2003 YZ450F oil pump

5 replies to this topic
  • Kermit21

Posted May 17, 2008 - 05:44 PM


Really need so words of wisdom.

Changed oil last weekend before big trail ride. I started the bike this week to run some stable through the carbs and checked my oil. No oil on the dipstick. Added oil, ran bike and checked oil again. Still no oil on dipstick. Repeated process till I added about one quart and noticed oil was about one inch below oil fill plug. I drained oil and noticed it was dark gray. I had the bike in deep water over the weekend so thought maybe water got in the oil. I carefully drained the oil, changed the filter, and put in new oil. Ran the bike and still no oil on dipstick. I loosened the "oil pressure" bolt and nothing came out. I took the bolt completely ount and a little oil would occasionally squirt out.

To me it sounds like one or both of my oil pumps died. What happened, is this a known problem. The bike has very little use and has been well maintained.

I'm going to open the case tomorrow and start inspecting. I'm afraid I might find dammage.

Anything I should check or do before splitting the case. I really don't want to do it but don't see any other option. Mostly just want to know if this has happened to anyone else and what caused the problem.

  • grayracer513

Posted May 17, 2008 - 10:53 PM


Only the failure of the return pump is indicated for certain. When you fill an '03, the oil goes in the crankcase, not the tank. It is only present in the tank after it is pumped there by the return pump.

Remove the right side crankcase cover and the clutch, and pull the oil pump out. You may find that it has simply sheared the return rotor drive pin. You should also remove the ignition cover and look into the sump to inspect the sump screen, too.

  • Kermit21

Posted May 18, 2008 - 06:20 AM


Thanks for the reply, I'm going to split the case now and then will report back what I find.

Does the main oil pump pull from the sump or the tank. In the manual they show it pulling from the tank. Question is, if main pump is still working was the engine continueing to get oiled after the return pump failed


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  • grayracer513

Posted May 18, 2008 - 07:56 AM


No need to split the cases yet. The pump is serviceable from the right side.

There are two pumps; two sets of rotors driven on a common shaft, one on top of the other in the same bore. The feed pump, or main pump, draws from the tank and feeds oil to the engine's lube system. The return, or scavenging pump, draws from the sump and returns oil from there back to the tank. If the return pump fails, oil will collect in the sump until it's all in the cases, and none of it is in the tank. Once this happens, the feed pump will no longer have an oil supply ro pump with, and the feed circuit will cease to operate, even if the pump is OK.

  • Kermit21

Posted May 18, 2008 - 11:12 AM


Ok, I'm really confused now. I just removed both side covers and took a look at the oil pumps. Both pump gears and pins were in one piece and things turned easily but show signs of light scoring.

I'm guessing now that the strainer must be blocked. Without splitting the case I can only see the top of the strainer so I don't think I would know for sure till I opened it up ,but I don't see what else it could be.

On previous oil changes my oil has alway looked good and clean. Now I seem to have a lot of sludge build up in the bottom of the case. I noticed a heavy buildup sitting on top of the strainer. I stuck a screwdriver in to scrape some off and it looks and feels kind of like a sandy mud. I also found a few pieces that looked like wood.

I did have the bike in about a waist deep mud bog last weekend just after my last oil change. I stalled the bike out once but once I got it out of the bog it fired right up. I don't see how but if you have the bike that deep is there anyway for the mud and water to get into your case. Oil thing I can think is that stuff got in through a breather then the water boiled off and left only the mud behind.

Any ideas?

If this is sand and mud I'm assuming engine dammage has already started. Where should I starty looking first and how much of the engine should I tear appart. Do I just flush out the engine and ride or should I do a complete rebuild replacing wear components like bearings and bushings.


  • grayracer513

Posted May 18, 2008 - 01:22 PM


(...all) I can think is that stuff got in through a breather then the water boiled off and left only the mud behind.

Any ideas?

Probably right. As the engine runs above an idle, there isn't much danger of this, but if it stalls, or you attempt to start it while the breather is submerged, it can easily slurp water.

At this point, a full tear down and a thorough flush of the frame and oil lines is in order.

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