Rattling noise in engine on startup and idle - Polaris 2008 Sportsman 500 H.O

The loud rattle that you hear when the cooling system turns on and when you turn the wheels may be caused by a few different issues. Here are a few possibilities:

1. Loose or damaged components: It's possible that a component in the front of your Polaris Sportsman, such as a fan blade, is loose or damaged and is causing the noise when the cooling system turns on. Check all components in the front of the vehicle to make sure they are secure and not damaged.
2. Loose wheel or steering components: The noise may also be caused by loose wheel or steering components, such as a wheel bearing, tie rod end, or ball joint. These components can become loose over time and can cause a rattle or clunking noise when driving or turning. Check these components for wear or damage and tighten or replace them as necessary.
3. Engine or transmission issue: It's also possible that the noise is coming from the engine or transmission and is being amplified by the cooling system turning on. Have a mechanic inspect the engine and transmission to determine if there are any issues that need to be addressed.

It's important to address any unusual noises in your vehicle promptly to prevent further damage and ensure safe operation. If you are unsure of how to diagnose or repair the issue, it's best to seek the help of a qualified mechanic.

Better check the Universal Joints in all those shafts under that thing.....If one comes loose while driving it could result in expensive damage and possible injury to the rider........

severe knock / rattle under load
excessive smoke as the crack normally occurs at the oil ring groove dropping that ring into the sump
describe the symptoms that you have as if it is a rattle under acceleration that will be detonation and is a air/fuel mixture problem or ignition timing too far advanced the skirt is what maintains the alignment of the piston crown so if it is cracked /broken off you will have no doubt of the noise at idle and at rpms
pistons seldom fail because of the engineering and material used so it would have to be an extreme operation that would cause the failure
other similar noises can be from loose valve seat insert
piston hitting valve head from failed valve spring big end bearing cam lobe worn out

Does it rattle after it warms up? If so, your lifters could be loose.

if it has independent suspension then the clicking noise may be a failing cv joint (" U" )in the drive axle
suspension don't click--rattle ,knock squeak yes but not click

needs ajusting

drive gears are worn loosening drive chain

If you're in to low a gear, the clutch might be slipping under stress from high revs. You might need a new clutch or stronger springs. Try using a higher gear and use 50% braking.

Could be a rod. Not going to be that easy to do. Valve noise is not a knock.

1st. change oil and filter.. use 10-40.. if that doesn't quiet them... .0025"-.003" on intake .004" - .005" exhaust should do it... if they are too tight,,it won't idle down fast or well.... or excessively tooo tight -won't start..too loose they rattle or if there is a lot of wear.. the rocker arms may need replacing