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Metalastik Coupling Sheared (6.25")


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2 minutes ago, john.k said:

Yeah,I see the wobbly shaft.now......more at home on a car than a boat............Didnt look,....rigid coupling will be OK.

 

For information. It seems common on mid-engine room narrow boats and I have seen it used on some Broads cruisers. Before the Aquadrive type coupling came out it was about the only way to avoid alignment problems. Still agree not well suited to be mounted low down in a boat, too much danger of water ingress into the needle rollers and the sliding joint if one is fitted.

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Nick at Brinklow Boat Services had a steel replacement coupling machined, and I fitted this steel coupling yesterday. Drive now working fine without the Metalastic coupling, as expected. Very nice to be back on a boat that can move again. Good test trying to cope with the excessive blanket weed on the Middle Levels.

 

Nick also confirmed that the Blackstone 2:1 reduction box has a thrust bearing on the output shaft as standard, so is not really suited to having a prop-shaft with a plummer block 'that does not take thrust' (to use Tony's words from above).

 

How can you tell whether your plummer block can take thrust ?

 

Ralph

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15 minutes ago, fladda said:

Nick at Brinklow Boat Services had a steel replacement coupling machined, and I fitted this steel coupling yesterday. Drive now working fine without the Metalastic coupling, as expected. Very nice to be back on a boat that can move again. Good test trying to cope with the excessive blanket weed on the Middle Levels.

 

Nick also confirmed that the Blackstone 2:1 reduction box has a thrust bearing on the output shaft as standard, so is not really suited to having a prop-shaft with a plummer block 'that does not take thrust' (to use Tony's words from above).

 

How can you tell whether your plummer block can take thrust ?

 

Ralph

The 2:1 box does indeed have a thrust bearing that is eye watering in price. Just shy of £1k when I last priced one up…that’s for a decent make not a cheap one made of Chineseum. 
 

I have a Plummer block fitted that takes thrust made by FAG….it’s not just the block but the bearing inside it. 
 

I’ve got all the paperwork back at base as I’m out boating at mo but when I’m back I can find you part numbers etc as I replaced all my bearings etc when I fitted a new stern tube a couple of years ago. 

 

 

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16 minutes ago, frangar said:

The 2:1 box does indeed have a thrust bearing that is eye watering in price. Just shy of £1k when I last priced one up…that’s for a decent make not a cheap one made of Chineseum. 
 

I have a Plummer block fitted that takes thrust made by FAG….it’s not just the block but the bearing inside it. 
 

I’ve got all the paperwork back at base as I’m out boating at mo but when I’m back I can find you part numbers etc as I replaced all my bearings etc when I fitted a new stern tube a couple of years ago. 

 

 

Mine is a Dodge 

image.png.b0d06e655f5950d757a5fd8bc23f2b75.png

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2 hours ago, fladda said:

Nick at Brinklow Boat Services had a steel replacement coupling machined, and I fitted this steel coupling yesterday. Drive now working fine without the Metalastic coupling, as expected. Very nice to be back on a boat that can move again. Good test trying to cope with the excessive blanket weed on the Middle Levels.

 

Nick also confirmed that the Blackstone 2:1 reduction box has a thrust bearing on the output shaft as standard, so is not really suited to having a prop-shaft with a plummer block 'that does not take thrust' (to use Tony's words from above).

 

How can you tell whether your plummer block can take thrust ?

 

Ralph

 

The bearing is unlikely to be an ordinary ball bearing, possibly a split trach angular contact bearing. There are usually collars around the shaft on both sides with grub screws in (as shown by Alan's post). The screws go into dimples drilled into the shaft to transfer thrust from the shaft to the bearing.

 

Even if you do have a thrust bearing in the box it is far from a good idea to expect Hooks joints to transmit thrust with the cardon shaft angled. At the least it will transmit side thrust onto the plumber block bearing. (I know it is common on narrow boats).

 

Anyway, if it had run for years with the Metalasic coupling there is no reason to suppose it won't go on for many more years with the solid coupling.

Edited by Tony Brooks
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Usually thrust plummer blocks have four bolts, two each side holding them down. They are also normaly fatter to contain often twin Timken taper roller bearings conically facing each other to take thrust in either direction. With grub screws through into indents in the shaft.

I used to get them from BRT Bearings. Dodge Fenner type.

Edited by bizzard
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5 hours ago, Tim Lewis said:

 

For interest, just come across this picture of mine of the last Metalastik coupling of ours the went, it is a 7.5" one

 

met1.JPG

Mine is basically the same as this, only smaller at 6.25 " diameter (approx). Brinklow Boat Sevices have some 'used' 7.5" Metalastik couplers from old working boats.

 

Here is my sheared 6.25" Metalastik coupler - part number 21/642/2 :

 

 

IMG_20220811_155338.jpg

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2 hours ago, fladda said:

Mine is basically the same as this, only smaller at 6.25 " diameter (approx). Brinklow Boat Sevices have some 'used' 7.5" Metalastik couplers from old working boats.

 

Here is my sheared 6.25" Metalastik coupler - part number 21/642/2 :

 

 

IMG_20220811_155338.jpg

 

Fulbourne is currently at Brinklow having a new bottom installed, will have to ask about spares!

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