I too had a microscopic crack between the cylinders on one half of my case.
Since my engine was 14 years old and < 500 hrs, despite the fact that these
cracks
are a known casting defect, I was solely responsible for the cost of repair.
The repair required replacing the case with a later design case (no known
casting defects and redesign in affected area) and a mating crankshaft.
Fortunately, I have some friends in the Rotax supply chain and got away
with a bill of ONLY $8000.00 for the engine rebuild(parts and labor).
The only other option was a new engine at a discount price of $17k.
Welding is not an option. The alloy of the case will distort and stress
will lead to more cracks with even expert gentle TIG. This is the uniform
Opinion of several Rotax experts, including one who I know plays loose
and fast with the rules of engine mods.
BTW, once detected, the source of the leak took days to find. The successful
approach involved taping squares of clear plastic kitchen wrap over a dusting
of corn starch on suspicious areas, then running the engine for five min
to pressurize the case interior.
--------
Ira N224XS
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