VDO Rev Counter - Revolution Pick Up Unit (Non Alternator)

[RunAgroundHard]

On my Perkins 4236 there is a small pick up unit (I assume) with VDO on the front. It is mounted in front of the water pump, is about 3 cm diameter, 4 cm deep, has two wires coming from it, both white. I am trying to find either a replacement or establish how it works. It may be a magnetic pick up but I don't know. The engine has two ancient alternators on it and I am sure that the RPM is not taken from them. The problem I have is that the Rev counter goes to full scale when the engine starts to rotate, not when the ignition is powered up.

I have searched the internet but can't find anything. I did find a video on replacing a perkins 4236 engine and it had the same device. Does anyone know what I am describing, can they help with a picture or description, or even a link to where I could find one? I tried swapping the wires over but the VDO still maxed out. Does anyone know how these devices work?

The engine is from around 1973.

Thanks in advance.

 

[Alex_Blackwood]

On my Perkins 4236 there is a small pick up unit (I assume) with VDO on the front. It is mounted in front of the water pump, is about 3 cm diameter, 4 cm deep, has two wires coming from it, both white. I am trying to find either a replacement or establish how it works. It may be a magnetic pick up but I don't know. The engine has two ancient alternators on it and I am sure that the RPM is not taken from them. The problem I have is that the Rev counter goes to full scale when the engine starts to rotate, not when the ignition is powered up.

I have searched the internet but can't find anything. I did find a video on replacing a perkins 4236 engine and it had the same device. Does anyone know what I am describing, can they help with a picture or description, or even a link to where I could find one? I tried swapping the wires over but the VDO still maxed out. Does anyone know how these devices work?

The engine is from around 1973.

Thanks in advance.

Picture may help!

 

[RunAgroundHard]

Picture may help!

Don't have one, I was hoping my description would prompt someone who had knowledge. I'll see what I can get next time at the boat.

 

[RunAgroundHard]

Found this image from YouTube

. The device on my engine is the same as the round device on the right hand side as you look at the picture, below the "rk" in Perkins.

 

[scottie]

Ask VDO or lancing marine
clean up snder as there may benumbers on it

 

[Alex_Blackwood]

Found this image from YouTube

. The device on my engine is the same as the round device on the right hand side as you look at the picture, below the "rk" in Perkins.


View attachment 153459

Thanks for that. Looks like it is a mechanically driven Generator producing a pulse related to engine speed, just as the alternator
Frequency increases with RPM. Llke you I cannot find any reference to this unit. Maybe that the display would work if connected to the alternator W connection. If you have, or can find a multimeter with frequency function you maybe able to get an idea of the output of your unit.

 

[harvey38]

It's a Hall Effect sensor that provides a magnetically driven pulse to the tacho, I have them on my Ford Sabres driven by the injection pump. If your tacho goes to max when the ignition is turned on, it sounds like you have a short somewhere, if you have a twin installation, you could swap gauges to see if the short is internal.

 

[ean_p]

Have a look here Wiring for Tacho Sender
and there may be some historical info to be found here if lucky https://vdo-webshop.nl/en/35-revolution-and-speed-sensors

 

[RunAgroundHard]

Thanks everyone for your feedback. When I am at the boat (this weekend I hope) I will investigate further. The information provided should help me troubleshoot the problem.

 

[Alex_Blackwood]

It's a Hall Effect sensor that provides a magnetically driven pulse to the tacho, I have them on my Ford Sabres driven by the injection pump. If your tacho goes to max when the ignition is turned on, it sounds like you have a short somewhere, if you have a twin installation, you could swap gauges to see if the short is internal.

Are you sure? I purposely used the term generator as there is no external indication in the pictures to identify the type. Anyway that is splitting hairs , no criticism intended. I just thought that with a possible elderly engine it would be a small ac output device or even just a cam operating a set of contacts, Unlikely but not unknown. Don't even know if the unit can be opened up?

 

[VicS]

Are you sure? I purposely used the term generator as there is no external indication in the pictures to identify the type. Anyway that is splitting hairs , no criticism intended. I just thought that with a possible elderly engine it would be a small ac output device or even just a cam operating a set of contacts, Unlikely but not unknown. Don't even know if the unit can be opened up?

More likely to be a small AC generator, as you suggested ,than a Hall effect device because a Hall effect sensor would require distinguishable connections for a power supply and a signal output but the OP says it has just two white wires.

 

[harvey38]

Are you sure? I purposely used the term generator as there is no external indication in the pictures to identify the type. Anyway that is splitting hairs , no criticism intended. I just thought that with a possible elderly engine it would be a small ac output device or even just a cam operating a set of contacts, Unlikely but not unknown. Don't even know if the unit can be opened up?

Only going from what I was told when ordered one when mine failed