Brunton Autoprop -- Brinelled Bearings

[Pauls]

The bearing failure in your picture is grotesque. The pattern clearly reveals the cause. Roller type bearings are lubricated by their movement (when rolling) in grease. When they are not moved enough they squeeze out the grease film which forms a lubricating film between the rollers and the races and from then on run in an inadequately lubricated condition until they are again moved a great enough distance to relubricate themselves.

I recently completed an engineering job dealing with highly loaded roller bearings which were only moving very small distances. We worked directly with the bearing manufacturer on this and it was clear that our mode of operation would quickly destroy the bearings. For us the solution was a design which allowed frequent (every 15 minutes) large movement of the bearing to redistribute the grease and lube everything, then back to 15 minutes of the high load, small motions.

Your prop only makes a significant motion when it is deploying/feathering. Under power the blades are making constant, very small motions while under load. This could go on for hours. In this operating regime bearing life will be determined by the load you put on the blades, and it will definitely be finite.

A grease loaded with extreme pressure solid lubricants would help. I don't know if molybdenium disulfide is a galvanic problem, you'd want to verify that.

[Nicholson58]

Ours is a 1984 Hundested variable pitch on a 115 HP engine. Adjustment is from the cockpit by hand crank. Disassembly is with an Allen wrench and an adjustable metric (Crescent ) wrench. No ball or other rolling element bearings. Grease is pumped in from the coupling at the forward end of the shaft. It will easily adjust to more aggressive pitch under load but flattening out is best done by first throttling down to remove torque. This is acceptable since we usually are entering a marina and slowing when we want the pitch reduced.


There are three blades and each is numbered. Each operator is number matched to the blade and its slot in the hub. These are little sliding bronze blocks. Ours is the original 1984 with many thousands of hours. I disassembled to rebuild the shaft gland and found little or no wear on the bronze parts.

This I probably not much help to the OP except to note that finding a way to let the blade rotation happen while unloaded could help. As a Machine designer and builder, it is bothersome to find rolling element bearings applied in such a harsh environment. Sometimes, the simple, old ways are more reliable. Bearings brinelled usually means high loads and insufficient lubrication (or inadequate design). You can help minimize the damage by using an extreme pressure lubricant compatible with the environment; reduce high loads as much as possible; make sure there are no unbalances. Avoid impacts & sudden or reverse loading. Extreme pre-load could also be a factor towards initiating failure.

Are there bearing numbers on the races? Bearings used by builders are usually stock components and might be purchased directly from a stocking distributor for a fraction of what you might otherwise pay. Common suppliers are SKF, Timken, Torrington, NGK. A good supplier can quickly cross-reference for you. Carry a spare set. If these races are integral with the bronze part then shame on the builder!!

[Frankly]

I have one of the older water lubed Autoprops that started giving some trouble a few year back. I sent it back to Bruntons to have the outer races remachined. Wouldn't believe the postage to ship that hog back to good old England from Florida. AB marine believed that the brinelling is caused because the procedure Bruntons recommends for bearing adjustment is too loose. This causes the blades to rock back and forth at the prop rotates. I now set the blades just as tight as I can get them while allowing for free movement. That was 7 or 8 years back and new procedure has worked so far.

I have had some shaft resonance issues when the Yanmar motor mounts wear a few years. New mounts solve the problem; but like Bruntons, Yanmar is mighty proud of their parts. Got a new set of 100's setting on my bench now to replace the softer 70's. See if they last a little longer.

Really like the AP (previous owner wrote the big check), but owning it has not been an all roses experience.

[lamadriver]

I just got the bearing kit and was shocked at the bill , with the tools and shipping about $600 .....

I am glad to hear it is fairly easy to do , as It is on my to do list sooner rather than later.

My boat came with an AP , thought the previous owner didnt disclose it was used... the serial # puts it 20 years old Brutons assured me it wasnt in the batch that had the issues.

It truly is awesome for motorsailing.

[Dockhead]

Originally Posted by lamadriver

I just got the bearing kit and was shocked at the bill , with the tools and shipping about $600 .....

I am glad to hear it is fairly easy to do , as It is on my to do list sooner rather than later.

My boat came with an AP , thought the previous owner didnt disclose it was used... the serial # puts it 20 years old Brutons assured me it wasnt in the batch that had the issues.

It truly is awesome for motorsailing.

There are only two fiddly parts to this -- getting the thrust bearing races out of the blades, and doing the seals.

