I have a D4 7U (SN 7U43126) and in addition to the service manuals I would like to buy the D315 engine manual. My question is does the engine have it's own serial number that is different from the tractors SN? If so where is it located? The serial numbers that come on the D315 engine manuals on Ebay dont match any tractor SN's.

At that time, the engine got the same serial number as the machine it was installed in. There are industrial engines that have their own serial numbers.

Whether one of those books would be a help is a good guess! There’s bound to be some differences in peripheral components like oil pump, oil pan and pickup, water pump etc. There supposedly was also a redesign of the D315 In the late 1950’s that’s different from the original engines, so a manual for one of those Orphans wouldn’t be any help.

You want the SRB for the 4-1/2” bore 4 cylinder, D4 6U/7U tractor, 112 grader, D315 industrial and marine. All that will be listed on the front. I’ve never see any serial numbers listed on the one you want.

The engine serial numbers plate is generally behind the the pony motor clutch and brake handles on the block. I don't have a D4 so I could be wrong. But a place to start looking.

Cat used the same number for tractor and engine,BUT the engine could of been replaced somewhere in it's life. So you need to find it if possible before looking for parts.

CATERPILLAR D315 ENGINE SERVICE 6U 7U CRAWLERS
www.tractorparts.com/PDFs/CAT_D315_Diesel_Engine_SVC.pdf

Awesome thanks for everyone's help!