GB2261514A

GB2261514A - Ignition timing aid

Info

Publication number: GB2261514A
Application number: GB9211846A
Authority: GB
Inventors: Adam Russell Kyte
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-11-16
Filing date: 1992-06-04
Publication date: 1993-05-19
Anticipated expiration: 2012-06-04
Also published as: GB9124402D0; GB2261514B; GB9211846D0

Abstract

An ignition timing aid for determining the correct position for ignition timing marks on an internal combustion engine. measures the height of the piston relative to the Top Dead Centre position, to determine the point at which the ignition should occur. It comprises a pushrod 20 acting against the upper surface of a piston, a flexible cable 13 and a pushrod extension 3 moving a pointer 5. The pointer 5 reads against a scale 9 which zeros itself at Top Dead Centre, when the crankshaft is rotated through 360 DEG . The device fits into the spark plug hole or injector port of the engine. It incorporates a means of catering for spark plug holes or injector ports which are not parallel to the cylinder bore. <IMAGE>

Description

IGNITION TIMING AID This invention relates to a device that will determine the correct position of ignition timing marks on an internal combustion engine.

To set the timing on any internal combustion engine, accurately positioned timing marks are essential. Once the correct position of the timing marks is determined, the engine may be timed by one of several methods. Dynamic timing "freezes" the timing marks, whilst the engine is running by means of a strobe light. Static timing (for engines that use conventional contact breaker points) relies on using a continuity test, and turning the engine over by hand, to see where the points open and close. For compression ignition engines (such as diesels), the process is slightly different but still requires accurate timing marks.

Because it is critical for the timing marks to be accurately scribed, it is a surprising fact that on many engines (particularly small motorcycle engines), the manufacturer's timing marks are often extremely inaccurate. Some engines don't even have any timing marks (or they may have worn or corroded away). This gives the mechanic the problem of scribing new timing marks. Another instance where new timing marks may be needed is when an engine is being race tuned, to extract the maximum possible performance from it.

To determine the correct position of the marks, the usual method is to find the Top Dead Centre (TDC) position of the piston, then either let the piston fall to a specified height Below Top Dead Centre (BTDC), or turn the crankshaft a specified number of degrees from its position when the piston is at TDC. The method of using piston height is more accurate. Using the method of measuring crankshaft rotation, it is difficult to detect any movement in the piston for the few degrees of crankshaft rotation as the top of the stroke is reached, thus making an accurate datum hard to find. (If the relevant manual or data book only specifies the ignition position in degrees before TDC, a relatively simple trigonometrical calculation can be carried out to convert this to a piston height below TDC.) It can however, be a lengthy job to measure piston height below TDC.The usual method is to use a Dial Test Indicator (DTI) mounted above the piston to measure its travel. This is sometimes possible by inserting the DTI into the spark plug hole (or injector port in the case of diesel), and rotating the crankshaft by hand.

Problems arise when the spark plug hole (or injector port) is not perpendicular to the surface of the piston. This usually means that removal of the cylinder head is necessary. Also many engines do not have sufficient clearance above the cylinders in which to fit a DTI. (For example, many motorcycles have frame tubes directly above the cylinder head.) This means that removal of the whole engine would be necessary, just to scribe accurate timing marks. Difficulties can also be experienced in holding the DTI. Jigs may have to be formed in order to clamp it firmly above the piston. It can also be difficult to observe the exact TDC height, in order to find the correct position.

According to the present invention, there is provided a device that gives an accurate means of determining the correct position of ignition timing marks on an internal combustion engine.

The device measures the height of the piston relative to a datum position. The datum position used is the Top Dead Centre (TDC) position of the piston. The device zeros itself at this datum position and measures the height below this position.

The device is designed to fit in a spark plug hole or injector port. It may be fitted directly into a standard 14mm spark plug hole, and adaptors are used to fit it into any other spark plug thread or injector port. The device incorporates a means of adjustment to cater for different spark plug / injector angles, and is designed to cater for engines with limited clearance above the spark plug / injector.

A specific embodiment of the invention will now be described by way of example to the accompanying drawings. Drawing no.l shows the pointer assembly in Third Angle Projection.

Drawing no.2 shows the pushrod mounting assembly in Third angle Projection. Drawing no.3 a pictorial view of the entire device, mounted in a small motor-cycle engine. For clarity, a cut-away view of the engine is shown.

Referring to the drawings the device comprise of a pushrod 20 which is located in a pivoting housing 15, and is free to slide up and down the vertical hole drilled down the length of the pivoting pushrod housing 15 (which locates in the cylinder head of the engine).

The pushrod 20 protrudes from the bottom of the pivoting pushrod housing 15. When the device is fitted to an engine, the end of the pushrod 20 butts directly against the top face of the piston. The pushrod housing 15 pivots about the pivot screw 16 to enable the pushrod to be set parallel with the cylinder bore. Once in this position, the pivoting pushrod housing 15 can be locked in position by tightening the knurled lockring 17 on the lockring stud 18. The body of the assembly 14 is threaded, and screws into the spark plug hole. It is held still by means of a large lockring 21, which may be tightened against the cylinder head, once the main body of the assembly 14 and the pivoting pushrod housing 15 are correctly positioned.

