Part of the Yanmar Parts Manuals.
An OHV gasoline engine comes apart quickly on the stand, and the job stalls just as quickly when you cannot put a real Yanmar part number on the ring set or governor spring sitting in front of you. This parts catalog, Yanmar publication Y00B4451, covers the GA120 and GA120RDZB gasoline engine and exists to answer exactly that question.
Across its 20 pages the catalog works through the engine assembly by assembly: Cylinder Block, Cylinder Head & Bonnet, Air Cleaner & Muffler, Crankshaft, Piston & Camshaft, Carburetor, and the Governor & Control Device. Each section lists the factory part numbers for components down to seals, pins, springs, and hardware, so a worn rocker arm or a cracked float chamber body gets ordered correctly the first time.
The PDF is small (0.41 MB), in English, and bookmarked by section. Bought once, it stays with this engine for every rebuild after this one.
What's Inside This Yanmar GA120RDZB, GA120 Parts Manual
| System | Pages | Key Topics |
|---|---|---|
| Cylinder Block | 1-3 | Cylinder Block Assy, Oil Seal, Gasket, Side Cover Assy, W/ Lub. Oil Gauge Cap, Lub. Oil Cap, Joint Filler |
| Cylinder Head & Bonnet | 4-5 | Breather, Breather Pipe, Cylinder Head Assy, Intake Valve, Exhaust Valve, Valve Spring, Spring Retainer, Rocker Arm |
| Label | 6-7 | Ohv Mark Label, Caution Label, Drain Label, Air Cleaner Label, Recoil Start Label |
| Air Cleaner & Muffler | 8-9 | Air Cleaner Assy, Air Cleaner Cap, Air Cleaner Element, Air Cleaner Body, Element Holder, Carburetor Gasket, Muffler Gasket, Muffler |
| Crankshaft, Piston & Camshaft | 10-11 | Camshaft Assy, Decomp Spring, Tappet, Push Rod, Crankshaft Assy, Crankshaft Gear, Idle Gear, Piston Assy |
| Carburetor | 12-13 | Carburetor Assy, Throttle Valve, Choke Valve, Pilot Jet, Spring, Needle Valve, Float Assy, Throttle Shaft |
| Governor & Control Device | 14-20 | Governor Spindle, Governor Lever Shaft, Governor Gear Assy, Governor Spring, Control Assy, Control Lever Assy, Control Base Assy, Base Assy |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Parallel Pin Size | 8x12 mm | p. 16 |
| O-Ring Size | P-18.0 | p. 2 |
| Stud Size | M8x18 | p. 4 |
| Key Size | 4x10 mm | p. 16 |
| Hose Diameter | D5/3 | p. 12 |
| Circlip Size | E-4 | p. 18 |
Yanmar GA120RDZB, GA120 Common Problems This Manual Covers
Carburetor gummed up from stale fuel
Fuel left sitting varnishes the float bowl and plugs the main nozzle, and the engine will not idle or starts only on choke. The Carburetor section lists the throttle valve, float assembly, float chamber body, and main nozzle so you can order the parts you find fouled instead of guessing.
Manual Section: Carburetor p. 12Power loss from a clogged air cleaner
A dirty element chokes the intake and the engine runs rich and down on power. The Air Cleaner & Muffler section identifies the cleaner assembly, element, and body by part number so replacements match what the factory fitted.
Manual Section: Air Cleaner & Muffler p. 8Low compression and oil consumption
Worn rings show up as hard starting, blowby, and oil disappearing between checks. When the engine is open, the Crankshaft, Piston & Camshaft section gives part numbers for the piston assembly, ring set, and rod assembly so the bottom end goes back together with correct parts.
Manual Section: Crankshaft, Piston & Camshaft p. 10Surging and hunting at idle
A stretched governor spring or worn linkage makes the engine hunt under light load. The Governor & Control Device section covers the governor spindle, shaft, lever, gear assembly, and spring, the usual suspects when speed control gets erratic.
Manual Section: Governor & Control Device p. 14Valve train noise and lost lash
Ticking from the head or a valve that will not seat points to wear in the rockers or valves themselves. The Cylinder Head & Bonnet section lists the head assembly, intake and exhaust valves, and rocker arm for reference when the bonnet comes off.
Manual Section: Cylinder Head & Bonnet p. 4Oil leaks at seals and bearings
Oil weeping from the block usually traces to an aged oil seal or a rough ball bearing behind it. The Cylinder Block section identifies the block assembly, oil seal, ball bearing, and cover assembly so you can replace the leak source, not just wipe it down.
Manual Section: Cylinder Block p. 1Exhaust leaks and a rotted muffler
Small gasoline engines shake mufflers and pipes loose over time, and a leaking joint gets loud and dangerous near the recoil side. The Air Cleaner & Muffler section lists the muffler and pipe assembly with their hardware for a clean replacement.
Manual Section: Air Cleaner & Muffler p. 8Frequently Asked Questions
Which engines does this parts catalog cover?
It covers the Yanmar GA120 and GA120RDZB gasoline engine, published by Yanmar under publication number Y00B4451. It applies to the engine itself regardless of what equipment it is installed in.
Is this a service manual with torque specs and rebuild procedures?
No. This is a factory parts catalog. It identifies components and their Yanmar part numbers by section, from the Cylinder Block through the Governor & Control Device, so you can order correct replacement parts. It does not contain repair procedures or torque values.
Does it break down the carburetor into individual parts?
Yes. The Carburetor section lists the carburetor assembly and its components, including the throttle valve, float assembly, float chamber body, and main nozzle, so you can replace individual pieces rather than the whole unit. p. 12
Can I find internal engine parts like rings and the crankshaft?
Yes. The Crankshaft, Piston & Camshaft section covers the crankshaft assembly, piston assembly, piston ring set, rod assembly, and camshaft assembly with its decompression spring, everything you need to identify for a bottom-end rebuild. p. 10
What format is this manual in?
This is a 20-page searchable PDF ready for immediate download. Works on any device, so pull it up on your phone while you're under the hood. No shipping, no waiting.
Is this Yanmar GA120RDZB Parts Catalog printable?
Yes, print as many copies as you want, and there are no restrictions. Many mechanics print the section they need and bring it to the shop floor.
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