The thrust bearing races are supposed "fall out", but they won't if they are stuck in grease. And there is no tool which I could find or think of which will pry them out. I even tried dental picks. I finally got them out by soaking in white spirit and rotating the races to dissolve the grease; then held the blade upside down, worked the race with a screwdriver and it popped out.

The seals come off with a good jerk with a pair of pliers, but putting the new ones in takes a lot of finger strength and patience.

Next time will be easier.

[Dockhead]

Originally Posted by Nicholson58

Ours is a 1984 Hundested variable pitch on a 115 HP engine. Adjustment is from the cockpit by hand crank. Disassembly is with an Allen wrench and an adjustable metric (Crescent ) wrench. No ball or other rolling element bearings. Grease is pumped in from the coupling at the forward end of the shaft. It will easily adjust to more aggressive pitch under load but flattening out is best done by first throttling down to remove torque. This is acceptable since we usually are entering a marina and slowing when we want the pitch reduced.


There are three blades and each is numbered. Each operator is number matched to the blade and its slot in the hub. These are little sliding bronze blocks. Ours is the original 1984 with many thousands of hours. I disassembled to rebuild the shaft gland and found little or no wear on the bronze parts.

This I probably not much help to the OP except to note that finding a way to let the blade rotation happen while unloaded could help. As a Machine designer and builder, it is bothersome to find rolling element bearings applied in such a harsh environment. Sometimes, the simple, old ways are more reliable. Bearings brinelled usually means high loads and insufficient lubrication (or inadequate design). You can help minimize the damage by using an extreme pressure lubricant compatible with the environment; reduce high loads as much as possible; make sure there are no unbalances. Avoid impacts & sudden or reverse loading. Extreme pre-load could also be a factor towards initiating failure.

Are there bearing numbers on the races? Bearings used by builders are usually stock components and might be purchased directly from a stocking distributor for a fraction of what you might otherwise pay. Common suppliers are SKF, Timken, Torrington, NGK. A good supplier can quickly cross-reference for you. Carry a spare set. If these races are integral with the bronze part then shame on the builder!!

The Hundested is a beauty! My next prop. They no longer make them for plant less than 150 hp.

Yes, the bearings are bog standard SKF 51110. They are widely available and cost $30 each, so $90 for the whole prop. You'd need seals and tab screws besides the bearings.

I might carry a spare set in future, although, on the other hand, brinelled bearings is not going to stop your cruise. The prop was working fine -- I only noticed this when I dried the boat out. I guess I could have sailed for another year with them like this with no ill consequences.

[a64pilot]

Seems bearings have a hardened surface, once they wear through this surface, wear is rapid.
I believe you caught it just right, before any damage was done. I'll have to start paying attention to mine when I clean it, rotate the blades feeling for roughness.
Good to know it can be repaired in the field

[Dockhead]

Originally Posted by a64pilot

Seems bearings have a hardened surface, once they wear through this surface, wear is rapid.
I believe you caught it just right, before any damage was done. I'll have to start paying attention to mine when I clean it, rotate the blades feeling for roughness.
Good to know it can be repaired in the field

It can be repaired in the field without a doubt, but a couple of steps took me much longer than I would have expected. The seals are fiddly and you can't use tools (need strong fingers), and I had a lot of trouble getting the thrust bearing races out of the blades (they fall out once the grease releases; soak in white spirits).

Definitely rotate and feel the blades for play or roughness, frequently. Grease the prop everytime you haul. Use the special waterproof grease.

These props are a lot of trouble, but worth it.

[a64pilot]

I only plan to haul every other year, I'm going for the inwater grease option.
I intend to install three 5mm SS zirk fittings, one in each blade of course and leave them in, I would still have to remove the plug to grease, but I think you should be able to grease in the water?
Using that supplied fitting in the water would make me nervous, looks like I could break the thing off too easily.
I haven't done it yet, this spring will be the first time.

I've heard grease yearly, and I've heard grease every other year, sounds like you say grease much more often that than, like quarterly?


I can see how having just a little play in the bearing could likely cause the problem you had, adjusting it so there is zero lash does sound like a good idea.

[Dockhead]

Originally Posted by a64pilot

I only plan to haul every other year, I'm going for the inwater grease option.
I intend to install three 5mm SS zirk fittings, one in each blade of course and leave them in, I would still have to remove the plug to grease, but I think you should be able to grease in the water?
Using that supplied fitting in the water would make me nervous, looks like I could break the thing off too easily.
I haven't done it yet, this spring will be the first time.

I've heard grease yearly, and I've heard grease every other year, sounds like you say grease much more often that than, like quarterly?


