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Hello, I have a 2008 800 that I bought used and as far as i know is all stock. It has been sitting for almost a year in the garage after last trip to Moab when it ran low on oil and overheated. Haven't touched it since due to life getting in the way.

Anyway, finally got around to looking at it again yesterday, charged battery, topped off oil (almost a full quart) and it started right up! The only problem is now it has a loud knocking noise at any rpm over about 2500, that sounds like it is coming from the valve cover, or at least in that area. It also will only rev to about 4300 rpm and only get to about 30 mph.

I have pulled the air filter, thinking dusted engine, but the intake tube is clean. So, I thought I would look for expert guidance before going off blindly. Where should I start looking to find out what is going on and how bad is it?

Thanks in advance.
 

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Compression check a good starting place. Suspect the engine is toast. That engine will use oil quick when the top end gets bad.
 

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Running it when it is low on oil is never a good scenario. I would do more than just top it off, I would replace your oil and see if there are any metal flakes in the pan. These use a flat tappet cam and hydraulic lifters which could have wiped them out. Low oil would also mean no oil getting to the top of the engine where the valves and rockers are. Could also be rod bearings - I've seen an engine that grenaded one of the rods because of low oil.

Start by replacing your oil. Then check to see if the PRV (Pressure Relief Valve) isn't stuck. There are threads on here how to do that. I would also check the clutch to make sure everything looks good in there.
 

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Doesn’t sound good, a quart low in I’m assuming a 2 quart system... No bueno.. an she got hott!!! Ouch dude probably toasted her
 

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Thanks for the replies. Kinda told me what I was already thinking, but I will start with changing the oil first and see what it looks like. Then I guess its a matter of deciding if its worth sinking the money into a new engine (from what I have been able to gather so far probably looking $3k-$4k all done?), or sell it as a project and get something else.

Thanks again for the replies and the help!
 

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Utvenginerebuilds has reman engines ready to ship. They were about $2000 last time I checked. I had an engine from them in a used rzr 800 that I bought and it ran fine. Had a friend of mine purchase an engine also with no problems.

You could drop a new engine in and then sell for more and at least get your money back.

My ‘08 800 had a tear in the intake boot that let dirt in. Polaris has upgraded parts so I changed both boots on the intake. If recommend you do the same if you install new engine.


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Those motors when low on oil wont build up enough oil pressure to properly pressurize the lifters, you let it sit for a long while which could add to the problem. The motor will sound like crap, wont rev out and will have no power until those lifters pump up. That said you also need to figure out where that quart of oil went. If the motor is dusted you can do just a top end for like $500 and the job is really easy. If you decide to sell it as is I might be a buyer depending on your location.
 

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Those motors when low on oil wont build up enough oil pressure to properly pressurize the lifters, you let it sit for a long while which could add to the problem. The motor will sound like crap, wont rev out and will have no power until those lifters pump up. That said you also need to figure out where that quart of oil went. If the motor is dusted you can do just a top end for like $500 and the job is really easy. If you decide to sell it as is I might be a buyer depending on your location.
I will keep that in mind. I am in NM. I am going to try changing the oil first and check that and maybe oil pressure relief valve? I’ll see how it goes.
 

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A compression check will tell you what condition the top end is in. Suspect it will be very low. If so changing oil and pressure valve is a waste of time.
 

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A compression check will tell you what condition the top end is in. Suspect it will be very low. If so changing oil and pressure valve is a waste of time.
Thank you for that lesson. I will try that first. Hoping to get a chance to work on it some tonight if life and chores would stop getting the way.
 

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I lost my engine last year. Same noise, same problem. Low oil. Probably due to dust. It is a very expensive mistake not to check the oil BEFORE every ride.
 

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I am new to the sxs at 62 been building things all my life have same problem bought a 2011 rzr 800s from a dealership that had been doubled o ringed on the oil filter and leaked out the oil for 1500 assuming I would have to rebuild the motor as it has aftermarket everything on it big lift kit new big tires beadlock rims warn winch sound system best of everything I knew I had a good deal well after I got it home it ran and drove good but low on powe still has noise in it and that fear of run with no oil well comp. check was 150 first hole 140 second hole didnt know to unplug the FI and may have washed the rings on the second one so next test was pulling the valve covernow I find a loose rocker arm about 3/8 of an inch travel at full valve seat stuck lifter? or burnt cam lobe/ anyone know how to tell
 

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I am new to the sxs at 62 been building things all my life have same problem bought a 2011 rzr 800s from a dealership that had been doubled o ringed on the oil filter and leaked out the oil for 1500 assuming I would have to rebuild the motor as it has aftermarket everything on it big lift kit new big tires beadlock rims warn winch sound system best of everything I knew I had a good deal well after I got it home it ran and drove good but low on powe still has noise in it and that fear of run with no oil well comp. check was 150 first hole 140 second hole didnt know to unplug the FI and may have washed the rings on the second one so next test was pulling the valve covernow I find a loose rocker arm about 3/8 of an inch travel at full valve seat stuck lifter? or burnt cam lobe/ anyone know how to tell
From 2011 on they were "HO" engines and the compression from the manual states they should be 165-185 psi. The non HO engines had compression of 150-170.

You should not have any play in the rocker. See this post: https://www.rzrforums.net/general-rzr-discussion/69513-rzr-800-rocker-knock.html#post865318

Since these are hydraulic lifters, you should check that your PRV (Pressure Relief Valve) is not stuck.

Find yourself a copy of the service manual for spec details and pictures. Here are a couple of excerpts:

-Inspect the wear pad at the valve end of the rocker arm for indications of scuffing or abnormal wear. If the pad is grooved, replace the rocker arm.

-The push rods can be visually checked for straightness while they are installed in the engine by rotating them with the valve closed. Push rods can
also be checked with a dial indicator or rolled across a flat surface to check for straightness.

-Lifters that are scored, worn, or if the bottom is not smooth should be replaced with new lifters and cam as an assembly. If replacing the lifters, the camshaft should also be replaced.
 
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