GB2206694A - Improvements relating to gauge devices for and methods of setting the tappet clearance of overhead cam shaft - Google Patents

Abstract

The invention provides that a guage shaft 24 is positioned by means of bearings 26, 28 on an overhead camshaft engine in place of the camshaft. The gauge shaft carries a measuring micrometer 36 whose leg can be zeroed in a position corresponding to the position of the heel of the cams which operate the tappets. The reading of the micrometer when the leg engages a bucket of a tappet is indicative of the actual tappet clearance and the tappet can thereafter be shimmed to give the tappet a predetermined clearance. The measuring micrometer is adjustable on the shaft by being carried by a block 38 which is slidable on the shaft. The shaft is slotted 34 to allow the feeler leg of the micrometer to pass therethrough. <IMAGE>

Description

Improvements Relating to Gauge Devices for and Methods Pf,Sing,h,TaPP,csarann%,Pf,Pu%rh Shaf,, This invention relates to gauge devices for and methods of setting the clearances between the cams and the valve stems in overhead camshaft internal combustion engines.

In the internal combustion engines of the type to which the present invention relates, overhead camshafts are provided with cams which engage the engine inlet and exhaust valves and operate same in sequence as the engine runs. Each of the valves comprises a stem which is loaded by a spring towards the camshaft and over the end of the stem is a bucket or shell which is the portion which is engaged by the cam during operation of the engine. Between the bucket and the end of the stem is placed a shim disc of appropriate thickness in order correctly to position the bucket surface in relation to the cam so that the valve will be operated correctly.

It is frequently necessary to set or re-set the clearance between the cam and the valve stem and to change the shim disc in order to obtain an optimum clearance. The current method of achieving this is to use a feeler gauge in order to measure the clearance between the cam and the bucket surface and then to replace the shim disc with one of appropriate thickness. The clearance is always measured when the cam is at the no-rise or heel portion of the cam in relation to the bucket surface, and the method of checking the clearance using a feeler gauge is awkward and difficult.

In my British Patent No. 1397985 I have disclosed a device whereby the checking of the clearance can be effected in a much simpler manner, and the device comprises a shaft which is installed (as a dummy) in place of the camshaft, and the shaft carries a measuring means such as a micrometer having a feeler leg and a display dial. The measuring unit is zeroed in an optimum position, in relation to the bucket, and the measuring unit reads the deviation fr-om this position which gives an indication of the clearance between the bucket and the valve stem, so that an appropriate shim disc can be used in order to return the clearance to an optimum value.

In the specific example described, the device can be used for measuring the clearance of one valve at a time, and after any valve clearance has been measured, if is is required to check the clearance of another valve, it is necessary either to remove the entire device, or to remove the measuring apparatus, repositioning the mounting therefor, and then re-mount the measuring apparatus on said mounting. Accordingly, more time than is necessary is consumed in repositioning of the measuring apparatus.

The present invention aims to overcome this difficulty, and in accordance with the invention, there is provided a gauge device for setting the clearance of the tappets of an overhead camshaft internal combustion engine, comprising a gauge shaft, bearings at the ends of the gauge shaft for seating in the bearing housings which receive the camshaft of the engine, a measuring means carried by the gauge shaft for measuring the clearance of the tappets, said measuring means being moveable along the gauge shaft so that it can be used for measuring the clearance of side by side tappets.

The measuring apparatus is preferably adapted to be locked in any position to which it is adjusted.

The measuring apparatus preferably is carried by a block which is slidable on said shaft, the block having a face to represent the heel portion of a cam in order to provide a datum, and the measuring apparatus comprising a micrometer with a sensing leg which passes through the block, and also passes through a slot in the dummy shaft.

Other measuring devices such as ultrasonic or laser measuring devices may be used.

The dummy shaft preferably is provided with removable bearings enabling it to be mounted in bearings of the engine block which normally receive the camshaft.

The shaft may have a means in the form of a handle enabling it to be rocked when it is in position in the camshaft bearings of the engine whose valve clearances are to be checked, although tests have shown that such a handle may be dispensed with and the shaft may be rocked by means of the micrometer.