The pushrod 20 transfers movement via a flexible cable 13, to the pointer assembly. The pointer assembly converts linear motion of the piston to rotary motion of the pointer.

The top of the cable is joined to an extension of the pushrod 3. Therefore any movement in the pushrod 20 is repeated in the pushrod extension 3, which is then transferred to the pointer 5 via a pushrod end 4 in the form of a hinge. The pointer 5 moves about a pointer pivot 6.

In order to ensure that the lower pushrod 20 stays in firm contact with the piston top face, and to ensure that there is no free play in the whole system, a spring 10 is incorporated into the pointer assembly. This keeps a constant backpressure on the pushrod. To ensure that the backpressure is sufficient to hold the pushrod 20 against the piston, but not too great so as to provide unnecessary friction in the system, a spring adjustment block and screw assembly 11 & 12 are used. This only needs to be adjusted when the device is first used.

Some engines will have deeper spark plug holes / injector ports than others. Also the distance from the bottom of the spark plug hole / injector port to the top surface of the piston (at TDC) will vary from engine to engine. This fact is catered for by a pushrod adjuster & lockring 2. When the device is used, the piston would be brought approximately to TDC and then the pushrod adjuster 2 moved until the pointer 5 is approximately at right angles to the pushrod extension 3. This will ensure that the measurement taken will be well within the range of the device.

As the piston is raised, it moves the pointer anti-clockwise (looking at drawing no.l). The pointer assembly also acts against the stop 7 on the scale 9. This has the effect of moving the whole scale 9 in an anti-clockwise direction, about the pivot 6, in the same manner as the actual pointer 5 itself.

As the piston falls, the pointer 5 ceases to act against the stop 7. The friction washers 8 therefore hold the scale in the position that it reached at the exact point when the pointer 5 changed direction, ie.the TDC position of the piston.

This means that the pointer 5 has now zeroed the scale 9 at TDC and the pointer 5 will now read the exact height of the piston below TDC against the calibrations on the scale 9.

To summarise, here is an explanation of how to use the device.

Screw the body of the assembly 14 into the spark plug hole (using the relevant adaptor if a different spark plug thread or injector port adaptor is required).

Tighten the large lockring 21 against the cylinder head.

Adjust the pivoting pushrod housing 15 until the pushrod 20 is parallel to the motion of the piston.

Tighten the knurled lockring 17 to clamp the pivoting pushrod housing 15 in place. Diagram 3 shows a cut-away view of an engine to show how the assembly should now be fixed.

Unscrew the pushrod adjuster 2 to its maximum adjustment.

If necessary, adjust the spring tension using spring adjuster assembly 11 & 12 so that the pointer 5 moves with the crankshaft (ie the pushrod 20 stays in contact with the upper face of the piston), and ensure excessive friction does not prevent smooth / free motion.

Bring the piston to approximately TDC.

Adjust the pushrod adjuster 2 (and tighten its lockring) so that the pushrod extension 3 is approximately at right angles to the pointer 5.

Rotate the crankshaft through 360 degrees, in order to zero the scale 9 at TDC.

Continue to rotate the piston until the pointer 5 reads the specified height BTDC (obtained from a manual or data book) against the calibrations on the scale 9.

If existing timing marks do not line up, scribe a new mark, which will line up with the mark on the crankcase.

FIGURE 1 TIMING DEVICE - ASSEMBLY DRAWING NUMBER 1 1 - MAIN CASTING 2 - PUSHROD ADJUSTER & LOCKRING 3 - PUSHROD EXTENSION 4 - PUSHROD END 5 - POINTER 6 - POINTER PIVOT 7 - POINTER STOP 8 - FRICTION WASHERS 9 - SCALE (NOT FULLY SHOWN) 10 - SPRING & RETAINING BOLT 11 - SPRING ADJUSTING BLOCK 12 - SPRING ADJUSTING SCREW ASSEMBLY 13 - FLEXIBLE CABLE FIGURE 2 TIMING DEVICE - ASSEMBLY DRAWING NUMBER 2 14 - BODY OF THE ASSEMBLY 15 - PIVOTING PUSHROD HOUSING 16 - PIVOT SCREW 17 - KNURLED LOCKRING 18 - LOCKRING STUD 19 - WASHER 20 - PUSHROD 21 - LARGE LOCKRING

