G'day Magilla,
The in and out movement is normal but the arm should not have sideways slop.
Check Crankcase Oil Level
Too much oil will push oil out of the weakest point—including the governor shaft.
Drain down to the correct level if overfilled.
Remove the breather assembly.
Clean the reed/flap or disc thoroughly with petrol/brake cleaner.
Make sure the breather only lets air OUT, not IN.
Reinstall.
If the breather sticks even slightly, crankcase pressure blows oil out the governor arm hole.
This alone fixes about 50% of “leaking governor arm” cases.
It just depends on what type of governor arm you are working with and without it apart you can't tell.
✅ 1. Bushing-Only Design (NO SEAL)
In some engines the governor shaft simply passes through a close-fitting bronze bushing in the crankcase.
Oil control relies on:
Tight clearance between shaft & bushing
Crankcase pressure being low
A light smear of oil acting as a film seal
When these wear, they always start leaking.
If yours has no visible rubber seal, this is likely the case.
👉 Fix:
Replace the governor shaft (if worn/grooved at the exit point)
Ream or replace the crankcase bushing
OR install an external retro-seal (see option 3 below)
This is the hardest and least common repair because it requires engine disassembly.
✅ 2. Grooved Shaft + O-Ring Design
Some models have:
A machined groove on the governor shaft
A small O-ring that sits in the crankcase housing right where the shaft exits
This O-ring acts as the seal.
Signs:
You see a thin groove or step machined on the shaft
The hole in the crankcase looks “counterbored” to fit an O-ring
No external rubber seal pressed in
👉 Fix:
Replace the O-ring with:
Fuel- and oil-resistant Viton O-ring
Correct size (often 1/4″ ID × 3/8″ OD × 1/16″ CS or metric equivalent depending on model)
If the groove is worn or shaft polished:
Replace the shaft
Or move to an oversized O-ring if slop is tiny (not ideal, but works temporarily)
✅ 3. Retrofitting a Seal (VERY common field fix)
If the original design had no seal or the bushing is worn, many mower techs do this:
Remove governor arm
Drill/clean the opening slightly
Press in a tiny rubber lip seal (like used on Briggs models—often 3/8" OD)
Reinstall arm and clip
This works surprisingly well if there is enough crankcase material around the shaft exit.
I can help you choose the correct dimensions if you want to measure the shaft.
⚠️ Also check for crankcase pressure
Even a perfect shaft-seal design will leak if pressure is high.
Check:
Breather valve working
No blocked breather hose
No overfilled oil
No stuck rings / blow-by
Install a retrofit lip seal around the governor shaft (the common repair techs do)
Because many old engines leak from this exact spot, mower mechanics often fit a small external oil seal into the crankcase wall.
How it’s done:
Remove governor arm and clean the area.
Measure the governor shaft with calipers
Lightly counterbore the crankcase hole with a drill or end mill to match a small seal OD.
Press a mini rubber lip seal into the hole (e.g.,
Shaft 6 mm → seal 6 × 12 × 4 mm,
**Shaft 1/4″ → seal 1/4″ × 1/2″ × 3/16″).
Reinstall arm and linkage.
✔ Works extremely well
✔ No need to open the engine
✔ Cheap
❌ Requires careful drilling and alignment
❌ Must not drill too deep into crankcase
This is the most practical fix for home and shop use.
3️⃣ Field-expedient fix: install an external O-ring in a shallow recess
If you don’t want to machine for a seal, you can:
Lightly countersink the crankcase hole
Fit a tight O-ring that the governor arm presses against
Apply a non-hardening sealant (Yamabond / Dirko)
It’s better than nothing, but not ideal.
Cheers
Max.
