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Thread: Engine Oiling Systems, Functional Description

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    Engine Oiling Systems, Functional Description

    This is a working draft of my understanding of the oiling systems. I thought I should post it sooner rather than later. Everyone can help improve this writeup. I'll periodically edit this post to incorporate everything learned. Additions, corrections, or questions are all appreciated.

    I have arranged the description headings in substantially the order in which oil flows through the engine. Item numbers referenced come from page 36 of the parts book (pic posted below).

    Oil Tank:
    The oil tank has 4 ports. On the right side, blue hoses connect for "supply" and "return" to the engine. The lower hose is supply. The upper hose is return. The return line runs inside the tank, and makes a 180-degree turn to dump oil back into the tank. The hose at the bottom of the tank on the left side is for crankcase ventilation. The crankcase vent hose connects to a pipe internal to the oil tank that runs to the very top of the tank. The hose at the top on the right side connects to the airbox and vents the oil tank.

    Oil Pump:
    The "oil pump" is actually two separate pumps driven by a common shaft. There is a scavenge pump and a pressure pump. The pressure pump supplies oil to all internal engine components. The scavenge pump returns oil from the engine sump to the oil tank (hence the name dry-sump system). The two pumps will be discussed separately in greater detail. It is interesting to note that the scavenge pump has a wider geroter (see: http://en.wikipedia.org/wiki/Gerotor) and thus greater pumping capacity than the pressure pump.

    Pressure Pump:
    Oil is drawn out of the oil tank through the blue bottom hose. It runs through one hard-line external to the engine (item #5), and another hard-line internal to the engine (item #3 behind the alternator cover). Oil is thus delivered to the inlet side of the pressure pump. The outlet side of the pressure pump delivers oil to the oil filter, but connects to the FCV as well.

    Flow Control Valve:
    The FCV (items #8-11) is a pressure regulator. It simply shunt excess oil flow from the outlet side of the pressure pump back to the inlet side of the pressure pump.

    Oil Anti-Return Valve:
    In another post, I incorrectly postulated that this component (items #12-17) was an oil-filter bypass valve. I now believe the parts book's description of "oil anti-return valve" is correct. (In English, "anti-drainback valve" might be a better translation, though.) A very small oil pressure is required to open the valve. However, when the engine is shut off, this valve closes and won't permit oil to flow out of the pathways by gravity. Because oil is essentially incompressible, there is zero time lag for the oil to start flowing through the internal pathways (once the system is primed). This means that the instant the engine is started, all critical components already have oil delivery. However, this also reminds me that, after an engine rebuild, it is important for the engine to be cranked without starting for a while in order to prime the system and ensure proper oil flow at the instant of start-up.

    Oil Filter:
    The oil filter (item #19) receives oil by way of the pressure pump/FCV interaction, and the anti-return valve. The oil filter itself contains an integral bypass valve. Normally this valve is closed and thus all engine components receive 100% filtered oil. However, if the pressure differential across the filter media becomes too great, the bypass valve opens and allows partially filtered / unfiltered oil to be delivered to engine. Oil flows through the filter from the outside to the inside.

    Oil Pressure:
    According to Micah's measurements, maximum oil pressure is in the range of about 112 to 122 PSI at any RPM above about 5,000. Oil pressure can be measured by removing the oil pressure switch (item #18) and installing a gauge (M10 -1.0 thread). The oil pressure switch is electrically "normally closed" and remains closes until the oil pressure rises above about 6 PSI. Again, according to Mica's measurements, normal (cold!) oil pressure at idle is about 75 PSI. The oil pressure switch is located on the outlet side of the oil filter.

    Internal Oil Pathways:
    Filtered oil is delivered to all internal components. There appears to be three paths out of the oil filter. One leads to the front head. The other two supply oil to the RH and LH crankshaft main bearings. These are plain bearings. A pathway through the clutch housing directs oil to the rear head. There is no O-ring or other special sealing at the clutch housing/crankcase interface (only the usual clutch housing gasket). There is a bolt right next to the passage, but this would seem to be an area to watch for leaks to ensure the rear head is properly oiled.

    Oil is delivered to the heads through the crankcases. There are two (one for each head) very small (0.5mm) orifices the oil must pass through to get to the heads. The bearings in the heads are ball bearings. Oil drains from each head back to the crankcase sump.

    There is an outboard seal for the crankshaft in the alternator cover. Oil is deliverd to the alternator cover via the hollow shaft for one of the starter gears. This shaft has an O-ring at each end. Amauri has cautioned us to be careful not to damage these O-rings (and outboard seal) when the alternator cover is installed. The oil that feeds through the alternator cover and into the crankshaft lubricates the big-end rod bearings!

