Shorten a driveshaft

[almetelo]

Hi!

A driveshaft can be shorten (25 to 20 inch) by cutting and welding the rod?
I´m sure it can but the real question is: It will last or is prone to break soon?
Other thing is I'm sure that have to be balanced.

Opinions or previous experiences are wellcome

[boscoe99]

I see no reason that it cannot be shortened (or extended). Just a matter of finding the right shop.

This sort of stuff happens quite often in other than the outboard motor world.

I would suspect that length and straightness are every bit as important (maybe moreso) than balance.

[pstephens46]

I am always impressed by these "axle doctor" guys. They come to the plant to cut and weld new spindles on 65000lb trailer axles. Pretty frequent that an entire wheel assembly just pops off. Usually in parking lots or other tight spots. Bearings rolling everywhere.

[99yam40]

if the spindle separates/breaks at the weld, the bearings should stay in the hub along with the spindle.
the wheel, hub, and spindle with bearings would just roll on down the road.

I had a spindle weld rust away on one of my boat trailers years ago.
the spindle worked it's way almost completely out of the tube/ axle.
luckily I made it back home and backed into the driveway.
Next day I noticed the boat leaning a little, then discovered what had happen

[pstephens46]

if the spindle separates/breaks at the weld, the bearings should stay in the hub along with the spindle.
the wheel, hub, and spindle with bearings would just roll on down the road.

I had a spindle weld rust away on one of my boat trailers years ago.
the spindle worked it's way almost completely out of the tube/ axle.
luckily I made it back home and backed into the driveway.
Next day I noticed the boat leaning a little, then discovered what had happen

Spindle seems to stay on. All the guts go flying. Had a truck turning around in the hood awhile back. The driver didn't know the wheel came off until he was some distance away. The "locals" grabbed the wheel and hid it. Guess they thought they could sell it for some cash.

[rodbolt17]

can you pay a machine shop to do most anything??? yep.
can you simply buy and install the correct part??? yep.

[99yam40]

then what you are talking about if bearing failure.
yes bearing falls apart and hub with wheel heads off on its own.
spindle is damaged sometimes beyond repair and needs replacing.
Getting the inner races off when they friction weld themselves to the spindle can be fun

[panasonic]

Hi!

A driveshaft can be shorten (25 to 20 inch) by cutting and welding the rod?
I´m sure it can but the real question is: It will last or is prone to break soon?
Other thing is I'm sure that have to be balanced.

Opinions or previous experiences are wellcome

Can it be done? Yes. Cut out section, center drill and taper for weld on lathe and pin the two sections back toghter. Have someone who knows how to weld....weld it without completely distorting it. Put it back in lathe and straighten it to run true...$$$

Is it worth it...no
Unless you got a lathe and decent welder doing it at home is not a option....never run true.

As Rodbolt says ...Go get the right shaft.

[boscoe99]

Let's not lose site of the big picture here.

If talking about a fairly new high HP model here in the US then by all means I suspect the vast majority would go the remove and replace route for the drive shaft.

Now if we are talking about a smaller HP model that is a number of years old, in a country where spare parts prices can be astronomical, where labour can be relatively cheap, and where there are shops that are known to be able to properly shorten a shaft, then I suspect the vast majority would then go the remove and modify route.

Mr. Almetelo's motor and country possibly fit the latter scenario. Up to him to decide really.

By the way, landing gear axles (a shaft if you will) are routinely overhauled and placed back into service. Same with many other expensive aeroplane components. I can't think of any air line that would replace expensive components when there are repair/modification procedures that can be done which provide an equivalent level of performance and life.

[panasonic]

Let's not lose site of the big picture here.

If talking about a fairly new high HP model here in the US then by all means I suspect the vast majority would go the remove and replace route for the drive shaft.

Now if we are talking about a smaller HP model that is a number of years old, in a country where spare parts prices can be astronomical, where labour can be relatively cheap, and where there are shops that are known to be able to properly shorten a shaft, then I suspect the vast majority would then go the remove and modify route.

Mr. Almetelo's motor and country possibly fit the latter scenario. Up to him to decide really.

By the way, landing gear axles (a shaft if you will) are routinely overhauled and placed back into service. Same with many other expensive aeroplane components. I can't think of any air line that would replace expensive components when there are repair/modification procedures that can be done which provide an equivalent level of performance and life.

Yes this very true, but that is a totally different ball **** now we are talking about now. I been in the MRO's that overhaul landing gear and in several Landing gear manufacturing plants on courses. To overhaul a MLG gear axle is a very big undertaking, and I could write a whole book on what happens to it.

But I agree there are many clever people out there in the world without the resources and money to simply buy a NEW shaft...so they do what they can do to make it work and they do. I thinks it would be hard to get it run true without spinning it in a lathe.

By the way a Piston/Axle assy from one of the jets we run costs much money....put it this way you could buy yourself a really nice boat with two big Yamahas on the back, with all the bells and whistles and still have money left over for the price of a axle assy.

[Inmyopinion]

I have seen the drive shafts cut and welded back together for outboards used for drag racing where the center section is shortened. They cut the drive shaft in the center remove the required amount then drill a hole for a centering pin in both ends of shaft. Bevel both ends of shaft weld it up. Turn on a lath to remove any trace of modification. I never saw one of these shafts fail. Motors were only used for short duration but high horsepower and torque application. This is not a low cost modification and I would think it would be cheaper to buy a standard size shaft.

[almetelo]

Hi guys!

Thanks for your comments.
This is as Boscoe stated... used parts market here almost dont exist and labor is much more cheap than in US and buy a new driveshaft is not an option as I belive that must be close to 400€ plus alll other parts needed.
I have a look on a F100 lower unit that is seized due of water intrusion for 200€ and just need new bearings but is 25 a inch shaft
I can buy the original bearings for less than 150€ and is my labor
If I buy them at a Yamaha dealer 500€ will not be enough just just for the bearings because are boxed on card/plast box saying Yamaha
This shaft doesnt allow make new splines.
Have to be cutted and welded.
A good used F100 lower unit worth over 1200€ and are rare to find
No one repair them when bearings or gears are damaged because price of parts here are very high (I wish we could have the prices of parts you have in US) so doesnt worth it and lately the stealing of F80/F100 lower units are very common (so people say are being sent to Spain) so I would like have a spair even having a ensurance that cover theft
Cut, weld and balance the drive shaft I'm sure will be much less than 50€

[99yam40]

I thought about the option of machining both ends of the cut shaft so one fits tight into the other before welding to help hold the shafts centered. Just have to be careful and weld in short bursts on different sides to keep it from distorting too much as you get it all welded up.
Just do not know how thick to make the welded part to hold the HP transfer

[panasonic]

I have seen the drive shafts cut and welded back together for outboards used for drag racing where the center section is shortened. They cut the drive shaft in the center remove the required amount then drill a hole for a centering pin in both ends of shaft. Bevel both ends of shaft weld it up. Turn on a lath to remove any trace of modification. I never saw one of these shafts fail. Motors were only used for short duration but high horsepower and torque application. This is not a low cost modification and I would think it would be cheaper to buy a standard size shaft.

Yes this is how it is done...shaft is "pinned" back together before welding.