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" Tango's Rev Counter


Guest biggles999

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Hi Gang,

Heres a brain teaser, yesterday "Tango's" rev counter quit on me, my question is

are they all electronic ? where on the perkins 4108 diesel do they connect ? please :Stinky

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The tacho drive on the Perkins engine is by an old-style speedometer-type cable. It's driven at half-engine-speed from an extension of the oil pump shaft and is located on the left-hand side of the engine block just behind the alternator.

It sounds like your cable has snapped. I don't know if it's still possible to get new cables but I'm guessing you might have to convert to an electronic tacho. I once, in the long distant past, repaired a speedometer cable inner by brazing. That had broken just below the speedo head very near to the squared end so the repair was quite successful but if it's gone at a bend that obviously wouldn't be likely to work, not for long anyway.

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If it is the cable and not the head or drive then Speedy Cables will make any size for you from the original measurements, it is unlikely to be a standard part anyway due to the large variation in length in boat installations. It may be better and more economically viable to fit either and alternator or flywheel sensed one from an aftermarket source.

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That's a useful link Antares. I wonder if they would make up a new inner to fit the existing outer. That ought to be cheaper.

I'd be interested to know if anyone has fitted an alternator-sensed tacho to a Lucas 11AC alternator and if so how it was connected and calibrated. Would it work on the 'AL' terminal that drives the field relay? I'm just waiting for the drive cable on mine to go and it would be useful to be prepared.

Incidentally this thread would have been better raised in the Technical Questions and Answers section.

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Biggles, Hi

As Mike says you could try repairing the cable but I had a similar problem with Mary-Jane's Elan and I fixed it by using some of that curtain cable that you stretch between two eye-hooks.

Today you'll probably only be able to get it with white plastic covering but if you strip that off to the correct length you can then braze both ends (to strengthen them)and grind them to the square section you need. It worked for many thousands of miles until we sold the Elan!!!

It may sound a lot of bother but when you investigate the cost of an electronic one I think you might give it a go!

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Are you a PBO subscriber John? :grin::naughty:

No, David and I haven't subscribed to PBO since we sold the Motor-Sailor (Friday Girl 2).

But to keep old cars (and old boats) going I had to become something of a Bodger (in its old fashioned meaning!) to keep them on the move. Also money was tight when the kids were young! :naughty::naughty::naughty:

I reckoned that with a bit of ingenuity, liberal application of Araldite (or my mig-welder) and a bit of luck, you could fix almost anything! I still do!

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If it is the cable and not the head or drive then Speedy Cables will make any size for you from the original measurements, it is unlikely to be a standard part anyway due to the large variation in length in boat installations. It may be better and more economically viable to fit either and alternator or flywheel sensed one from an aftermarket source.

That's a useful link Antares.

What link? Did someone remove it?

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No, it wasn't a link as such, just a reference to Speedy Cables which I was able to find with Google.

The curtain wire idea is quite neat but I guess it would be best to make sure that the direction of rotation tends to tighten the coils. It's a very long time since I looked at a speedo/tacho cable but I think a normal inner has a stranded core within the coils. Also on the cable I repaired all those years ago I seem to remember there was a collar fixed to the inner at the speedo end to prevent it slipping back down the outer.

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Hi Biggles, The discussion so far has suggested a mechanical tacho. Have you in fact verified that this is the case. It could be electronic driven off of the alternator, sometimes from an extra wire soldered to the rectifier. You may be simply suffering from no more than a corroded connector that just need cleaning up at either the engine end or the tacho end.

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Hi Biggles, The discussion so far has suggested a mechanical tacho. Have you in fact verified that this is the case. It could be electronic driven off of the alternator, sometimes from an extra wire soldered to the rectifier. You may be simply suffering from no more than a corroded connector that just need cleaning up at either the engine end or the tacho end.

Thats right ,

it is sensed off the alternator and not a cable, cheers

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As Tango is fitted with a Perkins 4.108 then unless it's been modified at some time in its life it's most likely to be a mechanical system. The fact that it suddenly stopped working suggests a broken cable. If it was an electronic system corroded connections would most likely cause intermittent operation (although it could just be a wire has fractured or corroded through). My money's on a flexible cable, though.

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Ok. - the penny's dropped. The ex-Richardsons boat with the hydraulic drive. :oops: I've lost my money, but at least I now know I can get a replacement for the cable on my boat.

So, is it possible there's a blown fuse in the 'ignition' feed to the tacho?

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I am not great with electrics but do remember the colours of the wires we used ;)

I dont think there is a fuse in the line but if it is not a loose wire off the alternator or a wire fell off the tacho then try giving the dashboard a thump next to the dials! sometimes a needle can stick if it has not mooved for a while :naughty::naughty:

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My money is on a lucar connector that has relaxed with age and festered over the winter. :ugeek:

Least I hope so for the sake of the owner's money cheersbar

So, is it possible there's a blown fuse in the 'ignition' feed to the tacho?
Just off the top of my head not sure if there would be an ignition feed to the tach maybe just alternator feed and earth, it is also very unlikely that it would be a fuse unique to the tacho and other things would be out of action i.e temp guage and maybe charge. Again if a fuse was involved my money would be on corrossion in the holder rather than blown.

On the issue of tachos, whilst if it is there I would want it to work, but given the choice between a tach on an engine that did not do above 2.5 K and a chocolate teapot I would consider the teapot to be more usefull

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Hi Gang,

First of all thank you so much for all the Information and Clive Thank you, well we moved "Tango" from Westview Marina to Denver on saturday,theres quite a nack to reversing her and after having twin engined before was frustrating, took me quite a few minutes to get out of Westview with all the boats parked, I did not really get the hang of steering at this point and the air turned blue :party2:

the engine didnt miss a beat, and after about ten minutes the rev counter started working again! ( must say something for Clives original Servicing ) lol,

it took 5.5 hours to do the trip with one lock at hermitage, the river is quite narrow at times and looks like winter, it was dammed cold and to add to my wife Mia's misery the Webasto heating refused to light up so we had to travel with gas rings on, with all the condensation problem to the windscreens that this makes,

then when we got to Dever the taxi firms where to busy to take us back to Earith or one wanted £60 *Barrys cars* not to be recommended, in the end *Sallys cars* got us and charged only £35 which was much more sensable.

I was to tired to check the fuel level to see what she had used but I will next Saturday when I go down to her, also Is there two stop cocks which feed the sea toilet? as it refused to flush, pumps ok but no flush Will report more later :Stinky

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Just off the top of my head not sure if there would be an ignition feed to the tach maybe just alternator feed and earth

Hi Gordon,

I was basing my comments on the data for the Faria instrument as I don't have personal experience with electronic tachos. For all I know there may well be others which don't have an ignition feed. Certainly in principle it would be possible to design one to take power from the same wire as the signal.

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