Also according to the invention there is provided a method of setting the clearance of the tappets in an overhead camshaft engine comprising removing the engine camshaft, replacing the tappet shims by standard size shims on all tappets, positioning a gauge shaft carrying a measuring device in the camshaft bearings, said measuring device defining a datum position corresponding to the heel of each cam, measuring the clearance between a first tappet bucket and said datum position to give an indication of required shim thickness for desired clearance of that tappet, moving the mesuring device on the shaft to a second tappet and repeating said measuring, repeating these steps for as many tappets as can be checked without removing the gauge shaft from the camshaft bearings, and inserting the correct shims in the respective tappets.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein:~ Fig. 1 is a diagrammatic sectional elevation of a valve stem of an overhead camshaft internal combustion engine and also shows the covering bucket; Fig. 2 is a perspective view of the operative part of the device according to the present invention; Fig. 3 is a side view, partly in section of the device shown in Fig. 2; Fig. 4 is a sectional end view of the device shown in Figs. 2 and 3; Fig. 5 is a sectional elevation of the mounting block shown in Fig. 2; and Figs 6 and 7 are sectional views illustrating how the measuring unit is zeroed in two different examples.

Referring to the drawings, in Fig. 1 is shown a valve stem 10 of a valve of an internal combustion engine operated by an overhead camshaft. The valve 10 is spring loaded in an upwards direction as indicated by arrow 12 by means of a compression spring 1 LI, the spring being retained by a collar 16 held in a groove in the stem 10.

Covering the collar and the end of the valve stem is a bucket 18 of which the surface 20 is normally engaged by the cam which operates the valve when the engine is in use.

Between the end of the stem 10 and the inside of the bucket 18 is shown a shim disc 22 which dictates the clearance between the bucket 18 and the heel portion of the cam. This clearance is critical for the satisfatory operation of the engine and frequently in used and worn engines the clearance has to be adjusted.

The device of the present invention enables this to be done quickly and effectively.

Referring to Figs. 2 and 3, the device according to the embodiment of the invention comprises a shaft 24 provided with bearing sleeves 26 and 28. Shaft 2Ll in fact forms a dummy camshaft and is positioned on the engine in place of the camshaft for the measuring of the clearance of the inlet and exhaust valves of the engine cylinders. Sleeves 26 and 28 in this regard sit in the bearings which normally receive the camshaft.

The shaft 24 is provided throughout the majority of its length with a slot 34 through which passes the feeler leg of a micrometer 36. The micrometer 36 is carried by a slide block 38 which in fact has a surface 40 which forms the datum for the setting of the clearance, and the surface 110 is located at the same radius as the heel portion of the cam which is used for the particular engine whose valve clearances are to be checked and adjusted.

Referring to Fig. 5, it will be seen that the block 38 has a threaded bore 42 for receiving a plastic collar 1111 and a threaded screw 116 having a knurled disc 48 for the screwing of same into bore 112.

Fig. 3 shows the arrangement when the screw 116 is in fact screwed into the bore 112, and it will be noticed that the collar 44 is deflected and forms a means for holding the micrometer in position as it bears frictionally against support sleeve 50 of the micrometer. The micrometer feeler leg 52 passes through the support sleeve 50.

As also shown in Figs. 11 and 5, the shaft 24 is provided with a groove 511 in which is engaged the end 56 of a locking screw 58. Screw 58 can be tightened so as to engage the base of the groove 54 in order to lock the block 38 in any adjusted position along the length of the shaft 211.

In the use of the device, the size of block 38 is chosen so that the surface 40 will lie in the same position as would normally the heel surface of the cam which operates the associated valve, and the bearing sleeves 26 and 28 are also similarly carefully selected. The dial of the micrometer 36 is then zeroed by the method shown in Fig. 6. A glass or other plate 60 is placed against the face 40 so as deflect the feeler leg 62 of the micrometer into the bore 611A in block 38, the said leg 62 extending through the slot 34 in shaft 24. When the feeler leg 62 is in the retracted position as shown in Fig. 6, the micrometer is adjusted so as to zero the pointer. The micrometer can now be locked in position by screw 116.

Known, nominal size shim discs are placed between the ends of the valve stems and the respective buckets.

The device is now positioned on the engine in place of the normal camshaft, the bearing sleeves 26 and 28 fitting in bearings normally received by the camshaft, the surface 110 of block 38 therefore lying in the correct position. The leg 62 of the feeler gauge will then project out of the block and engage the surface 20 of the bucket of the valve being tested, and the reading on the micrometer will be a reading of the clearance between the usual cam surface and the bucket 20 and the operator can then decide what size of shim if any is needed to replace the nominal shim disc at present in position. The screw 58 is tightened to ensure that the block 38 is locked in position whilst testing is proceeding, and an accurate minimum clearance reading may be obtained by rocking the shaft 211 using head 36.

In an example only, if the nominal shim thickness is 0.050" and the reading retained in the micrometer were 0.060", the total reading represented as 0.110 i.e.