I can see how having just a little play in the bearing could likely cause the problem you had, adjusting it so there is zero lash does sound like a good idea.

I would ask Brunton.

The manual says you might get away with every other year.

I would not do it in the water -- the bearing space is sealed and you definitely don't want sea water in there. But Brunton's can give you advice I think.

I grease at least twice, usually three or four times a year. Usually every time I haul but occasionally I may skip one haul for whatever reason.

The old grease which comes out always looks like it needed to come out, so I don't think I personally would do it less often than this.

But YMMV -- it depends also on how many hours you're doing and under what conditions.

The only thing about greasing -- you certainly want all the grease film you can get, to avoid that brinelling, which I suspect is a design "feature" of a bearing which carries a lot of load without rolling much.

Probably also a good idea to vary speed periodically.

I motored for about 7 hours at a constant speed of about 3000RPM, hurrying to get through the Kiel Canal before the tide changed in the Elbe (there was a crew waiting in Cuxhaven). I wonder if that contributed to this failure.

[unclemack]

Pauls' post got me wondering why ball/roller bearings were chosen for either of these applications in the first place.

Instinctively I'd think of tapered, bushed, adjustable plain bearings for resistance to wear when specific areas are subject to concentrated loading.

The blades' bearings aren't required to rotate at high speed and I'm assuming that water pressure on the blades/centrifugal force ought easily to overcome the slightly greater friction of plain bearings.

Can't support this opinion with even a scrap of evidence though. I've forgotten most of anything I ever learned so I'm often wrong

[Dockhead]

Originally Posted by unclemack

Pauls' post got me wondering why ball/roller bearings were chosen for either of these applications in the first place.

Instinctively I'd think of tapered, bushed, adjustable plain bearings for resistance to wear when specific areas are subject to concentrated loading.

The blades' bearings aren't required to rotate at high speed and I'm assuming that water pressure on the blades/centrifugal force ought easily to overcome the slightly greater friction of plain bearings.

Can't support this opinion with even a scrap of evidence though. I've forgotten most of anything I ever learned so I'm often wrong

I had exactly the same thought.

I am not, however, a mechanical engineer, and I guess Bruntons must have had good reasons. Bruntons by the way is a formidable engineering company which makes propellers for big ships. Not a niche maker of equipment for recreational vessels, unlike almost all other makers of propellers for sailboats. They have huge engineering resources. That doesn't mean, of course, that they never make design mistakes.

[a64pilot]

I'd guess you would need a ball or roller bearing to reduce friction, I assume if you don't have a very free rotation, that could lead to slightly different blade angles and that to vibration.
I'd assume that if you had a plain bearing, you would need to mechanically couple the blades together to ensure all were at the same angle of attack.
I've had people, seemingly mostly IP owners warn me of a washing machine out of balance type of vibration when reverse or forward is first selected. I assume this is from a blade not having the same angle of attack as the other two.
I've never experienced that, but I also first select either forward or reverse and then wait a couple of seconds to let the prop adjust pitch before I add throttle, and I think they are going straight from forward to reverse with no pause, most people do.
I assume if you had an even slightly sticking blade, this issue would be worse.
It may be that the thick section of keel on an IP in front of the prop aggravates this, but as I said I pause before throttle application.

[Frankly]

I pull the AP off Cbreeze in the water on a regular basis. Typically it is to clean and repaint the beast. Made my own wheel puller (just a typical disc puller with three holes to align with the zinc mount). Takes about 20 minutes and use a surface (80 cuft bottle) supplied hooka system. Don't do this in deep water because when that chunk of bronze comes off the shaft you are heading for the bottom at a rapid rate (reckon could use a safety line on the prop).

As to why Bruntons used ball bearings, those blades have to all assume the same precise angle of attack. Get a little weed in one of the bearing races (probably not likely on the sealed unit) and you will be off to the dentist to get your fillings replaced.

[Dockhead]

Originally Posted by Frankly

I pull the AP off Cbreeze in the water on a regular basis. Typically it is to clean and repaint the beast. Made my own wheel puller (just a typical disc puller with three holes to align with the zinc mount). Takes about 20 minutes and use a surface (80 cuft bottle) supplied hooka system. Don't do this in deep water because when that chunk of bronze comes off the shaft you are heading for the bottom at a rapid rate (reckon could use a safety line on the prop).

As to why Bruntons used ball bearings, those blades have to all assume the same precise angle of attack. Get a little weed in one of the bearing races (probably not likely on the sealed unit) and you will be off to the dentist to get your fillings replaced.

That's a good idea for you, A64. I didn't think of that.

You could surely do it this way.