GB2307533A - A method of adjusting valve clearance by determining cam shim thickness - Google Patents

Abstract

A method of adjusting valve clearance comprises 1) measuring, with a depth micrometer, the distance 11 between top surface 12 of cylinder head 1 and top surface 13 of cam follower 3; 2) determine, using a micrometer calliper, the radius of cam heel 10; and 3) using known required clearances between cam heel 10 and top surface 13 calculate the thickness of shim required. Before the measurements can be achieved the cylinder head 1 is split along a line of separation which leaves a lower portion that incorporates lower half 2 of a split camshaft bearing. If the cylinder head has an inclined plane (see figs 3 and 4) a straight round bar (17, fig 3) may be allowed to come to rest at the bottom of cam bearing (16, fig 3) and the distance (18, fig 3) between the top of the round bar and the top surface of the cam follower may be utilized as one of the above measurements.

Description

INTERNAL COMBUSTION ENGINE VALVE CLEARANCE ADJUSTMENT METHOD AND APPARATUS This invention relates to internal combustion engine valve clearance adjustment method and apparatus, such as may be used with respect to automobile engines Four-stroke internal combustion engines are very widely used for providing power for many applications includiing, but not limited to motor vehicles. With all such engines, valves, operating against the closing force of springs, are used to open and close apertures of the combustion chambers (or cylinders) of the engines above reciprocating pistons, these valves being used for the flow into, and out of the combustion chambers of the air fuel combustion mixture and the spent combusted mixture.

It has of course become fully understood that the valves, which include conical surfaces which seal against appropriately conically shaped seatings in the walls of the cylinder, wear with the seatings so that mechanical devices, either direct or indirect, used to open and close the valves in the appropriate time sequence for the combustion gases inlet and outlet require appropriate adjustments over time to ensure correct operation of the valves.

With the continuing development over the last many years of four-stroke internal combustion engines where valve opening and closing against the action of the return springs is done by means of a camshaft (carrying appropriately shaped cams) mounted above the cylinder head.

Such systems, much to the advantage of the mechanical performance of the engine, use almost direct action of the cams carried by the camshaft to open and permit closure of the valves of the engine for its combustion performance.

However the overhead nature of the camshafts and the cams carried thereby, and the fact that these are sometimes removed, when servicing an engine, due to the upper half of the camshaft bearings being integral with the cylinder head camshaft cover renders pracstical adjustment for worn or replaced valves to be a time consuming and complicated operation.

Thus the procedure usually requires, after removal of the cylinder head camshaft cover, and sometimes the remounting of the camshaft within specially provided halfbearings mounted upon the half bearings in the top of the cylinder head at the line of the split of the cam cover of the head from the head itseif. Thereafter the gap between the heels of the cams carried on the camshaft and the cam follower arrangements disposed upon the relevant valve stem are then measured by means of thickness measuring strips and compared with the required gaps, whereafter the difference is accommodated by means of appropriately shaped and sized interchangeable shims placed on top of the valve stem or the cam follower.

It is an object of the present invention to overcome or at least substantially reduce the time consuming and complicated arrangements for measuring and adjusting valve clearance just mentioned.

In accordance with one aspect of the present invention there is provided a method of adjusting valve clearance in an overhead camshaft internal combustion engine of the kind hereinbefore described, comprising removing the cylinder head cam cover of the engine together with or substantially to its camshaft half-bearings for the relevant operating camshafts; removing the camshafts; taking a measure of the distance between the bottom of the lower half of the split camshaft bearing to the top of the cam follower when the valve with which it is related is urged fully closed; taking a measure of the radius of the heel of the associated cam and, from the known required clearance between the cam heel and the top of the cam follower in the valve fully closed position, calculating the thickness of shim required between the cam follower and the valve stem and placing same in position; carrying out the same operation with respect to all valves with respect to that camshaft; repeating the same with each and every other camshaft and associated valves.

Where the engine design is such that the plane of split of the block and cover is disposed horizontally above the valves, the required distance measurement between the bottom of the bearing of camshaft and the top of the valve follower may be achieved by means of a micrometer depth gauge measuring between the plane of the top surface of the camshaft engine block to the camshaft follower, the diameter (and from this the radius) of the camshaft heel being measured by means of the micrometer calliper.

