MGB Tacho (Rev counter)

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Andrew Robson
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MGB Tacho (Rev counter)

Post by Andrew Robson » Fri Jan 04, 2019 2:21 pm

I have a 1968 BGT which is currently fitted with the original RVI tacho. I am thinking of installing a fully electronic distributor, but have read in several journals that the RVI tacho will not work with electronic distributors, and that the later RVC tacho is required. Can anyone please advise on that? BTW, the dissy would be the programmable 123 type as the engine has undergone various enhancements and I want to make sure that I use the most appropriate advance curve. Thanks in advance. Andy Robson.

Ian Fozzard
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Re: MGB Tacho (Rev counter)

Post by Ian Fozzard » Fri Jan 04, 2019 3:51 pm

Hi Andy. Can't help directly with your query, but I would have thought the manufacturer or retailer of the 123 distributor would be the place to get definitive advice? Quite a few of these must have been fitted to MGs I guess,

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

Robert Dickinson
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Re: MGB Tacho (Rev counter)

Post by Robert Dickinson » Fri Jan 04, 2019 4:40 pm

Don't know about the 124 dizzy but I'm running a 68 BGT with RVI tachometer and is fitted with Luminition Optronic ignition and all seems ok. The distributor has had the curve altered to suit the cam I'm using. Not sure if this helps.
Rob.

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Peter Cresswell
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Re: MGB Tacho (Rev counter)

Post by Peter Cresswell » Fri Jan 04, 2019 8:24 pm

Hi Andy
To start, after you have selected your distributor, I would contact the manufacturer to see if the 'electronics' are compatible with the RVI type tacho. I know the Aldon Ignitor type which uses a Hall effect pick up is not compatible, and here (https://www.123ignitionshop.com/faqs123 Ignitions - and under 'Technical Question, click on No.9 for tachos) you will see they suggest it isn't!

The cheapest way to change the tacho is to get a secondhand one and with the MG/Triumph show coming up you should find some there for £60 - £80. Alternatively you can get the RVI type modified by either JDO Instruments (See http://www.jdo1.com/) who are recommended by 123 Ignition or Speedy Cables (See https://speedycables.com/instruments/ga ... nversions/) but the cost of doing this is nearly the same as buying a new RVC instrument.
Pete
1969 MGB Roadster
2011 MG 6 TSE Magnette
2007 Mercedes SLK
Plus 32 other cars since 1965

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John Watson
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Re: MGB Tacho (Rev counter)

Post by John Watson » Sat Jan 05, 2019 3:09 pm

I run the Aldon igniter electronic system and my standard revcounter works fine, it’s on a 1964 B with positive earth
Hope this helps
John
John Watson
1964 MGB Roadster Mk1
2018 MG ZS Exclusive 1ltr Auto

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Peter Cresswell
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Re: MGB Tacho (Rev counter)

Post by Peter Cresswell » Sun Jan 06, 2019 10:42 am

Hi John,
Very strange, but Aldon's instruction leaflet does say the Tacho might not work correctly. If it doesn't it tends to swing about a lot and under read. I do know someone else though with an early car which is positive earth and has an Ignitor and that also works ok as well. I have an Aldon Ignitor and tried it but the Tacho doesn't work correctly - Mk2 car, so negative earth, so now I have a new Aldon distributor matched to the cam and with points, as the main advantage of the Ignitor seems to be it is tolerant of wear in the distributor. Car now starts almost immediately.
Pete
1969 MGB Roadster
2011 MG 6 TSE Magnette
2007 Mercedes SLK
Plus 32 other cars since 1965

Chris Bound
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Re: MGB Tacho (Rev counter)

Post by Chris Bound » Mon Feb 04, 2019 9:32 pm

Another company to consider is Speedograph Richfield of Nottingham. I've just had my 1977 (RVC) Tacho converted by them to operate correctly with the V8 engine which will soon sit under my bonnet. They charged just £55 plus postage and VAT, which I thought was reasonable. They did the job and had the unit back to me within a week.
I understand that the internal circuits of the RVI and RVC tachos are quite different. As you probably already know, on the RVI type, the white cable isn't actually connected into the unit but just loops around a sensor. The RVC type has a bullet connector on the back and the cable from the coil is actually connected to the internal circuits.
There is also a company called Spiyda which can supply everything you need to convert your existing unit. It's worth getting in touch with them.
http://www.spiyda.com/tachometer-electronics.html
Chris

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Re: MGB Tacho (Rev counter)

Post by David M B Leggeat » Wed Feb 06, 2019 2:27 pm

Andrew,
I have had a 123 electronic distributor fitted to my 1972 MGB for about 10 years.
I have not had problems with my tachometer type RV1 2430/00, negative earth.
Regards,
David.
MGB Roadster 1972
MGC GT 1968

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Paul Hollingworth
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Re: MGB Tacho (Rev counter)

Post by Paul Hollingworth » Sun Mar 31, 2019 1:05 pm

We have fitted the 123 distributor set to program 2 to Andy's GT and the rev counter works fine.
1971 MGB roadster & 2006 MGTF

JohnH
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Re: MGB Tacho (Rev counter)

Post by JohnH » Wed Apr 03, 2019 3:09 pm

I obtained a RV1 to RVC conversion kit and circuit board from https://www.spiyda.com/tachometer-electronics.html and fitted it out using their instructions. Suits any amount of cylinders. You just need one extra wire from the coil for the signal to update the car. Works with my basic Luminition Magnatron (ie hall effect -rotating magnets) which incidentally also works well with the fantastic Aldon Amythyst programmable mapping unit (you need a laptop to enter the values - they do supply many maps for the MGB too and you can compare maps stored in the unit from your dashboard!)
Chris is the man at Spiyda for RVC queries.

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