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Sir Nibble

CAV Co-axial starter rebuild

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4 hours ago, Sir Nibble said:

Field pole shoes. Two showing untreated rust and damage from armature rubbing. Two cleaned up with a coat of zinc plating flashed over them. This is a marine unit off a saltwater boat. Corrosion isn't defeated with a wire brush and wishful thinking.

IMG_20200206_113243.jpg

Do you plate them yourself?

Edited by WotEver

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Bush pressed in, now it must be bored to suit the pinion, lubricator aperture filled with a bit of card to keep swarf out.

15810859674402005998533166765073.jpg

Edited by Sir Nibble
Missing comma!
  • Greenie 1

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Seals. I'm using genuine parts from prestolite, the inheritors of the CAV brand. The seal on the left is a dust seal that comes with the repair kit. The one on the right is going in this unit which means I get to keep the other one. Unfortunately, the ones supplied these days are too tight and inflexible and restrict the movement of the pinion to the point where the starter won't engage! Fortunately I have a drawer full of good ones left over from years of saving them.

IMG_20200207_150404.jpg

  • Greenie 1

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1 hour ago, Sir Nibble said:

Unfortunately, the ones supplied these days are too tight and inflexible and restrict the movement of the pinion to the point where the starter won't engage!

And how many folk without your experience would realise that?  None, I wager. 

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1 hour ago, WotEver said:

And how many folk without your experience would realise that?  None, I wager. 

It would take a while to work it out first time a rebuild didn't work but after the swearing has died down.....

Obviously now I won't be progressing the job until Monday but I have enough pics and vids to do a "how it works" at some time over the weekend. Meanwhile, a rant. 

O rings left out. No no no. Absolutely not acceptable. O rings are not difficult to get in whatever size. They come under the heading of basic engineering supplies. No excuse. The missing spring. Same again. It's an important part as shown by it's omission resulting in accelerated wear and premature failure. Not being able to get it with A CAV part number on it is again no excuse. I use springs that differ from the original by 0.3mm in the outside diameter. They're brush springs for a French starter and I buy them in packs of ten. It just takes a little effort and a reasonable pride in your work.

Rant over.

  • Greenie 1

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Right, how it works. First the excuses. It's difficult taking useful video with one hand whilst functioning metalwork with the other. I've done my best.

Electrically it's dead simple. Three contacts. First contact connected to battery +ve. Second contact to the motor. Moving contact has its own connection to a bloody great resistor and thence to the motor, and also forms a bridge from first to second contact. 

Initial contact is on the right of the picture. Remember the solenoid plunger is carrying the pinion forward into mesh with the flywheel. First contact made current flows into the moving contact, through the resistor and to the motor which rotates slowly. This rotation ensures smooth engagement and with the pinion held by the flywheel, the spiral spline winds it forward into full engagement. A disc on the rear of the pinion trips a lever which releases the left side of the moving contact and it snaps down to the second contact, bypassing the resistor and supplying full power to the motor, cranks the engine. A picture is worth a thousand words.

Edited by Sir Nibble
  • Greenie 1

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Diesel engines, as we have all seen, can tend to cough and fart a bit before becoming self sustaining and if every half hearted semi combustion of under heated fuel were to kick the pinion back down the spiral spline out of mesh, then on a cold day you'd never get the thing started. So there has to be some means of locking it in the engaged position. This picture illustrates two things. The four segments held by their garter spring in contact with the shoulder that carries the pinion forward and more pertinent here, two rows of holes which accept small steel balls. the row nearest the non drive end is what we are concerned with at the moment.

IMG_20200207_091829.jpg

  • Greenie 1

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Don't you just love technology! Using and editing fine then suddenly it decides to absolutely refuse to respond the way it did a moment ago! That's why there's a zero second non video I can't edit out 😠

How it works completed. When my battery charges up I will get into the overspeed protection.

  • Greenie 1

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Overspeed. In this picture it can be seen that as the motor torque working through the spiral spline takes over from the solenoid to complete engagement, the four segments that drove the pinion forward initially, ride up the slope on the pinion and expand into their groove where they are held by the solenoids magnetic field. With these segments clear of the pinion there are only the locking balls preventing the engine driving the pinion out of mesh.

IMG_20200207_091852.jpg

Now the spring loaded sleeve that retains the locking balls in place. Notice the internal ramp.

IMG_20200207_092101.jpg

  • Greenie 1

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And that's it. Electrically simple, mechanically complex.

The hissing noise in the videos by the way, we don't have a leaky air system, it's an ultrasound cleaning tank.

Now you know why the British worker has productivity problems, he's busy illustrating the job for cwdf!

Back to work Monday and I shall show in the vice and test bench testing.

  • Greenie 1

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All the complicated stuff assembled. The resistor is visible around the circumference, highlighted by the white ceramic insulators. Connection to the moving contact at 5 o'clock, from resistor to second contact (motor) at 6 o'clock. 

IMG_20200210_081050.jpg

  • Greenie 1

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This antique octopus test bench expresses torque as hydraulic pressure. The conversion tables to take that information together with the number of teeth on pinion and test bench to reach a figure to compare with manufacturers test plan no longer exists. The unit is tested against my expectations based on experience. 

Current draw.

So, new plugs over the field connections, lubricator wick spring and it's retaining plug, new terminal nuts and washers, coat of paint and out the door 

It's only a starter motor, how hard can it be?😆

  • Greenie 3

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Can you do a bs5 next please? 

Have a couple under the bench and a box of remains that need a coat

Of looking at. 

Nice work by the way. 

Good gear the old CAV stuff. 

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A really good post.  Thank you Snibbs.

 

A second request for a BS 5 next please.

N

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Another vote for a BS 5 overhaul.  Thanks for posting......

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12 hours ago, crossley said:

Can you do a bs5 next please? 

Have a couple under the bench and a box of remains that need a coat

Of looking at. 

Nice work by the way. 

Good gear the old CAV stuff. 

 

1 hour ago, BEngo said:

A really good post.  Thank you Snibbs.

 

A second request for a BS 5 next please.

N

 

1 hour ago, NB Esk said:

 

Another vote for a BS 5 overhaul.  Thanks for posting......

The best I can do here is to say that I will bear it in mind. A BS5 is hardly an everyday job and although I do get them, being able to document the job has to be dependent upon the pressure of work at the time.

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