Epoxy vs Ethanol Test

Been a while since posting anything or tackling projects. Between full time work and school followed by the cold winter weather its been slow here.

I did a test on a well known 2 part epoxy putty that was recommend on numerous sites for port modifications, especially among 4 stroke car guys.

The epoxy product is called A-788 Splash Zone Epoxy. It seems to mainly be aimed at the marine industry for boat hull repair.

Once equal parts are mixed the it becomes a very dark green, maybe similar to the "stuco verde" mentioned by Jan Thiel? It is very thick and can be somewhat hard to spread evenly but one trick that is shown in youtube videos of the product is using a bit of water to smooth it out and make it more pliable which helped a lot! I used some silicone tipped clay tools for this and it worked well.

Here are some photos of an old piston I used to later test holding strength. One area of the crown was prepped by light 120 grit sanding. The rest was simply cleaned with a bit of brake parts cleaner.

You can see the one area on the piston skirt I smoothed with a bit of water.

The holding power of the epoxy was pretty amazing. The large globs on top I tried knocking off with a hammer and the actually epoxy broke and crumbled but never came unbonded from the metal. Same for the bit on the skirt, I purposely covered the piston window so I could pry on it from behind and it still never detached. So for holding power this stuff gets a 10 out of 10 for sure.

Next up came the important bit, the fuel test. I used regular gasoline with no alcohol/ethanol, gas with 15% ethanol and then some gas I had mixed up for riding which was 15% ethanol and some C16 leaded race gas with Klotz oil.

The pieces were fully submerged for 24hrs. As suspected the bits in the ethanol fuel showed softening on the outside, about .25mm-.5mm deep. This outer skin could be scrapped off with my nail with a bit of force. Not something I would feel comfortable running in an engine to be honest.

However, the non-alcohol/ethanol gas had no noticeable effect on the epoxy. It seemed exactly like the pieces that were never placed in fuel at all. So if non-ethanol fuel is used I think this epoxy would work great for any kind of porting projects.

Also, if you look there is a small bit of white urethane casting resin on the left. I also tested this as I was casting some small parts for a carburetor. I only tested it in the non-ethanol fuel and it also showed zero signs of being effected. So if you ever need a thin easily cast-able resin for making parts that will be in contact with fuel this product should work well.

Specialty Resins - Model Pro Resin

I will update this topic later in the year as racing season starts and I run both products on some engines.