I've got a 420E with just over 1500 hrs on it. The cylinder rod had scoring on the rod and had the chrome flaking off on the underside of the rod. one day last week I noticed the cylinder drifting down as soon as I brought the cylinder all the way up and let the control go. It would drift down a good 4 inches fast and then slowly over time would drift down more. I thought oh the cylinder is leaking via bypassing the seals internally as I knew eventually it would. Sent the cylinder to a shop got it resealed, new rod and possibly a hone on the barrel not sure. reinstalled the cylinder and its still drifting...so now I'm wondering is it possibly the load/lock check valve gone bad? bad centering spool spring? or possibly the spool itself has a score in it from the chrome flaking off... I was wondering if anyone had a hydraulic schematic of the 420e phc serial number so I could trace the system and try and figure it out. Is the phc schematic the same as the schematic for kmw?
Do you know exactly what the shop did to the cylinder..? If they honed the barrel did they use oversize seals for example..? KMW prefix Hydraulic schematic is not the same as PHC. PM me with an e-mail address and I'll send you the PHC schematic.
A quick check would be to swap the line reliefs. Swap the two line reliefs between the left and right stabilizer sections. One on each end of the valve bank. Assuming the cylinder is ok, I am thinking the poppet may have some debris in it and is causing the drift.
Thanks Lee, I will try this tomorrow night and see if that is the problem. Hopefully it is as its a quick fix! I know the cylinder got a new rod(after market, new piece of rod stock being the same dimensions as the cat rod was) and seal kit from cat. I don't know at the moment if the barrel was honed. I do know that they leak test the cylinder before they are done with it... Thanks very much I'll pm you my email in a minute...
well an update, after checking the line reliefs - ok both needle lock valves - ok and pulling the spool and it was -ok sent machine to dealer. turned out the cylinder wasn't repaired properly in the first place. the barrel had score lines on it about 4-6 inches long at the bottom of the barrel and the piston had a deep guage line on it. after i found this out and thought about things everything made sense then. at the start i had a fast drift 4-6 inches long and then slow and after the rod replacement and reseal had the same thing again. I really need to brush up on my diagnostic skills and get some tools that i can at least take the cylinder apart and be able to asses damage first before sending it away... Thanks again for the help everyone, Much appreciated! David