Sun Tach dwell meter help

[gotzskillz]

Hey everyone,
I've got a couple of Sun TDT-12 Tach Dwell meters and was wondering if anyone had a manual and/or could give me some information on calibration and used of them?

Thanks

 

[Bruce Rossiter]

To calibrate it, turn the top left side selector to dwell, connect the 2 test leads together, and adjust the dwell calibrator knob until the needle reads on the bat set line on the right side of the scale.

Once its calibrated, select the RPM range you want to use, select the number of cylinders in the engine, connect the red lead to the distributor terminal of the ignition coil, and the black terminal to a good ground and start the engine.

 

[Bruce Rossiter]

Oops, I almost forgot. Zero the meter before you turn anything on. the small dial at the bottom of the gauge is used to zero the meter.

 

[Mintgrun]

I recently acquired a Sun 404 distributor tester and I am having trouble with the dwell meter. I have followed the instructions in post number two above, which is the same as the directions in the manual, but the reading I am getting is around eight degrees lower than when I set the points on the engine, using the Innova timing light/dwell meter.

Today I connected an Actron dwell meter (also on the engine) and got the same reading as the Innova, which was sixty degrees. This suggests to me that it is the Sun machine which is in need of calibration. (that same gap reads as ~52 degrees on the Sun).

My understanding of electricity is limited, but I believe a dwell meter is essentially measuring resistance. I can imagine there are places within that circuit where excessive resistance could occur. I am hoping there is an internal method of calibrating the meter, which then allows the external knob to properly do its job (as in post #2).

I may be prematurely posting this question, but I am feeling like I could use some assistance. I will go and see if the Actron meter can be used WITH the Sun machine, to confirm that the readings do indeed differ. There is resistance in the 'active' ignition system, when the test is being done on the running engine, compared to the 'simplified' equation of having the bare distributor in the Sun machine; but the basic measurement of degrees that the points stay closed should stay the same and NOT require readjustment once it is back on the engine.

Any help with this puzzle will be much appreciated.
Tom

edit: I connected the Actron (cheapo) dwell meter to the distributor, in the sun machine, and found that it still reads approximately 60 degrees, with the Sun reading around 51 degrees. The tach on the actron reads less than the tach on the Sun, fwiw.

 

[Milton Shaw]

The dwell meter measures the time the points are open versus time they are closed. Not resistance. As a distributor cam wears the dwell per cylinder can be different and so the adjustment is on the average dwell of all cylinders. A scope will show the wear of the cam as the dwell marks do not line up on the screen. A scope will also show if the shaft is bent and causing dwell to change for each cylinder. As the point wear block wears the dwell is going to change and that is why everything since 1970's has had electronic ignition that keeps the dwell the same and does not start changing the minute the points start wearing.

 

[Mintgrun]

I do realize the function of the dwell meter, but was merely guessing as to how it arrived at the reading (resistance).

I recently purchased the Sun machine, so that I can recurve the distributor in my 1976 BMW 2002. I have a Pertronix unit, which I'd installed, but then took back out; because I want to 'fuss' with points. I had been plotting the curve and making some changes to the distributor using an Innova 5568 light/dwell meter, but doing all that over a running engine gets tiresome.

The Sun machine had a very weak strobe when I got it, but a capacitor kit fixed that problem. I am simply recognizing that it is in need of recalibration and looking for some guidance. I suspect I will be turning one or two of the dashpots in the photo below (I have not figured out how to bring them up into the text).

I also realize the reason(s) they eliminated points, but that is beside the point. They now make fully electronic distributors to fit the M10 engine, which you can program using your smart phone. You can create and store custom curves, which even make use of a vacuum signal. You can then switch between them using your phone. The "123 Ignition" is Super Cool, but not my kind of fun.

I was in the archives of a Chevy forum earlier, looking for an answer and a member said "I finally sold my Sun machine, when I realized I was spending more time working on it, than I was my car."

 

[Mintgrun]

In the case of the Sun's dwell meter, it is also used to measure resistance within the distributor, fwiw.

 

[Mintgrun]

Okay, I contacted Mark, at Paramount Distributor Company and he got right back to me with the calibration instructions. I purchased the capacitor kit from him and have been thoroughly impressed with his service. I may need to send these gauges to him and pay him to do it, because the instructions involve special-tools. I am a bit of a 'do it myselfer', so it is hard to give up just yet. I will come back to this thread with 'the fix' even though the guy that started it only made the one post (ever) and the person who replied only made those two... I doubt they are going to care, but it is still fun to share. Thank you for your input, Milton Shaw.
Tom

 

[Mintgrun]

Well, calibrating the dwell meter was even easier than I had hoped. I followed the instructions and when I was done, the meter read exactly 60 degrees; just like the new Innova meter.

I shared my success with Mark and told him I was a bit stumped about what to use as a 'standard' when calibrating the tachometer and he came through for me again, as he suggested buying this http://www.ebay.com/itm/140666635376?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT which I did and it will be in the mailbox this week. I think it will be a fun tool at the lathe as well.

As much as I love vintage tools, I do appreciate some of what modern technology has to offer. It is nice when the two can compliment each other.

 

[Mintgrun]

Just a quick update.

I calibrated the Sun's tach, using an Actron meter.
The Sun read 900 rpm, while the Actron said 800.

I will check it again with the laser tach, but my guess is that it will not need to be adjusted again. The calibration is very easy, using the outside adjuster on the potentiometer to do the lower (0-1000) range and the inside for the upper range.

I love the way they allow for adjustment; as opposed to the new Innova unit... which simply may never need it, due to modern technology(?)

 

[Tim66]

Resurrecting an old thread to ask if anyone has a wiring diagram of the Sun Distributor machine.

Tim

 

[convx4]

Tim66 Page 29 has a wiring diagram. Don't know if is the one you need. https://www.liberatedmanuals.com/TM-9-4910-622-14-and-P.pdf


This link has helped me calibrate my new to me 404. Also got the capacitor kit from Mark, at Paramount Distributor Company. He is very nice in answering questions I had.

 

[Stillgottimefor1]

Love that machine!


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