centre tube replacement

[Lazwal]

I wonder if members can assist me with a problem I have with my stern gear. My boat is currently out on the hard standing and I have removed the prop shaft, propeller, and centre tube. This was long overdue as it had shown signs of wear. My boat yard appeared reluctant to take on the work and I can now understand why. It took me a day to remove the old centre tube. My boat yard ordered the new parts, shaft stuffing box and centre tube. I started to fit the tube and it started to screw in fine but after only a few turns it stopped and was firmly stuck. I do not want to use my stillsons on it. I thought that something was not quite right and have now found out that the new centre tube is metric thread at the boss end and also at the stuffing box end, hence the problem. I have spoken to the boat yard and they say that they have never had this problem. Forgot to say my boat is 23 years old. They rang the well known chandlers and they said that the 7.5 inch centre tube is totally metric the large 10.5 tube can have both metric and imperial. So the one I have is not going to fit in the boss end. I now need to find somewhere who can make a new centre tube with metric at one end and imperial at the other end. I have been struggling with this problem for days. I would have thought that the boat yard would have known this or even checked when they ordered the parts,but that's life. So if anyone can help I would be grateful.

[RLWP]

Are you saying that your tube has a metric thread for the stuffing box flange, and the boss on the boat is imperial?

 

Richard

[Timleech]

I've never come across that before.

THIS well known chandler lists their short centre tubes (1 1/4" and 1 1/2") as all imperial.

 

Tim

Edited May 21, 2014 by Timleech

[bizzard]

I'd say the new tube has baulked up on rusty collar threads, they invariably do.

[n.b.Goldie]

I'd say the new tube has baulked up on rusty collar threads, they invariably do.

Perhaps have the collar cut out and a new one welded in.

[bizzard]

Perhaps have the collar cut out and a new one welded in.

Well dd if the thread is badly rusted away yes but usually they clean up ok by scraping around the thread with an angled pointed metal picker, small wire brush or Dremmel with a wee wire wheel, toothbrush then ideally a good blow out with an airline.

Hows the land lady dd?

Regards Bizzard.

[Lazwal]

A fellow boater who is also working on his boat out looked at it with a thread gauge and the old thread is coarser. I screwed the new tub in by hand it started o.k for the first few turns then locked up. I then used the old stuffing box tube. Again the old stuffing box started to turn easily for just a few turns then stopped. The boat yard rang the chandlers and was told that the new short tube has a metric thread both ends and a variation only comes with the larger tube. On web site of the chandlers the description states the thread to be 14 TPI and on checking the old one I can see 10TPI.

[Timleech]

Well dd if the thread is badly rusted away yes but usually they clean up ok by scraping around the thread with an angled pointed metal picker, small wire brush or Dremmel with a wee wire wheel, toothbrush then ideally a good blow out with an airline.

 

Regards Bizzard.

 

I have a crude tap which I made up by cutting the thread on a piece of old EN8 prop shaft, and cut a series of slots along the thread with an angle grinder.

It's good enough for cleaning crud out of the bosses.

 

 

A fellow boater who is also working on his boat out looked at it with a thread gauge and the old thread is coarser. I screwed the new tub in by hand it started o.k for the first few turns then locked up. I then used the old stuffing box tube. Again the old stuffing box started to turn easily for just a few turns then stopped. The boat yard rang the chandlers and was told that the new short tube has a metric thread both ends and a variation only comes with the larger tube. On web site of the chandlers the description states the thread to be 14 TPI and on checking the old one I can see 10TPI.

 

Is that Midland Chandlers?

It has the potential to affect a lot of people if they have changed what has been their standard product for years.

There is no recognised standard across the trade, although others have sold a matching product, and your original could well have come from another source.

 

Tim

[bizzard]

 

I have a crude tap which I made up by cutting the thread on a piece of old EN8 prop shaft, and cut a series of slots along the thread with an angle grinder.

It's good enough for cleaning crud out of the bosses.

 

 

 

Is that Midland Chandlers?

It has the potential to affect a lot of people if they have changed what has been their standard product for years.

There is no recognised standard across the trade, although others have sold a matching product, and your original could well have come from another source.

 

Tim

Good idea Tim. Its a very tedious job and takes time with the method I mentioned. If its not done properly the thread on the new tube can get torn and may not go right home when you think it has and may leak.

[Timleech]

Curiouser and curiouser.

Decided to check what I have.

I've got a used stuffing box, and a tap to match it, these have 2.125" x 12 tpi threads. This definitely was the most common size for 1.5" sterngear at one time.

I also have a 2" x 14 tpi tap, which is the size listed on the Midland Chandlers website for their 1.5" tubes. If this hadn't come up, I would have guessed that I'd made it for 1.25" sterngear.

 

Tim

[Lazwal]

I have just spoken to a young man at "the well Known chandlers" and he was a useful as a chocolate teapot. All he would say "was All our tubes have threads of 14 TPI, well that what the screen says" I have double checked my old tube and it is definitely 12 TPI. When I asked where they were sourced from it said "I think from abroad" I should have gone to specsavers! I now have to get another tube with 12TPI thread at the boss end and 14TPI at the other. Regarding the suggestion of cutting out the old boss, would have been the best solution but my boatyard would not be capable. I knew I should have taken it to a larger outside yard.

[Timleech]

I have just spoken to a young man at "the well Known chandlers" and he was a useful as a chocolate teapot. All he would say "was All our tubes have threads of 14 TPI, well that what the screen says" I have double checked my old tube and it is definitely 12 TPI. When I asked where they were sourced from it said "I think from abroad" I should have gone to specsavers! I now have to get another tube with 12TPI thread at the boss end and 14TPI at the other. Regarding the suggestion of cutting out the old boss, would have been the best solution but my boatyard would not be capable. I knew I should have taken it to a larger outside yard.

 

Is your old tube 2" OD, or 2 1/8"?

 

Tim

[Lazwal]

Tim, it is 2" at the boss end of the tube it has a rebate which reduces it where it comes out of the boss. I think that I will have to buy another longer tube and have it adapted by cutting it down and re threading a 12TPI thtread on the boss end.