Compression.... - Snowmobile Forum: Your #1 Snowmobile Forum
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post #1 of 21 (permalink) Old 02-06-2010, 08:48 PM Thread Starter
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Compression....

I just bought a 2004 700 Classic with 6K on it. It was owned by a Polaris Mech. and can see it was well maintained. I tought for giggles I'd do a compression test. Both cylinders were 120-122. It was not warmed up and doing furthur reading, I was not holding the throttle open. I am going to do it again tomorrow, but was just wondering what the change in compression might be with throttle opened.

It runs great and love the sled. I just have it in my head that I have to take it easy because of the higher miles...

Thanks Rob
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post #2 of 21 (permalink) Old 02-06-2010, 09:57 PM
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sounds like it's fine to me. I've done compression test, with throttle wide open and closed and my readings have always been pretty much the same. If your getting 120 with no throttle your in good shape IMO.
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post #3 of 21 (permalink) Old 02-06-2010, 10:05 PM
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If you get 130's to 140's you are getting excellent compression

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post #4 of 21 (permalink) Old 02-06-2010, 10:19 PM Thread Starter
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Thanks guys, I guess I'm just a worry wort and don't want to hurt the sled, I mean I just got it...I guess I should just run it like normal, aye? I hope it has plenty more miles before an overhaul.
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post #5 of 21 (permalink) Old 02-06-2010, 10:23 PM
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Quote:
Originally Posted by Brummo View Post
I just bought a 2004 700 Classic with 6K on it. It was owned by a Polaris Mech. and can see it was well maintained. I tought for giggles I'd do a compression test. Both cylinders were 120-122. It was not warmed up and doing furthur reading, I was not holding the throttle open. I am going to do it again tomorrow, but was just wondering what the change in compression might be with throttle opened.

It runs great and love the sled. I just have it in my head that I have to take it easy because of the higher miles...

Thanks Rob
Check back with the mechanic and see if the pistons were ever replaced- checking compression is all well and good but you should be more concerned about piston to cylinder wall clearance. If those pistons have 6000 km on them I can guarantee you that they are at or past their wear limit. Big bore Polaris twins are hard on pistons, the skirts collapse over time and the potential for breaking a skirt off is much higher than wearing out piston rings. Two new pistons and gaskets are less than $200, money well spent compared to repairing a trashed cylinder or cracked crankcase.
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post #6 of 21 (permalink) Old 02-06-2010, 11:07 PM Thread Starter
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Not sure if it means much but meant to say 6000 miles. I have no reason to fear the sled, it's just new to me and want to make sure it will last a while before any major problems. I don't forsee any, but like to know what I have before I get going too far.
That being said, the guy I bought it from said the compression was around 140psi, but at 120, I guess I'm glad it's not lower.

I did ask when I bought it about motor work done to it, and he said it's had nothing done and probably ouldn't need it for a while. Hope he's right.
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post #7 of 21 (permalink) Old 02-06-2010, 11:18 PM
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Quote:
Originally Posted by Brummo View Post
Not sure if it means much but meant to say 6000 miles. I have no reason to fear the sled, it's just new to me and want to make sure it will last a while before any major problems. I don't forsee any, but like to know what I have before I get going too far.
That being said, the guy I bought it from said the compression was around 140psi, but at 120, I guess I'm glad it's not lower.
If you want to make sure it will last awhile with no major problems changing the pistons would be a step in the right direction, IF they are original. Good compression is not a guarantee of a trouble free engine especially on a Polaris 700 twin with 6000 miles. It may very well have good compression right up until a skirt breaks off one of your pistons. Just speaking from experience here.
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post #8 of 21 (permalink) Old 02-06-2010, 11:27 PM Thread Starter
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Is piston/ring replacement easy enough to do? I'm pretty mechanically inclined, but something I've never done before. Is is a easy, for the most part, as getting a new piston and rings and swaping out the old ones?
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post #9 of 21 (permalink) Old 02-06-2010, 11:34 PM
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its fairly easy to freshen up that motor with new pistons rings etc.. id talk with the previous owner to get more advice as you said he being a mechanic, prolly could help u out with that. or at least give u some good directions. but as far as giving directions for a rebuild, my best advice is to get out there and attempt it...its the best way to learn if your a handson kinda person...
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post #10 of 21 (permalink) Old 02-07-2010, 09:13 AM Thread Starter
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I'm hoping to run this the rest of the year and think about doing it next fall when the carbs and stuff need cleaning. I think it should last that long.
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post #11 of 21 (permalink) Old 02-07-2010, 09:20 AM
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I really doubt you'd have any issues running it for jsut one season... It would be a good idea to do rings/pistons in the summer tho... I mean my sled only has 4k miles and im gonna do at least rings in it this summer

