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Old 21-12-2015, 07:42   #1
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shaft is too short

hey guys!

Im replacing volvo penta for perkins and just found out that I would need the shaft 3cm longer, that would solve all problems with engine mounts and engine bed ... but I dont have longer one and cant take the boat out of water at the moment

so Im thinking that I would put kind of spacer in shaft coupling - I mean the place where engine is connected to the shaft ... what if I put 3cm thick solid metal ring/spacer in between?

Im not asking for ideal solution but good and safe enough

thanks, tomas
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Old 21-12-2015, 07:51   #2
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Re: shaft is too short

Heya arecuk!

3cm doesn't sound like a ton... I don't see a huge problem... May be the perfect opportunity to put in a glass slipper sized flexible coupler though???
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Old 21-12-2015, 07:51   #3
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shaft is too short

Spacer ring is just fine, make sure though that it's machined with the correct boss to keep the flanges concentric.


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Old 21-12-2015, 07:53   #4
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Re: shaft is too short

cool! ... maybe 3-5cm, will see ... I mean something like this
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Old 21-12-2015, 07:58   #5
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Re: shaft is too short

Or you could add a flex spacer from the likes of PYI.

http://www.pyiinc.com/index.php?sect...shaft-coupling


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Old 21-12-2015, 08:01   #6
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Re: shaft is too short

Quote:
Originally Posted by Sailmonkey View Post
Spacer ring is just fine, make sure though that it's machined with the correct boss to keep the flanges concentric.

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A good consideration!

Quote:
Originally Posted by arecuk View Post
cool! ... maybe 3-5cm, will see ... I mean something like this
Yea! Like that... Billions of cars and boats spinning CV joints thicker than that...
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Old 21-12-2015, 09:51   #7
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Re: shaft is too short

That will work. Use some lock-tight to keep the nuts from backing off. You could also do a collar clamp(split halfs bolted together). somehow you need to key in the connection to prevent slippage.
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Old 21-12-2015, 09:55   #8
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Re: shaft is too short

So many good jokes with that thread title, but it sounds like you are getting some great advice. Please follow-up with pictures of your shaft solution. I know we all want before and after pictures...

Be wary of suction and weight gimmicks promising extra inches.

Those flexible adapters may work, but nothing beats a firm shaft. Are you satisfied with the girth, or is length your only issue?

Tankersteve
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Old 21-12-2015, 12:12   #9
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Re: shaft is too short

This night be a good chance to put on a automotive type rubber Flex disc
(guibo) they dampen a lot of noise.
vibration.
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Old 21-12-2015, 12:16   #10
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Re: shaft is too short

women have been complaining about this for years....smile
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Old 21-12-2015, 14:36   #11
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Re: shaft is too short

put in a thrust bearing if you have the space its worth the effort
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Old 21-12-2015, 14:48   #12
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Re: shaft is too short

Globe rubber makes something called a drive saver, though the one probably appropriate for your application is only 2.54 cm thick. Might work though.

It also isolates the shaft from the engine electrically.


https://www.gcsmarine.com/store/inde...t&pid=65&cid=0
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Old 21-12-2015, 15:32   #13
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Re: shaft is too short

If you decide to machine a simple spacer, I think you should include the small lip as on the coupling to lock it concentrically. Same as the coupling does.

Sorry, probably obvious but just wanted to mention this.

Edit to add...,.......bad form on me, didn't notice sailmonkey posted this already.
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Old 22-12-2015, 04:16   #14
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Re: shaft is too short

Quote:
Originally Posted by jimbunyard View Post
Globe rubber makes something called a drive saver, though the one probably appropriate for your application is only 2.54 cm thick. Might work though.

It also isolates the shaft from the engine electrically.


https://www.gcsmarine.com/store/inde...t&pid=65&cid=0
OHHH the temptation..shaft is too short.. but I will resist. I will get serious.
The above couplings are great. I have never had pockets deep enough to buy one.

I have bought nylon round and machined it. I have made three so far and all have performed flawlessly. The first one is long gone and it was on a 30hp V twin diesel. Damned if I can remember make or model.
.
One i have now is about 5" thick and couples a 135 hp Perkins 6354??? I think that is the right model number. Another is about 2" thick and couples a 28hp Yanmar 3gm

If yr interested enough I can go and get pictures. Unfortunately it is monsoonal here in Darwin and I will have to wait for a break in the weather to go out to the moorings.

Cheers from the top end of down under
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Old 22-12-2015, 04:40   #15
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Re: shaft is too short

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Originally Posted by arecuk View Post
cool! ... maybe 3-5cm, will see ... I mean something like this
Each time I needed a spacer it was because I had to replace one engine with a different make. Spacers allowed me to keep the old drive shafts and save big bucks.

When I made my first spacer I chose nylon because all the advice I received at the time knocked metal spacers. Dunno the reasons.

The nylon seems to absorb vibration and is more forgiving if the alignment is out a little. My latest effort was to replace a 3QM with a 3GM. Anyone want to buy a good 3QM engine block and matching gearbox??

As Sail Monkey says , machine in the lips or indents or whatever they are called to center the assembly.

Nylon Worked well for me.
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