Dizzy driven oil pump thread size

sidecar · Post by **sidecar** » Thu Nov 14, 2013 9:28 pm

Hi Guys,

My oil pressure switch is leaking oil from around the seal formed by the metal case and the plastic back, It was is an old three pin switch.

The switch was screwed into an adapter that was then screwed into the larger of the pump take off points, the oil pressure gauge is fitted to the other smaller take off.

I need to find out the thread size for both the pump and the oil pressure switch. I think that the pump is 1/2" UNC and the switch is 1/8" NPTF, can anyone confirm this.

I could do with a new adapter too, if anyone knows where to get one from and a switch that would be great!

Its a Rover lump BTW!

Cheers,

Pete

Muscle-Manta · Post by **Muscle-Manta** » Thu Nov 14, 2013 10:53 pm

Pete, I think Malc might have a spare timing cover with the pressure switch fitted, he should be able to tell me what thread they are. I will be seeing him Saturday (we're off to the NEC Classic show) I'll ask and let you know.

DaveEFI · Post by **DaveEFI** » Thu Nov 14, 2013 11:43 pm

The three prong type includes a switch for the fuel pump on a carb SD1. If you don't need this use a single terminal EFI one without - they are more reliable.

sidecar · Post by **sidecar** » Fri Nov 15, 2013 8:51 am

Hi Guys, Thanks for your replies, I've done a bit more Googling and I'm pretty sure that the thread on the actual switch is 1/4" 18NPTF. I know that one of the take off points on the pump has this thread but that one is already in use on my setup. I just need to sort out the larger thread size then get an adapter. I think that a Lucas switch will work for me... "SOB812"

The reason that I need a three prong switch is that I use it to control my fuel pump, I don't actually use it for the oil pressure warning light.

What I can not get my head around is the fact that oil was leaking from the back of the old switch. My understanding is that there is a diaphragm which isolates the oil from the back of the switch. The switch still worked so I would have thought that the diaphragm cannot be split. (Maybe is is only leaking past the diaphragm by a small amount so there is still enough pressure to operate the switch? I think that I'll cut it open and have a look)

I have heard that people have lost all oil pressure when the back of the switch has been 'blown out' by the oil which is a bit worrying!

DEVONMAN · Post by **DEVONMAN** » Fri Nov 15, 2013 9:06 am

The Tee pieces that are sold on ebay to allow a remote pressure switch are 1/2" UNF so I imagine at least one of the outlets on the pump cover has this thread.
The SOB812 may have this thread or it may normally fit directly into one of the other outlets without an adapter.

Regards Denis

sidecar · Post by **sidecar** » Fri Nov 15, 2013 9:21 am

Hi Denis,

Done a bit more googling...I reckon that you are right, it's 1/2" NPT!

‘Torques’ on ebay have adapter that I can use, I’ve used Torques in the past and they are very good people to deal with. They do 1/2 BSP and 1/2 NPT so after yet more googling I found that the threads are more or less the same and the parts can be interchanged in low pressure systems (i.e less than 100 PSI). NPT is just a tapered thread so I’ll go for that rather than the parallel BSP thread.

Cheers,

Pete

DEVONMAN · Post by **DEVONMAN** » Fri Nov 15, 2013 9:58 am

sidecar wrote:Hi Denis,

Done a bit more googling...I reckon that you are right, it's 1/2" NPT!

‘Torques’ on ebay have adapter that I can use, I’ve used Torques in the past and they are very good people to deal with. They do 1/2 BSP and 1/2 NPT so after yet more googling I found that the threads are more or less the same and the parts can be interchanged in low pressure systems (i.e less than 100 PSI). NPT is just a tapered thread so I’ll go for that rather than the parallel BSP thread.

Cheers,

Pete

Hi Pete,
Did you mean 1/4" NPT?

1/2" NPT and 1/2" BSP are massive.
My suggestion was 1/2" UNF

Regards Denis

sidecar · Post by **sidecar** » Fri Nov 15, 2013 1:04 pm

Hi Denis,

All these different threads 'do my head in'

I have an ETB sender unit which gives me my oil pressure reading and operates the oil pressure warning light, it has the same thread as the SD1 oil pressure/fuel pump switch and therefore the Lucas switch that I've just ordered. According to ETB's website the thread on the ETB sender is 1/8 NPTF. I guess this is why its screwed into the pump without the need for an adapter.

As to the adapter for my SD1 switch I measured the one that came off the pump, it measured 500 thou in diameter and thread looks pretty course to me. Unfortunately it is now a bit chewed up!

'Torques' do two adapters one is 1/2 BSP, the other is 1/2 NPT but according to the following post the threads are very similar...

http://www.turbominis.co.uk/forums/inde ... t&tid=4208

Regards,

Pete

DEVONMAN · Post by **DEVONMAN** » Fri Nov 15, 2013 7:35 pm

Hi Pete,
The point I was trying to make is that a 1/2" BSP adapter from Torque will be approx 800 thou outside diameter with a hole for a 1/8" NTP sender.

If the adapter you have at the moment is 500 thou diameter then it will be either 1/4" BSP or 1/4" NPT or 1/2" UNF

1/2" BSP size relate to the outside diameter of the pipe (eg gas pipe) that has a bore of 1/2" as the thread is normally cut on the outside of the pipe at connections. Very confusing unless you are a ancient plumber

Regards Denis

jrv8 · Post by **jrv8** » Fri Nov 15, 2013 8:15 pm

Pete,
The sizes on the RV8 oil pump can be a combination of 1/4 NPT and 1/2 UNF on SD1 and early R/R covers , or two 1/2 UNF on the later R/R housings.
ETB sender units are 1/8 NPT

Jim

sidecar · Post by **sidecar** » Fri Nov 15, 2013 11:28 pm

Crap, I've ordered the wrong stuff then!

Oh well thanks for your help guys, Jim I've order two adapters with the thread sizes that you supplied. (I'll keep one as a spare)

Cheers,

Pete