Converting 120 mph Speedo to 160mph

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Nigel Cousins
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Converting 120 mph Speedo to 160mph

#1 Post by Nigel Cousins »

I am looking for advice and a source for the correct magnet and hairspring to convert a VDO 120mph speedometer to 160mph range.
IMG_1101.jpeg
Many thanks
Nigel

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Nigel Cousins
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Re: Converting 120 mph Speedo to 160mph

#2 Post by Nigel Cousins »

Since my last post, much research has been carried and restoration of the original 120mph speedo has begun.

If you look at the first post, the number wheels were badly discoloured and flaking. The old paint was removed with a dental pick and then filled with fresh mat white enamel, I must say this takes a huge dollop of patience and I found that not trying to do too much in one sitting pays off, so work in progress.
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The rear case and fixings have been re zinc plated and the inside of the case painted white, along with the back of the trim ring to improve back light levels, it I amazing how discoloured and non reflective the original paint had become.
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Creation of the 160mph gauge artwork to create a screen print is also underway, I will share when complete.

The real challenge will begin with degaussing/ re-magnetising the magnet to change the needle ratio to the hair spring for a 160mph swing, an interesting find and to my amazement is that you can use your smartphone as a Gauss/Tesla Meter to measure your how strong the magnet is, as it has a compass inside and there are lots of free Apps that do the Math for you. So my fist step will be to check a few speedos I have to get the 120 base line UT reading.

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Nigel Cousins
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Re: Converting 120 mph Speedo to 160mph

#3 Post by Nigel Cousins »

While doing the 160mph Speedo, I have another 120 mph speedometer, 3 tachometers and a combination gauge that were in need of restoration.
These have proved a bit of a distraction but economy of scale makes it better to get all your parts zinc plated at once.
IMG_1068.jpeg
On opening up the VDO tachometers the back rubbers had badly perished, the VDO light tube rubbers had disintegrated completely and the red generator warning light lens was like powder and fell apart. After many hours on the internet searching for the parts with no luck. I had to find another solution!
Injection rubber moulding them was expensive with tooling each rubber was working out at £800 each. So I experimented with 3D printing them in TPU, a flexible polyurethane that adapts well to printing, phone cases are made of this.

I created a 3D STL model in CAD of the rear rubber.
IMG_1267.jpeg


Then using a friends printer and a reel of TPU ordered off Amazon, we went about printing them. It took a few practice goes to get the temperature and print rate right, but the results were amazing. The original is at the top and the prints are below. Price worked out at £6 each to produce.
IMG_1292.jpeg
The VDO light tubes were also produced in the same way using white TPU
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This material has great potential to offer low cost solutions for no longer available non engine flexible parts.

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Nigel Cousins
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Re: Converting 120 mph Speedo to 160mph

#4 Post by Nigel Cousins »

The Tachometer generator indicator lights had disintegrated over time and are NLA.

So on to ebay for some red acrylic rod and Amazon for some PolyWatch plastic polish used too take scratches out of plastic watch faces, its low price and works extremely well.

I ground up a carbon steel tool to cut the profile and then at slow speed turned the profile.
IMG_1323.jpeg
Then finish with 2000 paper and polish with the PolyWatch polish media.
IMG_1168.jpeg
Very happy with the result.

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David Jones
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Re: Converting 120 mph Speedo to 160mph

#5 Post by David Jones »

Fantastic work Nigel, never ceases to amaze me at how much talent is ensconced in our 356 community.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
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Martin Benade
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Re: Converting 120 mph Speedo to 160mph

#6 Post by Martin Benade »

Those parts look great. Will you find a way to completely repaint the face too?
I once had a B with a 160 mph speedo. A number of years after I’d sold it Myron Vernis called me to say he’d just bought the car to get the speedo and did I want to buy the rest of it.
I’m now very sorry I didn’t.
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Nigel Cousins
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Re: Converting 120 mph Speedo to 160mph

#7 Post by Nigel Cousins »

The 8000rpm Tachometer distraction continued this week with the crumbling of the blue 'High Beam' warning light lens.

Some blue acrylic and the same plain carbon steel form tool solved the problem, but the blue of the acrylic was not deep enough after machining. So some deep blue stained glass window paint applied to the rear surface gave a richer colour to the lens.
IMG_1339.jpeg
Space inside of the tachometer is limited for the light tubes, so I decided to draw up the whole tacho in CAD, to create a light tube that would work well with 40 degree offset of the light tube to the dial face and the flexibility of the TPU.

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An interesting observation on 3D printing these parts, is that by reducing the density of the inner lattice structure of the print from 40% to 20% created a much more flexible TPU part and offsetting this with different outer wall thicknesses also had a marked effect on the performance of the finished part. This is whole new area of engineering design that is exciting and very interesting to explore.

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Nigel Cousins
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Re: Converting 120 mph Speedo to 160mph

#8 Post by Nigel Cousins »

Following on from last weeks post, things have continued to move forward.
The tachometer new design light tubes one 10mm id and the other 11mm id 3D printed well in white TPU and present nicely to the gauge face.
IMG_1375 2.jpeg
The needle was painted in florescent white and the restoration of the gauge face, indicator lenses and machining of a new brass ferrel and tooling to hold the 3 component parts in place came together.
IMG_1374.jpeg
Back to the 160 Mph Speedometer, I have drawn up the blank for the Speedometer gauge front allowing enough material to metal spin the edge after screen printing. I will make the spinning jig in due course. I have been investigating 'dye sublimation printing' as an alternative to screen printing, this newly available technology looks very good for very small batches and one offs, I will do some trials in the coming weeks.
IMG_1356.jpeg
The blanks for the speedometers will be laser cut this week and then be painted and sanded in a base coat.

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Martin Benade
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Re: Converting 120 mph Speedo to 160mph

#9 Post by Martin Benade »

That’s all quite impressive, especially getting to the printing and spinning the face. I’m about to get into my tachometer which may have the same light guide tubes. Would it be appropriate to ask if you’d share the print files for those? I know nothing about that but a friend is a somewhat avid 3d printer.
I wanted to email you but your contact information is not available.
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Alan Klingen 2
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Re: Converting 120 mph Speedo to 160mph

#10 Post by Alan Klingen 2 »

I would give it to a proper insrament ahop like palo alto speedometer so that they do the conversion and check it's calibration also. Alan The Stable.

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Martin Benade
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Re: Converting 120 mph Speedo to 160mph

#11 Post by Martin Benade »

I don't actually know, but I bet they originally used the same magnet for 120 and 160 versions, and just altered the spring. Have you been able to measure both versions and find out?
Reading your thread make me think that the mechanical to electronic tach conversion I'm working on is a laughable effort. "Driver quality".
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Alan Klingen 2
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Re: Converting 120 mph Speedo to 160mph

#12 Post by Alan Klingen 2 »

Best thing to do is send it to a good instrament shop like Palo Alto Speedometer they can not only convert the speedo but but also put on the correct dial face. Alan The Stable. They can also calibrate it to be accurate. Alan The Stable.

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Re: Converting 120 mph Speedo to 160mph

#13 Post by Alan Klingen 2 »

Judging by the picture not something you should try on your own!!! Give it to a good speedo shop like Holly wood speedo so the can modify the instrament AND CALIBRATE THE SPEEDO Alan The Stable.

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Mark Forster
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Re: Converting 120 mph Speedo to 160mph

#14 Post by Mark Forster »

Nigel- Do you have any of the light bulb seals to sell? If not would you have the cad file available?
Thank you.

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