Your degreaser of choice (2 Viewers)

[ToyoHero]

Diesel is a great cleaner

 

[RedHeadedStepChild]

I believe (though I wouldn’t want to be cited as a source) that Simple Green will cause intergranular attack in aluminum parts.
Other than that, it’s good stuff.

 

[Green Hell Mustang]

I believe (though I wouldn’t want to be cited as a source) that Simple Green will cause intergranular attack in aluminum parts.
Other than that, it’s good stuff.

Yes, they do say on the website that it's fine to use Simple Green Crystal around aluminum, but it's not meant for prolonged exposure. The site says limit it to no more than 10 mins and rinse the part with clean water. So you can use it on aluminum, just be mindful. I'm guessing if you do go over the limit, the most you'll get is etching. Maybe use solvent on those aluminum heads.