How to Removing and refitting a dynamo pulley

How to Remove a Dynamo

Here you can How to Removing and refitting a dynamo pulley. The most common reason for removing a dynamo pulley is to fit it on a new dynamo — most replacement dynamos are supplied without one. When refitting an old pulley, or fitting a new one, take care to not bend or damage it. The surfaces inside the V where the belt runs must be smooth.

In many cases the pulley incorporates the dynamo cooling fan : its fins must not be bent or broken. Usually it’s best to take the dynamo out of the car before removing the pulley, though sometimes there’s enough room to figure with it still fitted.

Removing the pulley nut

On most dynamos the pulley is a tight fit on the top of the armature shaft. it’s held in place by a movable metal key between pulley and shaft, and secured by a nut. The shaft could also be tapered or parallel and is slotted to take half the key. the hole within the centre of the pulley is also slotted so as to take the other half.

That sort of locating device is called a Woodruff key. It is shaped sort of a shallow half moon and is about 136 in. (5 mm) thick. The pulley nut is usually very tight and is recessed into the pulley. Use a socket or ring spanner to free it. If the dynamo remains on the car, free the nut before removing the belt , which helps to carry the pulley steady against the force of the spanner.

You may also got to engage bottom gear to stop the engine turning – but make certain that the key is out. If you fail to move the nut, remove the dynamo from the car and dismantle it (See the way to fix a dynamo ). Clamp the armature during a vice, using pieces of wood or some other sort of packing within the vice jaws to protect it. they ought to hold it firmly enough for you to free the nut. Do not lose the Woodruff key.

Removing a pulley with the dynamo out

Undo the pulley nut by just a few threads, then, holding the armature in one hand, gently tap the nut with a soft-faced hammer to force the shaft out of the pulley. If this fails, reassemble the dynamo, so that the front cover is supported, and grip it during a vice, then remove the nut.

To prise off the pulley, insert two screwdrivers between the rear of the pulley and therefore the front plate. Gently force the pulley up at the centre not the rim, which could damage the pulley. If this method fails you’ll need to use a pulling tool, taking care to not damage the pulley.

Replacing the pulley

Before refitting the pulley, tap the Woodruff key well into its slot (curved edge down), with the front slightly lower than the rear , so that the slot in the pulley hole engages with it easily. Take care when tapping it in to not make any burrs which can stop the pulley fitting over the key. it’s a good idea to wash the sides of the key with a file before tapping it in, to make sure that there are not any burrs.

Line up the slot in the pulley with the Woodruff key within the shaft, then push the pulley home on the shaft. Usually it’ll be forced fully home as you tighten the pulley nut; however, it may be necessary to tap the pulley on to the shaft with a soft-faced hammer far enough to start out the pulley nut. Some dynamos may have a spacer or shim between the pulley and front plate: don’t forget to replace it. After refitting the dynamo, make sure the pulley is in line with the fan and crankshaft pulleys.

Replacing Dynamo Brushes

Undo the screws holding the brush cables. Push the spring to one side and remove the brush. Before refitting the endplate, push the end of the coiled spring from the top to the side of the brush to wedge it in the holder.

Removing the brushes

The carbon brushes are a sliding fit in oblong holders on the dynamo endplate. Coiled springs bear against the tops of the brushes to carry them in contact with the commutator. Each brush also features a braided wire or cable attached by a screw. The cable from one brush results in earth, which from the opposite to the dynamo output terminal.

Undo the screws holding the cables, push the ends of the coiled springs to one side of the brush holders, and pull the brushes out. Note exactly how they were fitted, so that if you refit an equivalent ones later, each goes back as before. If a brush is reversed, it’s going to not seat properly on the commutator. Measure the length of the brushes. If the carbon is worn down to a thickness of in. (10 mm) or less, fit new brushes.

However, even if the carbon thickness is down to in. (13 mm) it’s still best to exchange the brushes. If the brushes aren’t too worn they’re normally about 1 in. (25 mm) long – they’ll are sticking in their holders and not contacting the commutator properly. Use a fine file to remove any raised spots from the surfaces of the brushes. Clean out the holders with a petrol-soaked rag. Replace them in their holders and check that they slide freely and do not rock from side to side.

Refitting the brushes

Always clean the brush holders thoroughly before fitting new brushes. The ends of the brushes must be shaped to match the curve of the commutator. If they’re not, remove the armature and wrap fine glasspaper around it, abrasive side outwards (do not use emery paper). Fit the endplate over the commutator, and switch it in order that the brushes bear against the glasspaper and are shaped to match the curve of the commutator.

Replace the brushes in their holders and reconnect their cables to the output and earth terminals. Check that the brushes are a smooth, sliding slot in the holders. If they’re too loose they could tilt and jam within the holders. Make sure the brushes don’t stick out of the inner ends of the holders. Wedge them in situ by adjusting the ends of the coiled springs in touch against the edges of the brushes rather than the top.

Doing so enables you to refit the endplate and brush-holder assembly without damaging the inner ends of the brushes, which might otherwise catch on the commutator. With the endplate refitted, reassemble the dynamo with its two long bolts. Take alittle screwdriver, and dealing through the ventilator holes within the endplate (or the inspection ‘windows’), move the ends of the coiled springs from the side of every brush to the top, so pushing it down into contact with the commutator.

Inspecting the commutator

  • Glazing: The commutator segments have a varnished look. This coating may be due to dust and water inside the casing, or to particles worn from the brushes or the mica insulation strips between segments.
  • Scores and pits: Usually pitting and scoring of the commutator segments are caused by electrical arcing between the commutator and badly fitted, poorly seating or worn-out brushes.
  • Melted solder: Overheating can melt the solder connections between the segments and the armature windings. Sever cases show as a ring of melted solder around the inside of the casing.
  • Faulty insulation: The mica strips stick up between segments, stopping the brushes making contact. This is caused by wear or arcing removing surface copper. One of the segments has also cracked.

Check the condition of the commutator whenever you remove the dynamo from the car – even if you’re doing so only to examine the brushes. The job is best through with the armature faraway from the dynamo. Remove the top plate . Scratch alignment marks on the front plate and casing to make sure that they will be reassembled correctly later. Push out the armature, along side the front plate and pulley. Wipe the commutator clean with a petrol-moistened cloth and inspect it thoroughly.

Major defects to seem for are glazed, scored and pitted segments, or faulty insulation between them; soldered connections that have broken or melted together; and segments that have come loose. All but the loose segments are often repaired fairly easily, so long as they’re not too worn or badly damaged. Even loose segments are often re-soldered, but that’s delicate work which has got to be through with a powerful soldering iron due to rapid heat loss through the copper. it’s best left to an auto-electrician.

Cleaning the commutator

Grip the whole armature in a vice fitted with padded jaws. Put a strip of fine glasspaper – not abrasive – over the commutator during a half loop, then pull the ends of the strip backwards and forwards until the copper becomes bright and clean. Rub evenly all round the commutator and along its length.

If the commutator is just too worn or damaged for this treatment, you’ll be ready to have it skimmed on a lathe. Consult an auto-electrician. After cleaning or skimming, the mica insulation strips between the segments may have curtailing , as they’re going to be level, or nearly level, with the faces of the segments. They should be about 1mm below the extent of the faces. If they’re higher cut them back evenly along the entire length of every strip to offer an honest square groove.


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