In the May issue of Baggers, we looked at several weak spots in the Twin Cam's bottom end, mainly excessive crankshaft runout and drive issues relating to the chain-driven cams. One area we did not discuss was the Twin Cam's oiling system and associated problems found on stock and high-performance Twin Cam engines. Oil is the lifeblood of any engine, and the Twin Cam is no exception. But having too much oil in certain areas of the engine or too low of oil pressure can lead to oil puking out the cylinder head breathers and a noisy valvetrain. Since Feuling Parts has optimized their Twin Cam hydraulic lifters, cam support plate and pushrods to work with their oil pump as a "balanced system," Baggers decided to check out what they have to offer.
The Twin Cam 88 engine uses a dry-sump system for lubrication. A dry-sump system only circulates a minimal amount of oil in the engine at any one time, while the majority is stored in a remote oil tank. To perform properly, a dry-sump system must be properly sized to the engine's requirements and "balanced" on the feed and scavenge sides so all residual oil is removed from the crankcase at all engine speeds and conditions. Failure of the oil pump's scavenge side to satisfy such requirements typically results in "wet-sumping." Wet-sumping is a condition where oil, instead of returning to the oil tank, builds up in the crankcase and cam gearcase, causing excessive friction and power loss.
(1.)Shown is a stock Twin Cam cam support plate with the pressure relief valve, relief spr
(2.)Compare this photo of Feuling's billet cam support plate, pressure relief valve, relie
(3.)Shown is the Feuling pressure-testing tool mounted on a cam support plate. The arrow i
Moreover, excess crankcase oil is often whipped into a froth of air and oil by the machined paddles of the left flywheel. This condition is called oil aeration. Aerated oil makes scavenging much more difficult and can hinder the return of oil from the rocker box area. The combination of these conditions often results in oil being forced out the head breathers, air cleaner contamination, oil leaks, loss of oil supply, lifter clatter, premature component wear and potential engine failure.
The Twin Cam's oiling system requires a fine balancing act to maintain the correct amount of oil pressure, oil volume and scavenging to eliminate wet-sumping while maintaining quiet operation and optimized power production without generating excessive heat. In many cases, the genesis of the Twin Cam's oiling problems lies in significant parts wear, hardened oil seals, poor part alignment, inaccurate machining tolerances and catastrophic damage to key components.
To maintain proper oil pressure, the Twin Cam engine uses a spring-loaded pressure relief valve, which is located in the cam support plate. The purpose of the relief valve is to protect the engine from excessive oil pressure. However, a sticking valve will cause low oil pressure. For example, when starting a cold engine in 20-degree weather and using 20/50 oil, the relief valve will open and protect the engine from extreme pressures that can damage engine seals. In contrast, if the valve stops working properly and sticks open due to debris from worn chain tensioners or poor machining tolerances, oil pressure can drop below minimum requirements. Unfortunately, low oil pressure causes a domino effect. First, the hydraulic lifters start clattering due to a lack of oil. Additionally, the oil supply to the top end is reduced, further amplifying engine noise and clatter. To compound the problems, the piston cooling jets, when opened, usurp oil from the lifters.
The pressure relief valve consists of a plunger and spring. The plunger must move freely and seat properly to maintain proper oil pressure. In addition to being held open due to debris circulating in the oil, the plunger has been known to catch and hang up on a machining burr in the bypass port, thereby reducing oil pressure. Whenever you rebuild a Twin Cam engine or install new cams, it's important to make sure the pressure relief plunger moves freely and seats properly in the cam plate bypass port. Feuling makes a high-quality pressure relief spring for the Twin Cam with the correct spring rate to control and maintain proper oil pressure.
(4.)Feuling's pressure test tool makes it easy to bench-test the cam support plate and pre
(5.)In the event testing shows the pressure relief valve is leaking in the cam plate, you
(6.)Feuling's performance hydraulic roller lifters are CNC-machined, precision-ground and
(7.)Shown is one method for checking pinion shaft runout using a dial gauge. Always measur
Feuling also manufactures a neat pressure test tool that allows the engine builder to test the pressure relief valve operation before installation of the cam support plate to ensure the oil relief plunger moves freely, seats completely and seals properly. The tester includes a pressure gauge, 0-100 psi regulator, mounting plate, gaskets and related hardware. The tool allows the engine builder to know at what psi the relief valve opens. Spring tension can be adjusted as necessary through either shimming or stretching to achieve the desired pop-off psi.