Claims

CLAIMS 1 A device that gives an accurate means of determining the correct position of ignition timing marks on an internal combustion engine.
2 A device as claimed in claim 1, wherein piston height is measured in order to determine the correct position of timing marks.
3 A device as claimed in claim 1 or claim 2, wherein a mechanical probe that acts against the upper surface of the piston senses the height of the piston.
4 A device as claimed in any preceding claim, wherein the height of the piston is displayed by means of a pointer that is read against a scale.
5 A device as claimed in any preceding claim, wherein the motion of the piston is transferred from the piston to a pointer either partially or totally by means of a flexible cable.
6 A device as claimed in any preceding claim wherein the linear motion of the piston is converted, by some means, to rotary motion of a pointer.
7 A device as claimed in any preceding claim, wherein the device incorporates a means of zeroing itself at a datum point therefore giving a measurement relative to that datum point.
8 A device as claimed in claim 7, wherein the datum point referred to is that of the top dead centre position of the piston.
9 A device as claimed in any preceding claim, wherein the device zeros itself by means of a scale that moves to a datum point, then remains stationary, whilst a pointer rotates to the relevant calibration on the scale, as the engine reaches the position where the timing marks should line up.
10 A device as claimed in any preceding claim, wherein any free play in the mechanism is removed by means of a spring.
11 A device as claimed in claim 10, wherein a means of adjusting the spring tension is provided.
12 A device as claimed in any preceding claim, wherein the means of adjusting the spring tension is provided by a block supporting one end of the spring, which runs on a threaded rod with nuts locking against the block.
13 A device as claimed in any preceding claim, wherein the device enters the combustion chamber via the spark plug hole or injector port.
14 A device as claimed in any preceding claim, wherein the device is actually fitted into the spark plug hole or injector port.
15 A device as claimed in any preceding claim, wherein the device will screw into one particular size of spark plug thread, and adaptors are used to fit the device into different sized spark plug holes or injector ports.
16 A device as claimed in claim 15, wherein the particular size of spark plug thread is a 14mm spark plug thread.
17 A device as claimed in any preceding claim, wherein a means of catering for different angles of the spark plug hole (in relation to the plane of motion of the piston) is incorporated in the design.
18 A device as claimed in any preceding claim, wherein a means of catering for different angles of the spark plug hole is provided by a pivoting housing for the probe or sensor.
19. A device substantially as described herein with reference to figures 1-3 of the accompanying drawing.

19 A device as claimed in claim 18, wherein the pivoting housing is mounted into a component which fits directly into a spark plug hole.

20 A device as claimed in claim 18 or claim 19, wherein the pivoting housing may be locked in place by means of a lockring or locknut.

21 A device as claimed in any preceding claim, wherein a means of adjustment is provided to cater for varying heights of the top of the spark plug hole / injector port, in relation to the position of the upper surface of the piston when it is at top dead centre.

22 A device as claimed in claim 21, wherein the means of adjustment mentioned in claim 21 is provided by means of a threaded tube, which may be locked in position by a lockring or locknut.

23 A device substantially as described herein with reference to figures 1-3 of the accompanying drawing.

Amendments to the claims have been filed as follows 1. A device that gives an accurate means of determining the correct position of ignition timing marks on an internal combustion engine, wherein the device enters thecombustionchamber via the spark plug hole or injector port and a means of catering for different angles of the spark plug hole or injector port (in relation to the plane of motion of the piston) is incorporated in the design.

2. A device as claimed in claim 1, wherein piston height is measured in order to determine the correct position of timing marks.

3. A device as claimed in claim 1 or claim 2, wherein a mechanical probe that acts against the upper surface of the piston senses the height of the piston.

4. A device as claimed in any preceding claim, wherein the height of the piston is displayed by means of a pointer that is read against a scale.

5. A device as claimed in any preceding claim, wherein the motion of the piston is transferred from the piston to a pointer either partially or totally by means of a flexible connection.

6. A device as claimed in any preceding claim wherein the linear motion of the piston is converted, by some means, to rotary motion of a pointer.

7. A device as claimed in any preceding claim, wherein the device incorporates a means of zeroing itself at a datum point therefore giving a measurement relative to that datum point. The datum point referred to is that of the top dead centre position of the piston.

8. A device is claimed in any preceding claim, wherein the device zeros itself by means of a scale that moves to a datum point, that remains stationary, whilst a pointer rotates to the relevant calibration on the scale, as the engine reaches the position where the timing marks should line up.

9. A device as claimed in any preceding claim, wherein any free play in the mechanism is removed by means of a springsand a means of adjusting the spring tension is provided.

10. A device as claimed in any preceding claim, wherein the means of adjusting the spring tension is provided by a block supporting one end of the spring, which runs on a threaded rod with nutsf locking against the block.

11. A device as claimed in any preceding claim, wherein the device is actually fitted into the spark plug hole or injector port.

12. A device as claimed in any preceding claim, wherein the device will screw into one particular size of spark plug thread, and adaptors are used to fit the device into different sized spark plug holes or injector ports.

13. A device as claimed in claim 12 wherein the particular size of a spark plug thread is a 14mm spark plug thread.

14. A device as claimed in anyprecedingclaim, wherein a means of catering for different angles of the sparK plug hole is provided by a pivoting housing for the probe or sensor.

15. A device as claimed in claim 14, wherein the pivoting housing is mounted into a component which fits directly into a spark plug hole.

16. A device as claimed in claim 14 or claim 15, wherein the pivoting housing may be locked in place by means of a lockring or locknut.

17. A device as claimed in any preceding claim, wherein a means of adjustment is provided to cater for varying heights of the top of the spark plug holel injector port, in relation to the position of the upper surface of the piston when it is at top dead centre.

18. A device as claimed in claim 17 wherein the means of adjustment mentioned in claim 17 is provided by means of a threaded tube, which may be locked in position by a lockring or locknut.