How to check compression, how long does it take, and how much would it cost? - Snowmobile Forum: Your #1 Snowmobile Forum
http://www.snowmobileforum.com
Go Back   Snowmobile Forum: Your #1 Snowmobile Forum > General Discussion Forums > General Sled Chat


» Sponsors





Reply
 
LinkBack Thread Tools Display Modes
Old 11-29-2008, 10:53 PM   #1 (permalink)
Stop! Drop the monkeys!!!
 
PolarisHockey90's Avatar
 
Join Date: Mar 2007
Location: Chesaning Michigan
Posts: 264
Question How to check compression, how long does it take, and how much would it cost?

We're going up north Monday and stopping off at a dealer. Just out of curiosity and knowing what happened to my brothers old sled, I was going to check and see what my compression is for my sled.

When I start to accelerate, I feel and hear it "pop". I assume its the clutch engaging. When I go slow at first it feels like its...hmm whats the word I want to use....its like it goes like this-GO-UH-GO-UH-GO. You know what I'm talking about. Sorry probably not the best way to describe it but yeah. Almost like there are dead spots on my belt. But there isn't.

Does it take long to do?

If I go to a dealer, how much do you think they would charge? Or is it just one of them put something on boom I'm good deal?

Can I do it?

If I find its not at the right PSI or whatever you call it, what is the fix?
__________________


2004 Polaris 800 XC SP
PolarisHockey90 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 11-29-2008, 11:35 PM   #2 (permalink)
Super Moderator
 
BC_Dan's Avatar
 
Join Date: Jan 2004
Location: oregon
Posts: 12,425
Checking the compression is easy. Get a decent gauge, appropriate for small engines. Remove the spark plugs. Screw the gauge into one piston, make sure the ignition is off, tie the throttle handle down (use a piece of wire, and wire the ignition key to this wire, that way you won't forget you have the #*&^$^ throttle pinned), pull the rope 3-5 times or until the gauge doesn't rise any more. Mark that reading, do the other side. Mark that reading.

THEN UNWIRE the throttle (very important!!) put the plugs back, you're done.

Your compression should be 120 or so cold, a little lower when warm. If it's 100 or below, you may need a top-end rebuild.

I would also make sure the clutches are clean, binding clutches can also create problems. A track that is cold can make the kind of "noise" you are describing...
__________________
2007 Dragon RMK 700 155", 2008 RMK 600 155", 95 Prowler 550 2-up, Really OLD AC Cheetah

http://www.avalanche.org/accidents.php
BC_Dan is offline   Reply With Quote
Old 11-29-2008, 11:58 PM   #3 (permalink)
Registered User
 
jagermiester's Avatar
 
Join Date: Nov 2006
Location: INDIANA
Posts: 1,011
This is the best way to do a compression test to help determine the state of the rings, regardless if your gauge is accurate or not. As BC DAN said, after screwing the gauge into the cylinder, make sure throttle is wide open and pull over 5 times (with ignition off).

-Start sled and let run for about 30 seconds. After 30 seconds is up, shut sled off and check compression in all cylinders. If there is a 5lb, or greater, difference in compression from one cylinder to to another, that is an indicator that the rings need to be replaced

-Next, start the sled and let it run until the engine is at operating temperature; ensure that the thermostat is open and the coolant is flowing by either seeing a raise in coolant temperature on temp gauge or feeling for warm heat exchangers. Shut off engine and check compression of all cylinders with hot engine. If the difference in compression between this hot test and the previous cold test is 7lbs or more, that is an indicator that you need new rings

-Example; if the cold compression was 135lbs and the hot compression is 128lbs or less, then it probably needs new rings

-In addition, if the hot/cold compression difference is 10lbs or greater it is usually an indicator that new pistons are needed as well

Do this test yourself, the dealer will just throw a gauge on it and give you the readings and likely (depending on mileage) tell you that rings are in order whether you need them or not, depends on how the cash flow is going that month. Compression gauges aren't expensive and you have the peace of mind knowing yourself what is needed.
__________________
"If you're not the lead dog, the scenery never changes"
*************
98 Jag (for the kids)
03 MXZ-X 800 (Blair Morgan)
*************
[SIGPIC][/SIGPIC]
jagermiester is offline   Reply With Quote
Old 11-30-2008, 12:48 AM   #4 (permalink)
Stop! Drop the monkeys!!!
 
PolarisHockey90's Avatar
 
Join Date: Mar 2007
Location: Chesaning Michigan
Posts: 264
Wonderful thanks guys!

Just curious, why push the throttle open?

Take both spark plugs out at the same time you say then?

If the track is cold, why would it do that? Just curious on that..

Really appreciate the help
__________________


2004 Polaris 800 XC SP
PolarisHockey90 is offline   Reply With Quote
Old 11-30-2008, 04:26 AM   #5 (permalink)
Runnin Against The Wind!
 
SnowRida's Avatar
 
Join Date: Feb 2004
Location: Howell, Michigan
Posts: 8,053
One plug at a time. Do one side, then the other.
__________________
SnowRida
Against the wind, let the cowboy's RIDE!

Yamaha V-Max SOLD
02 MXZ 600
97 Polaris Indy Trail Touring

04 REV 600 HO Adrenalin


Official Sled of the Month Judge


SnowRida is offline   Reply With Quote
Old 11-30-2008, 08:34 AM   #6 (permalink)
Super Moderator
 
BC_Dan's Avatar
 
Join Date: Jan 2004
Location: oregon
Posts: 12,425
You take both plugs out so the engine turns over easier. The throttle is wide open to allow the maximum airflow to the cylinders. If you don't have the throttle open, your reading will be somewhat lower than actual compression.
__________________
2007 Dragon RMK 700 155", 2008 RMK 600 155", 95 Prowler 550 2-up, Really OLD AC Cheetah

http://www.avalanche.org/accidents.php
BC_Dan is offline   Reply With Quote
Old 11-30-2008, 08:38 AM   #7 (permalink)
Registered User
 
DnD800's Avatar
 
Join Date: Sep 2004
Location: NH
Posts: 710
Quote:
Originally Posted by PolarisHockey90 View Post
Wonderful thanks guys!

Just curious, why push the throttle open?
With the throttle open it allows the air to enter the engine allowing for good compression results. With the carbs closed it will restrict the air allowed into the engine.

Take both spark plugs out at the same time you say then?
If you pull the plugs the sled will pull over easier.

If the track is cold, why would it do that? Just curious on that..
I believe this is more like a car being cold. When things are cold they make weird noises as everything is stiff but I personally don't think that is your current issue.

Really appreciate the help

Anytime, that's what we are here for.
DnD800 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Powered by vBadvanced CMPS v3.2.2

All times are GMT -5. The time now is 05:19 PM.



Copyright SnowmobileForum.com

Search Engine Friendly URLs by vBSEO 3.6.0