GB2098738A

GB2098738A - Device for adjusting contact-breaker gap in engine distributors

Info

Publication number: GB2098738A
Application number: GB8213960A
Authority: GB
Original assignee: MORRIS BRIAN FREDERICK
Current assignee: MORRIS BRIAN FREDERICK
Priority date: 1981-05-14
Filing date: 1982-05-13
Publication date: 1982-11-24

Abstract

A device for use in adjusting the contact-breaker gap between points 7,9 in a distributor comprises a plate 13 having a part-cylindrical outer surface and an inner surface by which it may be located against the cam 4 as shown.A feeler gauge may then be used to fix the contact gap. The feeler may be chained to its respective plate 13 and several plates may be connected together like spokes in a wheel for ready selection. <IMAGE>

Description

SPECIFICATION Device for use in adjusting or setting contactbreaker gap in distributor of petrol engine The invention relates to a device for use in adjusting or setting the contact-breaker gap in a distributor of a petrol engine.

The distributor in a petrol engine includes a contact-breaker having a pair of contact points of which one is carried on a lever and the other is fixed but is adjustable towards and away from the one carried by the lever. The contact-breaker is opened and closed by a cam having lobes which engage the lever, the cam being mounted on the distributor shaft which is engine-driven and also carries the rotor arm of the distributor. The correct setting of the gap between the points has to be effected when the engine is not operating by adjustment of the fixed point towards and away from the point on the lever when the lever has been moved to the fully-open position of the points by a lobe on the cam.As the engine will not necessarily have stopped with a lobe of the cam in engagement with the lever at the position of maximum lever displacement, it is usually necessary, when adjusting or setting points, to have to turn the crank-shaft manually to an angular position in which a lobe of the cam has effected maximum displacement of the lever in the gapopening sense and then the gap has to be adjusted by moving the fixed point until the correct gap has been set, as determined by using a feeler gauge.

An object of the invention is to provide a device by which the contact-breaker gap can be adjusted or set regardless of the angular position of the cam with respect to the lever and thus the crank-shaft does not have to be turned to bring a lobe of the cam into the position of maximum lever displacement. This simplifies the operation of adjusting or setting the contact-breaker gap to its correct value and therefore enables the operation to be performed in a shorter time than hitherto and also enables an unskilled person to perform the operation.

According to the invention, the device comprises a curved plate having a part-cylindrical outer surface and an inner surface by which the curved plate is to be located against the cam of the distributor after the distributor cap and rotor arm of the distributor have been removed therefrom, the innner surface of the curved plate being locatable on at least one lobe of the cam in a position in which the outer surface of the curved plate is co-axial with respect to the cam and the cam shaft of the distributor and is spaced at a predetermined radial distance from the part of the internal wall of the curved plate which is in engagement with the part of the periphery of the or each lobe of the cam corresponding to maximum lever displacement.

Thus when the curved plate has been placed against a lobe or lobes of the cam, the lever arm will be held in the gap-opening sense away from the position in the periperhy of the or each lobe of the cam corresponding to maximum lever displacement by said known predetermined distance, multiplied by the ratio of the lever, regardless of the angular position of the cam with respect to the lever. The contact-breaker gap is then set by moving the normally fixed point towards or away from the point on the lever until the gap is equal to said predetermined distance, multiplied by the ratio of the lever, plus the required gap distance as specified by the engine manufacturer.The curved plate is then removed and so the gap will then automatically be reduced as the lever reengages the cam surface to a value equal to or less than the required gap or the points will close, according to the angular position of the cam with respect to the lever. The gap set when the curved plate is in position is determined either by using standard feeler gauges of the required total thickness which is determined by adding the predetermined distance, multiplied by the ratio of the lever, to the required gap width or by using a specially made feeler gauge having an actual thickness equal to said total thickness but marked as having a notional thickness equal to the required gap width.The ratio of the lever is the ratio of the distance between the point of contact of the lever on the outer periphery of the curved plate and the fulcrum or pivot of the lever to the distance between the centre line of the contact point on the lever and the fulcrum or pivot. This is often approximately unity but may be greater or less than unity.

The curved plate may conveniently have an inner surface of part-cylindrical shape which is co-axial with the outer surface tbereof, the radius of curvature of the inner surface being of a value to enable the curved plate to make contact on the cam by location on the radially outermost part of at least one of the lobes thereof. The radial thickness of the curved plate is therefore the aforesaid predetermined distance and can be accurately measured.

Alternatively, the curved plate may have an internal shape corresponding to a portion of the profile of the cam.

