Options for shaft adaptor?

[Per]

I'm working on a project that involves a 56ci OMC, a 15" mid and a V4 gear case. the engine will most likely be something like 16" because I need an adapter plate between the mid and gear case. The engine will be for my 15' tunnel used for Classic Offshore racing. Well that's the background...
I need to figure out how to best adapt and shorten the driveshaft of the V4 case to fit my -92 engine (multi spline)
My options so far seems to be:

Shorten the existing V4 shaft and have new splines cut. The diameter of the shaft is perfect but without the right connections the price might be high for the machining.

To get an upper part of a 3-cyl shaft and brace it to the V4 shaft. I think this would be quite straight forward and I can do the machining but it requires a 3-cyl shaft...

Square hole sleeve to couple the two shafts, this seems quite simple as well but requires a 3-cyl shaft and a square hole sleeve, My brother can do the machining of the shafts for me which is nice. I think there is room for the coupling just under the engine as well as just above the water pump, what would be best and why and would a 12mm or 1/2" coupling survive???

Please share your thoughts and experiences!

//Per

[champ20B]

Coupling shafts can be tricky. They need "perfect" alignment and strength along with balance, otherwise such a fabrication can be destructive to the gear-case and power-head and dangerous.

Your very best bet is to cut the shaft to height you want, then have a reputable machine shop cut the necessary splines you need. It is a relatively simple process and really shouldn't be too costly. Whatever the price is, it will be worth it to be put together right and solid.

[byrdsperformance@tds.net]

Cut the shaft off just above the water pump housing an use a 1/2" coupler.
You can buy coupler's from ron hill an seaway marine or make these. They are used on sst45's an other's .
To make a coupler weld two 1/2" drive socket's.
This way if you want to swap gearcase's just cut an square these to match.

[oledawg]

Why don't you just use a Nitro gearcase from a 49.87 cid Stinger 75hp, or an SST-60 gearcase? You will gain 3-5 mph with the smaller diameter case, and the 4 tooth spline and shaft will bolt right up?

[Bill Van Steenwyk]

[QUOTE=champ20B;145557]Coupling shafts can be tricky. They need "perfect" alignment and strength along with balance, otherwise such a fabrication can be destructive to the gear-case and power-head and dangerous.

Your very best bet cost wise is to cut the shaft to height you want, then have a reputable machine shop cut the necessary splines you need. It is a relatively simple process and really shouldn't be too costly. Whatever the price is, it will be worth it to be put together right and solid.





It is neither required nor necessary to put a solid connection between the power head and lower unit. Countless MOD and PRO motors over the years have run for years without such a connection at up to twice and over the RPM that would be encountered in this type application.

What is absolutely necessary and required is that the mounting surface of both the lower unit and power head be square and parallel with each other. I concur with the square drive shaft coupler idea and they can be purchased a lot of different places, or even made as described. The slight "sloppiness" is even desirable, if the power head and lower unit are not exactly in line square and parallel with each other as can sometimes be the case with a fabricated tower housing that is not constructed with the proper techniques.

If you want to spend extra money, that is your prerogative, but if using a factory mid/housing mis-alignment should not be a problem unless the housing has been welded on and consequently warped from the heat. That could be solved by placing in a mill of sufficient height and facing the top and bottom surfaces of same just enough to get an even cut on both surfaces. This is best done prior to cutting the drive shaft and assembling with the various couplers.

GOOD LUCK

[Per]

Thanks for the wise words everybody!
Seems I could go either way then, Think I'll let the price decide. I know at least one place to ask about cutting splines. I'll check with my personal outboard shopper to see if he knows where to find a shaft and what it would cost. Sockets are cheap at least:) have anyone tried using a deep socket and only using the hex part? that way there will be no welds. Of course the machining of the shafts will be a little harder...
I'm sure the case will be square to the engine but I'm a little worried about the alignment, I will have to rely on the hole patterns for the parts and their respective positions to the drive shafts I guess

I've started to work on a pattern for the adapter but my daytime job have gotten in the way of all sorts of fun projects lately:(

59515

Here are some pics, the gearcase is only for mockup purpose so that is something I need to buy as well.

59516

59517

[Hevi Kevi]

Is there a particular reason you are planning to use a V4 case? As Oledawg said, it's gonna be slow and a nitro will bolt right up. Just switch your crank to an older 4 spline. Lots of props for the nitro case around too.

[Per]

Is there a particular reason you are planning to use a V4 case? As Oledawg said, it's gonna be slow and a nitro will bolt right up. Just switch your crank to an older 4 spline. Lots of props for the nitro case around too.

