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Old 18-04-2019, 13:20   #1
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Belt Tension, and Tacho Options

Hello,

I was going to post a question about belt tension, but there might be a better way to fix this tacho issue I have...from the begining:

We have a Perkins 4.108. The original engine alternator was playing up so it was replaced with a new alternator from Trans Atlantic Diesels. The analog tach gauge is rock steady in its output (no bounce etc). (We also have a balmar house alternator).

We also have hooked up (piggy backing off the back of the tach gauge) a Actisense EMU-1 which gives us Tach output on the N2K backbone.

The output to this is pretty good, but does have a little gauge bounce in it (more than it used to when we first changed the alternator). I have also noted that the alternator belt does squeak a bit, on and off (not sure if it is the engine alternator or the balmar house alternator?)

My suspicion is that that belt isnt quite tight enough, which is causing the bounce in the digital readout, the analog gauge not suffering the same effect because its probably got some dampening in it?

So my original question was what should test should I use for tension the belt? I think the poor mans was was checking the amount of movement at the widest point, but how much?

The second thing I realised which might make the whole taco situation more reliable was, I see that the Perkins 4.108 does have a Taco port, is it just a case of buying the sender and hooking it up to the same analog gauge? Might this way be more reliable?

An old post from Gord May says:
Virtually all diesel engines have a port which will accept an RPM sensor*. This mechanism produces a reliable tach signal without regard to battery state of charge. The RPM sensor does not suffer from belt slippage, and continues to operate even if the alternator has failed.

Cheers

Al
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Old 18-04-2019, 19:52   #2
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Re: Belt Tension, and Tacho Options

I'd check with the tachometer maker, but yes, it's simple. I think they're much more reliable and accurate than taching off an alternator. It also allows you to use other alternators w/o a tach option. It's all I've used since the days of cable driven tachs.
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Old 18-04-2019, 20:06   #3
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Re: Belt Tension, and Tacho Options

I was not aware that the 4108 had a tach output which is why they use the alternator in its place. I would be interested if another solution was found though.
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Old 18-04-2019, 20:35   #4
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Re: Belt Tension, and Tacho Options

I think I am going to try swapping. How specific is the part for the port on the engine?

Also Lepke - do you have a house alternator? How tight is the belt? Ditto for engine alternator belt?

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Old 19-04-2019, 03:24   #5
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Re: Belt Tension, and Tacho Options

You should be able to deflect the v-belt about 1/4" to Ĺ" for each foot of distance between pulley centres.

Belt & Pulley:
1. ➥ Belt & Pulley - Cruisers & Sailing Photo Gallery

2. ➥ Belt & Pulley - Cruisers & Sailing Photo Gallery

Magnetic Proximity Tachometer ➥ Magnetic Proximity Tachometer - Tachometer Wiring Diagram Cruisers & Sailing Photo Gallery
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Old 19-04-2019, 09:09   #6
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Re: Belt Tension, and Tacho Options

I feed the analog tachometers from a Balmer 612 voltage regulator. Output seems to be very smooth and precise. And if the tachs stop working while the engine is running, I know I have a regulator issue. [A spare is programmed and mounted next to the working unit, so swapping wire harnesses is all that is necessary.]

Regarding belt tension [I have V-Belts] I look-up suggested tension in the Gates Belt Tension Guide. Then I check for that tension range using the requisite tension gauge recommended on the that page. [Read displayed text after you input your belt criteria.]

I then use a Gates 'Krikit' Belt Tension Tester (#91107) to confirm the belt is tensioned within the recommended range.

In case any of this is useful to your situation.

Cheers! Bill
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