    Scavenge Pump:
    The sump is evacuated by the scavenge pump. The inlet to the scavenge pump is covered by a small screen (as would be normal for any wet-sump oil pickup). Oil is pumped out of the engine through the internal hard line (item #1) behind the alternator cover. Another hard line outside the engine (item #6) returns scavenged oil to the tank via the upper blue hose. One curious feature here. The internal hard line has a hole drilled in it near the top. Not sure what this does. Obviously some oil will bleed out on its way back to the oil tank. Maybe this hole is just to oil stuff inside the alternator cover?
    Last edited by Jim Hubert; 06-15-2008 at 07:30 AM.

  2. #2
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    Page 36 of Parts Book
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    Last edited by Jim Hubert; 03-02-2008 at 09:14 AM. Reason: Used better picture

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    just another Aprilia fanatic amauri's Avatar
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    Here's an x-ray image of the oil tank and a diagram sketched by ETN550
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    Last edited by amauri; 01-20-2009 at 12:40 PM. Reason: added sketch from ETN550
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    The X-ray is very helpful, Amauri.

    I'm not seeing where the crankcase vent tube goes. Are there two tubes with 180-degree bends: one for oil return, and one for crankcase ventilation?

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    just another Aprilia fanatic amauri's Avatar
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    Quote Originally Posted by Jim Hubert View Post
    There is an outboard bearing (or bushing?) for the crankshaft on the alternator side. This bearing is lubricated through a hollow shaft for one of the starter gears. This shaft has an O-ring at each end. Amauri has cautioned us to be careful not to damage these O-rings when the alternator cover is removed/replaced.
    The oil that feeds thru the alternator cover and into the crankshaft is what pressurizes the rod bearings.
    There are no oil holes on the main journals of the crank that feed the rods.

    That is why it is extremely important not to damage that seal on the cover and the two very thin o-rings on the upper starter reduction gear shaft, oil pressure goes thru that shaft and into the alt cover.
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    just another Aprilia fanatic amauri's Avatar
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    The main vent from the LH side of the crankcase is shown on the RH image, you can see it sliced through vertically and it just ends at the top of the tank with a slight bend to the left.

    Just above that is the tube that connects to the hose going to the airbox.
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    I'll change the descriptions to incorporate those facts. Wow, the oiling of the rod bearings through the alternator cover is important to know. I'll share a tip I learned from 2-strokes. I always use an aluminum button between the crank end and the flywheel puller bolt. If a 2-stroke crank is even slightly dinged in that area, it can't be checked for "true" between centers. I'll post a pic of my Aprilia button in the Special Tools post. http://www.apriliaforum.com/forums/s...d.php?t=134937
    Last edited by Jim Hubert; 03-01-2008 at 11:56 AM.

  8. #8
    just another Aprilia fanatic amauri's Avatar
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    Quote Originally Posted by Jim Hubert View Post
    Wow, the oiling of the rods bearings through the alternator cover is important to know.
    It is extremely important to install the cover perfectly straight and prevent damage to that cover seal.

    The strong magnetism of the flywheel make it very difficult, I use two 6 x 40mm studs temporarily screwed into the crankcase threads to help guide the cover on straight.
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    I saw a couple small nicks in those O-rings and thought nothing of it -- plenty of oil will get to the bearing/bushing. The bushing is obviously not the issue.

    I'll use the stud trick and replace the O-rings for sure!

    EDIT: Now the hole in the scavenge return line makes more sense. I figured they relied on oil escaping from the alternator bushing to lube/cool the alternator cavity.

    2nd EDIT: It is not a bearing/bushing at all! It is a seal! All is clear now.
    Last edited by Jim Hubert; 03-01-2008 at 01:27 PM.

  10. #10
    just another Aprilia fanatic amauri's Avatar
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    Look closely at that cover seal with a pencil light, 90% of the ones I've seen have been slightly damaged.

    When you remove the seal you will think it was installed backwards.
    They did that on purpose according to the mechanics at the factory race shop in Ternate.

    edit:
    Aprilia issued tech bulletin #008-2008 with an updated oil seal on the alt cover, new p/n is 855031.
    The bulletin also states that it must be installed in reverse of the old seal.
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    Last edited by amauri; 09-27-2008 at 08:55 AM.
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    apriliaforum expert kimzx1000r's Avatar
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    how high with in the tank does the oil sit? Is it possible to fit a dipstick?

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    Kim, I don't think a dipstick would help. The oil tank is baffled above the lower fitting for the sight tube. If oil does not show on the sight tube, you would not be able to get a dipstick in deep enough to show anything either.

    I think relocating the bottom of the sight tube as cal550 and mtm100 have detailed is a better option.

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    just another Aprilia fanatic amauri's Avatar
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    Do not over tighten the FCV plug (19mm).

    Two people have contacted me lately about how to fix the threads they had ripped out in the crankcase from too much torque on that plug.

    Because of the oil passages behind that plug, the threads are not very deep. If you strip it, a simple Helicoil will not work.

    If you're worried about it worklng itself loose, wire it.
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