Adjusting an under reading speedo

[Benjy]

Ahoy All

The speedo on my car is seriously under reading by at least 20 - 25 kmh so I thought I'd do some research and see what could be done. I stumbled on to this very helpful video that appears to have the solution.

Not really surprising that a magnetic speedo would lose some of its magnetism over 50 plus years.

At some point I'll remove the speedo, strip it down and try this.

It's worth adding that the odometer is not magnetic so should be reading distance covered correctly regardless.

https://www.youtube.com/watch?v=uxJL4b-jt9U

Cheers

Lots Of Time Understanding Speedos

[Benjy]

Ahoy All

Well I bought myself some magnets and had a go at remagnetising my laggy speedo. I had fun getting the needle off. It needed so much force I was really worried about breaking something but knowing that it pops off was very helpful. In the end id did release and flew a few metres across the room thankfully undamaged. Taking the speedo apart is easy.

I followed the instructions although there was no mention of what position to replace the needle when reassembling. I placed it at 0 kph and pressed down the stop wire and lifted the needle over it so that there was just enough tension to keep the needle sitting on the stop wire. Then I went for a drive. The speedo is more steady, before it swung about a bit more and it is under reading less but still not correct. So I removed it, stripped it down again, tried more magnets and put it all back together again. Got the knack of removing and reinstalling the speedo now. Just slide the seat out, crawl in with a head torch and reattach the bits. I am becoming rather adept at this now. Of course it made no difference at all.

My question to all of you is: Is the Smiths speedo the same on all Europa models? The reason i ask is that this speedo was from a Special and my car is an S2. I was wondering if maybe the gearing from the gearbox was different  and that is why the speedo is under reading? Maybe my magnets are not strong enough. Maybe I should leave them stuck there for half an hour at a time? I shall keep experimenting but I'd like to know if the speedo was the same through all models...

Thanks!

Benjy

[314159td]

For a speedo, you must always FIRST ensure the odometer is reading correctly, then adjust the speedometer. I usually go on a long drive with an odometer app open, they are typically spot on unless someone has messed with the speedo gears.
The odometer is driven precisely by the number of rotations of the cable (with a mathematical reduction, of course), where as the speed readout needle is a bit of a guess, as you've witnessed.
What good is a car with speedometer that reads the correct road speed, if you have no idea when to change the oil?

[Benjy]

Good point!

I believe my speedo comes from a special and my car is an S2. As far as I can tell they have different part numbers and turn at different speeds so it's not surprising if the speedo under reads.

Can anyone confirm that the speedos are actually different and turn at different speeds? The part numbers are different, the S2 is SN5226/12 and the Special is SN5226/13 but I'm not even sure that is correct if someone could verify this info I'd be very pleased!

The next question then becomes, anyone got an excellent condition KMH speedo for an S2 they would like to swap for a almost new (800kms) Special speedo? It was new old stock and is in perfect as new condition.

Thanks

[Bryan Boyle]

Good point!

I believe my speedo comes from a special and my car is an S2. As far as I can tell they have different part numbers and turn at different speeds so it's not surprising if the speedo under reads.

Can anyone confirm that the speedos are actually different and turn at different speeds? The part numbers are different, the S2 is SN5226/12 and the Special is SN5226/13 but I'm not even sure that is correct if someone could verify this info I'd be very pleased!

The next question then becomes, anyone got an excellent condition KMH speedo for an S2 they would like to swap for a almost new (800kms) Special speedo? It was new old stock and is in perfect as new condition.

Thanks

Along the lower arc of the speedo face, besides the part number, should be a number like 2880 or some such.  That gives you the number of revolutions per mile of the cable.  (see the photo) THAT is determined by the ratio of the teeth of the driven gear in the transmission to the driving gear.

The S2 driven gear is 12 teeth, the TC gear is 19 teeth.  No idea what the pitch of the driving gear is, so, can't tell what the ratio is. (yes, I have 2 spare S2 gears that have been kicking around in my spares locker.  And a couple angle drives.  PM me off line when you need them and we'll work out a price.)

Use the right gauge that is matched to the right gearing, and you will get the right reading. 

Uh, not to be a nudge, but if you've taken the TC speedo apart a couple times and fiddled with it, it is probably not perfect.  Not casting shade on your skills, Benjy. 

[Benjy]

Thanks Bryan,

My toothed gear was half melted but I managed to rebuild the teeth by melting an old plastic tyre lever to it and filing it down to get the shape and it's still working so I'm pleased with that. Good to know you have a spare if needed. I'd like to keep the speedo as it is new old stock so does that mean I'd have to change the geared drive in the gearbox and the angled bit that fits to the gearbox where the cable attaches to? That would be a sensible solution if it could work? I'd appreciate your thoughts...

I have no fear of taking things apart. When I was a child I took everything apart and normally failed to put it back together but after 50 odd years of practice I have become rather adept at taking things to pieces and even putting them back together again, sometimes even improving them! If not for this skill I would never have dared to buy a Europa! These Smiths instruments are very easy to dismantle...

Cheers

[SwiftDB4]

Not sure just changing speedo gears solves the problem. A 336 box from an S2 has very different gearing than a 365 box from a TC Special.

[Bryan Boyle]

Not sure just changing speedo gears solves the problem. A 336 box from an S2 has very different gearing than a 365 box from a TC Special.

Not to mention the driving gear is matched to the driven gear.  I am thinking that someone on the circuit may have an S2 speedo kicking around.

[Benjy]

Thanks for the replies.

The serial number on this speedo is SN5226/21 and the revs are marked '620' it is in KMH. According to the GG Lotus page it should be a SN5226/12 for the S2 and a SN5226/23S for the Special.

No amount of searching can identify what car this speedo I have is actually from! Oh no, I've gone down a speedo rabbit hole now....!

Can anyone tell me what revs are marked on a SN5226/12 in KMH (S2) please?

Thanks

Benjy

[Benjy]

As I reach ever deeper into the speedo rabbit hole I came across this brilliant write up about magnetic speedometers and odometers. Very helpful indeed.

https://vintagetriumphregister.org/maintain/instruments/speedo_repair_2017.pdf

Cheers

[Benjy]

And here's a further suggestion: Correction gearboxes.

https://www.speedograph-richfield.com/shop/corrector-gearboxes