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Old 13 October 2009, 16:56   #1
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Small outdrive

Hi,
I know very little about outdrives having only had outboards in the past, so I have some basic questions.
I'm playing around with a 14 foot hull with a soon to be marinised 120hp water cooled motorcycle engine in it. Most outdrives seem to be geared towards larger engines, but I don't want the outdrive to be bigger than I need as this is a lightweight craft.

First question. Do all outdrives have electric trim and tilt?

Second question. I need the outdrive part of the project to be as cheap as possible, but I want to fit something that I can still get spares for and trim and tilt need to be remote. Anyone recommend a suitable unit and /or know where there is one for sale or how much I should pay? I see the Alpha 1 is a smallish unit that I assume is quite commonplace. Does it fit my requirements and are they available for reasonable money? I'm guessing like anything, if I buy a well known make and model and pay the right money for it it will not lose much money if the project doesn't work out and I have to move the unit on.

Third question. What goes wrong with secondhand outdrives? What are the most important checks?

Final question. As there is going to be some mild engineering to connect the motorcycle chain drive (I'm definitely keeping the 6 speed sequential gearbox to make up for loss of torque versus a marine engine!) to the outdrive, I'm interested to know what typically an outdrive has on the inside shaft end of it. Is this a standard thing like a splined shaft or rose joint or do they all vary widely.

Final, final question. I'm assuming the rules of thumb governing outboard prop height are the same for an outdrive (cav plate level with bottom of hull or up to an inch above it). Am I correct?

I'm already aware that shoving an outboard on the back would be quicker and easier and cheaper, so please dont tell me this! It's more to do with the perverse wish to use up a surplus hull and the bike engine in an interesting project.

Many thanks
Jake
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Old 13 October 2009, 17:16   #2
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Have a loo on Volvos site, they list all the old engines.
You can search by say stern drive, 120hp and petrol and it will bring up all engines that they used to produce with a similar combo which will hopefully point you in the right direction.
Volvo 250 leg might be suitable but they do weigh alot!
Bellows can go on outdrives and you can sink.
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Old 13 October 2009, 17:34   #3
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Quote:
Originally Posted by Jacob555 View Post
Hi,
I know very little about outdrives having only had outboards in the past, so I have some basic questions.
I'm playing around with a 14 foot hull with a soon to be marinised 120hp water cooled motorcycle engine in it. Most outdrives seem to be geared towards larger engines, but I don't want the outdrive to be bigger than I need as this is a lightweight craft.

First question. Do all outdrives have electric trim and tilt?
No-but those without are usually ancient.
Quote:
Originally Posted by Jacob555 View Post

Second question. I need the outdrive part of the project to be as cheap as possible, but I want to fit something that I can still get spares for and trim and tilt need to be remote. Anyone recommend a suitable unit and /or know where there is one for sale or how much I should pay? I see the Alpha 1 is a smallish unit that I assume is quite commonplace. Does it fit my requirements and are they available for reasonable money? I'm guessing like anything, if I buy a well known make and model and pay the right money for it it will not lose much money if the project doesn't work out and I have to move the unit on.
It's hard to find a good outdrive second hand.
Quote:
Originally Posted by Jacob555 View Post

Third question. What goes wrong with secondhand outdrives? What are the most important checks?
Corrosion. Water in oil. No impact damage.Parts missing if you're buying cheap and 2nd hand.
Quote:
Originally Posted by Jacob555 View Post

Final question. As there is going to be some mild engineering to connect the motorcycle chain drive (I'm definitely keeping the 6 speed sequential gearbox to make up for loss of torque versus a marine engine!) to the outdrive, I'm interested to know what typically an outdrive has on the inside shaft end of it. Is this a standard thing like a splined shaft or rose joint or do they all vary widely.
Why not turn the bike engine through 90 degrees and run a shaft straight from the splined output shaft of the engine to the drive unit?
Quote:
Originally Posted by Jacob555 View Post

Final, final question. I'm assuming the rules of thumb governing outboard prop height are the same for an outdrive (cav plate level with bottom of hull or up to an inch above it). Am I correct?
Yes.
Quote:
Originally Posted by Jacob555 View Post

I'm already aware that shoving an outboard on the back would be quicker and easier and cheaper, so please dont tell me this! It's more to do with the perverse wish to use up a surplus hull and the bike engine in an interesting project.

Many thanks
Jake
Why not use a jet drive? It'd be far cheaper, simpler and better suited to a bike engine.
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Old 14 October 2009, 09:08   #4
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I've not ruled out a jet drive, ust would prefer an outdrive If I can get hold of one due to the trim and tilt and the fact that I can easily get a variety of props to play about with the gearing.
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Old 14 October 2009, 17:32   #5
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Quote:
Originally Posted by chewy View Post
Have a loo on Volvos site, they list all the old engines.
You can search by say stern drive, 120hp and petrol and it will bring up all engines that they used to produce with a similar combo which will hopefully point you in the right direction.
Volvo 250 leg might be suitable but they do weigh alot!
Bellows can go on outdrives and you can sink.
250 is not normally power trim.

Volvo 290 was the first Volvo to come with power trim as standard.

Mercruiser Alpha 1 is probably your best bet. The lower unit of these is the same as Mercury V6 outboards - so will be able to use easily obtainable propellers for testing.

An Enfield will be light but no power trim or tilt.

Might be able to get installation instructions for an Alpha on the net which will let you know what the input looks like.
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