OT - Outboard Problem
Daddylonglegs - 1/8/11 at 06:24 PM
Any engineering gurus on here tonight?
I've just stripped down my outboard engine and found the gear selector mechanism has a bit that needs replacing/repairing. It is basically a
stepped piece of steel which sits on the end of the forward/reverse selector rod. It looks a little like the side of a jigsaw puzzle piece which takes
a tab if you know what I mean 
I guess it's hardened steel as it will take a fair bit of hammer. Basically the rod pulls on the actuator which
then presses against a spring-loaded shaft in the gear shaft which runs in a sort of diff setup. When under spring tension the crown wheel turns one
planet gear, then when the rod is pushede in, the other planet gear is selected so reversing the shaft direction.
Would it be possible to braze, weld etc. the bit in question, or is it possible to make a new one?
A replacement is pretty much a no-go as the engine is pretty old and it is highly unlikely that I could get a replacement, even second-hand.
Sorry for the essay 
Thanks.
JB
designer - 1/8/11 at 07:20 PM
We need a photo before we can answer the question.
Daddylonglegs - 1/8/11 at 07:31 PM
As if my magic:
Before:
Penta1
After:
Penta4
The change lever sits inside the broken end (or it did 
) and pulls the plate up to change gear.
David Jenkins - 1/8/11 at 07:54 PM
That looks like something just right for water-jet or laser cutting - there are a few experts on this forum - maybe one of them can tell you how to
get the shape defined in the correct format for one of those machines.
Alternatively - it's not beyond a bit of hand-crafting. If I was making that I'd probably use mild steel and case-harden it... what are the
rough dimensions?
daviep - 1/8/11 at 07:57 PM
quote:
Originally posted by David Jenkins
Alternatively - it's not beyond a bit of hand-crafting. If I was making that I'd probably use mild steel and case-harden it... what are the
rough dimensions?
Exactly what I was thinking:- Grinder, drill, half round file, job done
iank - 1/8/11 at 07:58 PM
If it lives a hard life I'd agree with David, water/laser cut and then hardened if necessary. Trying to fix it risks it breaking at an
unfortunate time.
blakep82 - 1/8/11 at 07:59 PM
send it to andyw7de (after contacting him first lol) and he'll be able to do you a new one
and it'll be an almost exact copy! which i don't think you'll really get by hand 
Daddylonglegs - 1/8/11 at 08:13 PM
Must admit, I was thinking of making one from mild steel then trying to harden it. From what I've read it's a case of heating to a certain
temperature then quenching in oil or water.
Dimensions are approx 45mm long x 5mm thick.
[Edited on 1/8/11 by Daddylonglegs]
David Jenkins - 1/8/11 at 08:31 PM
Case hardening is the best solution - IMHO - you heat the part in case-hardening powder (e.g. Kasenite) until it's red hot. Keep it that heat for
a while. Once it has cooled you'll find that it has a super-hard high-carbon skin over a resilient core of mild steel.
Just don't case harden it until the part is finished and polished, as you won't be able to modify it very easily afterwards!
[Edited on 1/8/11 by David Jenkins]
v8kid - 1/8/11 at 08:35 PM
quote:
Originally posted by Daddylonglegs
Must admit, I was thinking of making one from mild steel then trying to harden it. From what I've read it's a case of heating to a certain
temperature then quenching in oil or water.
Dimensions are approx 45mm long x 5mm thick.
[Edited on 1/8/11 by Daddylonglegs]
No. mild steel cannot be hardened this way as there is not enough carbon in it. If using mild steel you have to case harden it by heating it up to red
heat and repeatedly immersing it in a case hardening powder. this will harden the outer few thousands of an inch and help prevent wear. It will do
diddlysquat for the strength or toughness of the part.
Carbon or tool steel can be hardened by heating to white heat and quenching when it will be extremely hard but brittle. tempering it by heating it a
bit and allowing to cool will reduce brittleness but also reduce strength. The hotter you heat it the less brittle and strong it becomes.
Contrary to popular opinion it is a skilled trade - assuming you want a repeatable predetermined set of conditions. If anything will do - I guess
that's what you get.
Nothing to loose by trying it and seeing what you get. If the original was case hardened you will be able to drinn into the fracture - if not it is
tool steel and it,s more difficult.
Me? I'd try to get a second hand part its amazing what is available on places like smokestack.
Cheers!
David Jenkins - 1/8/11 at 08:42 PM
Depending on the size of the piece, you could cut it out of something the model engineers call "gauge plate", which is high-carbon steel of
a fairly precise thickness. It can be hardened, but doesn't come in big bits though (not easily obtainable, anyway). It's quite expensive
though.
Though, as v8kid says, hardening of critical parts is an art...
andyw7de - 1/8/11 at 09:15 PM
Ill make some calls tomorrow and see if i can get a small offcut of tool steel from one of my customers
If i can then Ill give you a shout, failing that ill cut you half a dozen so that you can experiment with case hardening.
Id need to check but I think stainless may be harder than standard mild steel, might be worth a try.
material aside these will be very cheap to cut, especially at LCB rates
Andy
rf900rush - 1/8/11 at 09:36 PM
Just a long shot. It might be worth listing the Make model of your Outboard just in case any one one here has spares.
A while back I needed a (£600+new) CDI unit for a suzuki outboard.
Many hours on ebay ended up with enough bits (-CDI and Gaskets) to build a complete engine.
So you never know.
Daddylonglegs - 1/8/11 at 10:35 PM
Thanks for all the replies chaps
Andy, I'll be back....with a drawing
BTW, the engine is an Archimedes (read Volvo) Penta 120, 12hp I think. twin 2-stroke.
Thanks guys, this forum never fails to deliver 
Peteff - 1/8/11 at 10:48 PM
You can buy 01 tool steel from Cromwells which can be hardened and tempered with a blowlamp and a domestic oven. Look for precision ground flat stock
on their website. You only need to heat it to cherry then quench it in oil, steel melts before it gets to white hot.
[Edited on 1/8/11 by Peteff]
