Author Topic: JCB 803 Saga  (Read 39065 times)

Offline PekkaNF

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Re: JCB 803 Saga
« Reply #200 on: August 31, 2015, 05:15:26 AM »
That bolt....on the picture before reminds one thing long ago. O-rings on Cetop-valves needs to be quite right and servo valves needs to be mounted pretty much right torque or the spool does not move reliably. On one setup we had problem of oil seeping on valve stack. Checked it once and doublecheeked shema and measurement....should be fine, but it's not fine. Then I checked and measured the bolts...fine, but ends had a slightly crushed thread.....what rhymes with a clacking bell? The threaded holes/threads were just too short (shorter than spesified) and some innovative cad user had reenginered the valve block thread upon on catalog bolt/stack height. Crapity crap! No thin rider/dummy block to mach next longer bolts, needed to get innovative with the bolts and order a new valve block, can't just leave someone else to find what's wrong with it.

For an electrical engineer hydraulics is weird sometimes, because if you can't trust the schema and you can't trace the pipes/hoses you are left armed only with your vivid imagination.

Pekka

Offline awemawson

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Re: JCB 803 Saga
« Reply #201 on: August 31, 2015, 04:20:52 PM »
Before I chucked it out I investigated the faulty diesel tanks 'Sender' .

The original was a capacitive one - an aluminium outer tube / housing with an inner tube made from plastic water pipe with a central stainless steel rod. Encapsulated in the large 2" hex nut (which was plastic) was an electronic module which presumably sensed the varying capacitance and emulated a varying resistor. Obviously the electronics had failed. Not much to see by the time I'd squashed it in the vice to crack the potting, but the date 1997 was on the pcb which is right for original equipment, and there were discrete transistors.

No idea how the replacement works - it measures 'genuine ohms' on a meter as the plastic doughnut moves up and down the stainless rod - I assume that the doughnut is magnetic, but what the variable resistive element is, is a mystery to me :scratch:
Andrew Mawson
East Sussex

Offline DMIOM

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Re: JCB 803 Saga
« Reply #202 on: September 01, 2015, 01:54:46 AM »
......No idea how the replacement works - it measures 'genuine ohms' on a meter as the plastic doughnut moves up and down the stainless rod - I assume that the doughnut is magnetic, but what the variable resistive element is, is a mystery to me :scratch:

Andrew,

I wonder if its similar to the magnetically-coupled corrosive liquid pumps - a magnet in the float and another magnet on a slider in the core running a wiper up & down a length of constantan or similar - actually I think it might need several magnets (min 3) to prevent too much drag on one side of the core.  Any patent nos. on it?

Dave

Offline awemawson

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Re: JCB 803 Saga
« Reply #203 on: September 01, 2015, 02:31:49 AM »
It's in the tank now Dave and I didn't take a look beforehand, so sorry I don't know, but I don't think that there were.
Andrew Mawson
East Sussex