The head gets it's oil from the right rear head bolt. That is the head's main galley. Anyone who has ever done their own top end will remember the o-ring that goes between the cylinder and the bottom end, and the o-ring/seal that goes between the cylinder and the head on that head bolt hole. I'm doing this from memory, so bear with me. Oil is directed to 2 places via a "galley junction/split" from that head bolt galley. One is being sent up the head bolt galley to the head. The other sent to the clutch cover galley, which then sends it to the crank. The clutch cover method redirects the oil through the cooler and back into the clutch cover galley, where it is dispersed onto the crank.
The head's oil goes up that head bolt galley, and fills up a large space behind the cam. The cam is hollow, and fills with oil. There are 2 chamfered oiling holes in the cam. The oil is pressurized through those holes, and is what lubricates the rockers, cam & bearings, and valves. The oil then drains back into the bottom end, via the cam chain passageway (I think I remember right). If you've ever had the clutch cover off and the top end off at the same time, you will see that the little oiling hole next to the head bolt threads goes directly to the clutch cover.
The crankcase is nothing but a garbage pit (that is why there is a mesh screen on your drain plug, which is the equivilant of the mesh screen on an automotive oil pump's pick-up tube). Nearly all debris in the oil gets sent to the crankcase after the oil has gone through it's high wear areas. The oil pump sends that dirty oil to the filter. Then it goes from the filter to the main oil galley, where it is sent to the main and cam bearing. This is how the lubrication system of a typical automotive engine works. This engine shouldn't be hardly any different, and I think we can all agree on that.
The big bear cooler is cooling filtered oil, and is sending it to the main galley. Which is great, but that oil is absorbing lots of heat before ever reaching the crank. The oil from a big bear cooler is CERTAINLY much cooler then oil of a non coolered bike. BUT, that oil can be made even MORE cooler using the clutch cover method. Here is why: That filtered oil in the main galley is sent to the junction where it goes to both the head and the crank, via the clutch cover. The clutch cover re-routes that filtered oil and dramatically cools it before sending it to the crank. This is still a closed loop system, so no pressure losse OR airiating is occuring.
I think the biggest reason why there is much speculation about which cooler is the better, is because in theory, BOTH coolers are cooling the oil about the same amount. HOWEVER, because the oil from the big bear cooler absorbs heat before ever reaching the crank, the engine doesn't actually run as cool as a clutch cover cooler.
The arguement has come up about the head recieving the cooler oil with the big bear, and the crank is recieving cooler oil with the clutch cover method. People view that with a "6 of 1, half a dozen of another" mind set. Others have argued why should they go through the extra effort to do the clutch cover method, when cooled oil is cooled oil, and the valve train needs it just like the crank. But, the valve train can do without the cooled oil MUCH more then the crank can. The valve train in most all engine requires much less oil then the crank does anyway. This is why high rpm engines (drag racing) will have modded oil drain back holes in the heads, and push rod valley, use aluminum roller rockers, and other goodies, so more oil stays in the crankcase to prevent oil starvation to the crank and mains. It used to be common practice to cross drill cranks so as to give a full 360* of oiling to the main and rod bearings, for high rpm drag cars.
So, you can see how both methods do their jobs. The oil from the big bear cooler is indeed much cooler then the oil of a non coolered bike. By the time the cooled oil gets to the galley junction for the head and crank, it has already obsorbed heat. That being said, I doubt the head actually recieves oil that is any cooler then the crank. Matter of fact, it is probably hotter then the oil that gets to the crank; because the oil for the head has to run up the length of the cylinder, where the most extreme heat is made from enternal combustion. So if you stop and think about it, how is the head getting cooler oil then the crank? It is probably a bit hotter, only because of the heat of the cylinder and combustion gases.
Now that I've said that someone will probably call me out and say that if that is the case, why do the crank bearings fail, if the head's oil is actually hotter? That can be answered by what I said earlier; the valvetrain requires less oil then the crank in most all engines. That is why cooler oil for the crank is a must. If there was a way to mod the oil drain back system in the head to get more oil to the crank, then this would be a mute issue, and I wouldn't have kept myself up this late writing this article, when I have to get up at 6 to start my day, lol. Enjoy the read.
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