stiff hydraulic steering

[Csail]

I have got Vetus hydraulic steering on a 31' colvic.The rudder is supported from beneath with a teflon bush which was replaced last year but the steering has got stiffer over the last season.The hyd. ram is free when dis-connected so is there any reason why the rudder gland may stiffen up even though greased every week?

 

[Talbot]

seem to remember that some bush material will swell underwater, which is why delrin is recommended. this may be the problem.

 

[Strathglass]

Exactly as talbot says. Afraid that The material you have used swells up when immersed in water.

You will either have to replace the bearings or it may be possible for you to ream our the existing new bearing to give more clearance in situ if you can remove the rudder.

You could try disconnecting the hydraulic drive and moving the rudder blade to confirm it is the bearings.

One of those things I'm afraid


Iain.

 

[Graham_Wright]

Teflon I think is PTFE (PolyTetraFlouroEthylene) which does not absorb moisture (it is used extensively in the broadcasting industry partly for this reason) but, although slippy, is also soft.

Delryn, recommended by Talbot, is acetal which is a hard plastic and also does not absorb moisture so should be a reasonable replacement.

Do NOT use nylon (by whatever name) as it DOES absorb water and will swell.

Another material recommended for this particular task is UHMWPE (UltraHighMolecularWeightPolyEthylene) irreverently described as Ummpy.
This is slippy but not as hard as acetal so it may be better from the point of view of stock wear (or it may make it worse!).

 

[snowleopard]

A swollen bearing sleeve is the prime suspect but not the only possibility. On mine the ball joint connecting the ram to the tiller seized up and was eventually freed by liberal application of WD40.

 

[Graham_Wright]

[ QUOTE ]
Exactly as talbot says. Afraid that The material you have used swells up when immersed in water. Iain.

[/ QUOTE ]

So please educate;- what is Teflon? I though it was PTFE.

I supply many PTFE components for mobile 'phone transmitters and PTFE is specified for its dielectric properties and its non absorbtion of water.

My customer advises that a sure test for water absorbtion is to leave the item to soak in water and then microwave it in a domestic microwave (include a bowl of water in the cabinet to save blowing the magnetron).

If it heats up, it has absorbed water.

 

[kandoma]

Teflon is a brand name for PTFE. PTFE is one of the "best" plastic available on this planet: high temperatur (above 200°C), selflubricating and many more good things. The bad side of PTFE is: price, very difficult to glue and most important: it gives way under pressure. I do not know the correct english word for it. We call it in german: it swimms. So it gives a very bad washer under a screw. The screw will be loose after a few days. Its almost perfect for bearings, where the swimming effect is not encountered.

Delrin is also a brand name, and has similiar qualities as PTFE. But it is much cheaper and has a much lower temperatur range then PTFE. It is very often used as a substitute for PTFE, when high temperatur is of no concern. Also the selflubricating effect is a little bit less, but of no importence to a bearing for a boat rudder.

You can find out by your self, what material is used: burn the material in question with a gas cigarette lighter: PTFE (Teflon) will get smaller and smaller, you will not see any smoke. Delrin will burn.

Peter

 

[Graham_Wright]

Swimms = flows in Engish!

The burn test can be very useful with practice. HDPE and UHMWPE give off a waxy smell like candles, nylon is very acrid. Don't know about acetal. But don't inhale;- they are all probably toxic.