce of oil per gallon is a real help for crank life. Hope this helps.
Rechecked compression
Understand that I have no ego on tHis subject. After your post I went to the shop and rechecked my boosted sled and two stockers. One was a2011 and one was a 12. Mine had 110 pounds and each of the stockers which each have 500ish miles on them had exactly 115 pounds. Can't explain the difference from the 123 earlier except maybe oil etc from assembly. I do wonder about lubrication. Premature ring wear seems a possibility. Good luck.
Understand that I have no ego on tHis subject. After your post I went to the shop and rechecked my boosted sled and two stockers. One was a2011 and one was a 12. Mine had 110 pounds and each of the stockers which each have 500ish miles on them had exactly 115 pounds. Can't explain the difference from the 123 earlier except maybe oil etc from assembly. I do wonder about lubrication. Premature ring wear seems a possibility. Good luck.
Turbos are hard on rings. 
Yup, huge difference,along with about 20 other things,hot,cold ect ect ...compression checks are bout worthless for checking true ring wear,yeah its a nice quick check to begin with but do yourself a huge favor and do a proper Leakdown check with a good leakdown guage before ya pull your motor apart.
Turbos are hard on rings.
Eli
In your opinion or experience, with all of the aforementioned issues aside. cooling, lubrication etc., how much more quickly will a turbo sack a set of rings than an identical motor normally aspirated? What is the estimated useful life of rings on a properly set up and maintained turbo given that it did not have issues with cooling, lubrication, excessive piston to wall clearance, etc.
What are you hearing about issues of piston rocking due to a combination of short piston skirts and substantial piston to wall clearance on pros? Resultant ring wear?
