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PostPosted: Mon Jan 06, 2014 3:21 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Hi, I know very little about ATV Engine internals so I would like to ask here.... I recently picked up a non-running, late 1990's Polaris Sportsman 500 four wheeler (4x4) for pretty cheap. No history provided me. Just not running. It looks like it's been sitting forever.

As a elementary test just to see if it was going to be even worth the cost of a battery to fool around with it, I took both side covers off (the broken pull-start recoil side cover and also the CVT clutch side cover) just to see if the motor (( Internal Combustion Engine ? )) was totally locked up or not. When turning the clutch by hand it turns the Engine very smoothly for one full rotation at a time, it then kinda hangs or binds in one spot of the rotation, pretty stubbornly. If I push it harder around it will move on past, if I reverse rotation slightly then continue rotation it will also move past that spot and continue to be free for one full rotation until it binds on that same spot again.

I didn't pay much and thus haven't much to lose but I ask here... should I gas it up, tap on the carb bowl, and try to start this thing up or does that sound like some internal trouble (that I may make worse) to you guys?

Thanks


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PostPosted: Mon Jan 06, 2014 3:26 pm 
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Joined: Sun Dec 24, 2006 5:58 pm
Posts: 1951
Location: near NJ rider
Is the sparkplug in or out?


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PostPosted: Mon Jan 06, 2014 4:06 pm 
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Joined: Mon Dec 15, 2003 2:40 pm
Posts: 22128
Location: Chicago
Think the hard spot you feel is it building compression or could the cylinder be rusted inside and its hitting the rusted spot?


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PostPosted: Mon Jan 06, 2014 4:24 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Yes Bull the plug was still in. And It kinda feels like its building a little compression on the way around, it doesn't just freewheel around.. its not a lot of resistance along the way- you have to help it some. I also hear the slight hiss of air as it moves, and even smell stale gas smell as it revolves.

Hoser, that's why I came here. The bind spot doesn't have that "spongey stop" feel that compression does (in my experience). I think it may possibly be rust in cylinder but that thought (and tearing something up) is what sent me in here to computer to ask you guys about this.


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PostPosted: Mon Jan 06, 2014 4:36 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Well, I just ran out there to try and make a youtube vid to show you. I just turned it a couple more times past the "bite" and it seems fine now. No mechanical noises and it feels like its building at least a little compression. I just finished draining the rest of the old gas out of the tank. I might run out for gas and a battery to try this piece out.

Regarding that cylinder... if that was rust doing that, should I pull the plug and spray some penetrant or something in there?


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PostPosted: Mon Jan 06, 2014 6:18 pm 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 4041
Location: Hope, B.C Canada
John l wrote:
Well, I just ran out there to try and make a youtube vid to show you. I just turned it a couple more times past the "bite" and it seems fine now. No mechanical noises and it feels like its building at least a little compression. I just finished draining the rest of the old gas out of the tank. I might run out for gas and a battery to try this piece out.

Regarding that cylinder... if that was rust doing that, should I pull the plug and spray some penetrant or something in there?


Why not pull the Engine and do a re&re ???
You will then have a reliable machine that will run forever in stead of a machine you don't know
when it will let you down. My friend has two of those and they are reliable and a lot of fun.
The only issues he has ever had was the bearings on the swing arm for the axels.
Do you really wana destroy a good Engine ?


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PostPosted: Mon Jan 06, 2014 8:23 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Yeh good idea and I likely will head that way. I just wanted to hear it run. See that it didn't have a bottom end rod knock, transfer case, or differential problems. Something that would total it.

For longevity I like the idea of a new piston, wrist pin, matching cylinder, gasket kit on ebay for $299 http://www.ebay.com/itm/POLARIS-SPORTSM ... 32&vxp=mtr" .".." ."...

Cant find a decent price on a new or reworked head assembly though. But if it had a major issue I wouldn't even put that much into it I don't think.

Thanks for mentioning the swing arm. This one has no suspension or wheel issues. It was all mudded up but it really doesn't look like its been ran all that much.


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PostPosted: Sat Apr 12, 2014 3:27 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Back on this project again.