Where the engine design is such that the spliz of the engine block and cover is at an inclined plane, it is necessary to provide a different method for measuring the vertical separation from the bottom of the bearing of the camshaft and the top of the cam follower. This can be done by utilising a straight round steel bar of accurate diameter (a distance roller) disposed in the lower half of the camshaft bearing, where the appropriate required separation is calculated from a micrometer measurement of the cam heel radius, together with the distance roller diameter, and the measurement, measured by means of a depth micrometer from the top of the distance roller (when laying free in the lower camshaft half bearings) to the top of the cam follower.

It will be appreciated that the object of using the distance roller is to provide a base from which to measure at right angles the cam follower depth. In practise the distance roller may be approximately one inch in length, of good quality round bar of suitable diameter of anything from between half an inch to three quarters of an inch.

Inevitably they will self-position themselves at the bottom of the lower half of the camshaft bearings.

In order that the invention may be more readily understood three embodiments thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows in section part of the upper end of an engine cylinder head from which the cam cover and camshaft have been removed, of an internal combustion engine of the kind hereinabove described; Figure 2 illustrates on an enlarged scale a cam carried by a camshaft for use with the arrangement of Figure 1; Figure 3 shows in section part of an engine cylinder head having an inclined plane of separation from its cam cover; Figure 4 illustrates on an enlarged scale a camshaft and its bearing for the arrangement of Figure 3; Figure 5 shows an engine head of the kind illustrated in Figure 3, but where the camshaft bearing is of considerably larger dimensions than the camshaft cam; and Figure 6 illustrates on an enlarged scale the cam and camshaft bearing for use with the arrangement of Figure 5.

Referring now to Figures 1 and 2 it is to be seen that a cylinder head 1 of an internal combustion engine of the kind described is separated in a horizontal plane from the cover therefor (not shown). As usual the cylinder head incorporates along the line of separation the lower half 2 of a split camshaft bearing, within which, in operation of the engine a camshaft 5 is seated running the length of the engine above a sequence of cam followers 3. The cam follower is disposed on a valve stem 4 which in turn connects to a valve (not shown) seated within a combustion chamber of the engine. The valve stem 4 at its upper end includes seating 6 for a valve spring 7 which in use holds the valve shut against the action of a cam 8 mounted on the camshaft 5 of the engine. The cam follower 3 is disposed upon the valve stem 4 and spring 7 and includes within it a spacing shim 9 for providing the correct operational separation between the heel 10 of the cam 8 and the cam follower 3 during the fully closed disposition of the valve. In the arrangement shown the valve clearance measurement in accordance with the present invention required for correct operation comprises the required valve clearance spacing plus the radius of the heel 10 of the cam and in addition the spacing 11 from the horizontal plane of the top surface 12 of the cylinder head 1 to the top surface 13 of the cam follower 3, measured with a depth micrometer.A typical example of the calculations of such an arrangement is now set out: Calculate or measure the diameter of the head 10, divide by two and add the required valve clearance, for example, say 1.250" + 2 = 0.625 plus, say 0.010" = 0.635".

Put another way, the calculatoion is one half of the diameter of the cam bearing plus the manufacturers specified valve clearance from the top face of the cam follower.

Referring now to Figure 3 and 4 it will be seen that we are here dealing with a cylinder block 14 where the split line 15 between the cam block and its casm cover (not shown) is along an inclined plane which again divides exactly equally the split bearing of the camshaft 2 into two parts, the lower part 16 being shown in Figure 3. In this case the camshaft bearing is of relatively small diameter as clearly seen in Figure 3. To assist in providing the necessary valve clearance measurement, a high quality straight round bar 17 (distance roller) of precisely known diameter is disposed and allowed to come to rest at the bottom of the lower half of the camshaft bearing 16, and by means of a depth gauge micrometer the distance 18 between the upper point of the distance roller 17 and the top of the cam follower 19 is measured.

