Yamaha Malta Prop

Boathook

Boathook

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Next project ......
Rubber bush on this prop had slipped too many times and the rubber had started to crumble. The bush was also out of centre. Had a look on ebay for rubber bushes, but what type of rubber should I be looking? Also, any suggestions on how much oversize the bush should be for it to grip. Whether I can push the lot together I will worry about once I have purchased the bush, as long as it isn't to expensive.
Another option is that I put groves on the bush and prop and fill the annulus with thickened epoxy resin, I'm thinking 403 Microfibres Adhesive Filler and 402 Milled Glass Fibre Blend (West System as I have them!). This should make the resin strong enough to hopefully stand the shear force, etc.

I know that I could purchase a new prop, but they seem to retail for around £60 to 70, and this is PBO forum and it is a knackered prop so scrap metal .........
 

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No idea about which resin or thickener but the first thing that springs to mind is the difficulty in getting the prop centred. If the sleeve is off centre at all, the vibration will destroy the gear box in short order. However, you may find a prop repairer who can fit a new bush for you.
Otherwise, I’d take a deep breath and buy a new prop.
 
I waste a lot of time playing with old cars and I'm aware that people are making their own suspension bushes with 2 part silicon (and possibly other 2 part rubbers). When I heard that I decided that if my o/boards suffer as yours is then that will be a fun project.
 
I think that, when forming a DIY bush, it would be almost impossible to hold the inner metal bush centered with the prop that is missing any outside cylindrical surface, while a bought rubber bush of the correct dimensions could be centered enough. Don't take this for sure: it's only my opinion.
Another surely centered solution could be a bronze bush slightly forced or pinned in the propeller and rotating free on the splined bush. A shear pin should make the driving connection.The nut on the shaft should not be completely tightened. The cotter pin would avoid its loosing.

I disapproove the lacking of a shear pin in this otherways excellent motor. It is not sensible to have to buy a very expensive propeller after just having hit an underwater snag - not a rare occurrence.

Sandro
 
I resolved by hammering about 4 nails in at equal distances. Crude I know but this was 8 years ago and still no issues!
 
anoccasionalyachtsman said:
I waste a lot of time playing with old cars and I'm aware that people are making their own suspension bushes with 2 part silicon (and possibly other 2 part rubbers). When I heard that I decided that if my o/boards suffer as yours is then that will be a fun project.
Click to expand...
Links to those two types of products would be appreciated. At least I will know what to search for.
 
Sandro said:
I think that, when forming a DIY bush, it would be almost impossible to hold the inner metal bush centered with the prop that is missing any outside cylindrical surface, while a bought rubber bush of the correct dimensions could be centered enough. Don't take this for sure: it's only my opinion.
Another surely centered solution could be a bronze bush slightly forced or pinned in the propeller and rotating free on the splined bush. A shear pin should make the driving connection.The nut on the shaft should not be completely tightened. The cotter pin would avoid its loosing.

I disapproove the lacking of a shear pin in this otherways excellent motor. It is not sensible to have to buy a very expensive propeller after just having hit an underwater snag - not a rare occurrence.

Sandro
Click to expand...
Personally I'm not bothered about the lack of shear pin. A shear pin takes one hit and goes, as I found found out on another outboard on a dinghy. Rubber bushes can take a few hits before they really fail imho. My main engine is an outboard with a rubber bushed prop and I only purchased a new prop as the old ones blades were too worn for economical repair; not a bush problem. This was after nearly 30 years. I would like to add that I carry a spare prop for my main outboard and only done a changes due to blade damage in 35 plus years.
Just hope that this post hasn't altered the chances ....
 
Boathook,
glad to hear that. My Malta rubber bush never broke but I was told that on a hit the rubber would tear completely and, hop! new propeller.
Now I remember; the one who told me that, was the Yamaha dealer that would sell the new propeller.
Thanks for my new peace of mind.
 
