Do not confuse the 2GM20 and the 2GM20-F, they are not the same.
These Altmount Kits by Balmar offer the opportunity to install a larger alternator than would otherwise be possible. They are designed to fit select engine models, the list expands every day so if you don't see your engine listed do give us a call. Alternator upgrades using a single drive belt are limited by the amount of power that can be transferred by the belt but using a serpentine belt considerably increases the possibilities. The kits include a set of serpentine pulleys to go over the crankshaft and water pump pulley and replace the alternator pulleys and come with a matching serpentine belt and a spare. They are sold for specific engine models only. The alternators need to be purchased separately. If you order an alternator with a kit it will come with the appropriate pulley pre-installed. Installation is relatively easy. The kit comes with two belts but purchasing an additional spare belt is recommended as these are not typical serpentine belts.
Yanmar kits are available for Yanmar 6L, 4JH, 3JH, 3GM, 3HM, 3YM, and 2 YM engines. The photos shown above are representative, I dont have photos of every kit or every installation
Read my BLOG POST about installing one of these kits.
My blog post has installation notes for a serpentine kit on a Yanmar