Oh, sorry Oledawg, forgot to answer your question, good thing you brought it up Hevi Kevi!
Maybe I can blame it on the flue and fever...

The main goal with the project is:
A short shaft engine, well it will be sort of:rolleyes: , because the boat starts to feel a bit top heavy and most likely I will jack up the engine even higher.
Stock transom clamps with built in trim / tilt, because of availability of parts and reliability.
A gearcase that can take surfacing (for a long time)
The need for speed, I've kind of run out of revs with the 1:2,42 stock 3-cyl case, I am right at the limiter and swinging a 28-ish cleaver
I will be able to keep all my props, this is kind of important since I also have several Volvo Penta VP700 engines that uses the same props.

Using a stinger case?
I thought that when jacking the engine high enough the performance penalty for the big house (VS the Stinger house) would not be so big, I might be wrong here of course!
A fellow racer told me that parts for the Stinger case is getting expensive and hard to find and also that the Stinger case doesn't take surfacing to well, a bad combination if you ask me.

I'm sure I forgot something but I'll be back!!

[champ20B]

[QUOTE=champ20B;145557]Coupling shafts can be tricky. They need "perfect" alignment and strength along with balance, otherwise such a fabrication can be destructive to the gear-case and power-head and dangerous.

Your very best bet cost wise is to cut the shaft to height you want, then have a reputable machine shop cut the necessary splines you need. It is a relatively simple process and really shouldn't be too costly. Whatever the price is, it will be worth it to be put together right and solid.





It is neither required nor necessary to put a solid connection between the power head and lower unit. Countless MOD and PRO motors over the years have run for years without such a connection at up to twice and over the RPM that would be encountered in this type application.

What is absolutely necessary and required is that the mounting surface of both the lower unit and power head be square and parallel with each other. I concur with the square drive shaft coupler idea and they can be purchased a lot of different places, or even made as described. The slight "sloppiness" is even desirable, if the power head and lower unit are not exactly in line square and parallel with each other as can sometimes be the case with a fabricated tower housing that is not constructed with the proper techniques.

If you want to spend extra money, that is your prerogative, but if using a factory mid/housing mis-alignment should not be a problem unless the housing has been welded on and consequently warped from the heat. That could be solved by placing in a mill of sufficient height and facing the top and bottom surfaces of same just enough to get an even cut on both surfaces. This is best done prior to cutting the drive shaft and assembling with the various couplers.

GOOD LUCK

Yes, pro-race motors have two piece shaft assembly's. The Yamato stock outboards do to. Many of the early OMC opposed iron racers were also made this way. But what is different is that these motors had/have specific bearing support in the gear-case for the pinion shaft portion or (lower drive shaft). They tend to be a little more robust for such an application in the upper bearing support of the foot, and the main connection/mid shaft is designed to fit "just right" between the power-head and lower. Today, there are folks like Howie Pickerell who I believe, makes a (22cid OMC to HotRod lower) custom shaft, but I think that is a whole one piece shaft. Basically for me, if it was made for a one piece, it might be better to keep it as such if it isn't too complicated. But if a two piece works and is cheaper, that's a good way to go too.

[Hevi Kevi]

Oh, sorry Oledawg, forgot to answer your question, good thing you brought it up Hevi Kevi!
Maybe I can blame it on the flue and fever...

The main goal with the project is:
A short shaft engine, well it will be sort of:rolleyes: , because the boat starts to feel a bit top heavy and most likely I will jack up the engine even higher.
Stock transom clamps with built in trim / tilt, because of availability of parts and reliability.
A gearcase that can take surfacing (for a long time)
The need for speed, I've kind of run out of revs with the 1:2,42 stock 3-cyl case, I am right at the limiter and swinging a 28-ish cleaver
I will be able to keep all my props, this is kind of important since I also have several Volvo Penta VP700 engines that uses the same props.

Using a stinger case?
I thought that when jacking the engine high enough the performance penalty for the big house (VS the Stinger house) would not be so big, I might be wrong here of course!
A fellow racer told me that parts for the Stinger case is getting expensive and hard to find and also that the Stinger case doesn't take surfacing to well, a bad combination if you ask me.

I'm sure I forgot something but I'll be back!!

Basically, what you are putting together with that powerhead is an SST-60. The nitro case is basically the same as an SST-60 case without the nose cone. Lots of SST60's and V-bottoms like mine out there with nitro cases and SST-60 cases with propshaft centerline running close to the bottom of the boat. I've been racing for 2 seasons now and haven't smoked one. You would probably be needing a 23 pitch prop for it. 1.87 ratio if I remember right. You'll be in for less work and have a faster boat this way.