Conveniently a plurality of curved plates each having a part-cylindrical outer surface of different radii and a differently-shaped inner surface may be provided, thereby to enable an appropriate curved plate to be fitted onto one of a range of cams each having different diametral distances across the lobes thereof.

The curved plate may be bevelled or flared at its lower end to provide a frusto-conical lead-on portion which is radially-outwardly tapered in the downward direction. The curved plate may have an outwardlydirected bevelled or flare upper end to form a portion to be gripped by the user to enable the curved plate to be placed on the cam orto be removed therefrom after use and also to enable the curved plate to be used either way up.

Alternatively the upper end may be formed with an upwardly-extending knob or handle to be gripped by the user to enable the curved to be placed against at least one lobe of the cam or to be removed therefrom after use.

The upper end of the curved plate may have an inwardly directed flange, tangs, or dimples to pre ventthe lower end of the curved plate from dropping too far past the lower end of the cam.

The curved plate may be made of a hardened steel, which would conveniently be a spring steel.

Alternatively the curved plate may be made of a hard plastics material.

By way of example, several embodiments of a curved plate constituting a device in accordance with the invention are shown in Figures 1 - 5 of the accompanying drawings, and with reference to Figures 6 and 7 thereof which are respectively a plan view and a vertical section through atypical distributor, from which the cap and rotor arm have been removed and showing the device in accordance with the invention in position to enable the contactbreaker gap to be adjusted.

Referring first to Figures 1 - 5, these show in Figure 1, a device which is a curved plate 13 having part-cylindrical inner and outer surfaces. The inner surface has a radius substantially equal to that of the outermost part of the periphery of a lobe of a cam of a distributor with which the curved plate is to be used. The inner wall located against the extreme radially outer part of the periphery of at least one of the lobes of the cam. The outer surface is concentric with the inner surface and is of a known radius and so the radial thickness of the curved plate is accurately known. The axial length of the curved plate is greater than the height of the cam above the contact-breaker plate on which, in use, the lower end ofthe curved plate is rested. The curved plate is used in a manner to be described hereinafter with reference to Figures 6 and 7.The curved plate may be of any hard material and is conveniently of hardened steel or a hard plastics material.

Figure 2 shows a feeler gauge 14 which has a thickness corresponding to the required gap to which the points are to be set plus the radial thickness of the curved plate multiplied by the lever ratio as aforesaid and as described hereinafter. For convenience the gauge 14 is attached by a chain 15 or other convenient means to the curved plate 13 and is of a shape enabling itto be lowered upright between the points while the gap is being adjusted.

The curved plate illustrated is that shown in Figure 1 but may be any of the illustrated, or any other curved plates, of suitable shape.

Figure 3 is a curved plate 13 provided with a preformed grip holder 16 attached to one end. The grip holder 16 is provided with a hole 17 to allow for the connection thereto of a feeler gauge and also to enable two or more curved plates of different inner and outer radii or of different thicknesses to be connected together and/orto be connected to a plurality of feeler gauges of different thicknesses.

Figure 4 shows two curved plates 13'; 13" connected end-to-end and each having a different internal radius for use with different distributor cams and having a hole 18 allowing forthe connection of feeler gauges of appropriate thickness suitable identified. The central portion between the two plates may be provided with a suitable designed grip.

Figure 5shows one example how two or more curved plates 13 each having a different internal radius and supported in a grip holder 16 may be connected together for swivelling about a central pivot 19 for use with different distributor cams. Each curved plate may be provided with a feeler gauge of the appropriate thickness. The curved plates 13 or their grip holders 16 may be marked to identify the make of distributor or model of vehicle with which it is used. The whole may conveniently be closed together by means of the central pivot 19 or opened to produce the required curved plate 13 for use with the appropriate distributor cam.

Figures 6 and 7 show a typical distributor having a lower casing 1 from which the interfitting cap has been removed. The casing 1 has an annular contactbreaker plate 2 through which the distributor shaft 3 extends. The shaft 3 carries the contact-breaker cam 4, which in a 4-cylinder engine has four lobes 5, and extends above the cam to provide a location 6 for the rotor arm, which has been removed to provide access to the cam and the points and so is not shown in these figures. The contact points in a typical distributor comprise the fixed point 7 which is carried on an adjustable mounting 8 and a movable point 9 which is mounted on a lever 10 pivoted at 11.

The lever 10 has a follower 12 which engages the profile of the cam 4. Where the distance between the centre-line of the point 9 and the axis of the pivot 11, i.e., the fulcrum of the lever 10, is greater than the distance between the follower 12 and the axis of the pivot 11 as in Figure 6, the distance of travel of the point 9 is greater than the distance of travel of the follower 12. Thus the ratio of the lever is greater than unity. In many distributors the ratio is substantially unity; but it could be less than unity, if the designer of the distributor so wished.

