M96 Oil System Description
06-01-2020 | 02:25 PM
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M96 Oil System Description
There has not been much technical content here lately so I am posting this in an attempt to reverse that trend.
Hopefully this will inspire somebody somewhere to do some actual work instead of parroting a parrot for the 4th time.
And credit for inspiring me to post this to the OP of this thread: https://rennlist.com/forums/boxster-...l-racecar.html
A description of the oil system of a 5 chain M96 engine equipped with CTSR dry sump system.
Pressure Circuit:
Oil tank atmospheric pressure pushes the oil column towards the pressure pump inlet at the front of the oil pump assembly, which is driven by a toothed belt at 96% (Pulley Ratio 24:25) of crankshaft rpm. (at 7300rpm the pump runs at 7008rpm and at the idle speed of 680rpm the pump runs at 652rpm) At high rpm, the flow capacity of the hose from the tank outlet to the pump inlet is very close to the total flow capacity of the pressure pump, therefore it is necessary, in order to prevent cavitation at the pump inlet, to ensure that the flow through this hose is not compromised in any way. Maintenance of the correct oil level is absolutely necessary.
The pressure pump features a relief valve. The valve reduces the oil pressure when the oil is cold, flattening the oil pressure/pump rpm curve significantly. The valve has no effect on the hot oil pressure.
The designed oil pressure at the main bearings is 4.0 bar at 250F oil temperature with 10W-60 oil.
From the pressure pump outlet the oil flows through a hose to the former location of the oil filter. The adapter block there feeds the pressurized oil into the engine's stock pressure circuit.
The intermediate shaft chain tensioner is fed with pressurized oil prior to the oil cooler. This is the first item to be fed by oil pressure.
From the filter adapter block the oil rises upward to the oil cooler and travels across the cooler before moving downward again into the main oil passage. The main oil passage is formed by the side of the crankshaft carrier mating up to a machined surface in the 456 engine case. The shape of the passage is cast into the engine case and is left unmachined. It is possible that there is pressure leakage between the case half and the crankshaft carrier.
The main oil passage directly feeds each of the seven main bearings. Each main bearing oil passage is approximately 5mm in diameter, drilled through the crankshaft carrier. At the ends of the passages there are 360 degree grooves behind the main bearings, which also feed a single piston squirter per cylinder.
The main bearings themselves have a 360 degree groove on the bearing surface which is necessary to feed the single passage on each main bearing journal which provides each rod journal with oil. This 360 degree groove preferentially feeds oil to the rod bearings and also, because each main bearing is effectively split into two narrow bearings, greatly decreases the load capacity of each main bearing. This explains why the rod bearings in these engines are so tolerant of intermittent oiling and also why the main bearings fail even though the loads are low due to moderate maximum rpm and low specific outputs.
The center main bearing has no drilling for rod oiling and instead has the axial thrust bearing for crankshaft end float. Each main bearing to rod bearing passage runs diagonally through the crankshaft webs and is 5mm in diameter. Each drilling is identical, straight through, with no plugs or intersecting passages.
The 123 engine case has a much smaller oil passage which is fed by a 10mm diameter and 140mm length hole drilled through the crankshaft carrier. This passage is also comprised of a cast area met tightly by the side of the crankshaft carrier. The 10mm passage crosses the parting line of the crankshaft carrier assembly. This may also be a leak point. This passage creates a small pressure drop which causes the oil pressure to be lower on the 123 cylinder head.
Each main oil passage feeds two head bolt holes on each cylinder head which distribute oil to the respective cylinder head. One of the head bolt holes intersects two oil feed passages and one bolt hole intersects a single passage. The oil flows around the head bolts in the annular passage made by the difference in diameter of the head bolt and the bolt hole.
In order to decrease the total oil flow and pressure to the cylinder heads, and to increase the total oil flow and pressure to the main bearings, a total of 6 oil restrictors are installed in each cylinder head. The details are described below. The design target was to reduce the cylinder head oil pressure to 60% of that of the main bearings. The restrictors greatly reduce the volume of oil captured in the heads. Under race conditions, the oil tank level is approximately 2 quarts higher than without the restrictors.
