Cylinder Head Fastening Structure for Internal Combustion Engines

This invention relates to a cylinder head fastening structure for an internal combustion engine and more particularly to an improved engine layout for an overhead cam shaft engine that facilitates servicing.

As is well known, the cylinder head of an engine is normally fixed to the cylinder block either by means of bolts or by means of studs and nuts. When the engine embodies one or more overhead cam shafts, the relative positioning between the cam shafts and the head fasters often results in compromise of the placement of either or both. For example, it is desirable to position the overhead cam shaft directly above the cylinder bore so that the valves can be located relative to the cylinder so as to insure good volumetric efficiency and breathing. However, it is also desirable to locate the cylinder head fastener in the same location. When both the cam shaft and cylinder head fastener are so located, servicing has been a problem with the prior art type of constructions. That is, retorqueing of the cylinder heads after a rebuild will necessitate removal of the cam shafts. To avoid these problems, it has been proposed to offset the cam shafts from a position over the cylinder bores, thus resulting in a less than optimum placement. The problem is particularly acute when two overhead cam shafts are employed. It is desirable to position the cam shafts as close as possible to each other to insure good valve placement in the cylinder and also so as to reduce the necessity for using interconnecting motion transmitting mechanism between the cam lobes and the valve stems. With prior art fastening arrangements, however, such close position has been impossible unless serviceability is sacrificed.

It is, therefore, a principal object of this invention to provide an improved fastening arrangement for the cylinder head of an internal combustion engine.

It is a further object of the invention to provide an improved cam shaft and cylinder head fastening arrangement for an overhead cam shaft engine.

This invention is adapted to be embodied in a construction for an overhead cam internal combustion engine that comprises a cylinder head that is adapted to be affixed to another component of the engine by at least one fastener. In accordance with the invention, a cam shaft is journaled for rotation relative to the cylinder head and is positioned in overlying relationship to the fastener. Means define an access opening passing through the cam shaft and adapted to pass a tool for tightening the fastener without removal of the cam shaft.

FIG. 1 is a cross-sectional view taken through one end of an internal combustion engine constructed in accordance with an embodiment of the invention about a plane perpendicular to the axis of rotation of the engine crankshaft.

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1.

In the drawings an overhead cam shaft internal combustion engine constructed in accordance with this invention is identified generally by the reference numeral 11. The engine 11 includes a cylinder head, indicated generally at 12; a cylinder block, indicated generally at 13; and a crankcase, indicated generally at 14. The cylinder head 12, cylinder block 13 and crankcase 14 are held together with a fastening arrangement constructed in accordance with the invention. The fastening arrangement includes a series of spaced studs, indicated generally at 15, and nuts, indicated generally by the reference numeral 16. The lower ends of the studs 15 are each formed with a male threaded portion 17 that is threaded into a respective tapped opening 18 formed in the crankcase 14. The central portion of each of the studs 15 is relieved, as at 18, and extends through aligned appertures 19 and 21 in the cylinder block 13 and cylinder head 12, respectively. At least some of the appertures in the cylinder block 13 and crankcase 14 through which the studs 15 pass are formed with respective counterbores 22 and 23. Pilot bushings 24 are received within these counterbores so as to locate the cylinder block 13 and crankcase 14. In a like manner, at least some of the bores which pass the studs 15 of the cylinder head 12 and cylinder block 13 are formed with respective counterbores 25 and 26 for receiving pilot bushings 27 to locate these elements.

The upper ends of the studs 15 are formed with male threads 28 that extend into the lower portion of bores 29 which, in turn, form extensions of the cylinder head bores 21. The bores 29 extend upwardly through cam shaft towers 31 formed integrally with the cylinder head 12. The nuts 16 have internal threads 32 that are received on the stud threads 28. The nuts 16 engage washers 33 and serve to affix the cylinder head 12 relative to the cylinder block 13 and the crankcase 14. The heads of the nuts 16 are formed with hexagonal socket openings 34 so as to facilitate tightening of the nuts 16, in a manner to be described.

A cam shaft, indicated generally by the reference numeral 35, is supported in each of the cam towers 31. The cam shafts 35 are journaled by spaced bearings 36 that are formed integrally with the cylinder head 12. Bearing caps 37 are affixed at spaced locations to the cylinder head by bolts 38 and cooperate with the bearings 36 to rotatably journal the cam shafts 35. One cam shaft 35 may operate the intake valves in a known manner while the other cam shaft 35 may operate the exhaust valves in a known manner. Preferably the lobes of the cam shafts 35 cooperate either directly with the stems of the intake and exhaust valves or with some suitable follower that will afford lash adjustment.

