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Old 05-06-2014, 07:45 PM   #1
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Feeling a little incompetent

This question is almost like asking, where do I put the oil? Well here goes. I have a 36 ft gulfstar as some of you already know. We are powered by two perkins 4-154 engines and borg warner velvet drive transmissions. The port side tach no longer works. I should say both port side tachs (helm and flybridge) don't work. Since both tach don't work I feel confident I can rule out the tach itself. Oh, they both read 0. It must be the pick. Where is the pickup? I figured transmission, and found what I thought to be the pickup but find no reference to this in manual. Can anyone help?

Ken
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Old 05-06-2014, 08:09 PM   #2
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Ken,

As I recall, the grey wire on the tachometer is wired to the "R" terminal on the alternator. It senses the AC frequency produced by the alternator and converts it to engine speed on the instrument. You might check that connection on the alternator.

Good Luck,

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Old 05-06-2014, 08:41 PM   #3
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Thanks Larry. Heading back next month. Fixing the tach is one of my projects. I will check the alternator.
Ken
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Old 05-06-2014, 09:03 PM   #4
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iI will be owning a 36 Mark II Gulfstar. I noticed almost all the wiring in my 1976 is solid core wiring with the exception of the various high current battery leads. I spent about 2 hours going over the wiring in the boat yesterday. I would recommend looking at the wires going to the alternators. If your's are solid like mine it's only a matter of time before the wire or connection will fail.
I had planned on a re-wire when I made the offer on this boat.
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Old 05-06-2014, 10:19 PM   #5
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Ken,

As I recall, the grey wire on the tachometer is wired to the "R" terminal on the alternator. It senses the AC frequency produced by the alternator and converts it to engine speed on the instrument. You might check that connection on the alternator.

Good Luck,

Larry
That's how my Perkins 4.236 twins are wired. They come from the alternator.

I find the port side (charges the start battery) doesn't read correctly unless there's a good load on the alternator. As the load drops off, the tach becomes less and less accurate until it finally dies. The stbd tach charges the house and keeps working as long as the load stays up. If one drops off, I tie the batts together with my combiner and RPMs recover. If both drop off, I increase load on the house (i.e., heater, coffee pot, etc) and recover both with the batts tied together.

It's one of my boat's peccadilloes, but I love her.
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Old 05-06-2014, 11:15 PM   #6
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Kinda weird.
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Old 05-07-2014, 12:04 AM   #7
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Kinda weird.
No picture?
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Old 05-07-2014, 12:07 AM   #8
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No picture?
It's not my boat.

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Old 05-07-2014, 06:34 AM   #9
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That's how my Perkins 4.236 twins are wired. They come from the alternator.

I find the port side (charges the start battery) doesn't read correctly unless there's a good load on the alternator. As the load drops off, the tach becomes less and less accurate until it finally dies. The stbd tach charges the house and keeps working as long as the load stays up. If one drops off, I tie the batts together with my combiner and RPMs recover. If both drop off, I increase load on the house (i.e., heater, coffee pot, etc) and recover both with the batts tied together.

It's one of my boat's peccadilloes, but I love her.
You've probably got a voltage drop issue on the tach circuit causing this as it is the AC frequency that sends the message to the tach gauge. Unless you have some massive belt slip issues the alternator load shouldn't affect the tacho reading.
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Old 05-07-2014, 09:51 AM   #10
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that is weird. So if you change the alternator to one with a slightly different pulley the tach is wrong?

I am pretty sure mine picks up off the flywheel or maybe the output shaft itself. i am basing that on the location of the wire.
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Old 05-07-2014, 10:11 AM   #11
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that is weird. So if you change the alternator to one with a slightly different pulley the tach is wrong?
Yes, but there is an adjustment on the back of the tach to calibrate it. Get an optical tach to get a reading off the front pulley and then tweak the analog tach to match the reading.

There will be times when there is no load on the alternator and the tach will not give a reading. The alternator needs to be supplying some load for the tach signal to work.

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Old 05-07-2014, 10:19 AM   #12
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i learn something new here every day.
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Old 05-07-2014, 03:34 PM   #13
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that is weird. So if you change the alternator to one with a slightly different pulley the tach is wrong?

No alt tach is accurate as belt loading will change the running diameter if the pulley. Slip counts as does the belt and pulley temperature.

A tach driven off a mechanical engine output is far more accurate , but so what.

Cruising at 1600, does it really matter if you are really at 1560or 1650?
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Old 05-07-2014, 04:13 PM   #14
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I agree the alternator isn't the best idea but it should be fairly close. Changing the pulley could throw the tach off but by how much? This isn't my area of expertise (if I have one at all). So it might be an interesting comparison if someone changed 1 or 2 alternators and the pulley to see the difference? I might be game on my Gulfstar I am thinking about running a 24vdc BalMar with a smart regulator on one engine. Leaving the other engines 12vdc alternator in place and see what happens?
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Old 05-07-2014, 04:20 PM   #15
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I ordered a pair of Aetna mechanical tach pick-ups for my Perkins 6.354s. I have four tach gauges, none of which matched what the hand-held laser tach showed. I also bought all new grey, marine-grade, tinned wire to run from the new pick-ups. Not cheap, but I'm hoping it'll be well worth the effort.
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Old 05-07-2014, 04:27 PM   #16
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I ordered a pair of Aetna mechanical tach pick-ups for my Perkins 6.354s. I have four tach gauges, none of which matched what the hand-held laser tach showed. I also bought all new grey, marine-grade, tinned wire to run from the new pick-ups. Not cheap, but I'm hoping it'll be well worth the effort.
I will probably do the same on my Gulfstar 4-236 Perkins. I couldn't believe the factory wiring to the alternators was solid core copper. Also the charging wires are woefully undersized. They are #10 from the high current charge terminal. It needs to be more like #1 or #1/0. It will be soon enough. The regulator wiring will be changed as well.
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Old 05-07-2014, 04:43 PM   #17
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I ordered a pair of Aetna mechanical tach pick-ups for my Perkins 6.354s. I have four tach gauges, none of which matched what the hand-held laser tach showed. I also bought all new grey, marine-grade, tinned wire to run from the new pick-ups. Not cheap, but I'm hoping it'll be well worth the effort.
Seems like overkill. It's really simple to tweak the analog tachs to get a correct readout.

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Old 05-08-2014, 06:36 AM   #18
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Seems like overkill. It's really simple to tweak the analog tachs to get a correct readout.


The readout will only be accurate at the same RPM, same alt output and with the same age belt .

But it is usually close enough.
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Old 05-08-2014, 06:48 AM   #19
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I ordered a pair of Aetna mechanical tach pick-ups for my Perkins 6.354s. I have four tach gauges, none of which matched what the hand-held laser tach showed. I also bought all new grey, marine-grade, tinned wire to run from the new pick-ups. Not cheap, but I'm hoping it'll be well worth the effort.
Seems smart to me, knowing an accurate RPM is a great step to insure proper loading and optimal fuel burn.
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Old 05-08-2014, 06:50 AM   #20
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Seems smart to me, knowing an accurate RPM is a great step to insure proper loading and optimal fuel burn.
I would agree knowing your true RPM is an important number to know. Not something I want to try and guess or do by the seat of the pants.
Bill
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