A single drilled passage feeds the chain drive end of each cylinder head. The drilling is 6.8mm in diameter and is 75mm long. The drilling intersects the cast head bolt bore at a high angle and exits at the inner surface of the cylinder head where the lifter carrier bolts down. An oil channel is formed by the channel cast into the cylinder head and the channel cast into the lifter carrier. This mating surface has no provision for sealing. This drilling feeds 4 hydraulic lifters, the cam phasing device, and the chain tensioner. This passage is left unrestricted, instead 1mm restrictors are installed in each hydraulic lifter feed hole. This allows the chain tensioner and cam phasing device to operate normally.
Branching from the above described passage, the 456 head has a 6.8mm diameter, 195mm long drilling to feed oil to the cam chain tensioner. The passage has a short intersecting drilling to deliver oil to the tensioner.
The 123 head has a much smaller and more direct drilling to the chain tensioner.
Both cam phasing devices are fed through the lifter carrier with yet another metal to metal sealing surface, with no provision for sealing.
The second oil fed bolt hole on each head contains two drilled passages. One feeds eight hydraulic lifters only through a 6.8mm, 75mm hole The other passage is 6.8mm and150mm long. This hole feeds the valve cover which then feeds one of the four cam bearings on each cam. The cams themselves are hollow and distribute oil to the remaining cam bearings. The final destination of the oil pressure system is the exhaust cam bearing nearest to the chain drive. This cam bearing is often damaged in engines that run with interrupted oil pressure.
On the 123 cylinder head 2.1mm restrictors are installed in each of these holes to the reduce the oil flow and pressure. The 456 head uses 2.0mm restrictors, due to its higher initial pressure.
Scavenge Circuits: There are four scavenge circuits.
The first is the standard oil pump which attempts to evacuate the oil from the sump area. Crankcase pressure pushes oil into the pickup where it flows to the pump inlet. The pump then pushes the oil though a cast in passage to the oil filter adapter block where it flows into a hose which takes it to the filter housing on top of the oil tank. After being filtered and defoamed, the oil falls into the tank. The pressure relief valve in the stock oil pump is left in place. The oil pressure at the pump outlet cannot rise high enough to activate the valve since there is little restriction on the pump output.
This circuit is assisted by the stock scavenge pumps, one on each cylinder head. Each scavenge pump attempts to remove oil from the chain area of the cylinder head. The oil then flows through cast in passages in the engine cases to plastic air/oil separators mounted in the sump area. Air is discharged into the cylinder jacket area while oil is discharged into the sump.
The second scavenge circuit attempts to pull oil out of the high volume Z-shaped area formed by the intermediate shaft area and the two cam chain housings. Under acceleration, oil runs backwards to the intermediate shaft chain area where it is collected by the scavenge system. This area collects several liters of oil otherwise. In order to prevent the intermediate shaft chain from running without lubrication, the scavenge point is higher than the lowest area that the chain occupies. From there the oil travels through a hose to the dry sump pump assembly.
The third and fourth scavenge stages pull oil from each cylinder head. The points are on the opposite ends of the cylinder heads from the chain drives. This arrangement, along with the stock scavenge pumps, gives effective oil removal from all four corners of the engine, so oil is effectively removed under any combination of G forces. The 123 head uses a hose that runs up the valve cover and across the top of the engine to the pump assembly. The 456 head uses a hose that runs along the rear of the engine then around the oil cooler to the pump assembly.
The outputs of the second, third, and fourth scavenge circuits are joined internally in the dry sump pump assembly and fed into an integrated rotational oil/air separator located at the rear of the pump assembly. The resultant defoamed oil is fed into a hose where is routed to the oil tank's oil filter. The now mostly oil-free air from the oil/air separator is fed through a hose into the side of the oil tank above the level of the oil.
Crankcase ventilation:
The four scavenge circuits are effective enough that the stock air/oil separator is no longer necessary. The crankcase ventilation crossover pipe from the 456 cylinder head is also unnecessary. The crankcase windage situation is no longer critical due to most of the oil being removed from the interior of the crankcase. There is no connection between the crankcase/oil tank and the intake manifold.
The oil tank is vented to atmosphere to allow crankcase gasses to escape freely. The gasses are vented at the rear of the car so the driver does not perceive them. The crankcase and the oil tank are also connected through a hose, which allows the crankcase and oil tank to remain at the same internal pressure. Lowering the crankcase pressure was tested and found not to be useful.
Other modifications:
Oil is introduced to the system at the oil tank instead of the crankcase, so the plastic oil filling plumbing is deleted and a cap placed in hole in the top of the engine case. This cap is an ideal location to install a crankcase pressure sensor.
The dipstick is no longer useful so that hole is also capped.
