Thread: bent skeg

hi to all
has anybody had experience on straightening a bent skeg [that is the lowest section of the g/box leg on an outboard motor which is cast aluminium. or any other ideas on repairing the same. thanks toby.

G'day Toby.
I'm no expert but a question springs to mind first off.
1) is the the bottom of the outboard leg still complete or is it in pieces?

If you try to straighten the skeg it will more than likely break off. If the leg is still together then getting it welded back on might be a bit risky as you don't know if the heat from welding will damage the internals or warp the case causing damage to the internals. If it is still together you could consider using an epoxy based adhesive like Aluminium Devcon. I have no idea what it costs these days but Blackwoods should carry it. If the parent metal is prepared correctly and you used the Devcon to build up around the join as well, I reckon it will do the job.

If you have the leg apart then a good aluminium welder should be able to tig the skeg back on without any warpage of the case. Maybe a good welder can do the job with the leg complete. Hopefully someone else with more experience than I in aluminium welding can comment here.

There is a bloke down Buttaba way who is a mobile welding specialist.
"Kevins mobile welding". or somehting like that. I don't have his number handy but I would think he will be in the white pages. Might be worth while giving him a call.

regards

bollie7

Originally Posted by toby.1944@hotma

hi to all
has anybody had experience on straightening a bent skeg [that is the lowest section of the g/box leg on an outboard motor which is cast aluminium. or any other ideas on repairing the same. thanks toby.

Skegs can be easily weld repaired or even fully replaced if completely broken off . It is a common procedure and will yield a competent and long lasting repair.
If you are entertaining any hope of repairing it using Tig avoid any adhesive glue or sealant on the thing.

Old salt encrusted legs are difficult enough to weld, in any case but with any aluminium thats had any treatment like that is almost impossible to weld.

I absolutely refuse to weld any metal that had any sort of bog or adhesive on it.

Its not worth the grief and any professional repairer will likely give you the same answer.

Grahame

thanks to both for replies. the skeg has a fair curvature in it i was thinking about heating it up with o/a and trying to straightening it first.if it snaps off i will make one up and tig it on . i have my own 200amp adv .square wave tig . like you said salt contamenated aluminium can be a problem on its own.

Originally Posted by toby.1944@hotma

hi to all
has anybody had experience on straightening a bent skeg [that is the lowest section of the g/box leg on an outboard motor which is cast aluminium. or any other ideas on repairing the same. thanks toby.

HI TOBY, Yes I have straightened many a Outboard Skeg. I am an Outboard Mechanic with Mallacoota Outboards (Yamaha & Mercury Dealers) here in Mallacoota. We use Oxy Heat and two Hammers generally a Club Hammer and a good size Ball Pein hammer. You use the heavier Hammer on the opposite side than the side Your hitting. It is best not to have the hammers parallel, but offset in relation to the bend.
Sometimes the Skegs we straighten are bent a couple of ways which makes it difficult. We have sometimes straightened them cold in a Hydraulic Press, but generally we use Heat and Hammers. With the Heat You need to get the Skeg reasonably warm, but not to hot. I have heard an old thumb rule that You heat Aluminium till a black mark is left when a Match (not the red end though) is struck across it. Then You can bend it without it fracturing. The Heat will need to be re applied a few times during the Process. You will notice a sound change when you do re apply the heat .
My Boss has Welded up countless Skegs using pieces of Aluminium Plate, a Skeg Kit or just Filler Rod. Depending on the individual Job at the time. Grahame is right about not using any type of Epoxy. Epoxy and Silicone make it difficult to Weld Aluminium. I agree that Salt can be a problem, but preparing the area to be welded helps. Use a Clean Flapper Disc on a Angle Grinder to clean the area to be Welded.
I hope this Helps You out. One last thing Do NOT try to straighten a Skeg Cold with Hammers, because it will break.
Cheers Stewart steran50

thanks for the reply stewart.
do you dismantle the gear/box first in case of o/heating the seals. the other rule of thumb on heating up aluminium is to blacken the part with an accetylene flame first then heat up with o/a flame until blacken disappears. [ right temp now for welding]
i would suppose you know that one?
thanks tobym.

OK !
A bit more more info for you, if you going to Tig yourself.

Firstly filler rod! It is certainly 5356 alloy filler rod required as the skeg has to be marine grade aluminium.

You should be able to buy a handful of loose filler rods .
Or at least 2.4 or 3.2 diameter at the welding supply place.Make the tungsten the same diam as the filler rod.