The usual method of adjusting and setting the points is to turn the crank-shaft of the engine until the radially outer extremity of a lobe of the cam engages the follower 12. The required gap is then set by adjustment of the mounting 8 on the plate 2.

In accordance with this invention, the need to turn the crank-shaft to bring the cam into the correct angular position is avoided by placing a curved plate 13 (e.g. the curved plate shown in Figure 1) provided by this invention against at least one of the lobes 5 of the cam 4, as illustrated in Figures 6 and 7. The curved plate 13 is located on the lobes 5 of the cam 4 and held in place by pressure from the follower 12 which is displaced by a known distance equal to the radial thickness of the curved plate 13 whatever the angular position of the cam. The point 9 is therefore displaced outwardly by the known radial thickness of the curved plate 13 modified by multiplying the radial thickness by the ratio of the lever. This modified distance is known, either by the manufacture of the curved plate or the user and thus the gap between the points has to be set to the modified distance plus the required contact-breaker gap. The adjustment is effected in the usual way by adjustment of the mounting 8 of the point 7. The adjustment may be made by a special feeler gauge, such as 14 in Figure 2, which need only be marked by the required contact-breaker gap dimension, although the actual thickness is that dimension plus the aforesaid modified distance. Alternatively, the user may set the gap by using a conventional feeler gauge by using leaves of the required total dimension. After setting the gap, the curved plate 13 is removed and so the points will close or the gap will reduce to the required gap dimension or less, according to the angular position of the cam. The use of the curved plate 13 reduces the time taken to set or adjust the points and also makes the operation easier, especially for an unskilled person, as the points can be adjusted when the cam is in any angular position.

Claims

1. A device for adjusting the contact-breaker gap between a pair of contact points in a distributor of a petrol engine, the device comprising a curved plate having a part-cylindrical outer surface and an inner surface by which the curved plate is to be located against the cam of the distributor after the distributor cap and rotor arm of the distributor have been removed therefrom, the inner surface of the curved plate being locatable on at least one lobe of the cam in a position in which the outer surface of the curved plate is co-axial with respect to the cam and the cam shaft of the distributor and is spaced at a predetermined radial distance from the part of the internal wall of the curved plate which is in engagement with the part of the periphery of the or each lobe of the cam corresponding to maximum lever displacement.

2. A device as claimed in Claim 1 in which the curved plate has an inner surface of part-cylindrical shape which is co-axial with the outer surface thereof, the radius of curvature of the inner surface being of a value to enable the curved plate to make contact on the cam by location on the radially outermost part of at least one of the lobes thereof.

3. A device as claimed in Claim 1 in which the curved plate has an internal shape corresponding to a portion of the profile of a cam against which the curved plate is to be placed.

4. A device as claimed in any preceding claim including a plurality of curved plates each having a part-cylindrical outer surface of different radii and a differently-shaped inner surface thereby to enable an appropriate curved plate to be fitted onto one of a range of cams each having different diametral distances across the lobes thereof.

5. A device as claimed in any preceding claim in which the or each curved plate is bevelled or flare at its lower end to provide a frusto-conical lead-on portion which is radially-outwardly tapered in the downward direction.

6. A device as claimed in any preceding claim in which the or each curved plate has an outwardly directed bevelled or flared upper end to form a portion to be gripped by the user to enable the curved plate to be placed on the cam orto be removed therefrom after use and also to enable the curved plate to be used either way up.

7. A device as claimed in any one of Claims 1-5 in which the upper end of the or each curved plate is formed with an upwardly-extending knob or handle to be gripped by the user to enable the curved plate to be placed against at least one lobe of the cam or to be removed therefrom after use.

8. A device as claimed in any preceding claim in which the or each curved plate has at its upper end an inwardly-directed flange, tangs or dimples to prevent the lower end of the curved plate from dropping too far past the lower end of the cam.

9. A device as claimed in any preceding claim in which the or each curved plate is made of a hard material.

10. A device as claimed in Claim 9 in which the or each curved plate is made of hardened steel.

11. A device as claimed in Claim 9 in which the or each curved plate is made of a spring steel.

12. A device as claimed in Claim 9 in which the or each curved plate is made of a hard plastics material.

13. A device for adjusting the contact-breaker gap between a pair of contact points in a distributor of a petrol engine, the device being constructed and arranged substantially as described herein and shown in any of Figures 1-5 of the drawings.