Rigid 38mm prop shaft coupling

[MtB]

Hi everyone,

 

The next step in trying to get my Kelvin gearbox clutch to stay engaged without hanging weights on the gear wheel (!) is to remove the CentaFlex coupling in the prop shaft and replace it with a rigid shaft coupling.

 

Does anybody know where I might buy a rigid coupling to join two sections of 38mm (1½") prop shaft solidly together please? I could do it with two flange couplings but that seems a little inelegant and I can imagine alignment problems persisting.

 

After a fair amount of Googling I've found a few suppliers of shaft-to-shaft rigid couplings these but none in 38mm. Plenty of 35mm and 40mm couplings about, but no 38mm.

 

Any suggestions please?

 

Many thanks,

Mike

[RLWP]

Hi everyone,

 

The next step in trying to get my Kelvin gearbox clutch to stay engaged without hanging weights on the gear wheel (!) is to remove the CentaFlex coupling in the prop shaft and replace it with a rigid shaft coupling.

 

Does anybody know where I might buy a rigid coupling to join two sections of 38mm (1½") prop shaft solidly together please? I could do it with two flange couplings but that seems a little inelegant and I can imagine alignment problems persisting.

 

After a fair amount of Googling I've found a few suppliers of shaft-to-shaft rigid couplings these but none in 38mm. Plenty of 35mm and 40mm couplings about, but no 38mm.

 

Any suggestions please?

 

Many thanks,

Mike

 

Get a 35mm and have it bored out? Should be an easy job

 

Richard

[Timleech]

Hi everyone,

 

The next step in trying to get my Kelvin gearbox clutch to stay engaged without hanging weights on the gear wheel (!) is to remove the CentaFlex coupling in the prop shaft and replace it with a rigid shaft coupling.

 

Does anybody know where I might buy a rigid coupling to join two sections of 38mm (1½") prop shaft solidly together please? I could do it with two flange couplings but that seems a little inelegant and I can imagine alignment problems persisting.

 

After a fair amount of Googling I've found a few suppliers of shaft-to-shaft rigid couplings these but none in 38mm. Plenty of 35mm and 40mm couplings about, but no 38mm.

 

Any suggestions please?

 

Many thanks,

Mike

 

Fenner RM16 with taperlock bushes should do it.

 

Eriks

 

Tim

[bizzard]

Hi everyone,

 

The next step in trying to get my Kelvin gearbox clutch to stay engaged without hanging weights on the gear wheel (!) is to remove the CentaFlex coupling in the prop shaft and replace it with a rigid shaft coupling.

 

Does anybody know where I might buy a rigid coupling to join two sections of 38mm (1½") prop shaft solidly together please? I could do it with two flange couplings but that seems a little inelegant and I can imagine alignment problems persisting.

 

After a fair amount of Googling I've found a few suppliers of shaft-to-shaft rigid couplings these but none in 38mm. Plenty of 35mm and 40mm couplings about, but no 38mm.

 

Any suggestions please?

 

Many thanks,

Mike

I presume that there are Woodruff key slots in the shaft ends and that the engine and gearbox are solidly mounted.

If so i'd use two half couplings, for 1,5'' shaft and perhaps get someone to machine up on an wood turning lathe a solid hard wood coupling,bored and with flange bolt holes drilled to fit,''all operations carried out on the lathe for accuracy'' between the two half couplings. Beech wood is good for this,i have seen this done twice with Lister HA's with the Blackstone gearbox.Accurate alignment shouldn't be a problem,using feeler gauges and homemade thin shims under mounting feet.Bizzard

[Timleech]

I presume that there are Woodruff key slots in the shaft ends and that the engine and gearbox are solidly mounted.

If so i'd use two half couplings, for 1,5'' shaft and perhaps get someone to machine up on an wood turning lathe a solid hard wood coupling,bored and with flange bolt holes drilled to fit,''all operations carried out on the lathe for accuracy'' between the two half couplings. Beech wood is good for this,i have seen this done twice with Lister HA's with the Blackstone gearbox.Accurate alignment shouldn't be a problem,using feeler gauges and homemade thin shims under mounting feet.Bizzard

 

I'm not convinced that the hardwood 'spacer', if that's what you're suggesting, will do anything more than increase the chances of bolt failure.

 

Unlikely to be Woodruff keys, BTW. They're the nearly semicircular ones.

 

These people offer muff couplings, apparently imperial as well as metric though only metric appear in their online catalogue, but the lead times seem to be very long.

Yes you could get one in 35mm, clamp it up with some packing on the flat faces and bore it out.

 

Tim

Edited August 12, 2011 by Timleech

[bizzard]

I'm not convinced that the hardwood 'spacer', if that's what you're suggesting, will do anything more than increase the chances of bolt failure.

 

Unlikely to be Woodruff keys, BTW. They're the nearly semicircular ones.

 

These people offer muff couplings, apparently imperial as well as metric though only metric appear in their online catalogue, but the lead times seem to be very long.

Yes you could get one in 35mm, clamp it up with some packing on the flat faces and bore it out.

 

Tim

I'd be convinced if i were you.I think you'll find that there are many hardwood spacers out there,especially in conjunction with old historical engines,with decent size 6 or more bolt couplings.They will bolt up rock solid. Maybe a drop of Rentakill now and then to prevent woodworm is the only maintenance needed.

Anyway lets wait and see if Mike returns to tell us of his exact setup.bizzard

[Timleech]

Hi everyone,

 

The next step in trying to get my Kelvin gearbox clutch to stay engaged without hanging weights on the gear wheel (!) is to remove the CentaFlex coupling in the prop shaft and replace it with a rigid shaft coupling.

