Reply to Al Letts:
Jaker
Find a good local starter/generator overhaul shop. It you have a good handle on the application or part number most places can change it over from 6 to 12 easily. Remember to get a new regulator and polarize all first.
al
Nothing wrong with an alternator on a diesel, even a slow speed diesel such as the old CATs, the problem comes when you do it the easy way and use one of those "one wire" Delco alternators. If these are used at the gear drive generator rpm, the diesel may never rev high enough to excite the one wire system and make it begin to charge. If you belt drive it and can gain some rpm from pulley ratio, then it might work ok as a "one wire".
If you use the regulator plug and an ignition switch or an oil pressure operated switch or some other means to supply battery voltage to the alternator regulator terminal, the Delco will excite at low rpm and most likely outperform any of the old generators. Also a lot cheaper to have repaired.
There are some direct drive adapter kits available to replace the CAT gear drive generators. These are the most expensive, but are a neat, simple installation. No chance of increasing alternator rpm since it's all determined buy the standard gear ratios.
Some folks have used a standard or shortened gear drive generator frame as a bearing support for a replacement (extended) shaft that can have a pulley on the end of it to drive an alternator/AC compressor etc.
Some of the older (than the U series) and newer (late U series and newer without the large single belt fan drive) tractors had a crankshaft pulley groove for a belt drive generator so you just have to fabricate a bracket to mount the alternator and tension the belt.
D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare timeπ