MD2B original rev counter


New member
15 Oct 2004
Essex man, Thames @ Leigh
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Katouf is fitted with the original VDO analogue rev counter supplied by Volvo in the instrument panel introduced in 1972/73. It reads up to 3000 rpm with max engine revs about 2500 on a good day, more usually 2200. It's recently been playing up; sometimes working, most times not.
The signal for the revs comes from the crankshaft via a magnetic pickup (my engineer friend said it's the 'Hall' effect) and then via 2 wires that go to the W and G terminals on the rear of the unit.
I've performed the following maintenance:
1)tested continuity of the wires with a meter between the pick up and the 2 terminals;
2)checked the + and - supply from the electrics - there is 12v going to it and the circuit is complete with no loose wires that I can see.
3)removed and cleaned the pickup head of oil and cleaned the spade connections for the two W and G wires;

Is there anything obvious I've missed or is there a way of testing the rev counter on the bench?
I don't really want to buy a new one because I aspire to be like the Tightwad sailor, and anyway a new one wouldn't fit the big hole in the instrument panel.

Katouf Centaur CR505


New member
14 Oct 2006
- up to my neck in it.
The pickup failed on mine & I had a sense of humour failure when I was told the cost of a replacement. I managed quite well without for about 10 years when I replaced the then 30 year old engine.

BTW, do not run the engine for long periods with the sensor removed, the flywheel carries some oil & this sprays off inside the engine casing as it rotates. With the sensor removed, some of this oil will spray out of the hole & your engine will run out of oil & could seize, possibly on passage . . .

We completed the journey under sail, but it took us an extra 6 hours to enter Douglas harbour as we couldn't sail against the wind & tide. That was my first engine rebuild, but I never replaced the sensor, I just put the old one back to fill the hole.


Well-known member
13 Jul 2002
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You can relax about the cost of the sensor, if that is what has failed. It is out of production.

maybe you can find one on a old engine