(0.050 + 0.060) and if the clearance required were 0.010" then the shim thickness required would be 0.110 - 0.010 = 0.100", and such a shim is available from manufacturers stock.

This procedure may be repeated for each valve simply by loosening the screw 58, and by moving the block 38 along the shaft 211 until it alignes with the next and subsequent valves.

It can be seen therefore that a quick and effective means is provided for checking valve clearances of valves of an internal combustion engine of the overhead camshaft type.

It will be appreciated that the sleeves 26 and 28 are sized depending upon the engine involved and separate devices may be provided for different engines, but it is possible to adapt the device for use with a different type or size of engine, by using different size sleeves 26 and 28; in such case, it is necessary to adjust the zero position of the micrometer 36 by the amount by which the sleeves 26 and 28 deviate from standard sleeves 26 and 28 designed specifically for block 38 and in particular designed specifically for the location of the face 40 of block 38.

Fig. 6 shows how the micrometer 36 may be zeroed where larger diameter sleeves are used in place of sleeves 26 and 28. A datum plate 64 having a milled slot 66 of depth D representing the difference in size between the sleeves used and the size of sleeves 26 and 28 is used.

The surface 68 of the groove 66 forms the new datum for positioning of the leg 62 of the micrometer. When the leg 62 is in position engaging the surface 68, the micrometer is zeroed.

If the sleeves used in place of sleeves 26 and 28 are of smaller diameter, then it may be necessary to have an insert which projects into bore 64A for zeroing the leg 62 at an inwardly spaced position.

In some engines, the camshaft bearings have upper and lower half shells or caps of white metal or the like, and when such engines are worn the centre of the upper shells or caps may be worn. It is preferred that such worn shells be replaced but if this is not possible the wear must be compensated for in selecting the shims to be used in the valve buckets. The cap wear is measured by measuring the thickness of the cap at the ends where there has been no wear compared to the thickness of the cap at the centre where it has worn and to increase the size of shims used accordingly.

Cap wear occurs as a result of the upward loading on the camshaft which arises due to the compression of the springs 111 by the cams in the running of the engine.

Instead of using a micrometer measuring device it is possible to use other devices such as ultrasonic, radar or laser devices.

Also a plurality of measuring devices may be mounted on the dummy camshaft, each being movable therealong.

Claims (1)

1. ~LA

   1. A gauge device for setting the clearance of the tappets of an overhead camshaft internal combustion engine, comprising a gauge shaft, bearings at the ends of the gauge shaft for seating in the bearing housings which receive the camshaft of the engine, a measuring means carried by the gauge shaft for measuring the clearance of the tappets, said measuring means being moveable along the gauge shaft so that it can be used for measuring the clearance of side by side tappets.

   2. A device according to Claim 1, wherein the measuring means comprises a micrometer having a feeler leg adapted in use to seat on the tappet bucket.

   3. A device according to Claim 2, wherein measuring means includes a block carried by the shaft so as to be slidable therealong, and the micrometer is carried by said block so as to be movable therewith.

   11. A device according to Claim 3, wherein the gauge shaft has a through slot therein and extending for substantially the length thereof and the feeler leg of the micrometer passes through said slot.

   5. A device according to Claim 3 or 11, wherein the block comprises a threaded bore carrying a locking screw which can be tightened against the gauge shaft to lock the block in any position to which the block is adjusted in said support.

   6. A device according to Claim 5, wherein the screw end which engages the shaft locates in a groove in the shaft to prevent the block from turning on the shaft.

   7. A gauge device according to Claim 1, wherein the measuring means comprises an ultrasonic, radar or laser measuring device.

   8. A gauge device according to any preceding claim, wherein said bearings are of predetermined size in relation to a datum of said measuring means to which the measuring means can be zeroed.

   9. A gauge device substantially as hereinbefore described with reference to the accompanying drawings.

   10. A method of setting the clearance of the tappets in an overhead camshaft engine comprising removing the engine camshaft, replacing the tappet shims by standard size shims on all tappets, positioning a gauge shaft carrying a measuring device in the camshaft bearings, said measuring device defining a datum position corresponding to the heel of each cam, measuring the clearance between a first tappet bucket and said datum position to give an indication of required shim thickness for desired clearance of that tappet, moving the mesuring device on the shaft to a second tappet and repeating said measuring, repeating these steps for as many tappets as can be checked without removing the gauge shaft from the camshaft bearings, and inserting the correct shims in the respective tappets.

   11. A method of setting the clearance of tappets in an overhead camshaft engine substantially as hereinbefore described with reference to the accompanying drawings.