Bukh 20 tacho problems

[TVgeoff]

Hi
Went down to start the engine, have a coffee, think about the coming season, noticed the tacho was not working. Checked the rear for wiring loose/dirty but all seems OK. Also the sender unit on the block, ditto.
Anyone had similar or am I looking at yet another big bill!

 

[cliff]

Hi
Went down to start the engine, have a coffee, think about the coming season, noticed the tacho was not working. Checked the rear for wiring loose/dirty but all seems OK. Also the sender unit on the block, ditto.
Anyone had similar or am I looking at yet another big bill!

Confused! The tacho is fed from the "W" terminal on the back of the alternator. The tacho head gets its power from the back of the panel. If the "W" terminal is clean and tight then I would take the panel off and check in there for power to the tacho head. The above assumes the alternator is actually working ("ign" light goes out once engine is running)

 

[TVgeoff]

Thanks for this Cliff, looking at the wiring diagram in my Bukh manual, I see there a four connections on the back of the tacho as well as two to the 12v bulb. The yellow goes to one side of the sender, the blue from the other side of the sender terminal goes back to the tacho. these via an eight way connector. The remaining two connectors seem to connect to the altenator (-) and the positive supply at the battery isolator switch.
So should I be getting 12v at the tacho, and 12v through the sender?
Thanks Geoff

 

[cliff]

Ahhh now it makes sense - you have an old type tacho - ok here we go.....
Yellow to terminal Z on the sender and Blue to terminal G on the sender. Both run back to the tacho head via an 8 way connector - check the connector terminals.
Power should be fed to the tacho head from the back of the oil pressure gauge (red and black wires) which in turn gets its power via a red cable that goes to the "ign" switch and a black cable that goes to D1 on the back of the alternator (old type of Tacho ......)

I would check the oil and temp gauges - do thy work? if so there should be power to the tacho head (can you see the little internal light? is it working - if so you have power to the head if npot put a volt meter across the black and red at the input to the tacho head - if power there the bulb is gone.
Next check the yellow and blue back to the sender if all appears ok (all terminals good and crimps ok and no visible broken wires disconnect the yellow and blue at each end and check electrical continuity - disconnect at both ends first. - if all ok I would suspect a duff sender or tacho head - to be sure the wiring is not at fault you could run new wires temporarily from teh sender to the head while the yellow and blue are disconnected.

 

[TVgeoff]

Hi Cliff,
Thanks for all the info, I'll try tomorrow with the check list you have supplied.
You must be a marine electrician or have had Bukhs for some time!
Thanks
report on progress to follow

 

[TVgeoff]

Hi Cliff,
Found the problem, its the head unit. (this by borrowing a similar unit from my local marine engineer) are you aware of anyone that repairs these obsolete units or has one for sale?

 

[cliff]

Hi Cliff,
Found the problem, its the head unit. (this by borrowing a similar unit from my local marine engineer) are you aware of anyone that repairs these obsolete units or has one for sale?

You could try Bukh in Poole 01202668840 - Al Pearson or Norman Griffith - Failing that I am sure some of the instrumenty guys will be along shortly to give the name of a repair house.

One could of course forget that one and buy a tinytach see www.tinytachuk.com or contact Richard Dunn on 07860 323255
If going down the TinyTach route make sure you get teh correct impulse sensor - they come in 6mm and ¼" ø varieties IIRC the Bukh is 6mm ø but do double check that.