Extending the drive shaft to make an extra long shaft model - can it be done?

[DonegalDave]

I have a 1969 Chrysler 9.9 that has a 5" extension making it a long shaft version. I have just bought another 5" leg extension with the idea of extending everything else.

It is for a boat that i have just built. I dont want to cut the transom down and if I did i would only get 2" anyway. As it is the cavitation plate is just below the waterline. In forward it digs in and that is fine. However, if i move forward in the boat, it lifts the engine too far up and the water pump sucks air.

By extending the leg another 5" the gearbox will be just above the keel, therefore safe from damage and the prop will sit where it can get max water. (The transom narrows to the keel)

I can extend the water tube with a flexible pipe. I am sure I can extend the gear shift either by making a new lower piece or inserting a section.

However, the drive shaft is the problem. It obviously takes the power and has to be up to the job. Can a piece on stainless rod be welded in successfully?

I have several ideas on how it could be done, but has this been done before??

Thanks in advance,
David

 

[gm280]

:welcome: to iboats DonegalDave...

Let me see if I understand what you're asking. You presently have a long shaft OB 9.9HP '69 Chrysler engine. And you want to lengthen it another 5" longer. If that is correct, Then my answer is maybe. I say maybe because a lot of things have to work out perfectly for it to work correctly. NO you can't simply weld a stainless steel section to the existing drive shaft because I don't think the present drive shaft is made out of stainless steel. So you may could use a quality steel section and weld it and turn it down to work. But that is going to take some really precision effort. You could even remake a longer one at a machine shop, but at what cost? And the housing would have to be cut and joined back together to make such an extension along with the shifting shaft and water output tube to the power head. Yes all those things can be made to work, but it is certainly a huge amount of effort. So again "Maybe" ! A very tall order and extremely ambitious in my thinking. There has to be another way to get you boating. JMHO!

 

[jbcurt00]

Don't J/E outboards come in a 9.9hp +/- XL lower? Sailboat kicker motors if I remember correctly that are a 25" leg.

Do Chryslers come in an XL?

I see smaller OBs regularly for sale, don't know how many are XLs but below 15hp, they might not be cost prohibitive, IMO, unless you really want to tackle an extended driveshaft.

Hows about a pix or 3 of your newly made boat? Loved making mine even though it's just a plywood canoe/kayak looking thing.

If I was going to attempt to weld on an extension, I'd probably try to find a 2nd driveshaft to use instead of a rod. Adding a rod, you'll have to put it in the middle of the existing to keep both gear ends, which means 2 weld joints. Using another driveshaft, you'll not only be using the exact same alloy whatever it is, and only have 1 weld as the newly added piece will have the gear end on it already.

Good luck.

 

[Frank Acampora]

1. the drive shaft is stainless 2. the water tube on these older engines used a 5 inch extension with a flare on one end to fit over the original short length pipe. Find another 5 inch extension to total 10 inches. 3. Chrysler DID make a sailor model with the extra 5 inch length. If you can find a junker, salvage the drive shaft out of that.Welding a piece into the existing drive shaft is a do-able but a bad idea. You might try Franz at franzmarine@aol for a used shaft but he certainly will be expensive.

 

[jerryjerry05]

Get someone to make a coupler like they do on the bigger Forces and some Mercury's.

Any good machine shop cut the shaft to the right length and make a coupler to fit them.
#4 in the pic. (hope that pic works)
http:// www. boats . net / parts /search/ Merc/Force /parts. html REMOVE the spaces

 

[flyingscott]

From your description another 5" won't cut it. You say the gearbox will be above the keel that has to be in the water. The gear box has the water pickups in and is water cooled has to be completely submerged.

 

[DonegalDave]

No Title

Hi GM280, I like your maybe! I generally have a gut feeling about all things engine and came up with a maybe as well. I considered 'splicing' in a larger diameter piece, with driveshaft sized holes in either end and either welding or screwing it together. My fear was the whole thing whipping and ending up putting strain on everything.

Good point JBcurt00, with the single weld. Buying another outboard would seem like giving up! I have totally rebuilt this one and feel it deserves to be used. I will try and attach a couple of pics of the boat. My avatar is of me in the boat when it was launched.

Hi Frank. I agree re welding being a bad idea. I have generally dismissed that mainly because my local engineer, who never says no, said no!

Jerryjerry05, I removed the spaces and still came up with a log in screen. I am probably doing something wrong. Thanks anyway

Flyingscott.. as it stands, the engine works. I will try and attach a photo to explain, but it is a wooden clinker fishing boat with a Y shaped transom. The cavitation plate sits just below the water line when the engine is in neutral, which is fine. In forward, the engine digs in and that is also fine. If I am in the boat alone and want to go forward to sort something, tie up or whatever, the stern rises enough to lift the engine, and the water pump sucks air.
With 5" more this won't happen and the fin is still above the keel line (just).

I don't know what length of shaft I have at the moment. The bracket to center of prop measurement is (from memory) 26".

On the Google I found part number 45-12367 which is the extra long shaft but I don't know what length it actually is.

I also found Bay manufacturing who make drive shaft extension kits for Mercury and Yamaha. I have a sneaky feeling they might fit. The leg profile is slightly different, but I don't need that bit.

And thirdly, I have a German friend who says his father-in-law has the machines to make one. (Free-of -charge)

The third option seems the best, but I am not sure of the reliability of the offer.

I will be in San Francisco in November (for a not so well earned three week break over thanksgiving) so getting stuff back from there will be practical.

So, I have two more questions that I am trying to get answers to.

1. What are the dimensions of part number 45-12367. (It is, I think, a Mercury part number?? but I am sure I found it on an exploded diagram of a Chrysler??)

2. My engine is currently back on the transom of my boat so I cannot easily check. Does anyone know what the diameter of the shaft is and how many splines there are as Bay Manufacturing my have the piece I need.


Sorry for the rambling reply but I kid myself that the more I type the better picture I paint when the reality is that I have had a glass or two of red wine and the fire is lit (August, I know!).

Thank you all again,

David