Author Topic: JCB 803 Saga  (Read 67988 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

Offline awemawson

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Re: JCB 803 Saga
« Reply #204 on: May 12, 2018, 11:16:28 AM »
I've had a weep of hydraulic oil from the oil cooler for a few weeks - not much but enough to be annoying. It drips onto the plate where the diesel water separator is mounted, and at first I thought it was a diesel leak, as being adjacent to the water radiator all there runs warm and the oil was very fluid. But no, eventually I convinced myself that under certain conditions one of the swagged joints in the matrix was leaking.Never mind - only 238 for a pattern one, or 100 more for a genuine one   :bugeye:

So I bit the bullet and ordered a pattern part. When it arrived it was damaged - the mounting lugs were all bent, which probably wouldn't be too much of a problem - they should stand up to bending back, but more seriously there was impact damage to the core. Only small as though it had been jabbed with a screwdriver, and if it had only been on the fins again it probably wouldn't have mattered - but no - it was straight onto one of the swagged joints so I wasn't prepared to take the risk.

The supplier was happy to replace it but had none in stock, so a few days passed then on Thursday I got a call to say that the replacement was ready to deliver, but could I pay for it please and they'd credit me on returning the faulty one at my cost. Trying to control my blood pressure, I gently explained that that wasn't going to happen and perhaps a brief reading of the 'distance selling regulations' would let him better understand his obligations  :lol:

So UPS turned up yesterday - (their local chap is always so friendly and greets me like a lost friend !) with the replacement, which I got round to fitting this afternoon.

With hydraulics you never know just how much oil is going to pour out when you change things. I've equipped myself over the years with male and female blanking plugs in all the common sizes and make a habit as soon as a joint it disconnected, to blank the male and females to avoid gushers - often the second joint opened will allow air in and you get covered in hydraulic fluid.

So, old towel under radiator, old baking try to catch oil, and basically just a case of undoing cleaning and replacing. In this instance remarkably little oil escaped, it all went to plan, and the only damage was to my wallet  :clap:
« Last Edit: May 14, 2018, 05:06:03 PM by awemawson »
Andrew Mawson
East Sussex