The YZF oiling system in detail

5 replies to this topic
  • trailriderjoe

Posted April 09, 2004 - 04:35 AM


Hey gang,
For those knowledge junkies out there wondering how our beasts are kept lubricated I thought you'd like a detail of how it all happens. It's pretty scary when you think about it, tear your motor down and you'll have a far greater appreciation of keeping the oil and filter fresh :). I know I do!

Let’s start with the heart of it all – THE PUMP.
The pump will be describes as a two stack pump. “Stack one” is a low volume high pressure 4/5 teeth gerotor pump (approx. 1/8”thick) used to pressurize the entire lubricating system. “Stack two” is a 4/5 teeth gerotor scavenge pump (approx. ½ thick) used to draw oil out of the gearbox and return it to the top of the frame. The same gear that is worked drives both pumps from an idler driven off the clutch hub. All this is located down and behind your clutch basket in the RH side cover.

Stack one (the heart of it all)
Oil is delivered to the pump via a tube from the frame port / screen to the RH case cover just below the clutch cover. Oil flows thru the side cover, into the pump, gets pressurized, and flows back out thru a check ball and seat in the side cover and is plumbed thru the casting design up to the bottom of the oil filter housing. This hole is seen as the large (1/4” or so) hole in the bottom of the housing out near the cover. Oil is forced in around the outside of the filter, thru the filter (hence filtering debris), and then works its way to the RH end of the filter (cover end). The oil now has two paths it can take; path one is fed thru casting passages to the steel tube that is bolted to the top of the side cover (which feeds both the head and the RH case half), the other path the oil can take leads it down thru casting passages in the side cover to the RH end of the crankshaft. This port is used to lubricate the entire crank assembly. To summarize what was just said; the oil filter cover passes oil to three places #1 the cylinder head, #2 the RH case half, #3 the crankshaft. Now let’s in detail understand these three paths.

Path #1 (to the cylinder head)
The oil entering the cylinder head comes from the steel tube as noted above. This oil enters the back of the cylinder head and feeds both of the RH exhaust cam bearing journals simultaneously. Through the design of the cam cover the oil is transferred up to the top of the LH cam journal, thru a passage down into the head, then back up another passage in the exhaust cam cover, across (right) and then down into the single exhaust cam bearing journal. A LONG WAY TO GO FOR THE EXHAUST CAM JOURNAL TO GET SOME OIL HUH! All oil drains back to the case via the timing chain passage, which is also a good way to lubricate the timing chain and the LH side ball bearings on both cams.

Path#2 (to the RH case half)
The oil entering the RH case half comes from the steel tube noted above. This oil enters the case, thru casting passages, and enters a long copper tube that connects to the LH case half. Both ends of this tube are flanged and have o-ring seals. The tube feeds oil into the clutch actuation rod bore. This bore lets oil run two places. One is to the LH end of the clutch shaft (sometimes called Countershaft or main shaft). Two is to the output shaft (sometimes called the axle shaft). Both of theses shafts are hollow and have cross drillings to lubricate the transmission gears as follows: the clutch shaft lubes three places; one at the 4th gear, one at the 5th gear, and one between the bushings in the clutch hub / basket. The output shaft lubes four places; three are found at first second and third gears, and one at the LH shaft bearing (located in the LH case half).

Path#3 (crankshaft assembly)
The oil feeding the crankshaft comes from the RH end of the crank (which is hollow). The crank is sealed to a passage in the RH side cover. The crank, much like the transmission, is lubricated thru cross-drilled holes which supply oil to both crank bearings, the rod, and piston.

Stack #2 (Scavenge pump)
All oil drains back to the case. Since the scavenge pump is way larger than the pressure pump, it has the ability to put more oil in the frame than the engine can supply. Hence why our bikes are called dry sumps. The oil is pushed out thru passages in both case halves to the line connected to the LH case half down by the neutral switch where it is then feed to the top of the frame reservoir. Also note that there is a pickup screen in the bottom of the transmission to help keep debris from entering the scavenge pump.

Some serious seals to care for:
The clutch actuator shaft seal (on top of the side cover) holds in pressure supplying the entire transmission with oil.
The output shaft seal (the one behind the sprocket) holds in pressure supplying the output shaft and all its gears with oil.
Those two little o-rings in the oil cover ensure oil passes thru to the entire lubrication system.

Pretty wild guys :D

So maybe next time your in the side cover checking on that clutch you might want to spend an extra hour or two and see how that little pump is doing!!! :D $It's a whooping $113.48 (list) if you decide it should be replaced.

  • pressurefreak

Posted April 09, 2004 - 05:08 AM


Well written and explained well. Thanks for the detail. I never realized how complicated the lubrication system was. I would hate to get gear matter or clutch material in those passages to the point of obstruction. :)

  • trailriderjoe

Posted April 09, 2004 - 11:00 AM


You aint kiddin. That's why I know the pump prices. Both the main pump and the scavenge pump were scored even after the majority of the gear debris was caught by the pickup screen. The minor debris still was enough to trash the tip clearance out to around .015in (spec is around .005in). I give the filter credit though, it kept the top end spotless!!! :)

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  • YZUL8R

Posted April 09, 2004 - 12:11 PM


Hey man..i noticed you said to keep an eye on certain seals..well my CS sprocket seal has been leaking slightly for about a 2 months now..Do you think this little leak is affecting oil pressure any??? If it is..i'll replace it very very soon. Like, before i ride again soon.

  • vetplus40

Posted April 10, 2004 - 05:12 AM


Nice job......:)
You should consider doing one for gearing as well. A lot of folks don't understand how the ratios change things and are too self conscious to ask.

  • slappie

Posted April 26, 2004 - 10:10 AM


Sorry to dig up an old thread. I've got a YZ-450F.

I bought an anodized aluminum oil filler plug and some of the anodizing chipped off when I was putting it in. I backed it out and could peel off the piece of anodizing that was too large. I am 99.9% sure that none of it broke off and got in the case (it wasn't inserted fully and the first thread on the hole essentially deburred the plug for me outside the bike), but if it did, should I be worried? It looks like it would get caught by the oil pickup screen, or the reservior screen in the frame if it got past that. Then the filter.

Again, I am almost 100% certain that it didn't enter the case but just wanted to make sure what the consensus was.

Another way to put it is: when you fill up your motor with fresh oil, does it get filtered/screened before going to the vital engine parts?


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