Petrol sender

[Tiger]

Hello
Now have the sender on the bench the arm is seized .
Any advice before I try to free it ?
Tim

[David Stepney]

The body of the sender is Mazak. I had the same problem with mine. I put some freeing oil into the bottom of the body, sprayed some liberally on .the outside by the pivot, and left it overnight. The following day, I very gently moved the arm back and to a little at a time until it would move it’s complete travel and then continued to move it to and fro until it was completely free. I then washed it out with electrical cleaner to get rid of the crud. Apart from a more recent float problem, it has been fine (or as near to fine as a 90 year old piece of electro-mechanical equipment can be) ever since. Be gentle though, as the internals are a bit delicate and replacements are somewhat problematical to find.

[Old Dave]

Thanks David - that is useful for me as well Tiger.

My sender was "working" in a fashion when I took it out although I suspect the earth return wasn't perfect, so I am rewiring that back to the gauge. 2 questions -

Is it worth me opening the sender plate to clean/improve contact inside? or I am likely to damage anything?

Is Mazak a thoroughly good conductor?

[Tiger]

If you have the sender on the bench I would do all you can to recondition it.
I shall use an electrical cleaner on the coil and contact arm.
Muzak is a conductor
By the way what size are the screws to the tank?

[Henry Harris]

5/32" Whitworth

[John Cornforth]

Hi

Apologies for repeating this, but inside the sender (at least on the ones I have seen) one end of the resistance wire is connected to the mazak body by trapping it under the insulated sleeve that goes round the 'live' connection to the terminal for the gauge. As resistance wire and mazak are dissimilar metals, a poor contact can result after decades. Dismantling, cleaning and reassembly should do the trick.

[David Stepney]

I removed the top sender plate to squirt the freeing oil into the pivot. The electrical cleaner not only removes the displaced crud but also cleans the contact and the resistance wire. Given that the tails of the resistance wire are very thin, I have not had the courage to dismantle the unit further.

[Old Dave]

"By the way what size are the screws to the tank? "

I am using the original screws - my tank manufacturer tapped the holes M4 I believe - strangely it seems the same with no forcing?????

[Tiger]

Original screws 5/32” are 3.97mm so slightly under size for a 4mm tapped hole.

[Hugh Barnes]

I believe that 5/32 BSW is what was used in Meccano sets?