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Rod knock or...?

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So today I noticed my 81 xl250s making a knocking noise at idle... Grabbed the stethoscope and poked around, the knocking was loudest when I had the stethoscope on the bottom end. Which sucks big time! However my first thought was to pull the right hand cover and check the oil filter screen, It was pretty nasty but there was no metal shavings that I could see nor any in the oil. I could not feel any shavings anyways...

Is this a for sure bottom end knock or could it be something else? You would think that there would be shavings in the filter if anything. The gears in the RH cover look excellent. No nicks or anything.

Is there any way to pinpoint the knock other than using the stethoscope? Pulling the top end off on these is a real PITA so I'd like to avoid it! But I may end up having to pull the whole motor and redo the crank..

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No I haven't. Can that make a knock, it's most noisy on the bottom end and on the left hand side of the engine, opposite of the cam chain tensioner... That's on the right hand side right? At least the 87 xr250 & xr600 motor I've torn into was...

I've got the bike all tore down so tomorrow I'm gonna pull the motor out and tear into it. See if I can come up with anything

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   Unless you have special tools, loosen the clutch nut,rotor bolt and advancer nut before you pull the engine out.

      lock the rear wheel with the brake, and stick it in 5th gear. 

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I got an impact gun always works well for me in pulling that stuff. I got the motor out and torn down to the cylinder being removed and both case covers.

Everything feels right there is no up and down play on the crank big end or small end. The cylinder looks immaculate. I can't find anything wrong here as far as the crankshaft goes

This motor has a balancer with 2 ends and a chain connecting the 2 balancers with the crankshaft. (On the flywheel side), the manual says under troubleshooting that excessive noise is caused by: worn crankshaft bearings, worn big or small end rod/bearings, and improper balancer timing, chain adjustment, or damaged chain. The chain was very loose, so I adjusted it accordingly and got her tight again. I am concerned that the timing is possibly off so I'm gonna pull the flywheel to be safe. Could this cause a knocking noise?? I mean that chain was super sloppy!

The noise was most noticeable on the flywheel side of the engine. I think I found my problem but want to verify that there is nothing else to check while I got the motor tore down.

Figure since I already got myself balls deep I will slap some new rings on it.. The rings seem fine but may as well... Plus that piston is covered with carbon..

Anyways back to the topic, could the chain being so sloppy cause it to literally knock and slap around at idle? Motor didn't feel like it had excessive vibration.

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Never seen a balancer chain with slack. Never had to replace one caused by wear. 

  If the adjuster bolt was loose, that may be why chain was loose.

  next thing could be a worn/knackered front balancer bearing.

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I checked for play in the balancer shaft, and listened for any roughness, all sounded/felt good

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No more knocking after I fixed the balancer chain. Changed the rings and honed it while I was in there, along with cleaning the valves and replacing all the seals. No leaks and she starts with ease and rides pretty good! Hopefully that stays true and I don't get an actual rod knock.. Thanks guys

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