The Gun Counter

I was wondering what the best choice for an ultralight engine would be weighing cost vs. time between overhauls?

Bumping this to brig it to the top. Termite should be along eventually with an educated answer, but if I had to bet, he's going to say Rotax.

The engine with the best track record is the Rotax 503. Unfortunately, They recently stopped production. Parts are still very easy to come by, but that may come to an end eventually. Hirth engines have a bad rap for not making it anywhere close to their TBO and a lot more random engine seizures than average. Cuyana engines are antiquated but pretty solid and 2SI engines seem to be regarded as garbage.

About the only new ultralight engine available is the MZ series at compactradialengines.com. They seem to be pretty solid, but they're fairly new, and don't have much of a track record yet.

If you see a purpose built 4 stroke ultralight engine on the market, be cautious. Most of them are vaporware, with the exception of the HKS 700E (Which it too heavy for most ultralight applications). There are also some people who mod existing engines for Ultralight/Experimental use (Like the Valley 4-Stroke, which is a modified Generac V Twin).

Most of the engines based on the VW engine seem to have overheat problems. I think it is because the VW engine was designed to be fan cooled.
It looks like a Rotax has the best record.
At the rate my finances are going down the tube it is not something I can seriously worry about.....dang it.