Secondly make sure you do not use any abrasive containing aluminium oxide as its the very stuff you want to get rid of.

There is a dedicated aluminium abrasive wheel available.

Be aware it takes double the melting temp of aluminium to melt through the oxide,so often on thin sections its possible to have the alloy melt and fall away before the oxide is penetrated. On 4mm and up it should not be a problem.
The skegs I have welded were stripped so the seals would not be melted.
Clean ,clean clean is what is required to successfully weld aluminium. Keep dressing or changing your tungsten as it will pick up the oxide.Even with out accidentally dipping it in the weld puddle .
I have probably forgotten something its been a while since I have done any Tig with ali.


Grahame

Hi Toby, You are welcome on the Reply. I actually have'nt heard of that other Rule of Thumb. No, it is not necessary to dismantle the Gearboxes for either straightening of a Skegs or Welding of a Skeg. I have never seen my Boss having to replace a Seal due to an overheat. Neither have I seen a Customers Gearbox end up with water in it after He/She have used it - at the next service or sooner. Whenever we get a Skeg to straighten or weld up we alway check for water in the Gearbox and bent Prop Shafts. Remember You are only Warming the Aluminium - we don't want to cook eggs on it.
I Heat them generally so as they are a bit to hot to touch. When You Heat them try to keep the O/A Torch tip fairly close. That way You wont burn the Paint as much. Also when Heating to straighten Skegs only Heat in the particular area You are working on at the time. Otherwise You will be straightening one area up only to find its going out of shape in another area.
When straightening Skegs too You will find sometimes You can't get it perfect. Do not worry about this as long as it is reasonably good it will be okay. The Filler Rods My Boss uses are 2.4mm Grade 5356. The Welder is a 'EMF Pilot Arc', this Welder is used both as a 'AC Tig' and a 'AC Stick Welder'. I am not saying Grahame Collins is wrong after all the Guy is an experienced Welder. From what I knew of Oxide in Aluminium is that it burns away (word may be incorrect) near the Melting point of Aluminium. I will do some homework for Myself on this anyway. I was hoping to upload some Pictures, but apparently they are to big in size. I will have to find out how to reduce them in size for the future.
Cheers Stewart (steran50)

Hi Stewart,
I don't disagree about the seals thing ,I just tend to be prudent as Murphy is always ready to strike.
Not being an experienced mechanic or indeed seeking more experince, I did not want to take take chances in damaged seals etc ,thats why I opted to remove seals.

Welding temperatures do go way over cooking eggs temperature-put your hand on the weld area accidentally and find that out.Aluminium is very conductive and will conduct heat.
This occurs quicker on thinner section and probably the thicker sections don't get that high.

You mentioned paint.i was never lucky enough to weld on a near new one.I seemed to score the old dungers.

In the welding world ,using the carbon smoke as a temperature indicating paint is fairly weld known.The premise is that the carbon deposit burns away at a temp close to the ideal pre heat temp.The charred match stick is another reliable indicator.

In reference to the oxides ,my training as a welder taught me that oxides of aluminium need removal (as much as is possible) from the surface to be welded because.

• Oxides contaminate the tungsten
• The oxides reform on the surface of the weld ( an aluminium weld of good appearance off the torch is actually shiny and polished looking)

AC current alternates or flicks back and forward 5O times/sec from negative to positive pole. On the negative side penetration of the metal occurs and on the other a cleaning action occurs.This will be noticed on the edge of the weld puddle and agitated oxides can be seen as the get pushed out of the way.

I can't remember burning ever being mentioned but bear in mind that the oxides melt at double the temp of ali,so the temp thats burns them also burns the parent metal.

If you are not shaky like me you won't accidentally stick the tungsten into the pool or touch it with the filler,but still find a deposit of crud on the tungsten. This is the oxides which are picked up on alternating current and coated onto the tungsten.

I hope that that these questions are now cleared up.

regards
Grahame

HI Grahame, Thanks for the info RE "in the welding world". I have not had a chance to do any Homework as Yet. Just to clear one thing up though. When I was saying that you are only "warming the aluminium" and that You don't want to cook Eggs on it. I was only referring to the Preheating temperature for Straightening of Skegs. Just for interest sake - I Myself have never welded up a Skeg, but I have straightened quite a few. I have however Welded up a couple of Propellors. My Boss with His (I would say 40 Years) Aluminium Tig experience does the majority of the Aluminium Welding.
All The Best for Xmas and the New Year.
Regards Stewart steran50