From: Marc Thomas [mmthomas@ix.netcom.com] Sent: Friday, October 27, 2000 4:32 PM To: 928 Subject: [928] 2/6 rod bearing failure David, Our testing has shown that the 2/6 rod bearing failure is caused by TWO issues, and the main reason for the failure is not the one most commonly thought. We have spent years understanding the issue, 3 engine builds testing "theory" and teardowns and lots of engineering and here is the summary. How good is the summary, well, they are good enough for Porsche AG to purchase our solution for their racing 928 customers! First, the 2/6 oiling path is the least contributing factor to the failure! This is the common misconception. The main factor is simply oil starvation, and the 2/6 rod bearing feed off the crank is the first to get the gulp of oil/air. Where does the air come from, well if you are cornering at 1g, the the oil in the pan is at a 45 degree angle, and depending on oil level, will uncover the pickup....hence the air! The secondary factor is from off angle oiling of the 2/6 journal off the crank. This is a minor issue and if oil pressure is sufficient, it is a non issue at any rpm. The oil starvation, or lack of oil in the pan is caused by the fact that oil is pumped into/upto the head in large quantities by high rpm and the head acts as a oil "pan" of its own. The crank also spins up a batch of oil and keeps it in suspension, especially at high rpm. This oil cloud circles the crank and is the reason most race engine have "scrapers" in the case. Up to two quarts of oil can be circling the crank at high rpm! In some cases it can be more as the S4 is known to "pump" oil up the oil filler tower and keep it there! When there is not enough oil in the pan (caused by the high rpm pumping of oil to other areas, like the head, etc.), then under cornering at 1 g, the oil pickup is uncovered! So, the worst thing you can do to your engine is this...a 6500 rpm corner entry, a 1 or more g corner force while maintaining 6000+rpm...you are sure to pick up some air...and do it enough times, the bearing will fail. It will happen more frequently and sooner on a S4 then on an early engine with the same cornering capability due to the fact that there are less places for the oil to stay in the head and the paths in the head are smaller. So more oil stays in the pan. The solution as originally develop by DEVEK is as follows...use our Accusump systems! The DEVEK Accusump systems have two levels, street and race and each one offers a different level of protection, but only for so long. Approximately 10 - 17 seconds depending on oil type, temp, etc. These are the systems that are purchased and recommended by the factory. An addition item is to decrease the amount of oil available to the head by increasing the spring pressure or my favorite, decreasing the feed orifice. The other method, again as developed by DEVEK (by the late Bob DEVore) and currently used by other racers, is a simple dry sump system that uses the original oil pump to feed the engine from a remote tank, rather than the oil pan and a scavenger pump to fill the tank... And of course, you can just dry sump the system externally and depend on no stock oils systems. On OUR Scat stroker cranks, we simply pick up oil off the number three main bearing to make is a straight shot to feed the 2/6 rod bearings...so as some one correctly pointed out, it is routed like a chevy. This is unlike our drilled cranks, which have a modified oil pathway. I hope this clears up most of the misconceptions about a weakness of our engines and clarifies why some folks believe that the engine will last longer if the rev's are lower.....less oil pumped out of the pan. Oh, by the way, can it happen to a non racer? YUP, if your oil level is low, and you are running at 6000+ rpm for a hundred miles of so...it can happen. And this has happened. More information is available in our catalog or give me a call or email.... Warmest Regards, Marc -- Marc M. Thomas DEVEK The White Car 450hp/470tq on the ground 210 mph 'on the street THE fastest 928 on the planet. 650-592-5287 phone 650-610-0557 fax http://www.devek.net From: mlschmidt@sprintmail.com [mailto:mlschmidt@sprintmail.com] Sent: Friday, September 27, 2002 6:07 AM To: 928 Subject: [928] Re: 8.5:1 #2/6 bearing.... factory solutions. >I have heard this right left rationale mentioned before... What is the >foundation for that effect. The pan and pickup are absolutely symmetrical. >What difference would it make whether it was a right or left hander. Is it >that the crank rotation makes the oil climb higher on one wall or the other? >Curious... It's left turns. I know some of you have heard about Louie Ott's "holy valve cover". He took a valve cover, cut a hole in it, and fitted a Plexiglass window over it. He made a bracket to mount a video camera and spot light, to be able top look through the Plexiglass window. He then had an instructor drive the car on the track while he observed and filmed the oil flow in the cam area of the head. The oil flow was nice and smooth during acceleration, braking, and right turns. As soon as the car would go into a left turn, the oil flow would turn to foam. This was with a GTS baffle and a street version of the Accusump on his GT. The 2/6 rod bearings have since been destroyed, and he's currently doing an engine rebuild. The pump pickup and pan are symmetrical, but left turns cause more of a problem due to the direction of engine rotation and those ribs on the floor of that flat rear section of the oil pan. Those raised ribs on that section of the pan are there to help direct oil forwards, back into the sump. The crank and rods throw the oil in the same direction as they're moving, and the angled ribs help to turn that sideways movement of the oil forwards. Those ribs also do a surprisingly good job of moving that oil to the right side of the pan. During a left hand turn with high G forces, the oil in the sump is pushed against the right side of the pan, the ribs are moving oil to that side, and the windage from the rotating assembly is also helping to hold the oil on that side. With the oil piled up on that one side, it doesn't take much before it runs out of the sump onto that rear flat portion of the pan. In some experimenting I did with my oil pan when I had it off, fluid in the sump would run up onto that rear flat portion of the pan before the pump pickup was in any danger of being uncovered and sucking air. The GTS baffle made no real measurable difference in the amount the pan could be tilted before the fluid ran out of the sump. After looking at it, and giving it some thought, I'm convinced that the baffle was put in the GTS due to increased windage problems from the longer stroke compared to the 5 liter engines. The crankcase breather was also changed on the GTS to help keep as much oil from being sucked out along with the blowby gasses, which would also indicate a change due to increased windage. The rotating assembly comes surprisingly close to that flat rear floor of the oil pan. It's so close that those two bumps in that section of the pan are actually clearance for bolts holding on the lower engine cradle. Once the oil runs up onto that flat rear portion of the pan, it wouldn't take much before the rotating assembly whips it into foam, the same way a blender makes a milkshake. This effect would occur the most when there was the most oil on that rear portion of the pan, and the rotating assembly was spinning at the fastest speed. High RPM left hand turns. On my pan I made a full baffle for the sump. Testing compared to either no baffle or the GTS baffle showed that the pan could be tilted a significant amount more before the oil would come out of the sump area with the full baffle. Mike Schmidt '88 928S4 Auto Black/Black "PORSCHE" cloth 928 Owners Club Charter Member PCA Chicago Region