S1 tach generators and tach

I am working on a 67 S1 4.2 which belonged to the late Andy Leavitt. Some of you may recall a “work day” we held 7 or so years ago when Andy was still with us. The car has sat for a while, and now Karen Leavitt
is retiring and wants to become active in club events with her 4.2. Lloyd came up to Morgan Hill to help get the brakes sorted out. The carbs had a peculiar bluish lacquer which had glued the needle to the jet and the jet to the bushing. With Ray’s support, we got the engine running yesterday (after replacing the gasoline). I discovered the tach wasn’t working yesterday and have done no further trouble shooting but that there was no output at all when I tried to measure voltage with the engine at 1000 rpm. I had planned to remove it and see if I had a broken drive dog. I decided to confirm whether MoMa was still in business since Margaret passed away a number of years ago. Joe, who worked for Margaret many years ago now owns the company. We discussed the S1 tach situation and that’s what I wanted to share: He says IF it is a failed Tach generator, the best solution is a new generator for $250. The cheapest solution for a failed tach generator is to rebuild for $125, but here’s where it gets sticky: If you rebuild the gen and then discover the tach dash unit is bad, it will be $175 more to rebuild that. Both of these prices assume they are rebuildable. Meanwhile,he charges $275 to convert an S1 tach to electronic. You mail him the instrument, and they convert it, even if the tach is failed. You leave the tach gen in place. He also offered to test both units before we did anything. Their tel no is 505-766-6661. I have no affiliation with Mo-Ma except that for many years I had a lot of affection for Margaret who helped me and other hobbyists. I also appreciated the way she took on the company which incorrectly manufactured speedo cables, She was told she shouldn’t complain about failed speedos because it was good for business! She was furious! Mike Moore

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Very easy to test the tach: Get an AC transformer like what is used for Lionel trains and attach the tach leads to the transformer. Turn the handle of the transformer and watch the tach needle go…or not. The workshop manual tells you how many volts / 1000 rpm it takes to move the needle.

Good tip Jack, Thanks, that is clever. We’ve decided to just send it in and have it converted to an electronic tach and be done with it. Although if I test the tach as you suggest and then discover the drive dog has failed…I may have to rethink this,
Best, Mike

Most of the time the tach shaft that connect to the camshaft has moved away from it’s placeand disengaes. . The was a disscussion here so it is somewhere in the archives. I took mine off and pushed everything in it’s place and used some high heat epoxy to hold things in place. Someone else used a screw tapped into the case.

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Here what mine looked like. If I remember correctly, I just pushed the shaft into the housing and put the big washer behind it, then I used some high heat epoxy to keep it from moving. I had to repair some wiring but that was a few years ago. I believe it was Erica who used the tapped screw method but I couldn’t find it in the archives and couldn’t figure out how to search the OLD Site.

PS I think testing the tach output with the motor running is the first thing to do. If it produces any voltage then it is working , if not, it is probably not engaged.

Of course I mean test the tach generator.

I have just converted a XJ6 cam to take a Generator , I did notice the drive dog C25426 , was very worn , a few more thousand miles and the drive would have been lost !

I will check the dog on her car. I had checked for voltage with engine at fast idle with no results. If I find a bad dog. I’ll stick one of my spares in it and see if it works. If not I’ll check the push-back problem. It will be hard to kustify sending that much money to fix something not broken,
Thanks for all the info.
Best, MIke Moore

Michael,

You don’t really need an AC supply to test the Rev Counter. Simply connect a 12 volt + and - into the disconnected tach. generator leads and the gauge should read 2400 RPM. Polarity doesn’t matter.

Art

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Thanks Art. Good tip!
Mike Moore

Works well…and no need for a signal generator. Brilliant

I have 3 tack generatos that do not work. Anybody knows who can rebuild them?

Are they not working because the shaft bushing has been pushed in? That is overwhelmingly the most common failure point. It’s a terrible design flaw. Anyone can fix this themselves. There are a bunch of existing threads about it.

I recently replaced the tach generator, Drive dog and snap ring on mine. When removing the generator someone had placed a penny behind the dog to raise it and I suppose to keep the dog from disengaging with the generator. Took me a while and some research to figure out why they did that.

Question? I didn’t realize you could rebuild these. Mine has a broken Bakelite and wire. How does one take these generators apart to rebuild?

Ted, at some point in time, the tach gen really should be replaced and not rebuilt. I diddled with mine a few years ago as the bushing had slipped as Erica has mentioned and her advice was fantastic in sorting the issue. It performed well afterwards, or so it seemed at the time. As several members pointed out later as I was discussing engine RPM and speedometer reading, it became obvious that the output was much lower than it should be. Simply the magnets getting weaker over time. I could have done serious damage if I had continued to believe the tach readings based on the weak output.

Are you able to find a replacement cap either new or scavenged? Alternatively you might be able to epoxy it if you have the segments. Has the wire fallen down inside? The way to dissemble is to tap back the 3 swaged marks holding the rear cap pn, then remove the circlip, and place it on a spread out vice upside down so the rear cap faces down, and the mounting ears are sitting on the jaws. Just tap the rotor drive dog lightly until it pops the cap off. Cup your hand under so it doesn’t fall to the ground and break.

Do the bushing pinning as Larry mentions so it doesn’t ever get pushed backward.