The cam shaft 35 has cylindrical portions 39 that are journaled in the cylinder head cam shaft bearing portions 36 and the bearing caps 37. The cylindrical portions 39 overlie the nuts 16 and, therefore, with conventional constructions it would be necessary to remove the cam shafts 35 before the nuts 16 could be tightened, retightened or removed. In accordance with this invention, however, each bearing portion 39 of the cam shaft 35 that overlies a nut 16 is formed with an access opening 41 that is sized to pass a tool such as a key wrench configured to cooperate with the nut socket openings 34. In a like manner, the bearing caps 37 are also formed with access opening 42. The bearing cap access openings 42 are normally closed by means of plugs 43. The plugs 43 are maintained in sealing engagement with the cap openings 42 by means of a cam cover 44 that encloses the cam tower 31. The cam covers 44 are affixed to the respective cam towers 31 by means of bolts 45 that are received in tapped openings in the bearing caps 37.

One of the cylindrical bearing portions 39 of the cam shaft 35 is formed with an enlarged cylindrical projection 46. The adjacent cylinder head bearing surface 36 and bearing cap 37 is formed with a complimentary recess so that the projection 46 and these recesses will serve to provide thrust location for the cam shaft 35.

In addition to permitting tightening of the head 12 to the block 13 and crankcase 14, the access holes 41 in the cam shafts 35 may be used to facilitate lubrication of the valve train and specifically the bearing surfaces provided by the cam bearing portions 39. For this purpose, each cam shaft 35 is provided with a longitudinally extending oil passage 47 that intersects the access holes 41. Oil under pressure is delivered from the crankcase 14 through an oil pump (not shown) to a suitable passage that intersects the area between one of the studs 15 and the locating bushing 24. The pressurized oil will then flow upwardly around this stud 15 through the clearance provided between its unthreaded portion 18 and the bores 19 and 21. When this oil reaches the cylinder head 12, it will flow into a cross-drilled passageway 48 that extends transversely across the cylinder head 12 and which intersects the bore 29 which surrounds the nuts 16 associated with the cam shaft 35 on the opposite side of the cylinder head 12. The outer end of the cross-drilled passageway 48 is closed by means of a closure plug 49. Another cross-drilled passage 51 extends through the cylinder head 12 from an area outwardly of the nut 16 associated with the stud 15 through which the pressurized oil is delivered. The passageway 51 intersects the cross-drilled passageway 48 approximately at its center and its outer end is closed by a plug 52.

It should be readily apparent that the lubricating oil that passes upwardly around one of the studs 15 will be delivered by the cross-drilled passageways 48 and 51 to the cylinder head bores 11 and 12 associated with the cam shafts 35. This oil can then enter the access holes 41 and flow axially along the respective cam shafts 35 through the lubricating passageways 47. The lubricate will be discharged through the access holes 41 of the various cam shaft bearing portions 39 so as to lubricate these portions as well as the associated bearing surfaces of the cylinder head portions 36 and bearing caps 37. Lubricant can be returned to the crankcase 14 through any suitable return passage. For example, a return passage arrangement similar to the delivery passage arrangement may be provided at the opposite end of the cam shafts 35. In addition, if desired, the cam lobes may be drilled so as to permit oil to flow from the passages 47 to lubricate the valve mechanism.

It is believed readily apparent that the construction described will offer ease of servicing of the engine 11 without necessitating removal of the cam shafts 35. If retorqueing of the cylinder head nuts 16 is desired, the cam shaft covers 44 need only be removed along with the plugs 43 so as to afford access to the bearing cap bores 42. The cam shafts 35 are then rotated so that their access holes 41 will be vertically disposed as shown in FIG. 1 to afford access to the nut socket openings 34. Rotation of the cam shafts 35 may be accomplished by turning the crankshaft (not shown) of the engine directly. Alternatively, rotation may be accomplished by rotating either or both of the cam shafts 35. For this purpose, each cam shaft 35 is provided with an exposed hexagonal section 53 at a point between the bearing caps 37. By applying a suitable tool to the hexagonal section 53, the cam shafts 35 may readily be rotated so as to line up the access holes 41 with the nuts socket openings 34. A suitable wrench may then be inserted through the bores 42, access holes 41 and bores 29 so as to permit tightening of the nuts 15. In addition to permitting this servicing, the access holes 41 may be used to achieve lubrication of the valve train, as aforedescribed.

In the illustrated embodiment the cam shaft access holes 41 were located in the bearing portions 39 of the cam shafts 35. Of course, the invention is equally as useful in conjunction with an arrangement wherein the access holes 41 are positioned at a location other than in the bearing portions of the cam shafts 35. This location will, of course, depend on the location of the studs 15 and nuts 16 since the access holes 41 are located above the nuts 16. The described construction permits the optimum location of the cam shafts 35 relative to the cylinder bores and permits the cam shafts 35 to be placed directly above the studs 15 and nuts 16. It should also be undertood that, although an arrangement has been disclosed wherein the studs 15 are threaded into the crankcase 14, the invention may be used in conjunction with an arrangement wherein the studs are threaded into the cylinder block. In a like manner, the invention can be used in conjunction with engines in which bolts rather than studs and nuts are used for affixing the cylinder head to the cylinder block. Various other changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.