This was acquired not running and very cheap as a result. I have cleaned it up, did some Engine CSI to determine no compression and some mechanical lockup inside, took the Engine out and top end off. Piston has several pieces broken off edge in one spot. Rings and cylinder substantially destroyed of course. I have the cylinder off of the case, and have thoroughly cleaned all small pieces out of the case. I don't think it was ran like this but for a second. I was able to contact the previous owner and he said he was riding it and the wheels locked up, he skid to a stop and it never ran again. The biggest chunk of piston was wedged in between the case and the crank weight section, causing the lockup spot. No visible damage in lower end that I can see. I have rinsed it all out well. All gears mesh correctly, no broken teeth, timing gears and chain all seem ok, rod still connected to crank has a very very little bit of side to side play, crank is rotating smoothly and no play can be felt in any axis, crank oil seals were not leaking, nothing seems sloppy anywhere. The edge of the inside of cylinder head, adjacent the intake valves does look like the piston pieces hit it on an up stroke and slightly mushroomed it there inside the cylinder. I noticed the head bolt alignment dowels (knock tubes) looked slightly bent. The valves don't look bad but I don't know how to check if they are bent, and if they are seating and sealing? The cam has no excessive wear, rockers look ok. No missing parts that I can tell.

I now have on hand 2 new alignment dowels, a new cylinder, piston, rings, and gaskets. My question, before I put this stuff back together... I am leaning towards taking my chances with the lower end, it just looks all ok to me but would you recommend I do anything with this head? How can I test it or is that strictly a machine shop service? Do you recommend a particular machine shop? Do any of you do this work? I think the service manual has some sort of cyl head leak down bench test... have you ever done this? What about the mushroomed area in the aluminum? I can get new valves and springs on ebay for another $160 investment but I have never lapped valves before, and even if I do that I have the small mushroomed section.

That's a lot of questions.. sorry. I do appreciate any advice.

Many thanks!


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PostPosted: Sat Apr 12, 2014 3:37 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
I also am thinking about what caused all of this and how to prevent it from happening again. I have not found anything foreign inside the Engine. Just the piston pieces. Could the piston have hit a stuck intake valve and broke the chunks off maybe? I have cleaned the head, oiled it and have turned the cam several rotations to watch valve movement. They aren't sticking now, and look like they are moving there full travel up and down, but I do have some carbon and muck inside the guide areas. I was thinking that with heat, maybe a valve stuck.. is this a fair assumption and a typical scenario?


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PostPosted: Sun Apr 13, 2014 10:03 am 
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Joined: Sun Feb 23, 2014 10:01 pm
Posts: 379
Location: Monette Ar
to check the valves place it at top dead center on the cam. (both valves will be closed). put a little starting fluid on the backside of the valves (through the intake and exhaust port). if it leaks into the cylinder side then they are leaking. for minor leaks get a lapping tool (suction cup) and some clover lapping compound. the hard part is removing the valve springs which takes some special tools.

I would atleast replace the timing chain. that could very well be the cause of the failure. they stretch and allow the timing to jump a tooth. I just replaced the intake valve on a Yamaha 400 from this. luckily the piston was fine.


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PostPosted: Tue Jun 03, 2014 9:17 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Well. thanks to those here that offered the words of encouragement and advice. I just got back from the final break-in ride. What a blast. This thing is so smooth... like a lazy-boy you can ride through the forest. It's running great. Todays ride was about 48 miles in varying terrain. Never thought I would own a utility type four wheeler but I do love it.

Final surgery was... new piston, rings, jug, thermostat, alignment dowels, gaskets, crank bearings and seals, wrist pin, circlips, water pump impellor, intake and exhaust valves, springs, keepers, timing tensioner, all hoses, CVT belt, carb kit, fluids and all filters. It was quite a project. But since my only investment here was my actual time and the cost of these parts... I'm pretty happy.

I "think" what caused all of this was a timing chain tensioner with a worn out spring. My timing chain actually measured to within specs in the manual so I kept it and the gears.


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PostPosted: Tue Jun 03, 2014 9:38 pm 
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Joined: Sun Dec 24, 2006 5:58 pm
Posts: 1951
Location: near NJ rider
Congrats ,where do you ride? In PA?


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PostPosted: Thu Jun 05, 2014 6:10 pm 
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Joined: Sun Apr 29, 2012 12:45 pm
Posts: 300
Location: South-Central Pennsylvania
Mostly I ride away from PA. I prefer desert and dunes but when I am in state I frequent the State forests (this time it was Michaeux) and also RAC. but I hate the rocks!

Where do you ride Bull?


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