Oil pressure switch GS 550 l 1980.

[Guest]

Can anyone explain to me how this switch works. Refitting the switch to a rebuilt engine and cant figure out how it operates the warning light on the light array.

[Brendan W]

The switch on the 850 is a brass disk on a spring loaded plunger. The oil comes up from below and lifts the disk off the seat. If the pressure falls the disk re-seats and earths the oil pressure lamp. The oil switch wire is generally yellow and green and comes down the back of the airbox and forward to the switch

[Grumpy]

Yeah Brendan that was how I figured it worked. I think the switch is knackered as there is a lot of play on the extended plunger.

[Brendan W]

Is it not earthing out to the case?
See if it's been taken apart and put back wrong. Did someone pot an o ring where it shouldn't be and the plunger can't reach down all the way. It's a fairly simple thing and not really a lot can go wrong with it.

[Grumpy]

Ive taken it apart and I think its a worn out spring as when the plunger is fully extended the spring is free to fall around in the tube.I would have thought the spring should put pressure on the plunger to force the brass disc against the casing.

[Brendan W]

Found this, you're not the only one.

http://www.thegsresources.com/_forum/showthread.php?192281-Info-needed-about-the-oil-pressure-sender-units-on-the-83-550s&highlight=oil+pressure+switch

How much free travel is there before you hit the spring ? When you fit it do you get continuity between the terminal and the case.
Pressure in the 850 is low. Anywhere between 1.4 and 7.1 psi at 3000 rpm is fine. The switch is more a flow switch than a pressure switch.
I'll take the 850 switch out later for a look.

[Grumpy]

The 83 models had a different switch to mine, I think they changed the switch in late 80 or 81. Regarding the spring, theres at least 10mm play before the base of the tube meets the spring. I'm guessing the spring should be in constant contact between the top of the switch and the disc end in order to form a circuit to eartf off the casing. If this is the case the spring is shot. Probably easier to buy a new switch.