Mike this is what the bulletin S-7964 says. Camshaft gear C 248 and C 264 engines. Camshaft gear # 6760 DA currently specified for production and/or service use in C-248 and C-264 engines is revised to provide a tighter and improved fit on the camshaft. Part # is advanced to DB to identify change. Reason to overcome field complaints of gear loosening on camshaft. Effective F 400# 21314 Engine # 155941. Effect on service parts: Furnish new soon as available for farmall 400 400HC and international 400 tractors and when old stock is exhausted in all other applications. Note to prevent damage to camshaft while pressing on new tighter fit gear, support camshaft from rear face of front bearing journal. Sent to all district offices, transfers and parts depots. This is dated 10-12-1955, but I think the production tractor was assembled in july 55. DB went on to 450 tractors also Mike hope someone has one of these bulletins for change from D to DA. Have thought about contacting the WHS to see if they could check or let a person look if in the area. Mike D is not as thick in hub as DA. Change in DA and DB covered above. Last print parts books and CIH site will only show updated parts if they fit earlier tractors, not when changes were made. My guess is SM tractors hydraulic system was easier on gear than 400 tractors and that lead to change above. I suspect IH didn't install the DA gear in tractors until after live hydraulic was offered. My opinion only though. Hard to say with a lot of gears changed out in last 50 or 60 years. I have torn very few of the engines down that the cam nut lock wasn't bent ( if used wasn't needed if cam was replaced with left hand thread type also production in some 450) more than once, indicating previous removal. Dave
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Today's Featured Article - Identifying Tractor Noises - by Curtis Von Fange. Listening To Your Tractor : Part 3 - In this series we are continuing to learn the fine art of listening to our tractor in hopes of keeping it running longer. One particularly important facet is to hear and identify the particular noises that our
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