JCB 3cx white cab hydraulics causing engine to cut out

[poitch]

Hi All i am having a bit of an issue with my 1983 white cab 3cx sitemaster s/n 303092. ever since i bought it the hydraulics are a bit weak. it digs but the hydraulics put a huge strain on the engine and when a ram comes to the end of its travel it causes the engine to shut down unless you rev it hard. i tried adjusting the main pressure relief valve and it has helped but it still shuts the engine off in low revs.it is making good pressure around 2800psi to 3000psi. Do i need a new MPRV (main pressure relief valve) or have i over looked something?. also what price are they and do they come preset?. thanks

[UnclejakeNZ]

Have you replaced the hydraulic filters?

I don't know your machine, but on the later 1980s units there's a filter in the hydraulic tank (on the right hand side of the machine behind the big round plate. There's a drain bung underneath that plate) and another (much larger) filter on the engine side of the firewall (also right hand side).

[essexpete]

How does the machine drive on the road in top gear?
Have you got and extending dipper or an external service?

[poitch]

UnclejakeNZ yep replaced both filters cleaned out the tanks fresh oil a full service so to speak. no difference.
Essexpete it is the sitemaster 4wd version with extended dipper arm and 4 in 1 front bucket only driven on road twice . its very slow hills are a challenge. so did compression test and the engine had good compression it was a couple of years ago when i did it so can remember the exact figures but it was good as far as i can remember. i also did and overhaul of the fuel system tank cleaned, injectors and injector pump refurbished and new lift pump so fueling should be good. it has had this hydraulic issue since i bought it. the previous owner used to stop the engine using the hydraulics as the stop cable was broken..

[Billy26F5]

Not a 3CX expert. I think I'm right in thinking you have a 4.236 engine from your serial number. Are you sure your injector pump and injectors were properly set? Sounds to me like that could be an issue (not all diesel shops know the correct settings for everything, we had a pump timing mark timed on the wrong cylinder during phasing causing endless trouble, you can't phase a DPA but you can still get things wrong when setting it up on the calibrating machine; the injectors are easy to check but do be careful not to get sprayed if you do it yourself). Is the air filter clean and are the tappet clearances correct? I recommend you retorque the head before resetting the tappet clearances. Also ensure you have the correct oil. Are you getting smoke of any kind?
Set the main relief valve to the correct pressure (3000 psi) and the auxiliary relief valve to 2500 psi. Check the manual in the downloads for other details, it's always worth it. It also covers engine details. At full pressure the engine should be able to run without throttle and only some 100 rpm slower (ensure you're idling at 700 rpm).
Sorry for all the questions but it's worth seeing all these thins are to JCB spec, if you still have trouble it might be worth doing a full clean of the hydraulics (not just the filters).
Sandy

[essexpete]

The non turbos are not very lively under load on the road but it does sound as though the power is down for some reason. Do you think the engine is being loaded in anyway without a service selected?

[UnclejakeNZ]

its very slow hills are a challenge. ..

My 1988 with 'apparently' 4,900hrs is the same. It digs no problem. Lifts no problem, can get along a flat road at around 25kmph at full throttle... but the slightest hill the engine revs drop and you're thinking very quickly about a gear change down to third or second.

I've not done a compression test but I have noticeable blow-by so figure the engine is to blame for the poor driving performance. My engine will stall if I try to lift a stabiliser leg past its stop at cold idle, but otherwise I don't have the same hydraulic issues as you and have no useful advice to offer (sorry).

We changed all the hydraulic filters a few weeks ago and it made zero difference to road speed. The biggest difference we ever made to power was cleaning out the fuel sediment filter and tightening up the screws on the lift-pump... which helped, but wasn't a huge help.

I'm genuinely thinking of upgrading to a newer turbo 4CX next year to reduce the horrendous noise the 3CX makes, to increase road speed and to reduce the number of times we get the front wheels stuck in sand

[Billy26F5]

I've not done a compression test but I have noticeable blow-by so figure the engine is to blame for the poor driving performance. My engine will stall if I try to lift a stabiliser leg past its stop at cold idle, but otherwise I don't have the same hydraulic issues as you and have no useful advice to offer (sorry).

Sounds like you do need to rebuild the engine, you should be able to have the main relief valve open at 3000 psi at idle from just started. The 3CX was much slower than the 3CIII, but it sounds like you have problems adding to that. With that I would expect to see blue smoke associated to oil burning.
Always look at the pedals, they can tell a far more accurate story on the worked hours, the moulded grooves normally go flat at some 30000 hours or so but not all pedals are the same (and I don't know the 3CX ones).
Sandy