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Discussion Starter · #1 ·
I have a 2011 Polaris Ranger 800 XP. With 485 hrs. Hard starting when engine is warm and lacks take off speed and top end speed. Compression test on both cylinders is 120 on both and holding. Dealer said 165 is normal. Do i need a rebuild or what should i look for still runs ok.
 

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Discussion Starter · #3 ·
BPS i have a new pump on order because i thought that was the main cause. I have never checked with a guage would that cause a low compression still if fuel psi was low?
 

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Fuel pressure and cylinder compression are not related.

120 is low but I don't feel it's low enough to cause the symptoms you're describing. Very low compression will cause hard starting when cold but you said it's only hard to start once warmed up. 2010-2012 800s are known for vapor lock in the fuel line and they tend to eat fuel pumps. I would buy/borrow a fuel pressure tester and start there.
 

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Discussion Starter · #5 ·
BPS thanks for the reply.

I thought 40 to 45 psi low on compression was enough to cause my symtoms.

Ya it only hard to start when engine is warmed up and top end is slow and losing power.
 

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2015 Polaris ranger 570 XP
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For the most part additives are snake oil. The one exception for engines might be the additive used in high mileage oils that reduces oil seal leaks. I had an oil leak in the rear main seal of my 5.3 Silverado with 190k miles, started using Mobil Synthetic High Mileage oil and the leak stopped. I used the same oil to try to stop a rear main seal lean on a 2000 Nissan Xterra 3.3 engine with no success at all. I suppose it depends upon the type of rear main seal, rubber vs rope type as well as the extent of wear, but I'm getting off topic for additives that help worn engines.

IMHO, it comes down to this; worn engines mean missing metal, and no additive is going to replace that material. Additives may increase viscosity so less oil passes the rings or increase compression slightly, but it's a minor increase and only a temporary fix at best.

Engines that have been abused or suffered lack of regular maintenance end up with large ring gaps, scored cylinders and/or stuck piston rings that are filled with carbon which keeps the oil ring clogged and all rings collapsed in the ring grooves so they can't wipe the oil from the cylinder wall or contain compression. If the rings aren't stuck too badly something like Seafoam added to crankcase oil as per directions may help clear the carbon and free them, but it's a long shot and you may add new problems such as increased oil leakage at seals or, if the engine is sludged up really bad, clogged oil passages which prevent adequate lubrication can cause even greater damage. The real solution is a tear down, inspection and rebuild.
 
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Those tiny little mechanics in mechanics in a can only make you feel like you've done something for about a few minutes . If the motor is worn buy a rebuilt exchange or have some one proficient do a rebuild .
 
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Discussion Starter · #11 ·
So 40 psi low for each cylinder think i can get away with just piston rings and gaskets?
 

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So 40 psi low for each cylinder think i can get away with just piston rings and gaskets?
There are multiple checks and specs for cylinder wear, cylinder diameter, taper, etc. The service manual will have those specs but you'll need the correct measuring tools. Most likely when you inspect the cylinder after pulling it you'll know just by looks and feel.
 

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Discussion Starter · #13 ·
BPS thanks. Any idea where i can get the service manual other then dealership? 2011 polaris Ranger 800 xp. Thanks for all the advice everybody.
 

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So 40 psi low for each cylinder think i can get away with just piston rings and gaskets?
Just as BPS states, there are several checks that need to be made before choosing only a top end rebuild. Before I tear down any engine with low compression I like to run a cylinder leak down test in addition to a compression test. Such a test can tell a lot more about engine condition and allow determination of leaking valves or head gaskets prior to tear down. This eliminates unnecessary ring/cylinder/piston work if the only problem turns out to be burned or maladjusted valves or a leaking head gasket. After this assessment you know more about what you're getting into before jumping into a top end overhaul and later finding out that rings/piston/cylinder work didn't fix the problem.

Of course a thorough tear down and inspection will usually reveal all of the problems without performing a leak down test, however thorough is the key word. That means checking the head for warpage, valve guide wear, valves and seats, compression release mechanisms (if equipped) and so forth.

Then comes the question of whether once you've gone as far as removing the top end why not take the extra step and spend a few more dollars for a complete engine refresh including crank and rod bearings and seals? The answer depends upon your budget, how long you plan to keep the machine, hours on the engine and previous history of maintenance as well as what you find after removing the top end.
 
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