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post #1 of 17 Old July 9th, 2019, 03:32 PM Thread Starter
 
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Broken Valve?

So I have a 2016 Polaris Lemon.. er... I mean XP4 Turbo, and it recently had misfiring issues so I ran a compression test which revealed 0 on one cylinder. A leakdown showed it leaking out the tailpipe so I pulled the valve cover and an exhaust valve is completely destroyed.

Is this a common issue? I can't figure out what could have caused this. The cam lobe looks a little damaged by that valve but nothing else seems damaged. The machine is unmodified and has around 100 hours. The machine has been a belt shredding piece of garbage but hasn't had any real issues apart from that, and I can't imagine a shredded belt would disrupt the engine timing..

Any help is appreciated.
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post #2 of 17 Old July 9th, 2019, 03:47 PM
 
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Re: Broken Valve?

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post #3 of 17 Old July 9th, 2019, 03:57 PM Thread Starter
 
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Re: Broken Valve?

If I'm missing something obvious or not realizing that this is a common problem, let me know for sure
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post #4 of 17 Old July 9th, 2019, 04:16 PM
 
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Re: Broken Valve?

I haven't heard of any motor issues. I put over 3000 miles on my 16 and it stage2 tuned for all of them. Maybe I was just lucky. But the 925 engine has been pretty tough as far as I know

AA level 2 tune, S2 clutch kit, half tinted windshield, polaris roof. Polaris lower doors, fang light kit, with more to come
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post #5 of 17 Old July 9th, 2019, 04:18 PM
 
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Re: Broken Valve?

Quote:
Originally Posted by Michigan man View Post
I haven't heard of any motor issues. I put over 3000 miles on my 16 and it stage2 tuned for all of them. Maybe I was just lucky. But the 925 engine has been pretty tough as far as I know






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post #6 of 17 Old July 9th, 2019, 04:22 PM Thread Starter
 
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Re: Broken Valve?

I just can't figure out what could have even caused it apart from the valve itself being faulty. No ridiculous temps, rev limited so no overrev causing valve spring issues.. no damage to the timing system.. No waterlock, nothing. It seems like the valve itself was just brittle and broke from regular use.
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post #7 of 17 Old July 9th, 2019, 04:24 PM
 
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Re: Broken Valve?

The plastic air intake box I call it that is attached to the throttle bodies under the bed was cracked on mine letting dirt and dust in. That ruined my head


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post #8 of 17 Old July 10th, 2019, 08:14 AM Thread Starter
 
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Re: Broken Valve?

Huh... I guess that could wear the valve seals down if it were cracked. Still, a valve cracking apart should only be from timing interference or extreme heat. Polaris doesn't seem to give a shit though so I guess I'll just have to fix it, sell it, and buy from a different company next time.
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post #9 of 17 Old July 10th, 2019, 08:16 AM
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Re: Broken Valve?

when you blow a belt, at speeds, foot to the floor, 75-80mph, when the belt blows the engine will "over-rev" and tag the rev limiter faster than the ECU can catch it and close the TB for the soft rev limiter. we have seen these engines around 8800-9000 start to float the valves, you might have blown a belt at some point, high speed, full throttle, BOOM, and the engine rev'd in excess of its 8650 soft limiter, and exceeded its 8800 hard limiter to the point that you might have cause valve float which ultimately led to the broken valve. the turbo has sodium filled exhaust valves, obviously the core of the valve is hollowed out. might have been an issue with them, i think the intake valves were powdered metal. i have seen a tremendous amount of stuff lately that polaris is going to powdered metal parts, all over the place. they are strong, until they arent....
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post #10 of 17 Old July 10th, 2019, 08:34 AM Thread Starter
 
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Re: Broken Valve?

Thank you, that definitely makes sense for sure. The recent belt break wasn't all too dramatic but I could imagine a very brief moment of overrev that could cause valve float. Although, the design is pretty shit if the valve springs aren't designed for a bit of over-rev. Probably didn't take more than a tiny tap with the sodium filled valves... Thanks for that idea.
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post #11 of 17 Old July 10th, 2019, 08:43 AM
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Re: Broken Valve?

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post #12 of 17 Old July 10th, 2019, 08:52 AM Thread Starter
 
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Re: Broken Valve?

Interesting... I think Polaris kind of shit the bed on the head design in general. Thanks a bunch for your help!
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post #13 of 17 Old July 10th, 2019, 09:08 AM
 
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Re: Broken Valve?

you said it was a belt shredder ? with only a 100 miles on it? how many belts have you broken, and how are you driving this thing. I know these are sport machines and you want to drive them hard. I would suggest a belt temp guage in any cvt equipped machine. it will help you learn what you can and can't get away with. my stage 3 18 turbo still has the original belt at 1500 miles. if you are constantly beating the crap out of it stuff will break. nothing is foolproof. and I agree with the previous post it probably tagged a valve when the belt broke. and the valve bending and straitening out when it closes most likely caused the failure.
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post #14 of 17 Old July 10th, 2019, 09:21 AM Thread Starter
 
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Re: Broken Valve?

100 Hours, 1400 miles or so. But man, who even knows. 7 or 8 probably, but the first handful ended up being due to a defective clutch setup that Polaris replaced (after a very drawn out and painful process). Since then, it hasn't been too bad but is still worse than it should be. Mix of woods and light dune riding (not mashing throttle over whoops or big jumps or anything like that). I realize dunes cause an excessive load due to the extra drag, but come on... I think the clutching system in the 2016 wasn't adequately designed to provide tension for the torque the motor provides. I might be wrong but I think it underwent a revision for the very next year?

But yeah, I've been planning on a belt blower and temp gauge to combat that issue.
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post #15 of 17 Old July 10th, 2019, 12:32 PM
 
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Re: Broken Valve?

sorry missed the hours thought it said miles. but anyway hopefully you didn't hurt the head ,cylinder, or piston to bad.
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