Quote "I’ve drilled the hub of a Malta prop and inserted a couple of self tappers to grip the metal bush. Lasted for about three seasons before I dinged The bottom again and decided to buy a new one rather than try resurrecting the old one again." End quote

I've done that, when the prop started to slip at the start of a 3 week trip, and there was no possibility of getting a replacement quickly.
I replaced the prop before the next trip, but it worked OK, although I was very gentle with the throttle for 3 week with three adults and a large dog on board the inflatable.
 
anoccasionalyachtsman said:
Some 'how' videos
Click to expand...
Thanks for the link. I hadn't a clue what to search for.
Now on order "Polyurethane Rubber *Firm* Shore A 85 304g Kit *Ideal for Poly Bushes* SLOW" from a company called DWR Plastics on ebay (no dealings with company apart from now). The remains of the old bush felt fairly firm so I hoping that this 'Shore A 85' rated product will do. I did find on the web a simple scale of hardness as below. Whether a softer one would have more forgiveness when something is hit I don't know. I suspect that now there will be posts saying that I should have used a 55 hardness.

Hardness Shore A Application
30 Art gum erasers
35 Rubber bands
40 Can tester pads
50 Rubber stamps
55 Pencil erasers
60 Screen wiper blades
65 Automotive tires
70 Shoe heels
75 Abrasive handling pads
80 Shoe soles
85 Tap washers
90 Typewriter rollers
95 Fork lift solid tires
60 Shore D Golf ball
70 Shore D Metal forming wiper dies
80 Shore D Paper-making rolls
 
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Not just by curiosity, but I may happen to want to do the same job one day.

I suppose you will cast the liquid Polyurethan in the propeller hub around the metal splined bush.
How will you hold the bush exactly in center and alined with the propeller hub? This one has no geometrical surfaces to refer to,
except inside.
A rough positioning can be acceptable for the car suspension bushes of the videos but in our case the slightest offset would cause noxious vibrations.

Sandro
 
Sandro said:
Not just by curiosity, but I may happen to want to do the same job one day.

I suppose you will cast the liquid Polyurethan in the propeller hub around the metal splined bush.
How will you hold the bush exactly in center and alined with the propeller hub? This one has no geometrical surfaces to refer to,
except inside.
A rough positioning can be acceptable for the car suspension bushes of the videos but in our case the slightest offset would cause noxious vibrations.

Sandro
Click to expand...
The 'nut end' of the prop is a fairly close fit and I will possibly hold the bush in place with some 'hot glue' that will also seal the annulus. It hopefully can't be worse than a damaged prop which my Malta presently has and the vibrations aren't to bad.

Having mentioned hot glue I wonder whether that would have done for the repair. The whole assembly would have to be 'hot' to allow the glue to settle well but any damage could be repaired by heating back up and possibly adding a bit more glue - a boat cooker job !
 
Boathook said:
The 'nut end' of the prop is a fairly close fit and I will possibly hold the bush in place with some 'hot glue' that will also seal the annulus. It hopefully can't be worse than a damaged prop which my Malta presently has and the vibrations aren't to bad.

Having mentioned hot glue I wonder whether that would have done for the repair. The whole assembly would have to be 'hot' to allow the glue to settle well but any damage could be repaired by heating back up and possibly adding a bit more glue - a boat cooker job !
Click to expand...
I was thinking of using three shims of hard plastic/grp/anything I could find equi-spaced?
 
In the meantime I answered my own question:

Having access to a lathe one could make two rings (aluminium? nylon?) to be left included in the polyurethan casting.
The upper ring should be widely holed to allow pouring the polyurethan.
This would give very good position accuracy.

Something like the attachment.

Sandro
 

Attachments

Sandro said:
In the meantime I answered my own question:

Having access to a lathe one could make two rings (aluminium? nylon?) to be left included in the polyurethan casting.
The upper ring should be widely holed to allow pouring the polyurethan.
This would give very good position accuracy.

Something like the attachment.

Sandro
Click to expand...
Yes, I should have said that 'my' shims would be left in place, but your method is very neat if the viscosity of the liquid allows.
 
anoccasionalyachtsman said:
Yes, I should have said that 'my' shims would be left in place, but your method is very neat if the viscosity of the liquid allows.
Click to expand...
On my prop the shim at the 'nut end' would only be 0.5mm thick as the annulus is only just 1mm. With it all resting on a flat surface I'm hoping that it will all be in alignment to an accuracy good enough.
 
What I fear is the push of the rather thick poly during pouring in. It could displace the metal bush if not strongly fit.

In the sketch I should have added a distancer under the metal bush to position it axially but I did not know where it should stay - flush, protruding, recessed, how much? Don't have the propeller at hand. Should be measured before destroying the old rubber bush.

Anyway I hope not to need this knowledge too soon.
 
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