Can you convert a 20" to a 15" outboard? - Moderated Discussion Areas

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Author Topic:   Can you convert a 20" to a 15" outboard?

Kelly posted 11-23-2004 02:20 PM ET (US)
I have a 1987 15 hp Nissan with a 20" shaft length. Can I convert this to a 15" shaft length?
Kelly
wwknapp posted 11-23-2004 07:08 PM ET (US)
Can and want to are two different things.
If the motor was made in both lengths, then changing enough parts will convert it. But I expect you will find the parts bill more than the motor is worth if you buy new parts.
Generally the differences are in the mid section, but best way is to get a full parts diagram for the two motors and compare. If they used a add on section it might be doable.
Personally, with a motor that old, I'd look for a new motor. Which could be a used one.
Walt
Joe Kriz posted 11-23-2004 07:22 PM ET (US)
Kelly,
It says in your profile that you own a Montauk.
The correct length shaft for a kicker motor on a Montauk is the Long, 20" shaft.
Why would you want to convert this engine to a short 15" shaft?
To use on a different boat?
Another option would be to install a Jack Plate to raise the Long 20" shaft engine up so it doesn't hang so low in the water.
sjohnson posted 11-24-2004 12:04 AM ET (US)
Sure, it's called tilt and trim . . . No really, I think Joe Kriz has this right on. Stick to the 20" or a jackplate, it really matters on that hull. Seems like you might cause more problems than you fix with a conversion. Why the desired change anyway??
-SJohnson
Kelly posted 11-24-2004 01:24 PM ET (US)
The 15 hp is on my older 13' model Whaler that has a 15" transom. It is a tiller set up and I have been using it with a home made transom adapter, but now I am going to build a console, thanks to Tom Clark for sending me the plans, and fix the boat up for my kids. I was just checking to see if there was an easy way to modify the motor. It works great and is a good motor for the boat. It looks like changing the motor will be too much trouble and expense.
I am checking on adapters or jack plates, but personally, I like the look with the motor lower. I will probably try to just find a good used short shaft motor. However, a new Yamaha or Nissan would be nice.
Kelly
Tom W Clark posted 11-24-2004 03:54 PM ET (US)
Kelly,
If the mid section has a 5" extension (as a lot of small 20" motors do) then it is a straight forward conversion.
You would need to buy a new drive shaft and shift rod and modify (cut) the water tube. Buying those parts would probably cost about $100 to $150.
Kelly posted 11-24-2004 05:13 PM ET (US)
Tom,
I looked at the motor last night, and it does not look like there is a separate mid section. It appears to be one section down to the small fin above the anti cavitation plate. I will look again to be sure.
By the way Tom, thanks again for the plans. I took them to work the other day just to show them off to another Whaler owner.
Kelly
ryanwhaler posted 11-24-2004 07:43 PM ET (US)
There are a lot of good articles on this forum about filling that low spot in the transom of the old 13's. Making the transom higher would give you a lot more choices in the future if you want to step up to a bigger motor.
Is that an option?
Kelly posted 11-25-2004 03:15 AM ET (US)
ryanwhaler,
If I wanted to get up into the 40hp range, I would probably buy a newer hull with the higher transom. For the way I use the boat, the 15hp Nissan works fine. There are also still some good new 15" shaft motors up to the 25 and 30 hp range to choose from.
Kelly
Binkie posted 12-02-2004 10:40 AM ET (US)
If you can find a dead 15hp Nissan, you probably can buy the midsection and clamps pretty reasonable,not much call for them. Then you have to deal with the 20" driveshaft. You could also buy the gearcase from the short shaft motor,could be expensive. A 15" driveshaft could be hard to find. A cheap way to fix this is to take the 20" shaft to a macine shop and have a 5" section cut from it and have both ends squared. There is a guy in the Midwest,(I could give you his E-Mail) who makes adapters that slip over the cut down squared drive shaft ends and bolts it all together so you now have a 15" shaft. It works well and is used on many race motors. Some people have welded the two ends together, but unless they are perfectly aligned It would shake like crazy . The bolt on coupling eliminates this. It shouldn`t be too hard to modify the shift rod and water tube. If your unable to do this mechanical work yourself, it would cost too much,and would`nt be worth it.
simbo posted 12-03-2004 12:28 PM ET (US)
look Bay Manufacturing Div. Hemco, I have a Mariner 25hp,15"shaft & I want to convert in 20, because my transom is 20". I check this extension kit cost $300.!@#$$%%
Kelly posted 12-06-2004 04:57 PM ET (US)
Thanks for your responses. It looks like the conversion would be too much trouble. I think I am just going to try and find a good short shaft motor. The Yamaha 25 in two or four stroke looks good and the Nissan is a possibility.
Kelly