The electronic dipstick is left in place to provide the oil temperature data to the stock ECU for cam phasing control.
Hopefully this will inspire somebody somewhere to do some actual work instead of parroting a parrot for the 4th time.
And credit for inspiring me to post this to the OP of this thread: https://rennlist.com/forums/boxster-...l-racecar.html
A description of the oil system of a 5 chain M96 engine equipped with CTSR dry sump system.
Pressure Circuit:
Oil tank atmospheric pressure pushes the oil column towards the pressure pump inlet at the front of the oil pump assembly, which is driven by a toothed belt at 96% (Pulley Ratio 24:25) of crankshaft rpm. (at 7300rpm the pump runs at 7008rpm and at the idle speed of 680rpm the pump runs at 652rpm) At high rpm, the flow capacity of the hose from the tank outlet to the pump inlet is very close to the total flow capacity of the pressure pump, therefore it is necessary, in order to prevent cavitation at the pump inlet, to ensure that the flow through this hose is not compromised in any way. Maintenance of the correct oil level is absolutely necessary.
The pressure pump features a relief valve. The valve reduces the oil pressure when the oil is cold, flattening the oil pressure/pump rpm curve significantly. The valve has no effect on the hot oil pressure.
The designed oil pressure at the main bearings is 4.0 bar at 250F oil temperature with 10W-60 oil.
From the pressure pump outlet the oil flows through a hose to the former location of the oil filter. The adapter block there feeds the pressurized oil into the engine's stock pressure circuit.
The intermediate shaft chain tensioner is fed with pressurized oil prior to the oil cooler. This is the first item to be fed by oil pressure.
From the filter adapter block the oil rises upward to the oil cooler and travels across the cooler before moving downward again into the main oil passage. The main oil passage is formed by the side of the crankshaft carrier mating up to a machined surface in the 456 engine case. The shape of the passage is cast into the engine case and is left unmachined. It is possible that there is pressure leakage between the case half and the crankshaft carrier.
The main oil passage directly feeds each of the seven main bearings. Each main bearing oil passage is approximately 5mm in diameter, drilled through the crankshaft carrier. At the ends of the passages there are 360 degree grooves behind the main bearings, which also feed a single piston squirter per cylinder.
The main bearings themselves have a 360 degree groove on the bearing surface which is necessary to feed the single passage on each main bearing journal which provides each rod journal with oil. This 360 degree groove preferentially feeds oil to the rod bearings and also, because each main bearing is effectively split into two narrow bearings, greatly decreases the load capacity of each main bearing. This explains why the rod bearings in these engines are so tolerant of intermittent oiling and also why the main bearings fail even though the loads are low due to moderate maximum rpm and low specific outputs.
The center main bearing has no drilling for rod oiling and instead has the axial thrust bearing for crankshaft end float. Each main bearing to rod bearing passage runs diagonally through the crankshaft webs and is 5mm in diameter. Each drilling is identical, straight through, with no plugs or intersecting passages.
The 123 engine case has a much smaller oil passage which is fed by a 10mm diameter and 140mm length hole drilled through the crankshaft carrier. This passage is also comprised of a cast area met tightly by the side of the crankshaft carrier. The 10mm passage crosses the parting line of the crankshaft carrier assembly. This may also be a leak point. This passage creates a small pressure drop which causes the oil pressure to be lower on the 123 cylinder head.
Each main oil passage feeds two head bolt holes on each cylinder head which distribute oil to the respective cylinder head. One of the head bolt holes intersects two oil feed passages and one bolt hole intersects a single passage. The oil flows around the head bolts in the annular passage made by the difference in diameter of the head bolt and the bolt hole.
In order to decrease the total oil flow and pressure to the cylinder heads, and to increase the total oil flow and pressure to the main bearings, a total of 6 oil restrictors are installed in each cylinder head. The details are described below. The design target was to reduce the cylinder head oil pressure to 60% of that of the main bearings. The restrictors greatly reduce the volume of oil captured in the heads. Under race conditions, the oil tank level is approximately 2 quarts higher than without the restrictors.
A single drilled passage feeds the chain drive end of each cylinder head. The drilling is 6.8mm in diameter and is 75mm long. The drilling intersects the cast head bolt bore at a high angle and exits at the inner surface of the cylinder head where the lifter carrier bolts down. An oil channel is formed by the channel cast into the cylinder head and the channel cast into the lifter carrier. This mating surface has no provision for sealing. This drilling feeds 4 hydraulic lifters, the cam phasing device, and the chain tensioner. This passage is left unrestricted, instead 1mm restrictors are installed in each hydraulic lifter feed hole. This allows the chain tensioner and cam phasing device to operate normally.
