Electronic/Mechanical Tacho for BMC 1.5

[Chris Lingwood]

Would my bmc 1.5 want a mechanical or electrical tacho. As with all these things I guess its probably different for each one. Where would they put the mechanical sender if there is one? I can't see a connection on the alternator either. What would they label it?

[Yoda]

Would my bmc 1.5 want a mechanical or electrical tacho. As with all these things I guess its probably different for each one. Where would they put the mechanical sender if there is one? I can't see a connection on the alternator either. What would they label it?

 

A readout of speed for engine revs would be from a 'tachogenerator'. A mechanical readout would be a rev.counter. Any electronic readout of speed will come from a generator, of any kind.

 

To find out on a boat what your prop speed is, you need to fit a pulse probe on the output side of the gearbox. This will give you a direct reading in RPS or RPM if you have a timebase recorder.

 

Prop speed is more important than engine RPM, in most situations. Do not exceed the given prop RPM otherwise you will cavitate and lose power.

[GUMPY]

Would my bmc 1.5 want a mechanical or electrical tacho. As with all these things I guess its probably different for each one. Where would they put the mechanical sender if there is one? I can't see a connection on the alternator either. What would they label it?

 

I went through this with my Ford

Tried various methods to get one to run off the alternator and after none worked accurately I settled for this:

 

http://www.tinytach.com/tinytach/diesel.php

 

available from here:

 

Contact: Richard Dunn

Email: itco@btopenworld.com

07860 323255 Message: 01342 305114

 

Works a treat, simple to fit and gives me service intervals, total hours run, and journey hours run,

OK so its digital, small and not tradional but who cares, it works.

 

 

J

[anhar]

Would my bmc 1.5 want a mechanical or electrical tacho. As with all these things I guess its probably different for each one. Where would they put the mechanical sender if there is one? I can't see a connection on the alternator either. What would they label it?

Hello Chris

 

Might be worth contacting Calcutt Boats to enquire about this. They are the BMC marine experts and have been for a long while. These days the engines are now made in Turkey and Calcutt import and marinise them but it's very likely they'll know about the older models too.

 

http://www.calcuttboats.com/engines.html

 

regards

Steve

Edited August 11, 2006 by anhar

[John Orentas]

Hi Chris.

 

These days rev counters are invariably electronic units and use a specific output on the alternator which obviously is made for the job. All this could cost you a lot of money if you have to buy the instrument and the alternator to go with it, your troubles may not end there as you may need to start messing around with the pulley sizes to calibrate it yet maintaining the right sort of speed for efficient charging.

 

This subject came up a few months ago and I remembered an advert in one of those posh free mags that sell brass chronometers and designer life-jackets, it was a fully self contained rev counter, (no alternator connection required) I even remember there was an option of 6,000 or 3,000 rpm models.

 

CAN ANYONE RECALL OR PREFERABLY DIG OUT THE MAGAZINE ?

 

Just spotted post by Idleness, I should read all the posts first. That looks pretty good. If you buy one please give us a report

Edited August 11, 2006 by John Orentas

[Sir Nibble]

Stick it on the alternator, it works, it's simple, it's cheap. The tacho output should be labelled "W". If it's not there then either post a photo of the alternator or give me the part number off the unit and I will give you instructions on how to fit one. It's really very easy.

[GUMPY]

Stick it on the alternator, it works, it's simple, it's cheap. The tacho output should be labelled "W". If it's not there then either post a photo of the alternator or give me the part number off the unit and I will give you instructions on how to fit one. It's really very easy.

 

Provided that you know the tickover RPM and the govenor RPM its easy, if you dont, calibrating it can be a nightmare.

I tried to do mine I knew the tickover rpm was about 700 and according to all the blurb I had read the max rpm was 2200 so I tried to calibrate it using those figures.

Spent a whole day messing around just couldnt get the thing to read the way I expected it to in the end gave up.

Fitted the tiny tach which needs no calibration and I find out that my engine has been de-rated ( or the governer is set low ) and the max rpm is 1900 no wonder I couldnt get the one off the alternator to read correctly!

 

BTW somewhere I have a revcounter that is surplus to requirements.

 

J

[Enfield Phil]

I went through this with my Ford

Tried various methods to get one to run off the alternator and after none worked accurately I settled for this:

 

http://www.tinytach.com/tinytach/diesel.php

 

available from here:

 

Contact: Richard Dunn

Email: itco@btopenworld.com

07860 323255 Message: 01342 305114

 

Works a treat, simple to fit and gives me service intervals, total hours run, and journey hours run,

OK so its digital, small and not tradional but who cares, it works.

J

 

 

How much in GBP?

[GUMPY]

How much in GBP?

Tiny Tach, is £55 inc vat and delivery

You do need to accurately measure the injector pipe and it needs a good ground on the engine.

I moved mine because I wasnt happy with the readings at first they were a bit jumpy.

 

J

[Chris Lingwood]

I went through this with my Ford

Tried various methods to get one to run off the alternator and after none worked accurately I settled for this:

 

http://www.tinytach.com/tinytach/diesel.php

 

The problem is I'm rather partial to a lovely big gauge flailing about the place. ESPECIALY if its got a nice chrome besel.

 

Stick it on the alternator, it works, it's simple, it's cheap. The tacho output should be labelled "W". If it's not there then either post a photo of the alternator or give me the part number off the unit and I will give you instructions on how to fit one. It's really very easy.

 

"W" you you say. I had a look at the back of the alternator last night and there were 3 wires. Two big red ones going to the starter solenoid (don't ask me why not just one) and one blue one going to the ignition light. +ve and field it should be fair to say. But one of those red ones might have had a W next to it. The guy who wired up the engine wasnt the master of all things electronics you see. EVERY wire on the wiring loom appart from the high current ones is blue. BLUE!!!!! ALL OF THEM!!!!! Not only that but the two wires connecting the battery to the engine are BOTH BLACK!!!!!! I'm not best pleased! I'll have a peek see what I can find out.

 

I've not found any mention of mechanical rev counters being used on this block after 1964ish (and that was for the petrol B series in an MGB) so for the moment I'm going to presume its alternator driven.

 

Provided that you know the tickover RPM and the govenor RPM its easy, if you dont, calibrating it can be a nightmare.

I tried to do mine I knew the tickover rpm was about 700 and according to all the blurb I had read the max rpm was 2200 so I tried to calibrate it using those figures.

Spent a whole day messing around just couldnt get the thing to read the way I expected it to in the end gave up.

 

Sounds like a pain, oh well...the price we pay for nice chrome things

[John Orentas]

I have a nice big electronic rev counter for sale but you will also have to buy the boat that is screwed to it.

[DHutch]

The guy who wired up the engine wasnt the master of all things electronics you see. EVERY wire on the wiring loom appart from the high current ones is blue. BLUE!!!!! ALL OF THEM!!!!! Not only that but the two wires connecting the battery to the engine are BOTH BLACK!!!!!!

All blue for the engine is a bit of a bummer, but the thick cables going to the battery both being black isnt uncommon, both ours are. With red insulating every 30cm all the way along the +ve one.

- Its just 35mm2 welding cable you see.

 

 

Daniel

[John Orentas]

Rev Counter. I have found the magazine where I saw the advert for the rev counter.

 

Force 4 Chandlery

Tel 0845 1300 710

www.force4.co.uk

 

The unit is 81mm dia. needs a 12 volt supply and the add says 'No sender required'.

Code 150006 ........ 4000 rpm ............ £69.95