Very stiff 1 1/4 BSP fitting

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noahdipaola03

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Hi All,

Recently upgraded my fuel sender form a WEMA one to an OCEANIC Systems NMEA2000 one. I went to screw it into place, and the first few turns were nice and smooth but after that it became solid! even with a spanner and a lot of elbow grease i could any get around 2/3 of the thread into the mount. My old WEMA sender was also stiff when screwing in and out, but not this bad. The WEMA sender did have a much shorter thread than the new one, but there is plenty of thread in the BSP mount to accept the new sender.

Any ides on why its so stiff? i actually watched the shaft flex as I tried to tighten it up. Some sort of teflon lubricant? Obviously the new sender has an O ring that needs to seated to form a seal, but its so stiff I cant get it any further down.

All ideas welcome :) thanks for reading. Have included a pic of both threads below. Screenshot 2021-03-14 at 21.09.46.pngScreenshot 2021-03-14 at 21.09.10.png
 
The 3271T is supposed to be a parallel thread. 3271N is the taper (NPT) one.
If you cannot screw it down to the O ring it must be a mismatch. Either a wrongly supplied sender for a parallel tank thread, or the 3271T is correct, but the tank has a tapered thread.
 
Caraway said:
The 3271T is supposed to be a parallel thread. 3271N is the taper (NPT) one.
If you cannot screw it down to the O ring it must be a mismatch. Either a wrongly supplied sender for a parallel tank thread, or the 3271T is correct, but the tank has a tapered thread.
Click to expand...
Than sender installed by the manufacturer was also tight... so assume that it’s a parallel thread?
 
I had a similar issue changing out a Wema aluminium headed sender for a Wema stainless one. The tank mounting boss was stainless steel. I ended up removing the tank top and running a tap throught the boss on that one.
I now have the same problem changing another alloy to stainless unit. Wema are very helpful and told me the tolerances between the aluminium and stainless senders is subtly different, the aluminium is a looser fit. They took my new sender back and are machining it to a looser tolerance. Great customer service.
They did say the thread pitch used have not changed, just the tolerances.
 
Tha
Dunx said:
I had a similar issue changing out a Wema aluminium headed sender for a Wema stainless one. The tank mounting boss was stainless steel. I ended up removing the tank top and running a tap throught the boss on that one.
I now have the same problem changing another alloy to stainless unit. Wema are very helpful and told me the tolerances between the aluminium and stainless senders is subtly different, the aluminium is a looser fit. They took my new sender back and are machining it to a looser tolerance. Great customer service.
They did say the thread pitch used have not changed, just the tolerances.
Click to expand...

Thanks for this. My previous WEMA Sender was also a stainless one, so not sure its that.
 
Hi I think Noah has the right idea, borrow or hire a thread tap and run it through the thread. Using some lubricant grease of course. A couple of passes of the tap should do the trick. BSP is a gas pipe thread so the chances are one of the hire shops have the tools.
 
I have had several issues when fitting oil pressure guauges on engines. If it doesn't screw in easily you need to assume it is the wrong thread.
The parallel threads are supposed to screw right down to the seat (or O ring)
 
Caraway said:
I have had several issues when fitting oil pressure guauges on engines. If it doesn't screw in easily you need to assume it is the wrong thread.
The parallel threads are supposed to screw right down to the seat (or O ring)
Click to expand...

YES, ABSOLUTELY!!!!!
 
A picture of the fitting on the tank may help.

What is the length of thread of the old fitting as the thread on the new one could be longer and the thread in the tank fitting may be shorter.
 
Rogershaw said:
A picture of the fitting on the tank may help.

What is the length of thread of the old fitting as the thread on the new one could be longer and the thread in the tank fitting may be shorter.
Click to expand...
The new thread is longer, but there is plenty off thread in the female mount to accept this sender.
 
philwebb said:
Hi I think Noah has the right idea, borrow or hire a thread tap and run it through the thread. Using some lubricant grease of course. A couple of passes of the tap should do the trick. BSP is a gas pipe thread so the chances are one of the hire shops have the tools.
Click to expand...
This would work, but the swarf would go in the tank, and thats the last thing I want as very hard to clean.
 
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