Outlaw 525s knocking noise at low rpm
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  1. #1
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    Outlaw 525s knocking noise at low rpm

    New to the forum! I just bought an 08 outlaw 525s over winter and i got it out today with the warm weather were having. After taking it for a short ride i noticed a pretty loud knock, generally while lugging it in reverse or first gear and a tiny bit while idling. I heard something about a crank bearing nut coming loose and making noise? Hopefully thats the issue but what else could it be. I dont know too much about these rfs motors yet but trying to learn. Any suggestions on where to start? Hoping it isnt in need of a rebuild. It was smooth every ride before this and sounded very healthy.

  2. #2
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    Most common cause of that is a loose primary gear nut. You have to pull the right side cover off and see for yourself. Itís the big nut on the crank. Itís left hand thread. If thatís not the knock, then youíre gonna need to be looking at the big end bearing or piston slap, most likely. However, an engine has a lot of moving parts, and there can be a lot of things that cause a reciprocating knock. Iíve even had people panic when a rock gets caught in a skid plate and they think their engine is about to go. If itís the primary gear nut, loctite 243 it, let it sit for 24hrs, then poor oil in it and test it out. I also recommend getting a gear hammer so you can torque the bolt correctly, people make pennies work, also.

  3. #3
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    I took the cover off. Nut is not loose. No shavings in the oil either. I was told it could possibly be spark knock? Im sure the gas in it is starting to get old so im gonna get some fresh stuff in it. On a side not does anyone know a good place to order oil filters for these engines?

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  5. #4
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    Check your valve clearances. Intakes Have a tendency to get real tight.

  6. #5
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    I plan on possibly taking it in to have the valves checked. Im not sure how to do it myself. But its definitely on the to do list before i take it trail riding. I also put some fresh fuel in so if theres any spark knock hopefully that is taken care of. Got to get oil changed first also

  7. #6
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    Look man, I’m sure this isn’t what you want to hear. But...
    The spark knock you’re referring to can be caused by extremely lean mixture or heat, as well as old/low octane fuel. Highly doubt Your stock 11:1 piston (I’m assuming it’s stock) would be knocking around idle even with the lowest octane fuel you can get from the pump. Not to mention spark Knock (pre-ignition) will increase in likelihood with increased rpm. Not go away. Unless there’s something seriously wrong, valves will chatter, they won’t make a distinct knock sound. If it’s not the crank nut, the symptoms you are describing is a conventional big end rod failure and/or piston slap.
    Think of it like this:
    You checked the crank nut, and it’s tight.
    You said it does it at idle, I’m assuming this is neutral. So very low chance it is transmission related especially because you had it happen at low rpms in different transmission selections applied.
    So you’re only options left are something to do with the engine part itself. valves, pre-ignition, or rod knock/piston slap. Unless you have something odd going on.
    You said it’s a knock, not a chatter, as long as that description is accurate a valve or valves out of adjustment can be ruled out (They could be out of adjustment still, but that’s not causing a knock) In theory, a valve that’s way out of spec can, in theory, lessen amounts of air and fuel coming in and out, so it COULD cause pre-ignition but it’s unlikely. I rebuilt a motor that broke the tappet bolt and wasn’t even opening a valve, it still didn’t have pre-ig issues. That leaves two options. You can go really high on compression and be fine at idle with 93 pump gas. Ive had 14.5:1 engines that I flushed out with fresh 93 pump at idle after running race gas. If you put fresh 93 in there and it still does it at idle, it’s not pre-ignition. Really sounds like it’s time for a full rebuild.
    Also, keep in mind there’s two filters and two screens. Did you check all of them? Oil gets sucked up through the screens, metal that has fallen in the oil is going to be seen by the screens before the cartridge filters. I’ll also mention that just because there isn’t metal in the oil or screens or filters, does NOT mean you don’t have a serious issue. Things slowly wear in such a fine powder it’s not visible to the human eye. There is technically fine metal that comes out with oil every time you drain any engine.
    Please don’t ignore the sound and ride with that knock going on, a blown up rebuild is usually way more expensive than a preventative one. When I changed oil on the motor I expressed previously, all the visible metal from the tappet bolt was stuck to the filter screens and in the oil/ignition magnet when I drained it. Almost nothing visible in the filters.
    I know it’s not what you want to hear, but I’m 90% sure it’s time for it to come down for a rebuild.
    Last edited by Youngwildandfree; 03-10-2020 at 04:32 PM.

  8. #7
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    Quote Originally Posted by jgosz2012 View Post
    I took the cover off. Nut is not loose. No shavings in the oil either. I was told it could possibly be spark knock? Im sure the gas in it is starting to get old so im gonna get some fresh stuff in it. On a side not does anyone know a good place to order oil filters for these engines?
    I run stock filters. You can get the 2 pack from RMATV.

  9. #8
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    You said it sounded and ran smooth b4 this last ride as parking it for some time. You checked the nut it’s not loose and no metal shavings in the oil. The RFS motors are rattle cans. Start with the easy stuff. New gas, New oil and filter change (fill oil up no more than 1/3 -1/2 in the site glass), spark plug and air filter. If you take it in to a mechanic to have the valves checked and adjusted, he should be able to tell whether or not he needs to dive deeper into the motor if the “knock” is extremely prevalent and potentially severe. Hopefully it’s not. If it is in need of a rebuild YWAF is correct, it’s a lot cheaper and easier to do the rebuild before it comes apart. Keep us up to speed.
    Last edited by steveo525; 03-10-2020 at 10:47 PM.

  10. #9
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    Does the noise go away when you pull the clutch in? If so it is normal. Check for metal in the filters and screens. There are two screens by the way along with the two oil filters.
    Mine:
    2017 Husky FX 450
    2009 505 SX
    2008 525 XC-modded for mx (currently 450 cylinder)
    Dad's:
    2009 450 SX
    2008 540 XC

  11. #10
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    I took it in to have it looked into. As of right now i was told he believes something loose is rattling around in the motor. Possibly a starter clutch. Will have to wait and see. Thanks for the replies!


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