Perkins 4-108 tach problem

[Tim Smale]

I have a Perkins 4-108 in my CD 36 with a tachometer problem. A few years ago it began working intermittingly, then suddenly stopped working altogether. I am unable to locate the schematic in my parts manual for the engine, and tried to trace any electrical problems using a multimeter. I thought I solved the problem when I traced the sending signal wire back to the alternator, and found that it was not hooked up, thinking that the alternator sends an electrical signal to the tach (using Nigel Calder's book as a reference). Since I had changed the original alternator out to a high output alternator, I though that I had left out an inportant connection to the tach. But then I realized that the tach quit working before I changed alternators, so this may not be the problem. Any suggestions anyone may have would be most appreciated before I give up on my attempted cruising mentality of fixing everything myself before I call a mechanic in.



tim@iga.org

[Jeff Barnes]

Tim:

I experienced a similar problem with my 4-108 on Jazman (CD-36 #68). The following, I inatalled a new alternator (Balmar), voltage regulator (Heart), and tachometer. In addition, I fabricated a new wiring harness from the engine compartment to the instrument panel in the cockpit. Assuming you are using the original harness you may want to run a new dedicated tachometer wire from the appropriate terminal on the alternator to the tachometer. Mine harness was in misearble condition and I'm sure causing some problems. Second, and somewhat obvious) is to make sure your tach is not faulty. There are plenty of direct replacements (Telex I think makes one that will fit the same hole and has a 0-3500 range. The new tach, if you replace it, will just have to be adjusted to match the number of poles on your new alternator.

Let me know if you need more help.

Jeff



jbarnes@oxbio.com

[Ken Coit]

According to the diagram I have, the tach should have a black wire connected to the ground terminal (0 Volts always), a purple wire connected to the ignition terminal and lamp(+12v when key switch is on), and a gray wire from the alternator connected to the S (sender?) terminal. If you would like a copy of the diagram, I can scan it and email it to you.

Ken Coit
S/V Parfait
Raleigh, NC

I have a Perkins 4-108 in my CD 36 with a tachometer problem. A few years ago it began working intermittingly, then suddenly stopped working altogether. I am unable to locate the schematic in my parts manual for the engine, and tried to trace any electrical problems using a multimeter. I thought I solved the problem when I traced the sending signal wire back to the alternator, and found that it was not hooked up, thinking that the alternator sends an electrical signal to the tach (using Nigel Calder's book as a reference). Since I had changed the original alternator out to a high output alternator, I though that I had left out an inportant connection to the tach. But then I realized that the tach quit working before I changed alternators, so this may not be the problem. Any suggestions anyone may have would be most appreciated before I give up on my attempted cruising mentality of fixing everything myself before I call a mechanic in.

parfait@nc.rr.com