[PSUBS-MAILIST] Minn Kota 101 - thread spec

Mon Jul 21 10:22:03 EDT 2014

 James, a couple of points.  First, to me the fewer the leak paths the better so I would not install the added plug.  The issue is how to get traped air out of the Md-101 when using oil compensation.   I like Alec and Hanks ideas for removing trapped air due to nipple protruding into body.  The other point is the wrap around tube volume can compensate for the small amount of air that remains trapped.  To deal with thermal expansion of the oil, first of all you are dealing with a small volume to start with so the tube/reservoir does not have to be all that large.  If you do a quick back of the envelope calc on the required volume to compensate for only thermal expansion of the oil you about need 3 US teaspoons for a MK 101 ( Assume oil has a thermal expansion coefficient of 0.00056 1/F and that there is one US pint of oil in the body of the 101 and that the temperature swing is 70F to 130F.  Delta volume is 0.125 gal * 0.00056 1/F * 60F =
 0.0042 gal*128 OZ/gal *6 US TSP/OZ = 3.2 teaspoons).  
To me the design pressure inside the ME 101 should be ambient pressure as they have lip seals on shafts.  Lip seals are design to take external pressure.  They re not designed to take internal pressure.  So a simple wrap around tube for oil compensation with say a volume of 5 US teaspoons should work just fine as this would allow for thermal expansion of the oil and a small volume of trapped air and because the tube is flexible, the pressure inside the 101 is ambient which makes the lip seal happy.  As to Alan's suggestion on omitting all pressure compensation and only relaying on the lip seal without any pressure compensation, I am not wild about this idea unless the boat is only designed for shallow water.  MK designers when they speced the lip seals for MK were designing shallow submergence of a trolling motor with a factor of safety.  So as you get deeper and deeper, you are starting to expose these lips seals to a significant differential
 pressure which causes them to overheat and fail at some point.  Is this 10ft or 50 ft or 100 ft.  Don't know but to me this exposes the boat to some risk particularly if use the 101's for depth stability rather than a VBT and dive the boat negatively buoyant, i.e., vertical thruster fails, boat starts to descend and pilot is forced into dropping ballast.  

To me a bigger question on air vs oil compensation is how much power are you giving up with oil compensation due to viscosity difference between oil and air.  

As both Alec and Vance point out, there has been a lot of bottom time on MD-101s with oil compensation without a lot documented failures.  

I have not decided in my own mind which compensation method I will use on my MD-101's for future boats.  

Cliff

________________________________
 From: James Frankland via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Monday, July 21, 2014 4:17 AM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

Hi Cliff,,
Others may disagree with this, but ive got a suggestion.  If your oil compensating the motors and are going to add the wrap around tube\bladder as per Alecs Snoopy, I would suggest, adding a vent hole somewhere near the aft bearing.  With my setup, ive put the tube going around the motor and its all ok.  But, I just cannot get the last dregs of air out.  No matter what I do.  I suspect that its because the pipe nipple protrudes a mm or so into the casing and so will not allow the last bit of air out.  It really irritates me and I worry that the motor is not properly compensated.  So, I am going to make a modification to the motor like this pic.  I think this will work, the suspect bit is mating the plug against the slightly domed motor case.  I think a large rubber washer should seal it.   The i should be able to rotate the motor and remove the last dregs of air.  What do you think?
Thanks
James

On 19 July 2014 01:38, Clifford Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Thanks
>
>
>
>Cliff Redus 
>
>On Jul 18, 2014, at 7:26 PM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> 
>Hi Cliff,
>>
>>
>>It is a parallel thread, 1 1/8" - 18.
>>
>>
>>Best,
>>
>>
>>Alec
>>
>>
>>
>>On Fri, Jul 18, 2014 at 8:04 PM, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>> Does anyone have any documentation on the Minn Kota 101 main support female thread spec?  It does not look like a tapered pipe thread and the threads per inch look to great. I put a digital caliper on this at it read 1.064-1.07 inches for the minor diameter.  I measured the threads and it is 18 threads per inch.    I looked in the machine handbook and the closest that comes is a 1-1/8  UNEF (Extra fine thread series).  The major and minor diameters for a 1-1/8" UNEF are 1.1250" and 1.0649"  respectively. 
>>>
>>>
>>>Can anyone confirm this?
>>>
>>>
>>>Cliff
>>> 
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