Thereafter the measurement of the required valve clearance comprises a sum involving the radius of the heel 20 of the cam 21, the bearing 22 of the cam 21, the diameter of the distance roller 17, and the valve clearance required. We now set out a typical example of the calculations of such an arrangement; Calculate or measure the diameter of the head 20 of the cam 21, subtyract the diameter of the camshaft 23, add the diameter of the distance roller 17 and add the valve cleasrance required (say 0.010").In practice, for example, this could amount to the following equation: 1.250" - 1.00" = 250 - 2 = 0.125" + 0.375" + 2 x 0.500" + 0.010" = 0.510" Figures 5 and 6 show a similar arrangement to that of 3 and 4, but here the split bearing 22 of the camshaft 23 is of a substantially larger diameter, and indeed is of a greater diameter than the largest diameter of the cam 24 carried on the camshaft.

It is to be noted that the distance roller 25 should in itself have sufficient diameter 29 to enable a valve clearance measurement of the distance 26 between the upper point of the distance roller 25 and the top surface 27 of the cam follower 28 (having a low diameter 30) to be made with a depth micrometer. As can be seen in this case the valve clearance measurement is obtained in the same way as that previously with respect to Figures 3 and 4, and a typical example of such measurement is now set out: Calculate or measure the diameter of the head 30 of the cam 24, deduct the diameter 29 of the camshaft 25, and divide by two, and add the distance 26 plus the required valve clearance to give the required measurement.

For example 1.250" - 2.00" = -0.750" + 2 = 0.375 + 0.500 = 0.125 + 0.010 = 0.135 It is to be appreciated that following all of the measurements set out above, and with a simple calculation, any variations from the required valve clearance (in the valve shut position) can be made by inserting an appropriately dimensioned shim disc in the space between the valve follower and the upper end of the valve stem, or where such an arrangement pertains, a shim disc seated on the top of the cam follower.

By means of the present invention we have provided a simple and effective manner of measuring and adjusting the required valve clearance of an overhead camshaft internal combustion engine of the type described which avoids the complications and long drawn out procedure hitherto practised.

It is to be understood that the foregoing is merely exemplary of methods of measuring and adjusting the valve clearance of an internal combustion engine of the type described in accordance with the invention and that modifications can readily be made thereto without departing from the true scope of the invention.

Claims (4)

1. A method of adjusting valve clearance in an overhead camshaft internal combustion engine of the kind hereinbefore described, comprising removing the cylinder head cam cover of the engine together with or substantially to its camshaft half-bearings for the relevant operating camshafts; removing the camshafts; taking a measure of the distance between the bottom of the lower half of the split camshaft bearing to the top of the cam follower when the valve with which it is related is urged fully closed; taking a measure of the radius of the heel of the associated cam and, from the known required clearance between the cam heel and the top of the cam follower in the valve fully closed position, calculating the thickness of shim required between the cam follower and the valve stem and placing same in position; carrying out the same operation with respect to all valves with respect to that camshaft; repeating the same with each and every other camshaft and associated valves.

2. A method as claimed in Claim 1 wherein the engine design is such that the plane of split of the block and cover is disposed horizontally above the valves, comprising achieving the required distance measurement between the bottom of the bearing of camshaft and the top of the valve follower by means of a micrometer depth gauge measuring between the plane of the top surface of the camshaft engine block to the camshaft follower, and measuring the diameter (and from this the radius) of the camshaft heel by means of a micrometer calliper.

3. A method as claimed in Claim 1 wherein the engine design is such that the split of the engine block and cover is at an inclined plane, comprising achieving the required measurement of the vertical separation from the bottom of the bearing of the camshaft and the top of the cam follower by utilising a straight round steel bar (distance roller) of accurate diameter disposed in the lower half of the camshaft bearing, the appropriate required separation being calculated from a micrometer measurement of the cam heel radius, together with the distance roller diameter, and measuring by means of a depth micrometer from the top of the distance roller (when laying free in the lower camshaft half bearings) to the top of the cam follower.

4. A method of adjusting valve clearance substantially as hereinbefore described with reference to Figures 1 and 2, 3 and 4, or 5 and 6 of the accompanying drawings.