08-12-2025, 04:46 PM
The Machine: A Worn but Workable Case 850
The Case 850 track loader, particularly models from the early 1970s, remains a recognizable workhorse in the compact crawler category. Built for utility work, site clearing, and light excavation, the 850 was often equipped with a backhoe attachment and powered by the Case 301 diesel engine—a 4.375" bore, inline 4-cylinder unit known for its simplicity and torque. But after decades of use, many of these machines show signs of fatigue: blowby, hard starts, cracked heads, and worn undercarriages.
In one restoration effort, a 1974 Case 850 was brought back to life after suffering from severe blowby and a dependency on ether to start. Upon teardown, the team discovered a 1" hole in one piston and a second piston with a smaller burn-through—classic signs of injector failure or prolonged ether abuse.
Terminology Explained
- Blowby: Combustion gases leaking past piston rings into the crankcase
- Ether Addiction: Reliance on starting fluid due to poor compression or injector issues
- In-Frame Overhaul: Engine rebuild performed without removing the engine from the chassis
- Balancer Assembly: A timed counterweight system inside the crankcase to reduce vibration
Engine Rebuild Strategy: Case 301 Diesel
The Case 301 engine, cast with “JIC” markings, was confirmed as original. The rebuild involved:
The ventilated pistons suggested long-term abuse. One technician speculated that poor injector spray patterns—possibly from clogged or leaking pencil injectors—led to localized overheating. Combined with frequent ether use, the combustion chamber temperatures likely exceeded safe limits, causing piston melt-through. The team flushed the fuel tank and replaced all injectors to prevent recurrence.
Rear Main Seal and Balancer Timing
Changing the rear main seal during an in-frame rebuild is possible but requires removing the torque converter and flywheel—a labor-intensive process. The balancer assembly, often mistaken for an oil pump, must be timed to the crankshaft using alignment marks. Improper timing can turn the machine into a “vibrating compactor,” as one mechanic warned.
Parts Sourcing and Manual Access
Rebuild kits were sourced from U.S. suppliers, and a reprint of the Case service manual was acquired via eBay. The manual proved essential for shimming the balancer and verifying torque specs. Aftermarket kits from brands like Clevite were considered, though some users noted they often exclude connecting rods and may require separate sourcing for seals.
Recommended parts sources:
The Case 850 may be decades old, but with careful diagnosis and a thorough rebuild, it can return to productive service. Whether it’s a cracked head, melted piston, or mistimed balancer, each issue tells a story—and solving them requires patience, precision, and a bit of detective work. As one restorer put it, “It’s not just about turning wrenches—it’s about listening to what the metal’s been through.”
The Case 850 track loader, particularly models from the early 1970s, remains a recognizable workhorse in the compact crawler category. Built for utility work, site clearing, and light excavation, the 850 was often equipped with a backhoe attachment and powered by the Case 301 diesel engine—a 4.375" bore, inline 4-cylinder unit known for its simplicity and torque. But after decades of use, many of these machines show signs of fatigue: blowby, hard starts, cracked heads, and worn undercarriages.
In one restoration effort, a 1974 Case 850 was brought back to life after suffering from severe blowby and a dependency on ether to start. Upon teardown, the team discovered a 1" hole in one piston and a second piston with a smaller burn-through—classic signs of injector failure or prolonged ether abuse.
Terminology Explained
- Blowby: Combustion gases leaking past piston rings into the crankcase
- Ether Addiction: Reliance on starting fluid due to poor compression or injector issues
- In-Frame Overhaul: Engine rebuild performed without removing the engine from the chassis
- Balancer Assembly: A timed counterweight system inside the crankcase to reduce vibration
Engine Rebuild Strategy: Case 301 Diesel
The Case 301 engine, cast with “JIC” markings, was confirmed as original. The rebuild involved:
- Removing the cylinder head and inspecting for cracks
- Extracting pistons and liners, revealing excessive ring gap (~0.20")
- Replacing pistons, rings, bearings, and gaskets
- Shimming the balancer assembly to correct backlash (~0.006–0.010")
- Replacing injectors and sending them for bench testing
- Installing a new water pump after the original failed during testing
- Head bolts: 200–210 ft-lbs
- Connecting rods: 95–105 ft-lbs
- Main bearings: 145–155 ft-lbs
- Valve lash: Intake 0.015", Exhaust 0.025"
The ventilated pistons suggested long-term abuse. One technician speculated that poor injector spray patterns—possibly from clogged or leaking pencil injectors—led to localized overheating. Combined with frequent ether use, the combustion chamber temperatures likely exceeded safe limits, causing piston melt-through. The team flushed the fuel tank and replaced all injectors to prevent recurrence.
Rear Main Seal and Balancer Timing
Changing the rear main seal during an in-frame rebuild is possible but requires removing the torque converter and flywheel—a labor-intensive process. The balancer assembly, often mistaken for an oil pump, must be timed to the crankshaft using alignment marks. Improper timing can turn the machine into a “vibrating compactor,” as one mechanic warned.
Parts Sourcing and Manual Access
Rebuild kits were sourced from U.S. suppliers, and a reprint of the Case service manual was acquired via eBay. The manual proved essential for shimming the balancer and verifying torque specs. Aftermarket kits from brands like Clevite were considered, though some users noted they often exclude connecting rods and may require separate sourcing for seals.
Recommended parts sources:
- Fawcett Tractor Supply (Ontario)
- MinnPar (U.S.)
- Local hydraulic and diesel shops for injector testing
- Case dealers for OEM gaskets and seals
- Engine displacement: ~4.8L
- Compression ratio: ~17.5:1
- Oil type: 15W-40 conventional diesel oil
- Coolant: Ethylene glycol-based with corrosion inhibitors
- Fuel system: Mechanical injection with pencil-style injectors
- Always perform a compression test before teardown
- Avoid excessive ether use—diagnose root causes of hard starting
- Inspect injector spray patterns and replace all units if one fails
- Flush oil passages and fuel lines during rebuild
- Use break-in oil for initial startup, then switch to standard diesel oil
The Case 850 may be decades old, but with careful diagnosis and a thorough rebuild, it can return to productive service. Whether it’s a cracked head, melted piston, or mistimed balancer, each issue tells a story—and solving them requires patience, precision, and a bit of detective work. As one restorer put it, “It’s not just about turning wrenches—it’s about listening to what the metal’s been through.”