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post #12 of 21 (permalink) Old 02-07-2010, 09:25 AM
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that is not the big block 700 they only made the big block 700 2 yrs along with the 900 in 05-06.

Can it! Then you'll at least sound like your keeping up!
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post #13 of 21 (permalink) Old 02-07-2010, 11:49 AM
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Could be your tester reading low... Can you compare it with another?
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post #14 of 21 (permalink) Old 02-07-2010, 12:14 PM
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Quote:
Originally Posted by xc sp 500 rider View Post
that is not the big block 700 they only made the big block 700 2 yrs along with the 900 in 05-06.
The '04 700 Classic is a big block- has the belt driven water pump.
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post #15 of 21 (permalink) Old 02-07-2010, 12:17 PM
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One very important thing that needs attention on those Polaris 700 engines is the water pump belt- you should change it every 3000 miles. They do fail, and when they do you have no water pump or oil injection pump.
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post #16 of 21 (permalink) Old 02-08-2010, 04:51 PM Thread Starter
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Just did another compression test yesterday, not warmed up, but with throttle open. It appears the compression is closer to the 130 on both sides. I looked at it closer this time..
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post #17 of 21 (permalink) Old 02-08-2010, 05:07 PM
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Add gas and oil and run it! You have nothing to worry about. compression is great and its a fairly new sled. I know a guy with a 2000 sks 700, and if yours really is the "big block" engine with no powervalves, it has many miles to go. The guy absolutely pounds on his sled, and has had it since new. 9800 miles and never been apart! 130 lbs per side! I understand the preventative maintenace thing completely dont get me wrong, but going through all that work when it may not be neccessary would suck. The fact it was owned by a polaris mech is another great thing, you know dang well its been maintained! Get out there and ride!

if you notice a drop in compression come spring time then maybe pull it apart, but right now, with a brand new sled (to you), you and I know both you dont want to be tearing nothin apart, you want to ride it! And you should!

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post #18 of 21 (permalink) Old 02-08-2010, 06:36 PM Thread Starter
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Quote:
Originally Posted by 69CRUZR View Post
Add gas and oil and run it! You have nothing to worry about. compression is great and its a fairly new sled. I know a guy with a 2000 sks 700, and if yours really is the "big block" engine with no powervalves, it has many miles to go. The guy absolutely pounds on his sled, and has had it since new. 9800 miles and never been apart! 130 lbs per side! I understand the preventative maintenace thing completely dont get me wrong, but going through all that work when it may not be neccessary would suck. The fact it was owned by a polaris mech is another great thing, you know dang well its been maintained! Get out there and ride!

if you notice a drop in compression come spring time then maybe pull it apart, but right now, with a brand new sled (to you), you and I know both you dont want to be tearing nothin apart, you want to ride it! And you should!

You hit the nail right on the head....
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post #19 of 21 (permalink) Old 02-08-2010, 10:45 PM Thread Starter
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Awesome riding tonight....4 inches, so far, of nice powdery snow...

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post #20 of 21 (permalink) Old 02-15-2010, 10:25 PM
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What about the same year and size sled with 3400 miles on it and the compression reads 110 PSI each side w/o opened throttle? Both are equal but seem are lower. Could gauges be that much different?

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