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Discussion Starter #1
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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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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Discussion Starter #6
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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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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Discussion Starter #8
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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///AIRDAM Clutches
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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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Discussion Starter #10
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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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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Discussion Starter #14
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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One of our groups broke a valve at around that milage for no apparent reason. Polaris warrantied the head, but it was only a couple of months old. They never did find a reason for the bad valve. took them a couple months to repair.
Thats a lot of belts. Mine was the same way, average 200 mile per belt. When you get tired of spending money on belts look up Adam @ Airdam clutch. It was hard to drop the money but when you add up belt prices ti kinda pays for its self.
 

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Discussion Starter #17
From what I've heard the 2016 is the worst for belts.. I think the stock clutching system just sucks. Perils of buying a first year new model...

And that's interesting for sure. Unfortunately I messaged Polaris and they basically said to piss off since it's outside of warranty. Kind of upsetting since it's obviously due to poor engineering :( I'll look into airdam for sure, I hadn't heard of them before.

And yeah, I'm hoping it didn't damage the cylinder or head. I'll probably need to replace the cam since it bugged up the lobe a bit. Hoping the piston wasn't damaged since the stem of the valve is such a weak point. Probably need to have the valve seats refinished at least.
 
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