RVI Tachometer Conversion

[billwill]

I'm just fitting a Spiyda Design kit and managed to mangle the two face screws (they where very tight) just wondering if anyone knows what size they are or where i could get two new ones?

They are probably tiny BA threads.

Personally I would take it into a local clock repairers and see if they have suitable screws.

[Grizzly]

Its all sorted now, i thought it would be more of an issue but i nipped into this model place just round the corner from me and they had some https://maccmodels.co.uk/ unfortunately i didn't see the size as he vanished into the back and reappeared a few moments later with them.

So just got to paint them Black now.

[Grizzly]

Well just finished fitting the Spiyda Design kit and it was very easy to do. Two things that where a bit of a Pita, removing the Bezel and removing the two face screws but i cheated slightly with the bezel as i was having no joy trying to get it off without marking it (Bought a new one and just bent the tabs back to get it off) if i was doing another one i'd buy a brand new screw driver to remove the face screws and clean the slot in the screw head well before trying to move them but as i found the screws are obtainable from Model engineering supply shops.

Another thing i found was when calibrating the Tach use a computer with a healthy head phone volume, i tried with an old laptop and it did work but the better volume the more accurate it seems to calibrate and as Spiyda say it makes life so much easier if you play the 100 and 200hz in a loop.

After adding a fresh Neg wire from the coil to the tach high voltage sensor it works great on the Accuspark ignition that's on at the moment.

I'm really happy with it, the Tach operates nice and smooth now with no judders. I would recommend the kit to anyone with tach issues.

Bit of an update, I had some issues with the Tacho jumping on start up which turned out to be the wrong watt bulb in the Ignition tell tail. I noticed the tell tail would be lit whilst the tacho was playing up (also the Alt wasn't producing any output) so i fitted the correct 5w bulb and all works fine.

[collins_dan]

Just order the spiyda kit. I have been running Petronix for about 15 years powered from fuse box and tach has been accurate, but a bit bouncy on shift. Recently, I have noticed it bouncing a lot more under hard acceleration, but still solid under lighter acceleration and when cruising or idling. I think after 50 years components must just be worn out. From another post, I see that Greg had the same issue. Wish me luck. One question that I am unclear on from his videos. Are you able to maintain all the old ground, power and signal connections? Thank, Dan

[mbell]

You need to connect the coil power feed together to supply the coil power of they are the plug in kind and then add a sense wire between the coil and the tacho.

[collins_dan]

I found another post which had this picture and write-up.

The green wire (and if you had only one green wire, you couldn't connect the wrong one) is supposed to power the RVC tach just as it powered the RVI tach. I don't agree with the instructions provided with your RVC tach. I believe the green wire (not the green one that goes from the ignition switch to the ignition light which should be white) should be connected where is says "To Ignition switch". The RVC tach should be grounded with the same black wire that grounded the RVI tach. The two white wires that used to form a loop inside the old RVI tach should be connected together and here is the most important part. An additional wire (pick a new color, mine is orange) should go from the new RVC tach where is says "To negative side of coil" to you got it.......the negative side of the coil.

I haven't received the spiyda kit yet, so not entirely sure what the back of the tach will look like after the modification. I am guessing that the original connection power (green) and loop (white and white-green) goes away and there are just two connection to ignition (green) and to coil negative (add new).

If anyone had a picture of the back of tach after spiyda conversion, I would love to see it. Thanks, Dan

[mbell]

I don't seem to have a picture afterwards but your description sounds right. The Tacho supply, ground connections stay the same, the white wires from ignition switch and to the coil get joined (outside). Then you add a wire/connection(s) for the new sense wire out of the casing.

The Spiydia has different number of inputs for different setups so you may want to bring more that one connection out. I am driving mine with low voltge signal from a electronic rev limiter at the minute.

[collins_dan]

Interesting. Which rev limiter are you using? I have petronix and there are plenty of left over wires. I’ll need to check which is low voltage signal. Thanks, Dan
PS. I can see the pic, that’s weird.

[mbell]

I have the petronix rev limiter. Using that to "drive" the tacho:
- Allows me to avoid running the sense wire as rev limiter has it own wire to coil
- Means the tacho stays max'd out when I hit the rev limiter.

I am a bit on the fence about the whole setup, the conversion was easy enough but in the end had to calibrate it on the car using a secondary tacho. The calibation is pick a rev point you want to it be accurate at. As then will likely under read at one end and over read at the other end of the range.

I doubt the original setup is particularly accurate across the whole rev range but I do wonder if it would be more accurate or not. Also driving it from the coil instead may be more accurate across the rev range.

[collins_dan]

Makes sense. I hope I can calibrate OK myself, as I don't have another tach and getting it in and out is no fun. Do you recall which color the sensing wire is that you are using? Thanks, Dan

[mbell]

I believe I use the white wire from the rev limiter to the tacho. My memory is the spyidia was four inputs, one very low voltage used to calibrate via audio output, a ~12v input, then two for connecting to the coil. Think i have all four coming out the tacho but use the ~12V connection.

I bought a $10 mower/boat tacho from amazon and then re-calibrated it in the car with the tacho removed from the dash. The amazon tacho is battery powered and pickup is just by wrapping its sense lead around the coil HT lead so very easy.

[collins_dan]

Just checked Petronix rev limiter instructions and white is right. Right now it is connected to positive side of the coil? I’ll disconnect and connect to new sensing wire. Do you think I damaged the rev limiter by having it connected to the coil positive? Thanks for your help with this. Dan

[mbell]

No idea if it could have damaged it. I'd hope/expect it's robust enough to cope but friends in the circuit used which I don't know.

[collins_dan]

I know exactly what I did, just checked the archives, connected the white from the tach to the white on the rev limiter and no go. So connected both to the coil positive and car started. I guess that means the rev limiter has not been doing anything, since it’s getting no signal from the coil positive. Argh. Oh well. Dan