[oledawg]

Kevin is right on the mark. The Nitro case is 1.86:1 ratio, so you will not over rev props. There are some 2.42:1 Nitro cases used on the OMC, 2 Cyl. motors around 50-60 HP. You of course, do not want the 2.42:1 ratio. We ran the Nitro and SST-60 cases quite high on tunnel boats in SE & SST-60 class without problems. Also, there are heavy duty rear bearing carriers available for same. We suggest pinning the carrier in either event. Please, forget the bigger V-4 case. It will only disappoint you.

[Per]

OK, so maybe I have been heading in the wrong direction here...
So the alternative for me would be to try to find a Nitro case and then just solve the Trim parts (which I already have the pump for)

I do have an old 55hp? 3-cyl engine that used to sit on the short mid I plan to use for the build, wonder if that crank could be used?
59521
59519
59520


There is also a Johnson Formula E engine for sale not far from where my brother lives, very expensive and most likely with unknown history. I also question the shape of the skeg (see attached pic)

59518

[oledawg]

Yes, you can use the crank from the 3 cyl. 55hp as long as it has the 4 tooth spline. I'm sure it does. Just be sure to run the 1.86:1 ratio.

[Hevi Kevi]

[QUOTE=Per;145616]OK, so maybe I have been heading in the wrong direction here...
So the alternative for me would be to try to find a Nitro case and then just solve the Trim parts (which I already have the pump for)

I do have an old 55hp? 3-cyl engine that used to sit on the short mid I plan to use for the build, wonder if that crank could be used?



There is also a Johnson Formula E engine for sale not far from where my brother lives, very expensive and most likely with unknown history. I also question the shape of the skeg (see attached pic)

I love the fresh over spray on the prop and the ground in that picture haha. Those lowers come up from time to time on here. You can maybe even get a new SST-60 one from Seaway Marine? I've bought gears from there before. What trim parts do you need? I make these brackets and the bracket for the motor.

http://i1272.photobucket.com/albums/y382/HeviKevi/IMG_05671_zpsacq3k2ou.jpg (http://s1272.photobucket.com/user/HeviKevi/media/IMG_05671_zpsacq3k2ou.jpg.html)

http://i1272.photobucket.com/albums/y382/HeviKevi/IMG_05661_zpsllwqcawc.jpg (http://s1272.photobucket.com/user/HeviKevi/media/IMG_05661_zpsllwqcawc.jpg.html)

http://i1272.photobucket.com/albums/y382/HeviKevi/IMG_0721_zps185b26b9.jpg (http://s1272.photobucket.com/user/HeviKevi/media/IMG_0721_zps185b26b9.jpg.html)

No need to drill extra holes in your transom to mount it. Also works as inner transom plates. The last pic shows the added brackets for trim pump and battery box. That way there is no need to drill into the floor to mount extra brackets either

[LakeRacer99]

WOW, hevi kevi...nice work. just what i am looking for.

[Per]

Indeed, VERY nice work!
I have been listening to what all you guys said and got my self a Evinrude 75hp short shaft, Money and motor has not changed hands yet but the seller seems very dependable and the plan is to fetch it within two weeks. It is not the formula E Engine...
Spent the easter at my brother's place and we was supposed to pick up a trim & tilt unit for the project, when we arrived at the store I noticed an old 3-cyl mid and asked about it. It all ended with me leaving without trim & tilt but with a lot of 3-cyl stuff... Now I have a very nice 4-spline crank to put in my 56ci engine:)

Hevi do you still sell the adapter for putting a 56ci on a 49ci mid?

[sharpeye Mike]

Should make a great motor Per, just picked up an other short shaft Stinger yesterday for parts or a latter project, one of my all time favorite motor.

[Hevi Kevi]

Indeed, VERY nice work!
I have been listening to what all you guys said and got my self a Evinrude 75hp short shaft, Money and motor has not changed hands yet but the seller seems very dependable and the plan is to fetch it within two weeks. It is not the formula E Engine...
Spent the easter at my brother's place and we was supposed to pick up a trim & tilt unit for the project, when we arrived at the store I noticed an old 3-cyl mid and asked about it. It all ended with me leaving without trim & tilt but with a lot of 3-cyl stuff... Now I have a very nice 4-spline crank to put in my 56ci engine:)

Hevi do you still sell the adapter for putting a 56ci on a 49ci mid?

I missed this post. Yep, I do still make the adapter plate. Sounds like you have what you need to put together a nice machine now.