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Author	Topic: Can you convert a 20" to a 15" outboard?
Kelly	posted 11-23-2004 02:20 PM ET (US) I have a 1987 15 hp Nissan with a 20" shaft length. Can I convert this to a 15" shaft length? Kelly
wwknapp	posted 11-23-2004 07:08 PM ET (US) Can and want to are two different things. If the motor was made in both lengths, then changing enough parts will convert it. But I expect you will find the parts bill more than the motor is worth if you buy new parts. Generally the differences are in the mid section, but best way is to get a full parts diagram for the two motors and compare. If they used a add on section it might be doable. Personally, with a motor that old, I'd look for a new motor. Which could be a used one. Walt
Joe Kriz	posted 11-23-2004 07:22 PM ET (US) Kelly, It says in your profile that you own a Montauk. The correct length shaft for a kicker motor on a Montauk is the Long, 20" shaft. Why would you want to convert this engine to a short 15" shaft? To use on a different boat? Another option would be to install a Jack Plate to raise the Long 20" shaft engine up so it doesn't hang so low in the water.
sjohnson	posted 11-24-2004 12:04 AM ET (US) Sure, it's called tilt and trim . . . No really, I think Joe Kriz has this right on. Stick to the 20" or a jackplate, it really matters on that hull. Seems like you might cause more problems than you fix with a conversion. Why the desired change anyway?? -SJohnson
Kelly	posted 11-24-2004 01:24 PM ET (US) The 15 hp is on my older 13' model Whaler that has a 15" transom. It is a tiller set up and I have been using it with a home made transom adapter, but now I am going to build a console, thanks to Tom Clark for sending me the plans, and fix the boat up for my kids. I was just checking to see if there was an easy way to modify the motor. It works great and is a good motor for the boat. It looks like changing the motor will be too much trouble and expense. I am checking on adapters or jack plates, but personally, I like the look with the motor lower. I will probably try to just find a good used short shaft motor. However, a new Yamaha or Nissan would be nice. Kelly
Tom W Clark	posted 11-24-2004 03:54 PM ET (US) Kelly, If the mid section has a 5" extension (as a lot of small 20" motors do) then it is a straight forward conversion. You would need to buy a new drive shaft and shift rod and modify (cut) the water tube. Buying those parts would probably cost about $100 to $150.
Kelly	posted 11-24-2004 05:13 PM ET (US) Tom, I looked at the motor last night, and it does not look like there is a separate mid section. It appears to be one section down to the small fin above the anti cavitation plate. I will look again to be sure. By the way Tom, thanks again for the plans. I took them to work the other day just to show them off to another Whaler owner. Kelly
ryanwhaler	posted 11-24-2004 07:43 PM ET (US) There are a lot of good articles on this forum about filling that low spot in the transom of the old 13's. Making the transom higher would give you a lot more choices in the future if you want to step up to a bigger motor. Is that an option?
Kelly	posted 11-25-2004 03:15 AM ET (US) ryanwhaler, If I wanted to get up into the 40hp range, I would probably buy a newer hull with the higher transom. For the way I use the boat, the 15hp Nissan works fine. There are also still some good new 15" shaft motors up to the 25 and 30 hp range to choose from. Kelly
Binkie	posted 12-02-2004 10:40 AM ET (US) If you can find a dead 15hp Nissan, you probably can buy the midsection and clamps pretty reasonable,not much call for them. Then you have to deal with the 20" driveshaft. You could also buy the gearcase from the short shaft motor,could be expensive. A 15" driveshaft could be hard to find. A cheap way to fix this is to take the 20" shaft to a macine shop and have a 5" section cut from it and have both ends squared. There is a guy in the Midwest,(I could give you his E-Mail) who makes adapters that slip over the cut down squared drive shaft ends and bolts it all together so you now have a 15" shaft. It works well and is used on many race motors. Some people have welded the two ends together, but unless they are perfectly aligned It would shake like crazy . The bolt on coupling eliminates this. It shouldn`t be too hard to modify the shift rod and water tube. If your unable to do this mechanical work yourself, it would cost too much,and would`nt be worth it.
simbo	posted 12-03-2004 12:28 PM ET (US) look Bay Manufacturing Div. Hemco, I have a Mariner 25hp,15"shaft & I want to convert in 20, because my transom is 20". I check this extension kit cost $300.!@#$$%%
Kelly	posted 12-06-2004 04:57 PM ET (US) Thanks for your responses. It looks like the conversion would be too much trouble. I think I am just going to try and find a good short shaft motor. The Yamaha 25 in two or four stroke looks good and the Nissan is a possibility. Kelly