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Discussion Starter · #1 ·
I was waiting to post on the forum, but I'm thoroughly stumped. So here's the full story:

Got a 2016 Sportsman 570 from a guy who put a rev6 bottom end in it because pickup tube came off. Says he couldn't figure out timing.

So we take it apart, set the timing, and had no compression. Took off the head and the intake valves were bent. Sweet! So after replacing all 4 valves and setting the timing it works!

But wait, it doesn't. Figured out that after it gets to temp (fan turns on) we get this horrendous knocking. Once she cools for 5 minutes, it goes away until completely warmed back up.

So we take it apart down to the stator cover (everything but the crankcase cover, flywheel, etc) and there's nothing to be seen. So we carefully put it back together, and it still does it.

We take it apart again, and there's slight marks on the case by the gear between the starter and main gear on the one way clutch. The pin and everything is intact, and there seems to be no way that it possibly could've contacted. Also don't remember if the marks were there the first time we took it apart or not.

So we just run it hard and wait until we can see something obvious. After we did hours of Google searches and looking it over all we can hope for is an obvious sign of failure. Fast forward to this week, and we take the clutch off. Still makes sound. We take the flywheel off and discover the lower timing chain guard is missing. So we find out that only one dealer in the country has one of them, and we overnight it.

Put it back together and still does it. Here's a list of what we know isn't wrong and things we aren't sure of

-No piston slap
-Chains are perfectly fine
-Bearings in the bottom end are fine
-Its not the clutch
-It only happens when its hot
-The big starter gear on the one way clutch has about 1/4 of an inch of play on the shaft between the flywheel and the chain guard.

It doesn't lack any power and doesn't have an issue running. If any of you have any idea as to what our issue could be, please comment it. Thanks guys!

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· Registered
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Discussion Starter · #3 ·
Update, we got it working. The previous owner who replaced the bottom end must nut have completely pressed the bearing in for the crank, causing the counterbalance and crankshaft weights to contact. Pressed in the bearing and runs great!
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