Wheel Horse 500H Series Power Steering Conversion

[Damien Walker 246]

Dear All,

 

On Dennis Thornton's suggestion (thank you Dennis, good idea!), I have written up my 518H Power Steering Conversion into a pdf.

 

It reaches just to 8 pages long and so is quite detailed. I have included photos where I can, but words are also necessary, particularly as I have documented the project after completing the build. I should have taken photos en-route but didn't because I was never certain that it would all fit together and work until the final engine start! I'll know better next time!

 

Obviously I have had to add a disclaimer - you modify your tractor at your own risk, but I will help as best I can via this forum if anyone wants to have a go. It seems a complex project at first glance but it's not really, it is about as straight forward as it can be.

 

Please let me know if there is anything that I could explain better in the instructions (e,g, hose lengths and fittings required - difficult for me to document now - sorry!) or if you find any errors that need correcting.

 

Wheelhorse 518H Power Steering Conversion Step by Step.pdf

[Damien Walker 246]

I've just been looking at my C175 and I just thought I would note some obvious differences:

 

1) Column top bearing would have to be different. The C175 dash frame is cast alloy and so it would not be possible to weld in a steel top bearing tube! An aluminium tube, TIG welded in place might work though. It is important to protect the steering valve from axial and lateral forces and so a robust top bearing is important.

2) The lift valve appears to be mounted nearer the centre of the tractor and/or it sits on a wider mounting plate. I don't think this  will interfere with the conversion but it looks as though there is a little less space available.

[seuadr 488]

thanks for sharing!

[Damien Walker 246]

Some further thoughts:

 

Standard Wheel Horse steering ratio appears to be one turn lock to lock (that's what my C175 is)...no wonder it is heavy!

The power steering conversion on my 518H turns out to be 4.5 turns lock to lock which I think is a little too much (probably ok once I get used to it or if I use a wheel spinner).

 

My guess is that somewhere in between would be more convenient.

 

As far as I recall, my steering valve is an OSPM32 ie 32cc per revolution, so that implies my ram volume is 144cc and there appears to be about 9cm (3.5") of travel....which in turn implies a ram piston diameter of about 4.5cm (1 3/4"). I don't think these numbers are very accurate (piston diameter appears to be approx 1.5" because it is difficult to tell without stripping the ram!) but they are roughly in the right ball park.

 

Danfoss make a range of mini steering valves with capacities varying from 32cc to 100cc per revolution (Danfoss now owned by 'Sauer' it would seem) and the good thing is that the diameter of their bodies and their 4 bolt mountings, appear to be common across the range with only the length varying between valves of different capacities....and so it should be relatively easy to adapt my modification to take a larger (longer) valve.

 

If 32cc gives 4.5 turns lock to lock using the ram from a 520xi, then my guess is that the following turns ratios would be the result, using the following different valves:

 

OSPM32: 4.5T

OSPM40: 3.6T

OSPM63: 2.3T

OSPM80: 1.8T

OSPM100: 1.4T

 

and I'd say all of the others would be better than my labour intensive 4.5T!

 

My guess is that steering effort would not be affected (because it is the hydraulic pressure that does the work ... any experts out there?)

 

You could also reduce the diameter of the ram and again, as it is the hydraulics doing the work, I think the steering effort would not be affected...perhaps I should find a smaller ram and try the idea!

 

Anyway, the conclusion is: to get the numbers of turns lock to lock down to a more drivable number, I should have used a valve with a larger capacity or a smaller ram.

[Damien Walker 246]

Ok! I have swapped the steering ram for a smaller diameter one.

 

The combination of a Danfoss OSPM32 and the 520xi steering ram resulted in a turns ratio of 4.5:1 (Original tractor is 1:1). This is too high. I have now replaced the 520xi ram with a privately sourced 1” diameter dual acting ram and the turns ratio has been reduced to 1.5:1 and remains finger tip light. The new ram is longer than the original (at 6” stroke) which meant repositioning the chassis mount to the right hand side and drilling a new hole for the ram mounting. The details are slightly different but the concept is exactly the same.

 

I've updated my step by step instructions but it the change is essentially as I have written here.

 

Wheelhorse 518H Power Steering Conversion Step by Step Rev 2.pdf

[Damien Walker 246]

I found another useful photo....showing the top bearing welded to the dashboard....

I have also up-issued the step by step to include this.

 

Wheelhorse 518H Power Steering Conversion Step by Step Rev 3.pdf

[Damien Walker 246]

Apologies, I have been very busy...but here is the (hopefully) final version of my Power Steering conversion step by step....now includes the Ackerman geometry correction.Wheelhorse 518H Power Steering Conversion Step by Step Rev 4.pdf