(also posted in earthmoving excavators) Komatsu PC45R-8 Weak boom I am thinking of buying a neighbours Komatsu PC45R-8 Excavator. He tells me the main boom cylinder is weak (but not the others). He has rebuilt the cylinder but has been told that is a most likely a valve problem and that the valve will cost over $1000 to fix. I know nothing about excavators but have a reasonable mechanical knowledge. So, any ideas? What does it sound like? Also, is there a way to stop oil from pouring out if I start dismantling valves/hoses. ie, when are things under pressure and what is the best way to relieve any pressure in the system? (I hope that makes sense!) Also, if I work on the hydraulics, do I have to bleed air from the system afterwards? How? Aah, serious newbie alert siren going off here!
there is a few ways to relieve system pressure it varies by manufacturer, it should be listed or explained in manual best results are to take off bucket place hitch on ground very gently with dipper arm vertical lower blade to ground then carry out manufacturer relief method as for stopping the oil coming out of your excavator during dis-assembly now that's a hard one drain the hydraulic tank as a start but theres no way to stop all of it if you have the resources you can cap off every pipe, hose and fitting as you undo them but oil will still fall just have plenty of buckets or drain trays to catch it all as for cylinder being weak check your system pressure or perhaps even check the pressure available at the cylinder there could be a number of faults but none can be solved from a computer screen process of elimination will be required flow may also be a factor can you give any more details on the "WEAK" cylinder
Hi there, thanks for coming back with some helpful comments. The main ram on the boom has been rebuilt with new seals. There are no oil leaks on the excavator. The main ram doesn't have much strength - It can't lift the excavator enough to lift a track off the ground. So I assume its digging capability will not be great either. I think it will be probably most cost effective to get a hydraulic mechanic out to troubleshoot the system. Once I know what is wrong I shouldn't have any trouble fixing it (except for the potentially huge hole in my wallet!) I don't have a hydraulic pressure guage, so I should better get santa to sort that one out... Just ordered the workshop manual on CD, so that might help a bit.
while trying to lift the machine with boom apply a small movement to the dipper arm so that the machine loads up a little more (dont move the dipper, just apply load) if the machine becomes more responsive there may be a bypass in the valve for boom control e.g. blown seal or Oring or score in the spool and/or bore just something else to consider