Proper lifter-to-lifter-bore clearance is imperative for maintaining adequate engine oil pressure and correct lifter operation. Since the hydraulic lifters control the flow of oil to the engine's top end, the top end will be starved for oil when the lifters are insufficiently pressurized. Insufficient pressurization not only increases lifter noise but also reduces performance, because valve lift and timing are lost. Feuling recommends a lifter-to-bore clearance of 0.001 inch to 0.0015 inch for optimum lifter performance. An out-of-tolerance lifter-to-bore clearance further escalates the problem of noisy lifters and valvetrain. Maintaining optimum clearance should keep the lifters "happy," even under extreme oil temperatures when the engine oil is thin. Additionally, sustaining adequate oil pressure to the lifters ensures proper oiling of the rocker arms, shafts and valvesprings for quiet operation. Since the rocker arms operate in plain bearings, Feuling recommends a minimum of 7 to 10 psi of oil pressure per 1000 engine rpm to lubricate the rocker arms and provide proper cooling for the valvesprings.
Feuling manufactures high-performance, CNC-machined, precision-ground hydraulic roller lifters that are a drop-in replacement for stock lifters. The Feuling lifters are available in standard and .001-inch and .0015-inch oversize (.842 inch is standard lifter O.D.) to maintain proper lifter-to-bore clearance.
A serious problem with the Twin Cam engine is excessive crankshaft runout, which is a result of the flywheels shifting on the crankpin. Under harsh acceleration, deceleration or burnouts, the Twin Cam's pressed-together crankshaft can shift out of true by as much as .030 inch or even more. For comparison, a well-built Twin Cam crank will exhibit .001 inch or less of runout, although factory tolerances are often .004 inch and sometimes more. When a crank drastically shifts out of true, the pinion shaft (right side) wobbles severely, usually causing catastrophic damage to the oil pump, cam support plate and other related parts. Additionally, oil pressure and scavenging decrease, allowing excess oil to fill the crankcase and gearcase areas. Once the excess oil builds up to a certain level, it is usually blown out the cylinder head breathers and into the air cleaner assembly. Warning signs of a shifted crank include loud noises from the gearcase area, noisy lifters and significant amounts of oil being tossed out the breather hoses. Typically, the crankshaft, oil pump, camshafts, cam support plate and cam drive mechanism require replacement when a crank shifts significantly out of true. Refer to our May installment for additional information about shifted cranks.
Cam Support Plate
The stock cam support plate does a decent job of supporting the camshafts and directing oil, but it can flex and warp under prolonged severe operation and high valvespring pressures. A wobbling pinion shaft will score or even break the oil pump housing and gerotor gears, since the pump is mounted over the shaft. Additionally, as a pump wobbles, it scores the cam support plate at the pump mounting surface, decreasing oil pressure while allowing the feed and scavenge sides of the engine's oiling system to intermingle, causing more havoc in the engine.
(8.)Here's an example of a mildly scored, stock '99-'06 cam support plate. The scoring was
(9.)All Feuling billet cam support plates include enlarged, kidney-shaped feed- and scaven
(10.)The kidney-shaped oil channels machined into this Factory SE cam support plate measur
Feuling makes a hard-anodized, 7075 billet aluminum cam support plate that works great when hopping up an engine or replacing a damaged cam plate. Since the cam support plate has a dual function of supporting the camshafts and acting as an oil distribution point, Feuling not only made their plate extremely robust to handle high valvetrain pressures but also included several additional improvements for better oil distribution to the camshafts and engine.
For example, Feuling machines their cam plates with larger, kidney-shaped channels and internal oil galleys for greater oil flow throughout the engine. Also included are additional oil passages for the 2007-and-newer (2006-and-newer Dyna) engines with large camshaft journals. These modifications not only improve lubrication but also can reduce engine operating temperatures up to 20-25 degrees at the cylinder head. Feuling cam support plates are available for all years and models of Twin Cam engines; however, take note that the plates must be used in conjunction with Feuling's high-volume oil pump.
Gerotor Oil Pump
Twin Cam 88 and 88B engines use a small, die-cast, gerotor-style oil pump turning at crankshaft rpm that utilizes a spring washer to preload the pump gears against the cam support plate and pump housing. Over the years, the Factory made several improvements to the Twin Cam's gerotor oil pump, with the late-model 2007-and-newer (2006-and-newer Dyna) pumps being the best of the lot. Nevertheless, what you want in an oil pump is a pump that can supply the pressure and volume of oil required at both low- and high-rpm conditions in addition to sufficient scavenging capability to eliminate wet-sumping (sometimes called oil carryover).