 

Does anybody know where I might buy a rigid coupling to join two sections of 38mm (1½") prop shaft solidly together please? I could do it with two flange couplings but that seems a little inelegant and I can imagine alignment problems persisting.

 

After a fair amount of Googling I've found a few suppliers of shaft-to-shaft rigid couplings these but none in 38mm. Plenty of 35mm and 40mm couplings about, but no 38mm.

 

Any suggestions please?

 

Many thanks,

Mike

 

One other suggestion - if it's 1.5", then look for 1.5". 38mm will be wrong, the difference (about 4 thou) is very significant in this sort of case.

 

Tim

[Speedwheel]

That's your problem Tim, you haven't seem enough old historical engines. Maybe a Fray Bentos pie tin would work better.

 

BTW I mean't to ask you today, someone said you were removing the Kelvin from Kennet. Is this true? Have you persuaded Pochins to part with one?

[MtB]

Ok thanks for all your responses.

 

Firstly the prop shaft is almost certainly 1½" not 38mm. I wasn't measuring it that accurately and I assumed it was metric, but looking at Midland Chandlers' website I see stainless steel propshaft is actually still supplied in imperial. So that's prolly what I have.

 

Here's a pic of the CentaFlex I want to remove from the drivetrain. As you can see, this coupling needs to hold the two bits of propshaft straight and in alignment so beech coupling flanges etc are out!

 

I think I need something like one of these but in 1½" size.

 

 

The alternative is a new solid length of 1½" shaft but one end will need to fit into the smaller, weird-size Kelvin coupling at the right of the photo. I don't have access to a lathe to turn it down myself hence my decision to look for a rigid coupling to join the two bits of proshaft I alreay have in the photo.

 

If a rigid coupling is difficult or not available then it will be easier to find a piece of 1½" prop shaft and find a machine shop cut to it to length and turn down the end to fit Kelvin coupling. (Does anyone know what size the Kelvin coupling is, but the way?)

 

Mike

 

Fenner RM16 with taperlock bushes should do it.

 

Eriks

 

Tim

 

Tim, thanks for the suggestion. Will the RM16 pull and hold the two sections of shaft into accurate alignment? It's not clear from the web page.

 

Mike

[RLWP]

Mike, is the existing shaft turned down to fit that Kelvin coupling? It almost looks like a full 1.5" diameter in your photo

 

Richard

[Timleech]

Ok thanks for all your responses.

 

Firstly the prop shaft is almost certainly 1½" not 38mm. I wasn't measuring it that accurately and I assumed it was metric, but looking at Midland Chandlers' website I see stainless steel propshaft is actually still supplied in imperial. So that's prolly what I have.

 

Here's a pic of the CentaFlex I want to remove from the drivetrain. As you can see, this coupling needs to hold the two bits of propshaft straight and in alignment so beech coupling flanges etc are out!

 

I think I need something like one of these but in 1½" size.

 

 

The alternative is a new solid length of 1½" shaft but one end will need to fit into the smaller, weird-size Kelvin coupling at the right of the photo. I don't have access to a lathe to turn it down myself hence my decision to look for a rigid coupling to join the two bits of proshaft I alreay have in the photo.

 

If a rigid coupling is difficult or not available then it will be easier to find a piece of 1½" prop shaft and find a machine shop cut to it to length and turn down the end to fit Kelvin coupling. (Does anyone know what size the Kelvin coupling is, but the way?)

 

Mike

 

 

 

Tim, thanks for the suggestion. Will the RM16 pull and hold the two sections of shaft into accurate alignment? It's not clear from the web page.

 

Mike

 

I'm confused

 

OK, I know, it doesn't take much!

 

Is the green thing with the through bolts a form of muff coupling, not part of the gearbox, joining two bits of shaft, as that's how it appears to me?

 

If so, surely you just want a piece of shaft to go from your left-hand, sternmost, split half-coupling into this muff coupling?

 

Edit - or possibly better, directly into the gearbox coupling itself though I don;t know what goes on inside there.

 

Getting a bit of shaft turned down to size would be cheaper than buying yet more couplings, surely?

As Richard says, there's not any size difference very evident in the photo.

 

Tim

 

 

 

 

Tim, thanks for the suggestion. Will the RM16 pull and hold the two sections of shaft into accurate alignment? It's not clear from the web page.

 

Mike

 

Yes, it would. Taperlocks are pretty good so long as the shaft is in good order and you follow the instructions.

Edited August 13, 2011 by Timleech

[Timleech]

Mike

 

Is your PM box full?

[MtB]

Mike

 

Is your PM box full?

 

 

Yes!

 

I'll empty it....

 

And yes the green coupling on the right is a Kelvin component that clamps down on the 1 3/8" (approx) output shaft from the gearbox. The section of 1½" shaft fitted into it has been turned down to fit it.

 

What I really want is a single straight section of 1½" shaft to go from the green coupling on the right into the flange coupling on the far left. But a piece of 1½" stainless 18" long is going to cost a bob or two AND I've got to find someone to do the machining. Taking the CentreFlex in the middle off and relacing it with a rigid coupling would be far easier!

 

(The gap inside the CentaFlex between the ends of the two sections of prop shaft it joins is 15mm.)

 

This is just an experiment to see if a rigid shaft stops the clutch constantly disengaging. This is a common problem with Kelvin transmssions and it seems this problem has a strong correlation with a CentaFlex coupling being fitted in the transmission, so I want to remove mine to see if it makes any difference.

 

Cheers, mIke