Bottom End Blues!

[Nos4r2]

Originally Posted by codprawn

Obviously the casing - as I said it all depends on the design. Remember - unless a bearing is siezed there shouldn't be much force on it unless it is a thrust bearing.

Wrong, sorry mate. In turning the drive through 90 degrees you will get stresses induced by the power transfer. The secondary (driven) bevel gear in the case of an outboard gearbox is stressed downwards and backwards. Remember the difference between crank rated power and prop rated power? Thats where the missing (approx) 5% goes.

For finishing a weld on aluminium I'd recommend a grinder flapwheel-lots less stress on the weld for a start but it makes a much smoother job on the 1st use as well. I use them for any weld dressing I do now.

[Jono]

Lots of "interesting" views on what causes weld failure... any one of you experts want to have aguess at what caused this weld to fail? Its 13mm thick 304H s/steel, by the way....

[Nos4r2]

Looks like it wasn't welded properly or there was a defect in the weld at the point I've circled-but there's no obvious stress cracking there or crack progression so I'm unsure. That's firebricks on the plate isn't it? Someone's not been cooling the plate down with water have they? Rapid Expansion/contraction will cause what 's happened there but it's rather corroded so it's hard to tell-much easier with a freshly failed weld. It's hard to tell if I'm not there in person either.

[Jono]

Originally Posted by Nos4r2

Looks like it wasn't welded properly or there was a defect in the weld at the point I've circled-but there's no obvious stress cracking there or crack progression so I'm unsure. That's firebricks on the plate isn't it? Someone's not been cooling the plate down with water have they? Rapid Expansion/contraction will cause what 's happened there but it's rather corroded so it's hard to tell-much easier with a freshly failed weld. It's hard to tell if I'm not there in person either.

I am taking the p**s somewhat, as it's impossible to tell by picture, descriptions etc, which was rather my point.. but I'll give you some more information and see what you come up with... the weld was 100% radiographed at manufacture.... the equipment runs in the high 700's (centigrade)... The cooling rate when it comes off stream is measured in days, not hours..... it's not corroded at all.... Top marks for the "firebrick" that's close.. ....

[stan_deezy]

Originally Posted by Jono

I am taking the p**s somewhat, as it's impossible to tell by picture, descriptions etc, which was rather my point.. but I'll give you some more information and see what you come up with... the weld was 100% radiographed at manufacture.... the equipment runs in the high 700's (centigrade)... The cooling rate when it comes off stream is measured in days, not hours..... it's not corroded at all.... Top marks for the "firebrick" that's close.. ....

?? Part of a nuclear reactor

[Jono]

Originally Posted by stan_deezy

?? Part of a nuclear reactor

Oil refinery... but now I'm making it too easy....

[stan_deezy]

Originally Posted by Jono

Oil refinery... but now I'm making it too easy....

cat cracker

[Nos4r2]

And I thought it was part of a ships boiler or something like that lol...

Couldn't tell you then-not there. It does have a layer of corrosion though-that or oxidised nickel.it'd be bright if it was stainless and not corroded.

What DID cause it?!

[Nasher]

Think I started something here.

Remember the crack isn’t in the gearbox itself, it’s in the Exhaust chamber between the box and the prop. The bearing it’s closest to is the one held in a ‘spider that sits just behind the prop.

I’m struggling to find somebody to weld it at the moment, although I may have located a spare casting, but the guy involved can’t check it’s the right one until later in the week.

Nasher.

[stan_deezy]

Originally Posted by Nasher

Think I started something here.


Nasher.

yeah but it sure beats working !!

[Jono]

Originally Posted by stan_deezy

cat cracker

Yup

[stan_deezy]

Originally Posted by Jono

Yup

Grangemouth?

wot do I win????

[Jono]

Originally Posted by stan_deezy

Grangemouth?

wot do I win????

Nope... although I did build the same parts for Grangemouth! It's a refinery in Qatar... close but no cigar

[stan_deezy]

As long as you didn't build the 1989 vintage (if memory serves correctly). They're still pulling bits of it out of the river............

[Jono]

Originally Posted by Nos4r2

And I thought it was part of a ships boiler or something like that lol...

Couldn't tell you then-not there. It does have a layer of corrosion though-that or oxidised nickel.it'd be bright if it was stainless and not corroded.

What DID cause it?!

What appears to be corrosion is in fact carburization.. that is the steel has been burnt. What has happened is a two stage failure. Firstly they had a temperature "run away" which is what burnt the steel, then they had a high sulpher content in the feed stock (stuff what goes through the equipment) which combined with elevated temperatures caused the catastrophic failure in the S/steel welds that's pictured here...nice

[Jono]

Originally Posted by stan_deezy

As long as you didn't build the 1989 vintage (if memory serves correctly). They're still pulling bits of it out of the river............

Ssshhhhh....!


Naah! We didn't have nuffin' to do with either the '87 ot '00 explosions... honest Mister.. it woz a steam pipe wot went "pop" not the cracker...

[stan_deezy]

yeah yeah, I believe you Mr Jono.......mind yer head on the cell door! oops sorry!

Back to the picture: looks pretty lethal that failure, but I didn't think it was part of an outboard yuk yuk yuk!

[codprawn]

Originally Posted by Nasher

Think I started something here.

Remember the crack isn’t in the gearbox itself, it’s in the Exhaust chamber between the box and the prop. The bearing it’s closest to is the one held in a ‘spider that sits just behind the prop.

I’m struggling to find somebody to weld it at the moment, although I may have located a spare casting, but the guy involved can’t check it’s the right one until later in the week.

Nasher.

I would try lumiweld if all else fails!!! seems designed for the job..........

[Nasher]

An update

I struggled to find somebody to weld the crack in the casing. One guy that tried started and another crack opened up alongside.

I decided to have a go with the JB Weld so I could use it over the weekend and take a chance, especially as there was going to be another boat with me. So, spent all Thursday evening grinding, cleaning, mixing, applying etc and was very pleased with the result. It went off rock hard, and the two bits of scrap alloy I glued together have taken a lot of serious abuse to separate again.

Then on Friday I had a call from the ever helpful MB Marine in Fareham to say they had a spare used bottom casting and gear set. So I spent all Saturday afternoon swapping my water pump and gearchange mechanism into the new casting and fitting it to the leg.

Had a great day out on the Solent yesterday.

I’d like to know how the JB Weld would hold out, so may one day put the repaired leg on and try it close to shore with another boat about. The JB Weld will also now be a permanent addition to my toolbox.

Nasher.

[Richard B]

Yeh, TIG is a specialist job!

If you need welding to the gearbox case, speak to either of these people:
Gordon at Autoweld in Southampton (He probably won't do it himself but will know a man who can) - I haven't got Gordon's number immediately to hand to shout if you need him, or Andy Clarke at The Bosun's Mate http://www.bosunsmate.co.uk