Feuling was the first company to offer a performance oil pump that addresses the needs of the Twin Cam engine. Feuling's high-volume bolt-in replacement pumps are made of 6061-T6 billet aluminum and aerospace materials that result in a high-efficiency pump without the need for a high-friction spring washer between the gerotors. The pump features 40 percent larger gerotors on the pressure side and 60 percent larger units on the return side when compared to the '99-'06 factory oil pumps. Compared to the '06 Dynas and all '07-and-later oil pumps, the Feuling pumps show a 20 percent increase on the pressure side and 30 percent on the scavenge side. The Feuling pump was specifically designed to increase oil pressure and volume while maintaining sufficient oil scavenging to eliminate wet-sumping.
When setting up a Twin Cam's oiling system, you ideally want the engine to have just enough oil pressure and volume to keep vital engine parts lubricated, hydraulic lifters operating properly without collapsing or pumping up (even in hot stop-and-go traffic) and sufficient oil volume to keep the engine cool while having excess scavenging capacity so that oil is quickly removed from the flywheel cavity and gearcase under all conditions. Be aware that running excessive oil pressure-or even volume-is akin to running too much valvespring pressure: Both waste horsepower.
Odds And Ends
Building a bulletproof Twin Cam oiling system starts with a properly modified crankshaft, quality parts, proper prepping of components and a basic understanding of how the oiling system works. However, several other details should be addressed.
(11.)The large, kidney-shaped feed- and scavenge-side oil channels in this hard-anodized,
(12.)Feuling's cam support plates are machined from 7075 billet aluminum and then hard-ano
(13.)Feuling's high-volume bolt-in replacement oil pumps are made from 6061-T6 billet alum
For starters, oil passages between the cam support plate and engine case are sealed with O-rings. Oil leaks can easily develop if the O-rings are pinched or hardened, overloading the gearcase with excessive oil. Always check that the O-rings are soft and supple, not hardened, and the correct size when assembling a Twin Cam engine. Make sure all oil and breather lines are free-flowing and not pinched. It is best to use two separate vent lines (instead of one line) from the cylinder heads. For maximum performance, vent the breather lines to the atmosphere. To remain EPA-compliant, you'll have to route the lines to the air cleaner. Be sure to align the oil pump using the procedure described in the factory's service manual. Make sure the umbrella valves in the rocker boxes are in good condition and not brittle, warped or torn. Also, make sure that engine oil passages are not accidentally blocked due to an incorrectly stamped gasket.
Excessive piston ring blow-by (combustion chamber gases entering the flywheel cavity) will pressurize the crankcase cavities beyond normal levels, potentially leading to wet-sumping. The sealing ability of the piston rings can be checked by using a leak-down tester. Feuling makes an oil tank breather kit that releases power-robbing pressures from the oil tank and crankcase, reduces blow-by, helps prevent dipstick blowout and promotes proper oil flow to and from the remote oil tank.
Keep in mind that a properly functioning oiling system is a system of interrelated subsystems requiring quality parts, proper prepping of components and correct installation procedures. Under some conditions, even a stock engine can tax the Twin Cam's oiling system. And a large-displacement motor-roughly 100ci and larger-makes the situation worse yet. To achieve an efficient oiling system, the entire system must be balanced for oil pressure, oil volume and oil scavenging capability.
Don't forget that excessively high oil pressures or volume is a power robber and can lead to wet-sumping and oil leaks. Conversely, very low oil pressure is most conducive to high-rpm racing engines or street engines using solid lifters. For street engines, you need sufficient oil pressure to maintain proper hydraulic lifter operation during low-rpm stop-and-go riding in the hot summer months when the engine oil is thin. Installing an oil cooler and thermostat will not only improve the longevity of engine parts but also reduce the potential for power-limiting detonation. Feuling's system approach to the Twin Cam's oiling system is a major step in the right direction for eliminating the Twin Cam's "oiling system blues."
(14.)Shown are the size differences (diameter and thickness) of the feed gears used in thr
(15.)This photo demonstrates the size differences (diameter and thickness) of the scavenge
(16.)Shown is the Feuling oil tank breather kit designed to help release power-robbing pre
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