even though I had a longer than expected (online) meeting today I had to go out to check out my oil pressure sender and found a couple of strange things:
The first one is the installation: on my engine the sender sits high on a hex shaped neck
Usually, the pics in the ROM are quite accurate. Are/were these hex necks common for all engines?
The second one relates to the electric connections: one wire at the top spades is indeed white/brown, but the second one on the same connector is black. However, it does not ground the sender directly, but goes to a blue condenser like device mounted nearby at the carb:
Any ideas about what it does and why it doesnāt short the sender? There is āDubilier British Patentsā on the blue thing and Dubilier produced condensers (capacitors).
Finally, the hex at the base of the oil pressure sender indeed has a strange size. While my replacement part indicated ā19/26ā (18.56 mm), yet mated with a 17 mm spanner at 16.96 mm, the original part would not let that 17 mm spanner get on. A 3/4 spanner is too big to exercise serious pressure without fear of ruining the hex. - So it could well be that it actually measures 19/26". - Of course, I didnāt have a well-suited spanner. Sometimes it is appropriate to accept that you canāt beat the enemy on a particular day, and so I packed my things and returned home ā¦ Seems like I have to find an (unusual) 18 mm hex (if that is enough) or grind wider an old 17 mm spanner.
The capacitor should be connected between the OP spade and ground. When used (optionally I think) its function is similar to that of the capacitor across the fuel pump points and the capacitor between the IVR and ground. First, is suppresses the spark that occurs between the contact points, extending their life (particularly with an inductive load). Second, the voltage transient that occurs when the points open can radiate and be heard as a click on AM radio (similar to the āwhineā of a generator); capacitors suppress those clicks and whines, but are only needed when listening to AM.
As mentioned the nominal wrench size of the Smiths senders of this vintage is Whitworth (3/8). Thatās 18.03 mm. An 18 mm wrench (not an uncommon size BTW) is a good tight fit on 3 of them that I just tried. Itās possible that some of them might be within tolerance and yet not fit 18 mmābut I doubt it. IMHO.
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I believe you, Robert - but would like to know, if possible, the details on this set-up. Just inquisitive - probably doesnāt apply to Jochenās problemā¦?
My SI diagram shows a plain variable resistor - but then; the diagram may not show the Smith set-upā¦
how cool was that?! You hit the nail on the head! But slowly ā¦
Tonight I undertook another attack with improved arms;-) In our workshop I found an 18 mm spanner and - as per your advice a 3/8" Whitworth. Getting to the car, bringing a mirror in position and trying the spanners was a matter of minutes. The 18 mm was still a bit sloppy, but the 3/8 Whitworth fit snugly. It took some pressure, but certainly nothing superhuman and the sender was spinning off. The new one got in within a few minutes.
Interestingly, the new one didnāt only have that smaller sized hex, but it felt like it had more play in the thread, but nevertheless spun in freely, let itself be tightened and was oil-tight during the subsequent test run of the engine. On the Smiths website I found the following indications for the original sender C46272:
PTR1001-10EC, 1/4 BSP, 19 Tpi, 100 PSI.
And the best of it: my oil pressure guage indicates 40 - 60 psi on a cold engine! Of course, I still have to take the car to some serious driving, but everything seems absolutely fine so far.
The hex neck carrying the sender is also a mystery. I found this pic of a 78 engine and it has the sender sitting right on top of the oil filter head just like in the ROM illustration.
Jochen,
Could the pictured engine be a later unit? Iām not sure about the distributor but I do believe you donāt have the later spin-on filter. Maybe not a 78? The āgiraffeā style might have been a temporary S2 situation, or someone needed it for some reason - maybe a makeshift adapter after the threads were stripped, or so?
Glad itās sorted. My oil pressure seems to be dropping as the years go byā¦ maybe time for an oil change, or bearings. And thereās this ticking noise!
Donāt we like those mysteries after all; enjoy driving.
David
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ā¦āas the years go byā, David - you sure must have changed filter and oil more often than thatā¦
As an aside; clogging filter will reduce oil pressure, of course. And upping the oil viscosity is one (temporary) option to increase oil pressure with sloppy bearingsā¦
Hi Frankā¦here is the Cct diagram of the sender and guage from An XJ6 S1 service manual page P67ā¦there is a full description of operationā¦my statement in a post above that its a variable resistance is incorrectā¦its actually a switching on and off of a resistance thus changing the current flow in the CCt that the guage responds toā¦Steve
youāre right - I should have done my homework better! The hex neck is not part of the cast engine block, but in fact an additional part (C.26898) between the oil filter head and the oil filter transmitter that was used only for a engines after 8L.9781, cf
Iām happy that you found this to be original - can imagine this feels much better
Interesting how the sender works.
