outboard prop blade repair

Hi all! I am a new (old) boat owner. I am starting to go through the boat and motor. The motor is a 35 hp eveinrude lark. It has a 3 blade aluminum
prop which has 2 of 3 blades bent. One was bent a little and another more.
They are both smooth curvy bends. I am guessing it is some kind of cast
aluminum.(???) I wasn't sure how hard/brittle to expect it to be. So I got out my polyurethane mallet and laid it over a piece of 2 inch round steel rod.
I slowly worked out the less severe bend. It came out without any cracking
visible but there was a fair ammount of resistance which leads me to believe that it has been heat treated when made. The other blade had about twice the bend and I dont want to push my luck. I took out about 1/4 to 1/3 of it's bend but I stopped there. I am thinking I would like to warm the thing
slightly to relieve the the work hardening I have done and to allow it to
unbend the rest of the way and not get a crack doing so. I know that
some alloys you can bake them in your home oven for a short time and
relieve stress or slightly un-do heat treatment. I am sure it depends on
what alloy it is as to what time and temp. to use.

Anyone done this before and/or know what alloy and time-temp to use?

I know this might be a monster of a question ........ If all else fails I guess
I can try calling Evenrude..... !

Tim
PS Can I Tig weld it if my repair goes bad ??????

 

Your prop is shot. No novice can straighten a prop and expect it to work right again. You can take it to a prop shop and they'll straighten it right out, but this costs more then a new prop, hence the reason your prop is trash. A replacement prop like yours will run about $100 retail, depending on size, pitch, number of blades, etc. A good composite will be about $110 and a stainless prop about twice this.

 

What you can or cannot do with a prop depends on skill and experience only.

Many years ago during holidays in the mediterranean I made a mistake and damaged all three blades on a submerged rock, one sheared off almost completely. No spare, no other boats, just farmers and small dusty villages.
Without any hope I asked around and was pointed to the local smith.

He looked around for a rock with the proper curve, got his welding torch, some aluminum leftovers and then - without goggles - built up the missing parts. After half an hour of welding, grinding and hammering I had an almost perfect prop that took us back to civilization the next day where I ordered a spare prop in the marina.

 

I would argue that both of the above are correct.

It is possible to get a working prop from a damaged one, but remember a prop is going to spin at hundreds if not thousands of rpm, any slight imbalance can cause serious damage to the engine or transmission driving it. Plus it will vibrate terribly.

That being said if you need a get home prop they can be worked with nothing more than two rocks ( I did this once when I ran aground in the dink). But I like CDK then went to the shop and bought a new one. A $100 prop just isn't worth risking the drive train over.

 

A good used prop is about $50.00. Florida has plenty of them around too.

 

Okay, I have seen some old school welders and prop guys that could beat a prop back into shape and it wouldn't vibrate so bad as to not get you home, but this is the very rare exception folks. I could probably do a fairly good job of it, but it would vibrate enough to warrant displacement speeds until back in home port.

Props are cheap unless you're looking for something special.

 

prop-

The engine in question was basicly a freebie so sending the prop out to just
have done what I would do seems like a waste of money. There is no missing
material anywhere to change balance- but nothing says it was balanced to
start with being 50 years old. Balancing should not be a problem anyway.
A piece of shaft and some magnets makes a perfect balancer. Works for
model airplane props which go up to 40,000 rpm. That should be enough ....
I can put it in the lathe and track the blades. I thought I would bead blast it and dress the edges after the re-bending - then maybe a coat of epoxy primer. I guess I will go ahead and do it the way my intuition guides me. See how it goes. My dad always said that everything that was ever made was made by somebody. ( when someone said "you cant do that ! )

Cheers- Tim

 

All the power to ya Vamp.

Let us know how it turns out.

-Tom

 

They fix props all the time here, and they are not 35HP iether some are twin 200 or 4 x3oo

Alluminium is not heavy and you would have to be a long way out to vibrate and damage an outboard.

Hammer it straight --if it breaks weld it back on,-- a new blade can be moulded back on with an oxy acetylene cutter it has to be a cutter to get the heat in to the blade that needs to be clamped to an anvill or cylinder block or similar.

A new blade can be made up with some ally plate 3/16 or what ever.

I assume it is not a cush drive hub with the rubber insert because that is toast.

Get a flat bowl of cement and push the prop into it, then pull the prop out. When it is set you will have the shape and pitch of at least one good blade as a pattern.

Its not so much balance but pitch difference that can cause vibration,--but on 35HP!!!!