Ever since I wired up a very nice period Smiths RVI 8k tacho in my 850, the ignition has been crap. The car has been impossible to start and has run like a chaff cutter with a hairy goat stuck inside. Strangely enough, the tacho itself was working beautifully, with a stable needle and as accurate as a modern VDO unit that I borrowed out of my race car.

Now these old Smiths tachos use the ignition coil to distributor circuit to provide the impulse signal for the tacho. However you end up with a very long ignition LT wire, often with several connections to pass through the firewall etc. Too many points of failure for the ignition system and plenty of room for gremlins to creep in...

Having disconnected the tacho on Friday night and restored the original coil to distributor wire the car is running perfectly again (still on good old points, albeit 32 ounce S points) I took it for a good run up a steep hill and it was pulling like a train. So, how to get the RVI tacho to work, and still have a functioning ignition?

I found a tip on the Mk 1 Forum and thought it was worth a try. Leave the normal coil to distributor wire in place and wire the tacho impulse circuit in parallel. I was sceptical, but it is working perfectly. The tacho is happy and I have a good solid ignition!

Yep...can cause problems...and with Electronic Ignition, you could try this...

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"Show me the Mini!"

Yep, I have used the Spiyda modification in the race car and it works beautifully. Great mod and relatively easy to do.

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1970 Cooper S ex-Bathurst & ATCC
1964 Austin Cooper S ex-Group C race car
1967 Morris Cooper S ex-Group B
1962 Mini Speed sports sedan
1968-71 ex-Peter Manton Shell car

I might have to try this, I replaced my coil when i wired in my RVI tacho and i have not had any issues yet.

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http://www.flickr.com/by_dan
Current: 1970 Mini K 2014 Focus ST
Past: 93 Rover, 64 850, 97 Rover, 66 Deluxe, 66 Moke
81 Austin Estate, 2006 R53MCS, 66 Deluxe, 1978 Clubbie
2014 Land Rover Defender 90

As the RVI is a current sensing circuit you can pick it up in a number of places.
The MGB is in series off the key as an example. No long wires to go wrong.

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1960 Morris Mini Minor

Interesting comments here.
I have also researched the Spiyda external module as an option if my problems are ongoing, and in case I ever fit any kind of electronic ignition module, as that will almost certainly cause the RVI tacho to play up from all accounts.

The external Spiyda module allows you to keep the RVI tacho original if it is working fine (as mine is so far). The internal Spiyda modification is a great option, but means you have to open up the Smiths tacho which is a bit fiddly. You can pay someone to do the conversion, but I suspect it would become costly...

I had my RVI converted by Gauge Works ([url]gaugeworks.com.au[/url]) here in Adelaide, the guy there has an internal board of his own design. From memory it cost around $180 including checking/servicing, and they reused the original rolled on bezel without damaging it.

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*witty signature*

Sapphire Blue Deluxe spread across three parts cars, two sheds and a driveway...

Just bearing in mind that your maybe 40-50+ year old RV1's components could still be prone to failure...so, for some, just buying a newer instrument might be an easier path to take...

Further electronic component reliability reading here

https://users.ece.cmu.edu/~koopman/des_ ... lectrical/

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"Show me the Mini!"

I agree. The new one has a stepping motor so works smoothly on points or electronic.
I still restore some and have made my own horseshoe circuit as a direct replacement for the original.

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1960 Morris Mini Minor