Happy Easter. I ācelebrateā by making use of the cheaper fuel.
youāre certainly right - with limited entertainment options and marvellous spring weather people seem to be attracted to their two- or four-wheeled means of transportation of choice. Yesterday I took a 40 km ride on my bicycle and spotted a Spitfire, a Mercedes /8, one post 1983 911, one early G-model Carrera, one Caterham 7 and even a Buick Skylark Convertible, which is a rare sight around here. Of course, there were tons of recent or current convertibles and motorbikes out there.
Getting back to the oil pressure transmitter: while I think I understand the pulse functioning of the transmitter, I still cannot understand why power and earth are on the same connector and it works nonetheless ā¦ But then, I donāt have to understand it all ā¦
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The picture doesnāt show the whole text, sir - but the gist is fair enoughā¦
A sort of ātremblerā switch varying connection time with oil pressure - effectively producing a square(ish) pulse to the gauge. Average pulse current produce useful currents as would a variable resistor - in a different wayā¦
Thank you, one and allā¦
:
Frank
xj6 85 Sov Europe (UK/NZ)
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According the the diagram posted above, the sender connects only to the gauge. Earth is through the senderās body to the engine. On my V12 the sender has only one spade connection.
Nevertheless, I still canāt understand exactly how this contraption achieves pulse width modulationā¦
I guess the resistor/heater bends the bimetallic arm/contact back and forth making/braking contact all the time, being adjusted by the pressure varying gap ?
Old voltage regulators used to work this way, and very famously unreliableā¦
There is no earth wire. The block is earth and the sender is bolted in just as the temperature sender is. The diagram shows earth, but it is not via the wire and certainly not on the same connector. If the āotherā wire on the connector to the capacitor, that does not ground it.
We took the mx5 today and we didnāt see much - amongst the usual Mercedes crowd (Swabian Alb) three old SLs, a C3 corvette and a few mustangs and such. Last week a nice black S2 XJ with I think british plates who waved back. And getting back to my oil pressure, itās seen a lot of 15W40 and itās about time for an oil change, also, ever since I changed the wiring loom for a much nicer unit the oil pressure is indicated lower. Iām not worried - I help on rebuilding an XK engine just now and if
Spot on I think - modern cars, I donāt know but would have guessed a little piezo. Thereās a lot of possibilitiesā¦ my post was from yesterday, but the forum crashed or something got stuck.
The other spade, I still think, is for the capacitorā¦? But Iām not sure.
I am glad that the end of the post was success!! Not that I expect to use what I learned, but, it was interesting to follow. for sure at least it exercised my grey matter. that is good.
I think I lost a post yesterday. this thread or elsewhere, not sure., No big loss at all. J-L was quirky.
Then aha !! Gunnar posted. āDown for maintenanceā!!
Not down for long, came back sure and steady.
Aristidesā comment brought back memories of old 6v generators!! The one on my "Tā had only one coil. The ācut outā as it was known. Closed to deliver volts when the engine ran. Open when not turning. No volts flowed from battery to generator. Very reliable as I recall. An electro mechanical diode so to speak.
Some regulation by an adjustable third brush. Remove the cover over the brushes and nudge it one way for more amps and the other for less. Not many either 15 or 30 max!! Rpmās also governed output, Battery over charge could take place. Rough solution. turn on he lights, even in day light on long hiway runs at speed. 45 60 mph or so!!!
Then a bit later, my college job. My boss took a course and bought the tool to adjust the three coil voltage regulators of the āmodern carsā. I watched and 'almost" but not quite understood it .
A friend and I decided to go in to a Christmas tree venture. We had a āgroupā camping trailer we built from sa discarded carcasss. Added high sides for more capacity. Hooked it to my 37 Ford. One coil 6v generator/ After a day of cutting a load. of trees. hand saw and axe! Chain saws not even a dream to us. In our latre teens stron and lots of enmergy!!
No steeet lights in the new Mexico back country gravel roads!! Mountains as well!!! Drove in second or even low to get more light out of the old head lights. It did have a sealed beam conversion!! Ate more gas than planned.
The solution and the end for another dayā¦ Generator coil point illustratedā¦
Gee my GM alternator has a healthy 140 amp capability!!! Wow !
seems we all got lost in our conversation last night - at least one post of mine could not be uploaded.
Today I had a nice ride in the Jag. Fine oil pressure and the new sender even seems to send a bit more than the old one used to. Looks much nicer on the guage;-)
Aristides and David, I forgot about the basic principles of capacitors - they do not connect and as such the black wire, even though it leads directly from power to the capacitor, does not earth the sender.
