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Discussion Starter · #1 ·
2002 300ex. Rattle noise coming from motor. Seems to get louder as bike heats up. Sounds like its coming from bottom end. Does not sound like bearing. Bike still runs smoothly except for engine noise. SOUNDS LIKE SOMETHING IS LOOSE INSIDE. Anything special I should check? Did change oil and filter but know help with noise. Any ideas would help before I start tearing motor apart.

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The 300EX and the 250X have a slight rattle anyway but I would check the valve adjustment just to be sure I would lay a good bet that is what you are hearing.
 

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He said it is coming from the bottom end...
 

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I doubt it is to be honest with you but it's not unlikely. thats why I mentioned the valve adjustment the easiest thing to do is get an engine stethascope warm up the quad until you hear the noise and listen and key locations, eg. the valve cover the jug then the crankcase.
 

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I agree. Sometimes noises will fool you in an engine. It's hard to pinpoint the location of a noise without using an engine stethoscope. I would try adjusting the valves first.
 

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Discussion Starter · #6 ·
All ready adjusted valves. .004 intake/.004 exhaust (I have been a cnc machinist for 20years so I know my way around mechanics quite well) Just really didnt want to tear motor all apart if I dont need to. The bike sat in someones back yard for about 5 years with bad axle bearings. Previous owner said noise was not there when bike was last run. I know the guy so I believe what he is saying. Thought it could have been broken rings but compression test was good. Sounds almost like something not getting oil.

Thanks for input.
Just want to know what you hardcore guys are thinking.
 

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Could be the oil pump, or possibly your rod bearing. How rapid is the noise? Real fast or like every other revolution? The speed of the noise will tell you alot. Valves are fast, low end will be a slower knocking sound.
 

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Its more of a slower knocking sound that speeds up with throttle. To check rod bearings am I correct to say that I need to split cases? Will this blow motor if not fixed quickly? How hard to check oil pump?

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grb3963
 

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Its more of a slower knocking sound that speeds up with throttle. To check rod bearings am I correct to say that I need to split cases? Will this blow motor if not fixed quickly? How hard to check oil pump?

Thanks
grb3963
To check the rod bearing, you will have to pull the cylinder/jug off and grab the rod and try to wiggle it up and down. If it has any up and down movement/slack at the big end of the rod, the rod bearing is bad. A little side to side movement/slack is normal. If the rod bearing is bad, it needs to be fixed as soon as possible because it won't last long and it will do a lot of damage to the engine.

You can check the oil pump to see if it's pumping by loosening the bolt that holds the external oil line to the head cover. Pull your sparkplug wire off and ground it. Next loosen the bolt that holds the line on. Don't take it all the way out, just loosen it about 1 turn. Next crank the engine over and after a couple cranks, it should pump oil out the end of the line. You don't won't the engine to start when doing this, that is the reason for pulling the sparkplug wire off and grounding it.
 

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Exactly what helmut said. ^^^^ My guess if its a slow knock your rod bearings went. If its slow and it happens at idle and gets faster when you rev it. Mine did the same thing but i didnt run it after that noise. I shut it off because it can throw a rod or have catostropic failure. And if we are correct yes you will have to split the cases. I would check the oil pump when you do fix it thought no matter what. Because that is what caused mine to go. If you need any help through the process let me know as i have done this not to long ago.
 
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