I have a crack in a cover for a small engine tranny. Is there an epoxy that would patch it? It would need to be oil resistant.

A good question since there seems to be a huge assortment of epoxy products to choose from.

In general, the five minute/fast set formulas are not completely waterproof, only good for about 200F heat and not as strong.

The strongest formulations are usually slower setting (1-2 hrs or more) They have greater strength, resistance to heat and solvents. The strongest formulas are often combined with powdered metals. (ie JB Weld products)

In this case, if the crack simply needs filling, the epoxy alone should fill and adhere well enough to seal the crack. If the crack is not stable, I would seal it first, then lay a reinforced patch over the area as a second coat. Fiberglass or screen mesh can be used for reinforcement. Be sure there is no oil remaining in the crack, rinse with solvents, blow out with air, etc.

Slow set epoxy should work well.

I recommend Pro-poxy 20 for this application. It is a "full-bodied" epoxy.

As to all epoxies adhesion is the primary concern. I often us a Dremel (various bits do fine) to roughen the surfaces. Then after extensive mixing of the parts I firmly knead some of the product into each roughened surface. I follow by topping with the remainder. With this product you can smooth the finish with a wet finger.

I understand the oil/grease concern. I think this stuff would work. In addition, could you finish with a couple coats of enamel paint?

JB weld to me is the best, would not hesitate to use it. 24 hour cure though. Yes rough up the surface a bit prior to spreading it around, if it might move, a stiffener, filler always helps.