Branching from the above described passage, the 456 head has a 6.8mm diameter, 195mm long drilling to feed oil to the cam chain tensioner. The passage has a short intersecting drilling to deliver oil to the tensioner.
The 123 head has a much smaller and more direct drilling to the chain tensioner.
Both cam phasing devices are fed through the lifter carrier with yet another metal to metal sealing surface, with no provision for sealing.
The second oil fed bolt hole on each head contains two drilled passages. One feeds eight hydraulic lifters only through a 6.8mm, 75mm hole The other passage is 6.8mm and150mm long. This hole feeds the valve cover which then feeds one of the four cam bearings on each cam. The cams themselves are hollow and distribute oil to the remaining cam bearings. The final destination of the oil pressure system is the exhaust cam bearing nearest to the chain drive. This cam bearing is often damaged in engines that run with interrupted oil pressure.
On the 123 cylinder head 2.1mm restrictors are installed in each of these holes to the reduce the oil flow and pressure. The 456 head uses 2.0mm restrictors, due to its higher initial pressure.
Scavenge Circuits: There are four scavenge circuits.
The first is the standard oil pump which attempts to evacuate the oil from the sump area. Crankcase pressure pushes oil into the pickup where it flows to the pump inlet. The pump then pushes the oil though a cast in passage to the oil filter adapter block where it flows into a hose which takes it to the filter housing on top of the oil tank. After being filtered and defoamed, the oil falls into the tank. The pressure relief valve in the stock oil pump is left in place. The oil pressure at the pump outlet cannot rise high enough to activate the valve since there is little restriction on the pump output.
This circuit is assisted by the stock scavenge pumps, one on each cylinder head. Each scavenge pump attempts to remove oil from the chain area of the cylinder head. The oil then flows through cast in passages in the engine cases to plastic air/oil separators mounted in the sump area. Air is discharged into the cylinder jacket area while oil is discharged into the sump.
The second scavenge circuit attempts to pull oil out of the high volume Z-shaped area formed by the intermediate shaft area and the two cam chain housings. Under acceleration, oil runs backwards to the intermediate shaft chain area where it is collected by the scavenge system. This area collects several liters of oil otherwise. In order to prevent the intermediate shaft chain from running without lubrication, the scavenge point is higher than the lowest area that the chain occupies. From there the oil travels through a hose to the dry sump pump assembly.
The third and fourth scavenge stages pull oil from each cylinder head. The points are on the opposite ends of the cylinder heads from the chain drives. This arrangement, along with the stock scavenge pumps, gives effective oil removal from all four corners of the engine, so oil is effectively removed under any combination of G forces. The 123 head uses a hose that runs up the valve cover and across the top of the engine to the pump assembly. The 456 head uses a hose that runs along the rear of the engine then around the oil cooler to the pump assembly.
The outputs of the second, third, and fourth scavenge circuits are joined internally in the dry sump pump assembly and fed into an integrated rotational oil/air separator located at the rear of the pump assembly. The resultant defoamed oil is fed into a hose where is routed to the oil tank's oil filter. The now mostly oil-free air from the oil/air separator is fed through a hose into the side of the oil tank above the level of the oil.
Crankcase ventilation:
The four scavenge circuits are effective enough that the stock air/oil separator is no longer necessary. The crankcase ventilation crossover pipe from the 456 cylinder head is also unnecessary. The crankcase windage situation is no longer critical due to most of the oil being removed from the interior of the crankcase. There is no connection between the crankcase/oil tank and the intake manifold.
The oil tank is vented to atmosphere to allow crankcase gasses to escape freely. The gasses are vented at the rear of the car so the driver does not perceive them. The crankcase and the oil tank are also connected through a hose, which allows the crankcase and oil tank to remain at the same internal pressure. Lowering the crankcase pressure was tested and found not to be useful.
Other modifications:
Oil is introduced to the system at the oil tank instead of the crankcase, so the plastic oil filling plumbing is deleted and a cap placed in hole in the top of the engine case. This cap is an ideal location to install a crankcase pressure sensor.
The dipstick is no longer useful so that hole is also capped.
The electronic dipstick is left in place to provide the oil temperature data to the stock ECU for cam phasing control.
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