I believe you're 500 machine has a decompression system built into the camshaft, that is either not working properly or has broken.
Sportsman 500 hesitates to turn the motor over
I've just joined and haven't researched on here about this problem so am just going to ask for help here. Have a '97 Sportsman 500 that am having several issue on so I'll start with this one. When you turn on the key, and press the start button, you hear the solenoid click, and the starter trying to engage the engine, but some of the time the starter hesitates to spin the engine. If you continue to hold the starter button in, sometimes the starter after hesitating a second or so will then spin the engine, but sometimes it wont. If you let off the button and retry, sometimes will do the same thing or it may actually spin the engine immediately, as it should. Has a new starter, new fully charged battery. Have cleaned the battery cable ends and connection at the battery and at the solenoid. Have also checked resistance across the solenoid terminals while the solenoid is engaged, (connection made) with the cables off of the solenoid. It shows .3 to.4 ohms. To me that checks good. Battery cable connection at the starter is also clean and tight. Trying to start with the pull starter is impossible. Have even subbed a car battery in trying to get this machine to start consistently and not much difference. Any ideas?
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On some older machines (especially ones that were started a lot due to short trips) the decompressor ball wears a grove in the exhaust rocker arm rendering the system ineffective. On others there may be a broken spring on the decompressor actuator rendering it non-functional. Keep in mind the decompressor is only functional on the first few strokes of the engine. when the crankshaft reaches a speed of 850 to 1000 rpm, the decompressor is not involved in the cranking of the engine.
Thanks for the responses. Have now watched videos showing and explaining the repairing of non-functioning decompression system on these machines. Have the left side coolant inlet and cam cover off. Have the right side cam sprocket cover off, the valve cover off, and the spark plug out. The decompression lever/weight and spring on the end of the cam seems to be operating as it should, in other words, keeping the lever up against the dowel pin. Upon trying to pull the starter rope to bring the piston up on tdc, am finding that pulling the starter rope even with the plug out is VERY difficult. I know I've gotten old and I'm no muscle man, but this thing just seems like it's way tighter than it should be to turn over.
How long have you had the unit ansd when was the last time it was run?
Have had the machine about three weeks now. Was run yesterday. When you do get it to start it seems to run well. Have done the usual drill after buying a "sitter", in other words something that hasn't run for some time. Drain the old gas, cleaned out all the mice nests, repaired some chewed wiring, remove, clean, and adjust the carb. As I watch more and more videos about the non-working decompression problem, it seems that this is a common problem with these machines, and a number of posters say Polaris made many of these units with soft cams which soon wore out and was a good part of the reason the decompression failed. This machine does have another problem (or two or three) but am trying to deal with this issue for now.
I have been through this. Tried different high quality trickle chargers, batteries, and starters. Some very expensive batteries. Expensive process to say the least.
Some things I have learned:
Don't leave your battery hooked up to a trickle charger. When the charge is complete disconnect the charger. The trickle chargers (and I have tried two high quality) will certainly fry the battery if left hooked up indefinitely.
My Polaris seems to be picky about batteries. I have tried Polaris replacement batteries and Deka replacements. In a pinch bought an Autozone Duralast Gold. The Autozone Duralast Gold is best battery I have ever used. Automotive or ATV.
Some things I have learned:
Don't leave your battery hooked up to a trickle charger. When the charge is complete disconnect the charger. The trickle chargers (and I have tried two high quality) will certainly fry the battery if left hooked up indefinitely.
My Polaris seems to be picky about batteries. I have tried Polaris replacement batteries and Deka replacements. In a pinch bought an Autozone Duralast Gold. The Autozone Duralast Gold is best battery I have ever used. Automotive or ATV.
Polaris did not have soft cams - those owners experiencing worn out cams and rocker arms caused the problem by letting the engine idle for extended periods and saving money by using oil that did not meet the API rating specified by the manufacturer. Note: Polaris oil does not have an API rating, but I will guess it is about an API SH rated oil. Oil rated higher than SJ should not be used, but any oil meeting the JASO MA rating will be fine.
In continuing to work on and research this possible decompression problem, am finding some conflicting information concerning valve clearance/timing at top dead center. Some info says that after moving the piston to top dead center, valve clearance for both intake and exhaust should be .006", but if the decompression mechanism is working properly, wouldn't there be no clearance on the exhaust valve at tdc because the exhaust valve is being held open slightly by the decompression mechanism, as some have indicated.
The self proclaimed 'expurts' because they have a phone and can make a video have a phone that is smarter than they are!In continuing to work on and research this possible decompression problem, am finding some conflicting information concerning valve clearance/timing at top dead center. Some info says that after moving the piston to top dead center, valve clearance for both intake and exhaust should be .006", but if the decompression mechanism is working properly, wouldn't there be no clearance on the exhaust valve at tdc because the exhaust valve is being held open slightly by the decompression mechanism, as some have indicated.
The exhaust valve is opened a few thousandths of an inch about 5 to 10 degrees before the piston reaches TDC to lower the compression and then the valve is closed at TDC - set the valves to .006 at TDC or even 20 degrees past TDC and it will be OK.
During starting, the exhaust valve is opened a few thousandths only on the stroke or two - if operating as designed, when cranking speed is about 850 rpm or higher, the decompressor is taken out of the equation.
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