big difference between a and non a heads is the large casting that holds the cross shaft bearings in. The A series casting has a large bore with about a two inch wear surface for the row unit to flex up and down against instead of riding against the narrow 3_16" plate which will quickly cut a groove in the pivot casting and cause all kinds of crazy movements in the row units. also the wear surface in the A's have a grease zerk and will continue to flex smoothly (if you grease it every day). the verticle hex drive shafts for the belts and rotary knife chain drives will wear and soon be out of alignment and this will cause the bevel gears to wear unevenly which drove me nuts. . New shafts, and new bearings every 5-600 hours will keep them decent, but really labor intensive. If the bearings would lock on the darn shafts it would not wear out. Go figure. Still needs a set of spring tighteners on all the belts, and all the chains to eliminate 98% of all daily adjustments. also need to cut the fine threaded shaft off the top of each of the rotary knives and weld a 5_8" coarse threaded bolt in it's place with a double nut on top to lock it, because the fine threaded one will jiggle out the threads and never stay adjusted up tight. The spring tensionor inside the rotary knife assembly is worthless because unless that knife is tight enough to get warm when it runs, it will not cut crap and stay clean. learned all this after about 30 years of running first a 454 non A, then a 454A, then a couple of 653A's. Sold them all and have a 920 now, so there you go. gs
