Replacing a Failed 12.5L — John Deere 9520 Complete Block Build

This John Deere 9520 didn’t just need parts — it needed a second chance. In this video, I take a completely failed 12.5L engine and build a brand-new complete block assembly from the stand up, showing every critical step along the way. The original engine failure was caused by a failed water pump that allowed coolant to intrude into the engine oil, which led to main bearing failure and rapid internal engine damage. This was not operator error or neglect — once coolant contamination occurs, bearing damage can escalate quickly and replacement becomes the only reliable repair. This video documents the complete, start-to-finish build and setup of a 12.5L complete block assembly, including injector installation, rocker assemblies, valve and injector adjustments, timing setup, front cover and seal installation, turbo and fuel system components, oil system assembly, and final preparation before the engine is ready to go back into the tractor. I put the Milwaukee 3/8” Drive SAE & Metric Deep 6-Point 43-Piece Shockwave socket set to work during this build and they performed exactly how I expect Milwaukee tools to perform: excellent fit, clear markings, and zero issues even during high-torque work. These sockets worked perfectly on this job and quickly earned a permanent spot in my tool cart. Grab yours here if you want the same set I’m using: https://www.acmetools.com/milwaukee-3... If you’re a technician, mechanic, or owner looking for a real-world, no-shortcuts reference on a large displacement Deere engine build, this one’s for you. 00:00:00 Intro 00:03:39 Stripping down the old engine 00:03:57 Install new block to the stand 00:05:50 New engine on the stand — ready to start the build 00:05:50 Installing injectors and rocker shafts 00:16:13 Installing flywheel 00:19:43 Setting engine to #1 TDC 00:20:34 Torque rocker shaft down / install push tubes 00:22:26 Adjusting valve clearances & injector preload 00:30:48 Installing new injection harness 00:32:14 Installing rocker cover 00:33:41 Installing intake manifold 00:35:57 Installing front timing cover 00:36:01 Installing oil cooler assembly 00:38:09 Installing outer timing cover 00:39:26 Installing front main seal 00:40:11 Installing thermostat housing 00:41:02 Pressing front main seal onto damper 00:41:50 Installing damper / front main seal onto crank 00:43:05 Exhaust manifold & turbo install 00:43:38 Installing high pressure fuel pump 00:44:24 Installing oil pump pickup tube & pan 00:47:13 Installing water pump 00:48:15 Pre-filling oil filter — FINAL STEP! Want to see the best of ZK MasterTech? Check out my top repair and service videos here:    • Best of ZK MasterTech!   Follow me on TikTok!   / thezkmastech   Follow me on Instagram @zk_mastertech Want some ZK merch? https://zk-mastertech.myspreadshop.com/ Check out my Amazon store front! https://www.amazon.com/shop/zkmastertech Want a career with Sloan Implement? https://www.sloans.com/career Thanks to Sloan Implement and John Deere for their continued support. Subscribe for more in-depth diagnostics and field fixes. And as always — keep that green iron moving! #milwaukeetools #nothingbutheavyduty