601 hydraulic lift cover

My grandson bought a 601 diesel with a front
loader on it. The lift has not worked in years. I
have pulled the top off twice and replaced the
unloading valve O ring with the one that comes
with these Chinese gasket and O ring sets. Cleaned
up the unloading shuttle and the bore good and
bright with 400 grit paper and washed and blew
everything down. Still no lift. I even pulled the
pump and checked everything out. Nothing wrong
with it. Primes good and seems to have good
pressure and flow.

Since I first posted I have taken the hack
pressure/check valve/s out and inspected. OK.

Pulled the lift cylinder and control housing and
even pressed out the two bushings, control valve
and unloading valve bushings. Probed all the
drilled passage ways to the bottom of the holes.
probed the auxillary adapter plate passages and
all are open to their next openings.

With air pressure to the pressure port on the
cover at right front corner I can cause the
unloading valve to open and close with the control
valve is moved in and out but when the unloading
valve goes to the raise position it seems to just
block the air and it does not go to the ram
cylinder piston.

Still no lift

Any ideas would be appeciated.

Thanks, Zane

You've sure cover the bases Zane. It seems to me that your pump is working and the top cover is in great shape. That only leaves the path between the top cover and the pump. Since the o-rings are not leaking, the only thing left is the relief valve. Any chance that it has failed? I know they rarely go bad but maybe!

The spring for the check valve was too strong and too long and when the plug was tightened it pushed the ball down on the seat with no way for it to get pushed off. Jammed down.

Backed the plug up a bit and it worked great. First time in 50 years of fixing these lifts that I've run into something like this. PO must have been having problems with it and put the wrong spring in it. Probably the reason it was sold at auction cheap.

Zane