Missing something?

[Ganzdachhaus]

Took my tachometer out today to see if I could figure out why it's not working.
Am I correct? Is it missing a small but critical piece?

Rev Counter missing iron core?

[Craven]

https://img1.wsimg.com/blobby/go/1975f8 ... 6555388667

[Ganzdachhaus]

Oddly, that version of the Gentleman's Guide is missing the same thing.

There's an update to it that has an Appendix C. that includes details + a pattern on making a replacement for the missing bit.

[Quart Meg Miles]

Page 7 of Craven's link shows your Iron Core is internal and just a double prong of metal sticking out. I can't see from your photo if you have that. My own RV1 (gen 1) seems to have another U shaped piece of metal over the top but the picture on page 7 looks similar to your wiring.

Two questions:
1] Is your car still Positive earth?
2] Are you still using original contact breaker ignition (not electronic ignition)?

If the answer to both is yes then your tachometer would seem to be broken or has lost its power or earth connection;

If 1] is NO then the tachometer may not have been changed over (not difficult to fix if you or a friend have some electrical knowledge);

If 2] is NO then you need to read the posts on this forum to advise the source of a conversion to RVV type, or convert the car back to standard ignition.

[Craven]

OK This is the missing piece, although in this pic the plastic block required is not shown.

Smiths_Tach_Pick-up_Loop.jpg (62.87 KiB) Viewed 845 times

[Andy8421]

Craven is quite right.

That crappy bit of bent metal is in fact one half of the core of a pulse transformer. The other half is inside the rev counter. If it is missing, the rev counter won't work.

I have never understood why Smiths used this method, voltage sensing is far easier. My only guess is that this allowed the rev counter to be fitted to cars where a rev counter was optional, and required no changing to the wiring loom.

[Ganzdachhaus]

As Craven & Andy say, that was the missing piece.

I probably should have mentioned. This is on a car that was nearly completely restored, but then never finished up before I got it. The result is that it has a few odds and ends that need attention. Currently going though the car bit by bit to find everything.

In case useful to anyone else, Rev 2. of the Gentleman's Guide to Smiths Tachomenters (https://www.triumphclub.co.nz/wp-conten ... ters-1.pdf) has details on cobbling up a replacement bit.

I was a bit ambitious this morning & decided to give this a go. Not being much of a EE, I don't have any old transformers hanging around & seems that all the thin sheet I have in the workshop is aluminum.
One thought was to use the lid from the canned tomatoes from last night's dinner, but after cutting a suitable piece, I decided that modern cans are a little too optimized when it comes to minimizing material usage. I did happen to have a pile of cheap USB memory sticks on my desk, all of varying grades of functioning (promo things we bought in bulk years ago to give to customers). Some quick measurements showed the outside bit of the plug on it to be fairly close to what's needed. Only took 4-5 tries and I found one that was dead. A few minutes of pliers, snips, and small drill bits later & I had something that was close enough.
Sorry, no pictures of the replacement bit. It's kinda ugly (but works). Someday I'll get around to making one that's nice enough to take a photo of.

Another note that might be useful to someone. The steering column was just enough in the way to prevent me from getting the tach out. Removing the platic cover for the blinker stalk did nothing to help. Seems that the usual advice is to remove the column, however I was able to get enough room by just loosening up the two clamps that run along the column & could just leave it in place. A bit easier I think.