Delrin rudder bearing opinions please

[ostra4]

Iv just removed the lower rudder bearing on our Dufour 38 as the rudder had been getting harder to turn over the past couple of years . I had to use a substantial pile driver to get the shaft down through the bearing and the bearing itself took an awful lot of time to finally remove it from its aluminium bearing cups .The bearing is self aligning and the removed bearings looked perfectly okay .Iv spent a while polishing the 74 mm stainless rudder shaft and the bearing now fits onto the shaft with the help of a wooden block and tapping it on . Whilst I can easily fit a new bearing I'm thinking I may well end up with same problem a few years down the line and I'm wondering if I can simply get the old bearing reamed out slightly so it slides easily to its location on the shaft ,any reason why that wouldn't suffice ?A new bearing is £300 plus which I'd be fine with if I knew the problem was sorted for a long time but I'm sceptical .The bearings are made of Delrin I believe which apparently absorbers water and swells ! This is the first time Iv tackled such a job so any advice would be welcome .

 

[DinghyMan]

Delrin absorbs a minute amount of water and doesn't swell much - I make loads of products that spend all their lives underwater.

I think you are confusing it with Nylon which does absorb water and swells and I'm sure I've read somewhere that early Dufours had nylon bearings.

 

[ostra4]

To be honest it looks like a lump of nylon to me although seems seriously hard , I'm easily confused about most things . I don't know what kind of fit the bearing should be on the shaft but from a point of no experience in these matters it does seem tight although relatively light tapping removes or replaces the bearing .It required two people with great effort to turn the rudder after I'd disconnected the steering quadrant prior to driving the rudder out .

 

[ostra4]

I should have said the boat was manufactured in 1999 .

 

[Tranona]

That does not sound like Delrin at all and you should not have to use any force at all to put on the shaft. Delrin does not absorb water significantly - that is why it is used for rudder bearings. It has to be machined to specific tolerances to provide the right clearance o the shaft as it is water lubricated.

What you have definitely needs replacing.

 

[RichardS]

The delrin "doughnut" should slide smoothly into the well-greased alloy hull casting and swivel with just a slight resistance when swivelled by hand. The doughnut should also slide easily onto the greases stock with no resistance and preferably no tangible play or jiggle space either.

If the doughnut is tight on the stock it can be sanded down .... but it sounds to me as if it is nylon which has expanded rather than delrin/acetal. If the doughnut is too tight the outside can be similarly sanded a little .... but check that the alloy housing is polished and corrosion-free inside as that is often the reason for a jammy doughnut.

Do a forum search for delrin bearings for the names of companies which can make up new bearings quite cheaply.

Richard

 

[DinghyMan]

I think they are made from Ertalyte http://www.par-group.co.uk/site-con...tics/3.79-pet-ertalyte-sheet-rod-tube-tds.pdf which absorbs the same anount of water as Delrin/Acetal - i.e. next to none.

The ball and socket ones sound like https://www.jp3steering.com/en/rudder-bearings/type-1and-15/

 

[ostra4]

Yes I think the bearing has expanded , the force required to drive the shaft out was immense , would nylon be strong enough to retain such a grip without breaking or cracking I don't know . I'm actually delighted Iv managed to get the thing out in one piece and at least have a pattern for a new one .Iv not dared use my autopilot all last season in case the strain caused damage so I'm looking forward to getting this back to non jammy doughnut - many thanks for the useful replies which is helping my learning curve !
I have cleaned up the aluminium bearing retains cups and can now reinsert the bearing with little difficulty but it still needs gentle tapping to get it back in position , maybe now it's out some more polishing/ sanding might do the trick .

 

[ostra4]

The delrin "doughnut" should slide smoothly into the well-greased alloy hull casting and swivel with just a slight resistance when swivelled by hand. The doughnut should also slide easily onto the greases stock with no resistance and preferably no tangible play or jiggle space either.

