Komatsu PC300-7 hydraulic fault

[dingo]

im trying to fix a komatsu pc300-7 hydraulic fault. when i compound function boom raise and arm in AND boom raise and bucket curl at low idle my boom stops. At high idle it slows the boom considerably. Boom movement returns to normal when other functions are relieved. i have removed and inspected the boom and boom hi compensation valves, they look slightly worn but servicable. the boom shuttle valves are working and the boom spool isnt damaged. Safety suction valves look ok. Merge/divide valves seem to be ok but i believe boom and arm run off the front pump. LS pressure and pump output pressure are within spec. I am convinced the compensation valve is faulty but i need to make sure before i change it out....any ideas???????:Banghead

 

[rare ss]

I'm not a full bottle on komatsu's, silly question, have you checked the fuses & wiring for the pump?.. i had a similar fault on a EX300-3 when you tryed to use two or more functions at once it would stall the machine after a day of f&#king around we found a blown 1 amp fuse which was causing the variable swash plate in the pump to be on max flow causing the engine to stall
might be the other way round on yours limiting pump flow for some reason?.. just a thought mate, hope ya sort it out

 

[michel]

Hello dingo, if you think the boom compensation is the problem, try to interchange it with the arm compensation and check again.

 

[Dr Komatsu]

What weight is the Pc300-7, i'm assuming its equivalent to a Pc340-7 UK machine as we don't have Pc300-7 in Europe ? Whats the serial no range and smr ? I've done alot of compensator reseals ,you replace the seals and not the complete valves .
If you swap compensators they must be identical,ie have the same no of rings on the circumfrence of the valve and same no of notches on the flats as the have different internal diameters and can only be swapped like for like,a good indication for compensator seals burst ornot sealing is to hold each circuit over relief at operating temp and after a good few seconds if you start to get creep and watch f & r pump pressures they start to gradually drop. Is it a gradual drop in performance or sudden ? If you remove the compensator valve ,take the slug out reverse it ,put it in they should require pulled out with pliers ,if the pull out easy they're not sealing well,also spray the slug with cleaner and shake it and listen that the shuttle ball inside is free.

 

[dingo]

hmm interesting ideas. machine details are pc300-7(30 ton or there abouts) ser# ive got no idea machine has about 8500 hrs on it and is in poor condition. the owner is a quarry and construction cowboy. the only other valve that is identical is the boom hi comp valve. all the rest are different in some way. i swapped them over and tried it but made no difference. Dr Komatsu you mentioned about reversing the poppet(slug) that cant be done on this valve as the poppet has a 20mm tail that locates inside a spring which then fits inside the outer comp valve housing. The performance drop is instantanious with the second operation. I will try the cylinder stall test you mentioned though.

 

[dingo]

you wouldnt read about but engine RPM at high idle was 500 RPM down. Just goes to show dont trust the customer......check it yourself!!!!!!