I've always loved vintage instruments, especially sun tachs. I run a half sweep in my hot rod, and I've been wanting to do a modernized Super tach for a 60's project. The new Sun Super Tach II does have a very similar look and feel to the original piece, but it doesn't have quite the same appeal. The similarities make it an ideal choice for this swap.
Now please note that I had a second original tach in the photos, I did the conversion with two 8k tachs, not the 6k in the picture for reference only. First step is to disassemble both tachs. For the new super tach II it will be a simple matter of removing the plastic chrome bezel and glass by prying it off. Careful it's real glass. Then there are simply two hex head screws in the back to remove the movement from the plastic cup/case. If you do not have an extremely thin wall socket you can drill out the plastic until you can get your socket down there. Most of this stuff is all trash except the movement....
Taking apart the original tach will be a little more involved. Start by removing the chrome bezel, you will find a second bezel more tightly crimped holding the lens assembly together under it.
Now we will have to remove this bezel. It is soft metal, and although you can grind off the crimped edge I chose to work around the edge with tool and pry it apart so we can reassemble it later the same way...
With the assembly apart the movement in the old tach unbolts with three nuts on the back side of the case. Depending on whether or not your tach used a transmitter or not the back may differ. In my case, I have a solid metal cup that will work nicely for this project.
Now the fun begins. Remove the original face from the original movement by removing the two screws on the face. Be careful not to touch the face or loose the screws. To make this work I'm simply putting the original face on the new movement. In this case the 360* sweep lined up perfect, zero and 8 on both faces were in the identical spots. You will notice that the screws that held the original face on the original movement are probably not in the same location as the screws that hold the new face on the new movement. That's ok because you can leave the new face on the new gauge and simply slide the original face over it without even removing the needle. You now have the original face covering the new face on the new movement. Carefully position the face where it needs to be and use a small finger drill or hand drill right through the two holes on the original face, then use the original screws to fasten the face directly to the face underneath it. Make sure the needle will clear the new face across the entire sweep. Now we need to mark the original case where the new movement will meet up to it. Using a drill press I needed to put 4 holes in the case, two that fasten the movement to the case, one in the center for the wires to come out, and one at the bottom for the 4-6-8 cylinder switch to stick through. The original light bulb socket hole allows access to the light bulb mounted in the new movement nicely.
Now we only have to button it up. Mount the new movement with the original face into the original housing, running the wires through the new hole in the back of the case. Make sure the glass will clear the needle and crimp the bezel back around it. Then the chrome ring will pop back into place. The whole tach can now be mounted into the dash or into an original cup and hooked up with the same 4 wire connection as the new donor tach used. You now have a tach that any onlooker would be hard pressed to know isn't totally vintage but has the accuracy and long life of a modern tach.
The tach works flawlessly, the original glass with the rev pointer covers the ugly center of the new needle too.
The Jalopy Journal