If the doughnut is tight on the stock it can be sanded down .... but it sounds to me as if it is nylon which has expanded rather than delrin/acetal. If the doughnut is too tight the outside can be similarly sanded a little .... but check that the alloy housing is polished and corrosion-free inside as that is often the reason for a jammy doughnut.

Do a forum search for delrin bearings for the names of companies which can make up new bearings quite cheaply.

Richard

Richard , looking at the companies for a new bearing would it be enough to explain that the old bearing which I will need to send for a pattern is too tight and let the person who makes the new bearing allow the correct new clearance for the shaft ?The shaft measures 74mm at the bearing location using my digital caliper .

 

[lw395]

Is the delrin bit under compression from the metal shell?
Perhaps as a result of corrosion of the metal?
I have this problem on a dinghy gudgeon, but at least the new part is only £15 or so....

 

[RichardS]

Is the delrin bit under compression from the metal shell?
Perhaps as a result of corrosion of the metal?
I have this problem on a dinghy gudgeon, but at least the new part is only £15 or so....

That is indeed a likely explanation for a tight bearing on the rudder stock whilst the doughnut is in the housing. However, in the OP's case, the doughnut is tight on the shaft even after the doughnut has been removed from the bearing housing.

Richard

 

[RichardS]

Richard , looking at the companies for a new bearing would it be enough to explain that the old bearing which I will need to send for a pattern is too tight and let the person who makes the new bearing allow the correct new clearance for the shaft ?The shaft measures 74mm at the bearing location using my digital caliper .

I would send the old bearing along with your measurements taken at different diameters across the shaft at the point where the bearing locates. If you measure the inside diameter across the bearing itself on different diameters is that 74mm as well? It probably is as the tightness is probably only a fraction of a mm.

If your current bearing is indeed nylon I would have a new delrin/acetal version made. It sounds like it is nylon if the rudder used to be fine but is now tight when out of its housing. If it is already delrin/acetal and was always too tight because of poor initial manufacturing then I would just sand it down with some wet and dry around a suitable former. The problem is that I don't think there's any easy way to tell the different materials apart unless you have identical pieces of them to determine the density.

I'm sure that Peter Squire at Versatile Marine http://versatilemarine.co.uk/workshop-services/ will be able to tell what it's made from once he sees it. I would give him a call and ask his advice. He's very helpful and, if it is delrin and in good condition, I'm sure he will hone it for you for at a sensible price rather than make you a new one.

My rudder stocks are 39mm on a 40 foot boat (although I do have two of them) and are very heavy. Your 74mm stock sounds absolutely massive .... it must weigh a ton!

Richard

 

[rudolph_hart]

I would send the old bearing along with your measurements taken at different diameters across the shaft at the point where the bearing locates. If you measure the inside diameter across the bearing itself on different diameters is that 74mm as well? It probably is as the tightness is probably only a fraction of a mm.

If your current bearing is indeed nylon I would have a new delrin/acetal version made. It sounds like it is nylon if the rudder used to be fine but is now tight when out of its housing. If it is already delrin/acetal and was always too tight because of poor initial manufacturing then I would just sand it down with some wet and dry around a suitable former. The problem is that I don't think there's any easy way to tell the different materials apart unless you have identical pieces of them to determine the density.

I'm sure that Peter Squire at Versatile Marine http://versatilemarine.co.uk/workshop-services/ will be able to tell what it's made from once he sees it. I would give him a call and ask his advice. He's very helpful and, if it is delrin and in good condition, I'm sure he will hone it for you for at a sensible price rather than make you a new one.

My rudder stocks are 39mm on a 40 foot boat (although I do have two of them) and are very heavy. Your 74mm stock sounds absolutely massive .... it must weigh a ton!

Richard

Another endorsement for Versatile Marine from me. They know their stuff.

Send them the old ones (even if they've been butchered by the removal process) and they'll turn them around very quickly. They'll also 'fine tune' them if they don't quite fit.

