The Classic Machinery Network

Hi...as I've previously posted, my Hymac is very sloppy on the slew..she tends to creep to the right, when I am on a hill although turning to the left is ok and she holds ok..
I've changed check line valves and checked the cross-line relief valve, bled the suction tank and keep her topped up with hydraulic oil. It must be internal seals in the slew motor/staffa motor..

It is not a serious problem at the moment as I am clearing trees and undergrowth from an area that I drained last year but it will become more of an inconvenience if I am loading a trailer...I have been quoted £100 for the seal kit and it is a lot cheaper than a second hand motor which might be as bad as the existing motor. My question is....is it a big job and could a relative amateur like myself do it?...I have workshop manual...Thanks in advance...
Here are some pictures of my progress..The first picture is from last year

Hi Alex; to be fair I am not sure if you can do this job in-situ or not, but the job is an awkward one which ever way it is tackled, if you decide to take the slew motor off the machine you will need some lifting tackle to lift the slew motor off the machine, the seals should not be too much of an effort to replace.
I recall from sometime back in the past of hearing that someone managed to replace the seals on one of these without taking the slew motor off; however they had to leave the one cylinder on the motor as it cannot be accessed without removal of the motor, I suppose if you removed the hydraulic feed pipes and securing bolts you could turn the motor where it sits in the machine? Let us know how you get on.

Jeremy

Thanks Jeremy...I previously have rebuilt the transmission gearbox and have many years experience servicing old tractors on the farm but I am reluctant to do the slew motor as it might not be so straight-forward. I intend to do the rotary distributor seals when I next get the machine back to the yard. I will have a summer of contemplating..lol
No doubt it would improve the machine greatly though..

strontium90 wrote:Thanks Jeremy...I previously have rebuilt the transmission gearbox and have many years experience servicing old tractors on the farm but I am reluctant to do the slew motor as it might not be so straight-forward. I intend to do the rotary distributor seals when I next get the machine back to the yard. I will have a summer of contemplating..lol
No doubt it would improve the machine greatly though..

Edit:- If you are at some of the vintage shows during the summer and get a chance, I would be grateful if you could get some information from someone who has done this before...To be honest, if I could do it in-situ, it would be much easier as I am on my own, Would it just need the seals replaced on the pistons or would I have to remove the crank, which would mean removing the motor from the machine....Thanks in advance

Hi Alex,
I have removed and replaced the slew motors on the 580s which is not the easiest of jobs. It was always difficult to achieve sufficient torque when tightening the bolts securing the motor to the base plate. I have known them come loose and even distort the plate so make sure they are clean and Loctite them well. ( Priestmans used the same Staffa Motor on the Mustangs and used Hollow dowels round these bolts to prevent this problem).
I have resealed some of these motors for Priestman machines and though it's a long time ago, from memory, I can't see how you could do the complete reseal with the motor in situ.
You could easily get at the spool valve seals in the housing at the top of the motor but not the piston seals. From memory the pistons push in to the motor after removing the con rod retainer rings and crank and you'll need a good circlip plyers if you remove the con-rods from the pistons. With the amount of work involved it's certainly not worth cutting any corners.

Fred

Thanks Fred your experience is priceless.

Jeremy

Thanks Fred...I had never even thought of re-torqueing the motor back in...It's a job I will put on the back burner for now...

Hi guys. It looks like I’m going to have to do this same job on my 580C as it doesn’t stop well when you let go of the controls plus now it is leaking really bad out the bottom around the gear. Can you guys provide any part numbers or info on the seal kits so I can hopefully source them locally in Canada.

Canada Hymac 570c wrote:Hi guys. It looks like I’m going to have to do this same job on my 580C as it doesn’t stop well when you let go of the controls plus now it is leaking really bad out the bottom around the gear. Can you guys provide any part numbers or info on the seal kits so I can hopefully source them locally in Canada.

Hi Dan I would just take your old seals for samples to a local bearing/drives and seals supplier they should be able to help you out.

Jeremy

Hi Alex,
To be honest I doubt if your local supply will match these seals as they are a bit specialised.
These motors are fitted in all sorts of industrial applications and I'm sure you will find a supplier on line if you Google "Staffa motor parts." or "Staffa motor seals." I think they are now part of Kawasaki hydraulics.
Fred