took my 69 series 2 ots in for tuneup. also overhauled the 3 su’s that i installed 40 yrs ago.
now my tach is very bouncy.
bouncy at idle and even while accelerating. at 2000rpm it will jump to 3000rpm than back to 2000rpm.
i understand that the tach is electrical and has a resistor. could it be a faulty resistor as tach was fine before tuneup.
note: series 1 and 2 have different tach set ups.
any help greatly appreciated.
ed
check connections to distributor. Mechanic may have loosened some connections.
dave collins
thanks. will do that. could the ballaster connected to the coil be the issue?
The Series 2 used an inductive tachometer, model RVI, in which the power for the ignition passed through the tachometer to the ignition coil. The tach was isolated from that voltage and used a pickup coil to read the current pulses in the wire. It used a rather simple circuit inside the tach to read those pulses and convert them to a voltage for the meter movement. It worked just fine if the original ignition system was used, but any variation in dwell or current would confuse the circuit and make the readings unreliable.
What was changed during the tune-up? Did he install a new coil, or an electronic ignition? Were any other changes made? You might want to check the dwell or points gap yourself to be sure it is correct. It is unlikely that your tach chose this particular moment to coincidentally go bad, but even when new they were finicky about the signal they expected to see. At 50+ years old the tach could be a lot more finicky now.
There’s an electrolytic capacitor in there that goes bad. If you can use a soldering iron, take it apart and replace the capacitor. That usually fixes it.
thank you everyone for your replies.
service included:
points, plugs
rebuild 3 su carbs
oil and filter
no new electronics or coil.
possibly a loose wire on or in distributor?
where is the capacitor located?
If you’re running points, he must have replaced the condenser in the distributor. Some of the new condensers on the market are dicey. I’d go back the the mechanic and ask the question.
idle now is smooth no surging. i have a video(15 sec) but cant upload it. can i send it to someone to upload here?
You could upload your video to Youtube and then post the link to it here
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ive never uploaded anything to Youtube.
will look into it.
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Old post, but I recently had the ignition system upgraded to electronic on my 69 S2, and now my tach bounces all over the place. Seems OK at low RPM, but as you get to 3,000 it varies wildly +/- 500 to 1,000 RPM. Engine runs smoothly.
I’m thinking that if the solid state points have some resistance, the current in the ignition line would be reduced, potentially giving a weak signal to the tach. My plan is to wire a 6 Ohm resistor in parallel with the ballast resistor, so instead of the 1.3 Ohm, it would drop to 1.1 Ohm. If I add a second 6 Ohm, also in parallel, it would drop to 0.9 Ohm.
I don’t know the resistance of the solid state points, but assuming the mechanical points were zero Ohms, and assuming the coil primary is 1.3 Ohms, dropping the ballast resistance from 1.3 to 1.1 to 0.9 Ohms would increase current from 4.4A to 4.9A to 5.3A.
Has anyone tried this?
Also, NiSonger says on their website they can rebuild the tach, but elsewhere says the instrument repair shop was closed following Hurricane Ida several years ago. Don’t know if it ever re-opened.
My understanding is that Nisonger are no longer in the business of refurbishing Smiths instruments. Search the archives for other suggestions - there are several companies who get good reviews from members here. As for your proposal to add resistors in the ignition feed line, I don’t know whether it will work, but it seems to me that you run the risk of affecting the primary function of that line, namely powering the ignition circuit. The problem is with the tach which simply monitors the current waveform in the ignition line, so changing the current waveform to suit the tach seems like putting the cart before the horse to me… A search of the archives will yield suggestions on who can modify the tach to operate reliably with an electronic ignition system.
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Hi Art,
See my message above from Sep 2022. You should check the specs of your new solid state ignition system and see how much current it will allow. That said, increasing the current will not necessarily help solve your problem. Nisonger does not do any repairs any more but I have an upgrade for the RVI tachs that allows them to work with electronic ignitions.
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Nissonger only sells new now.
You can always use the Spyda conversion, which ditches the entire RVI circuit in the tach and replaces it with an RVC board. I did this last year when my tach bit the dust:
Mike,
I did see your message above, that’s why I thought the reduced resistance would generate a stronger voltage blip in the tach coil. However it looks like there are several electronic conversion kits out there. Where do I get more information on yours? I see lots of clock related content on your website, but nothing on the tach upgrade. I feel comfortable taking the tach apart (bigger deal is getting it out of the car - do I need to remove the top of the dash?), so if this is a DIY kit, that works. Or, do I send it to you?
Thanks,
I do not know what signal the S2 tach reads, But I question if change in amps is the issue. You seem to be implying your electronic ignition reduces the amps, which one might assumes reduces the spark output. Not what some would consider an upgrade. Many modern electronic ignitions improve ignition by using lower resistant coils and then manipulate the dwell. I wonder if the problem is the tach is designed to receive the dwell of a points system but is receiving the manipulated dwell of the electronic system?
Maybe someone here has examined this situation and has some answers?
Tom
My understanding (as a newbie - might be wrong), is that the S2 uses an inductive tach. I have a screengrab from a clocks4classics video that I think shows the internals. As you can see, the white wire, which runs from your ignition, through the tach, and on to the primary side of the spark coil, runs through this coil inside the tach. So every time there is a blip of current, it will generate a voltage spike on this coil.
Admittedly, my first thought was that if there is less current, there is a smaller blip in the voltage, and so the tach could be mis-reading, and a higher blip would fix that. However I did not think about the aspect of dwell. Energy to charge the capacitor can come from normal current with a normal dwell, it can also come from lower current with a longer dwell, or even a higher current with a shorter dwell. The sensing circuit in the tach is likely tuned to a certain expectation of waveform, so my idea of increasing the current is likely not helpful.
Since I started this query, it has come to my attention that several companies make solid state circuit boards that replace the internal electronics, Mike Eck’s (above) among them. So I think it prudent to go with his tried and true solution, rather than trying to rig something on my own that might damage the coil (or burn my car to the ground).