 

[Neil_Y]

To make a bearing we need to know (accurately to at least +/- 0.2mm) the shaft OD and the carrier ID. The actual clearance will depend on both as the thermal and moisture change are a percentage of the wall thickness of the bearing.

But to give you an idea for a rudder bearing with shaft 74.00 and carrier ID 100.00 (This was for SS shaft and GRP carrier) the running clearance for our material is 0.23mm. To work this out we run a calculation that includes the thermal expansion rates of the shaft, the carrier and the bearing as well as allowing for moisture. Often the biggest change in size is from thermal change.

 

[Spirit of Glenans]

The ball and socket ones sound like https://www.jp3steering.com/en/rudder-bearings/type-1and-15/

I have followed this thread with great interest as I have a rudder bearing problem with my Dufour Clasic 30, of similar vintage to the OP's. My rudder was displaying excessive play when I bought the boat. The surveyor recommended new bearings.
I ordered new ones from the Irish agent for Dufour and duly had them fitted by the boatyard where my boat resided at the time. When I checked the job I found no improvement, but the boatyard manager suggested that the lower bearing should expand when immersed for some time (the upper one was perfect). A couple of years later and many miles under the transom I cannot get the original boatyard to sort it out, but I am indebted to DinghyMan for posting the jp3steering link, as I can now see what the problem might be; that the metal carrier may be loose, or worn. Not a pleasant prospect if it's laminated in and has to be removed!

 

[ostra4]

Yes it will have been , when I eventually got the bearing out there was a build up of white powder from the aluminium, didn't look that much but had a big effect !

 

[ostra4]

Well as an update following everyone's very helpful advice -: firstly the boat is currently in Greece and the purpose of my visit is to try and sort the rudder bearing prior to the season starting in May so Iv a couple of weeks to mess around trying different things .Following the sanding and polishing advice Iv been on the case today and first I used a wet and dry on the shaft with some metal polish and gave it a real going over all round the bearing location area , after that I took my sand paper to the bearing itself and sanded the inside for half an hour or so then a good going over on the outside . Following a cup of tea I introduced the bearing to the now shiny shaft , yesterday the bearing required gentle tapping with wood block to get it in position , today it slid straight down shaft with no problem and no jiggling to its intended spot , O could easily turn the bearing with no play at all ..result! I cleaned up the cup holders again and introduced waterproof grease all over the area and inserted the bearing , all was smooth and I could insert the bearing and turn it till the shaft hole lined up by hand . At the start of removing the bearing I had a four foot pole inserted in there and could just about move it backwards and forwards so as you can. Imagine I was very happy with the result.The rudder can be removed without digging a hole so after more grease was applied I offered up the shaft into the hole and the blade of the rudder I managed to rest on. A block of wood whilst I had a breather , I gradually raised the rudder on blocks of wood until the shaft head reached the upper bearing area , after numerous trips up and down the ladder to look at the alignment from the emergency steering hole the shaft was I to the upper bearing and I gradually tapped more blocks and wedges under the blade till fully home .
Back. Inside now and shoe horned myself into the quadrant area from one of the aft cabins and replaced the auto helm linkage and through bolts for the shaft , everything tightened up and down ladder , removed blocks and tried rudder which had previously taken two big blokes an effort to move , result , one hand from lock to lock so I'm more than happy . Thanks to all who gave me their valuable input and I shall certainly be keeping a close eye on detecting any stiffness I future but next time I shall know more about what I'm doing .

 

[Laysula]

https://www.youtube.com/watch?v=9upUBC2tu1c&feature=youtube_gdata_player

This is a Bavaria rudder but sounds like the same as your Dufour.

 

[Tammany]

Theirs a chap on ebay that makes custom rudder bearings using aectal. Had a pair for mine made for £45

 

[ostra4]

Almost identical set up for the lower bearing , I was lucky in that eventually I managed to remove the bearing in one piece albeit after much patience and a few hours messing about getting to moving .