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Prop Shaft Size
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SoloBob
North Forida
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November 2, 2013 - 12:32 pm
Member Since: March 24, 2013
Forum Posts: 37
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I'm looking forward to a repower project on my DE38, and I have a question for those of you that have a non original engine, or have installed one.

The original engine was an Atomic 4, 32 HP Diesel, which sat for 12 years unused... I managed to resurrect it, but my strong suspicions that electrolysis probably had taken it's toll on it, were realized when a connecting rod, became unconnected. [Image Can Not Be Found]

I've looked fondly at the Beta engine line, and really like them, however the one issue I could not get past was the overall length of the engine and tranny.  There isn't really an over abundance of room between the stuffing box and the coupling to begin with, and this was going to decrease that ( as best I could tell) .

So I've moved on to the Yanmar products, focusing on the 54HP 4JH5. ( the 40 HP 3JH5 is still in the possible list, but being old school, I kinda want that 4th piston ) .

The length is actually less than the Atomic 4, so I'm gaining on that respect.

Here is my question... my original prop shaft appears to be 1", on your newer engine, is the prop shaft still 1", or has it been upgraded? 

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S/V The Last Farewell,

Currently laying Panchos Marina

Marathon, Florida

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Scott Carle
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November 2, 2013 - 1:19 pm
Member Since: October 10, 2009
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SoloBob said:

The length is actually less than the Atomic 4, so I'm gaining on that respect.

Here is my question... my original prop shaft appears to be 1", on your newer engine, is the prop shaft still 1", or has it been upgraded? 

 

I'm not sure I understand.... do you mean does the new engine use a 1 inch shaft? I would assume that you could use a 1 inch or a 1 1/8 or larger with the new engine. Just depends on the adapter that the prop shaft goes into. I would ask the engine manufacture or place selling you the engine. The DE38 did and does come stock with a 1 inch shaft and I would not want to change that. If you do you will need to change the stuffing box, and cutlass bearing if you can. Regardless you will probably need a longer prop shaft if the engine and transmission are shorter on the new engine. I had thought you could get a straight drop in replacement for the stock atomic 4 diesel that used the same mounts and was the same length? Beta Marine marinizes Kubota engines which is what the old Atomic 4 universal diesel was.

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Scott Carle DE38 Cutter s/v Valkyr
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SoloBob
North Forida
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November 2, 2013 - 9:06 pm
Member Since: March 24, 2013
Forum Posts: 37
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Sorry, I wasn't clear on that... the reference to length, is a reference from the face of the transmission coupling flange, to the front of the crankshaft pulley. ( or forward most engine component)

The Beta does not offer a "drop in", for the Atomic 5432 ( AKA Universal M5432 ) which is my current engine.  The largest drop in is the 28  HP model.  IMO the 32 HP was undersized, so the last thing I want to do is go down in horsepower.  That leaves me with the 35 HP Beta  as the next step up, and it's 35 1/4 " long ( as is the 38 HP )    The Atomic M5432 was 34 1/2 long.

The Yammer 54 HP is 34 1/4 long.... within a quarter of an inch to what the Atomic 4 was.

If I go with the 40 HP, 3 cylinder Yanmar, it's even better, it's only 30 3/8 ( which I have to admit, having that much more shaft showing before the stuffing box really interests me ).

Regardless of which way I end up going, I'll need to, and plan to replace the prop shaft.
Probably with Aquamet 22.

I got off track......

The question was, has anybody changed the Stern Tube, and Stuffing Box out, to a larger size?

Looks to me like a major PITA to say the least, and in fact, I'm not so sure there is enough hull around the stern tube area, that it would accept anything bigger.

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S/V The Last Farewell,

Currently laying Panchos Marina

Marathon, Florida

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Scott Carle
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November 3, 2013 - 8:13 am
Member Since: October 10, 2009
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I don't think that the 3/4 inch longer length of the beta marine engines will be a significant problem for you if you decide to go that way. There is definitely that much extra space there from what I remember. Don't hold me to it but I seem to remember a couple hand widths of shaft between my stuffing box and where the shaft terminates at the engine. However going from 35 to 30 inches would give a significant amount of extra space back there.

 

I would not change the stern tube and stuffing box out to a larger size.. I think you would be building a large additional  project into the re-power that you don't need. On top of that it will really confuse any future owners 🙂 

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Scott Carle DE38 Cutter s/v Valkyr
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carmine
Long Island, NY
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September 29, 2014 - 10:13 pm
Member Since: November 7, 2009
Forum Posts: 20
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Hi:

 

Kind of late to comment but I just read this post.  I repowered to a 48 HP perkens prima and kept the 1 inch shaft but here is the rub.  The shaft diameter must be able to accommodate the increased engine torque.  After doing the homework I found that conventional SS shaft could not deal with the additional torque but upgrading to a stronger alloy would put the shaft back into spec.  I used aquamet or something that sounds like that. 

 

My reference was The Propeller Handbook.

 

Carmine

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Scott Carle
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September 30, 2014 - 12:35 pm
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good call on that. 🙂

how much difference in a 1 inch aquamat shaft and a larger size SS one? I bet it wasn't to bad. Just guessing though 🙂

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