2002 Yamaha 70 2stroke bottom plug rusty

kevin11mic

Petty Officer 3rd Class
Joined
Oct 12, 2010
Messages
96
I don’t think this is weldable. The metal is super thin here with corrosion on the back side. If you could even get in there to weld it I don’t think you could get a clean weld due to the aluminum oxide trying to bubble up through the weld pool. Mig welder would be your only shot at accessing the spot Just due to the only access you have to work through is the exhaust port. My history with mig on aluminum is it in not precise enough or gentle enough for a repair like this. It’s a very fast and messy way to weld aluminum. I guess it wouldn’t hurt to try? I wouldn’t want to dump much money into this block at a machine shop just due to the metal loss it’s already seen. If I was successful in fixing this hole there will probably be another one pop up somewhere else sooner than later. I keep it flushed but the corrosion is hard to stop once it’s gotten this bad. Ive seen JB weld do some impressive things. I’m thinking lather some on and roll the dice. If I can get another duck season out of It while I save my pennies for a new powerhead I’ll be happy. Even if the JB doesn’t hold I’m just back to where I was and I ran it all last year like this. I don’t see this resulting in a catastrophic failure. Just have to change the bottom spark plug often and maybe put some oil down the hole for storage. Thanks for all the help. I’d say this concludes the saga. I’m the meantime If anyone comes across a good used Freshwater powerhead or crankcase let me know.

Happy Boating!
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Will need to scrape/remove a thin metal layer around the crack for the putty to adhere well.. Post results after a long wot run, should work well...

Happy Boating
 

kevin11mic

Petty Officer 3rd Class
Joined
Oct 12, 2010
Messages
96
Well I’m back. Engine ran good first outing. Second outing it decided to eat some aluminum about a mile from the ramp. I will get to see how well the JB weld has held up when I split the case to see where in the world this aluminum came from. Was running WOT and engine started knocking then slowed down and died/locked up. Got home and pulled the head and found this. Will move to it’s own thread if it’s not an obvious issue I find. Might have to splurge for the new powerhead after all.
 

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Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Yep, in such case a new powerhead is mandatory along peace of mind...

Happy Boating
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,310
Not sure about this. Is that actual lumps of ally in the pictures ? The other picture looks like it’s had water cleaning the piston. Presumably there is no water in the oil injection reservoir? What does a compression test show ? That would be the first thing I’d do now I think.
 
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