How To Hook Up A Dwell Meter

When fitting new contact-breaker points in the distributor , the normal way of checking the gap between them is with a feeler gauge .

Points that have been in apply for some time develop a peak on one face up that corresponds with a crater on the other, acquired by spark erosion as the points open up. When this happens, a feeler gauge no longer gives an accurate measurement of the gap.

A dwell meter measures the bending of rotation of the cam through which the points are opened and closed, and registers the dwell bending - the menses when they are closed.

Information technology can therefore exist used to cheque the gap on worn points with more accurateness than a feeler gauge, and can be used without removing the distributor cap and with the engine running. The meter can also, of course, be used when plumbing equipment new points.

A dwell meter is usually office of an musical instrument used for various mechanical checks. Such instruments may be sold as analysers or test meters, and have to exist switched to dwell for a reading.

How a dwell meter works

When the distributor shaft is rotating, the contact-breaker points open every bit the heel of the moving indicate is pushed outwards by a lobe of the cam, and shut while information technology is over the flat expanse betwixt ii lobes.

If, for case, the angle of rotation between the centres of the lobes on the cam is 90 degrees, the dwell angle - the period with the arm over the flats and the points closed - may be 52 degrees; the remaining 38 degrees are taken up by the action of opening and closing. This would exist a typical dwell bending for a iv-cylinder engine .

A dwell meter continued betwixt the distributor or ignition coil and earth registers the dwell angle on a scale , and must remain steady at the prescribed figure while the engine is running. If the dwell bending is not the aforementioned for all cylinders , the issue is rough running and poor fuel economic system because the moment the spark-plug fires varies from cylinder to cylinder.

Points opening every bit the lobe of the cam starts to lift the contact-billow heel.

The dwell angle varies according to the make of car; cheque it in a service manual. There are two scales on the meter, one for 4-cylinder engines and i for half-dozen-cylinder engines. Eight-cylinder vehicles are taken from the four-cylinder scale and halved.

Connecting the meter

Follow the maker'south instructions. Normally ane lead is continued to the side last of the distributor if information technology is outside the distributor body, or the CB (contact-breaker) terminal on the curl , and the other to earth.

About mod cars have negative earth: connect the blackness (negative) atomic number 82 to earth and the red ( positive ) lead to the distributor or curlicue.

On a vehicle with positive world, connect the ruby-red (positive) lead of the meter to globe and the black (negative) lead to the distributor or scroll.

Measuring the dwell angle

If you have just fitted new contact-billow points, fix them to approximately the right gap with a feeler gauge .

With the dwell meter connected, start the engine and permit information technology settle to a smooth tickover. If information technology will non tick over steadily, check the cause(s) and rectify whatsoever faults .

The meter reading should stay steady at a steady engine speed. If it does not, increase the idling speed slightly until it does (Come across Preparing for carburettor adjustment ).

Compare the steady reading on the advisable scale with the desired dwell angle for your make of car.

If it is likewise high, the contact-billow gap is too pocket-sized. If information technology is too low, the gap is besides wide.

Before you switch off the engine to adjust the gap, brand the following checks. Start inquire a helper to press the accelerator to increase the engine speed slowly to most 1,000 rpm , then let information technology drop dorsum to idling speed while you note the reading.

The angle should remain about the same, with no more than two or iii degrees divergence.

Secondly, increment the engine speed quickly to about 1,500 rpm, so let it drop back to idling speed while y'all again annotation the reading.

The angle should once again remain the same, fluctuating past no more two or 3 degrees.

Conduct out these two tests several times so that you can take an average of any differences in the readings.

If the reading constantly fluctuates more than than 2 or three degrees, the distributor-shaft begetting or advance-retard plate may be worn, or the cam itself damaged. Fit a new distributor (See Removing and refitting the distributor ).

Switch off the engine before making whatever adjustments necessary to the contact-breaker gap.

Adjusting the gap

With the meter yet connected, remove the distributor cap.

Using a spanner on the crankshaft pulley, plow the engine by hand in its normal direction of rotation until the contact-billow points are held fully open by one of the cam lobes .

Loosen the contact-breaker fixings slightly (See Fitting and adjusting contact-breaker points ), on some distributors yous may have to remove the rotor arm to do this, and adjust the gap as needed. Reduce it to increase the angle if the reading was too low; increase it to lower the angle if the reading was besides high.

Replace the rotor arm if removed, and the distributor cap. Switch on the engine and check the dwell-meter reading over again. If the effigy is withal not correct, switch off and reset the gap.

Continue the procedure until you lot obtain the correct reading.

Source: https://www.howacarworks.com/ignition-system/checking-the-dwell-angle