... saw a Yanmar 186D 4WD, vintage mid 1980's. Man was I impressed with this tractor ... it's sparked my interest in Yanmar! All I've read so far for these tractors has mostly been very good. Anyone have one?
They are impressive. Think the 'Toyota' of the small tractor world. Totally bulletproof.
I have a YM240, one size larger than you asked about. This is the US-market twin to the gray market YM2000, which is the tractor with the best parts support of any gray-market. They are like early VWs, CJ jeeps etc with aftermarket parts support that will be available for years to come.
My US-version Yanmar was neglected and looks it, but aside from appearance it seems to be like new. When I got it the loader bolts were loose, the fuel was like mud, and the idiot lights were dangling by my feet. A couple of weekends tinkering and a couple hundred $ renovation (battery, dash lights and headlights, fluids change etc) and it hasn't needed anything since beyond normal 50 hour servicing. It starts instantly and runs like new.
My photos usually show it in use, rather than showing off the spring wax job like some people we know.

This photo below shows a 3-point backhoe (Kubota K-650) I just found for it. This is the right size and was made in the US for Kubota around 1980, so its generic in contrast to the proprietary stuff Kubota offered later. This does a great job of removing stumps in the orchard.
The Yanmars sold by Yanmar Corp - USA are rare. Deere soon contracted them to build for Deere and cease US sales. I like to think my model was the one that impressed Deere into forming that contract!
Presently the gray market Yanmars outnumber the legitimate imports by some large multiple - 50:1???. There have been large numbers of good used tractors brought over but also some are repainted in Vietnam so beware. I think for most, the condition under that nice paint is about comparable to mine but some of the VN "factory rebuilt" units can be repainted junkers. Japan sells *NO* parts to VN so apparently any rebuilding is done with handmade parts. Buyer beware if you see flawless paint on a 25 - 30 year old Yanmar.
Buy from a dealer-importer who offers support if you aren't comfortable dong your own service work since Yanmar-USA no longer has dealers and Deere won't touch them. The largest parts sources are Hoye Tractor in Texas and Fredricks Equipment in Alabama.
Aint she purty?!
