How to replace lawn mower oil seal
too much oil
Overfull oil level will cause excessive crankcase pressure.
Common engine oil leaks
Too much engine oil
Diagnosing an engine oil leak
I use a oil seal puller to remove the seal but you don’t necessarily need one. You’ll need to remove the engine from a tractor mower and just the blade and blade Boss from a walk behind mower.
The tools required for this are are a basic selection of wrenches and sockets.
An impact gun would be nice but not necessary.
The tools you’ll need to fit an crankshaft seal include:
- Engine de-greaser
- Oil drain
- Adjustable wrench
- Wood screw
- Large socket or soft faced hammer
- Engine oil
Replacing Mower crank seal
Replacing a lawn mower crankshaft seal isn’t that difficult. However, a walk behind mower is easier than a tractor.
The walk behind mower will require the removal of blade, blade boss, plastic shroud and drive pulley (if fitted) from the crankshaft in order to gain access to the oil seal.
The tractor mower will require cutting deck, drive pulley and engine removal.
Crankshafts usually have a buildup of grass and corrosion, so cleaning them thoroughly with a wire brush and lots of wd40 will help when it comes to removing the drive pulley, especially on a walk-behind mowers.
An impact gun does make life easier when it comes to removing walk-behind mower blade bolts and very useful on tractor mower clutch assemblies /PTO’s.
Note of caution, when removing the old seal, you’ll need to be very careful not to damage the sealing surfaces of the crankshaft and oil pan. Using a screwdriver to gouge or pry will damage the metal and the new seal will leak.
Steps as follows:
Drain the engine oil to begin and pull your walk behind mower spark plug wire (prevents mower starting).
Always turn walk behind mower over with carburetor side facing up - prevents oil spill and starting issues.
Fitting a walk behind mower seal - remove blade and boss.
Fitting a tractor seal - engine out.
Take a picture
Ease it out
Gently does it
Fitting the crankshaft seal
Most seals are fitted using a wipe of engine oil to help fitting and sealing, however some seals need to be fitted dry, so consult with your part supplier first.
The mating surfaces need to be clean and free from dirt, but do not use anything metal to clean the surfaces, likewise do not use sandpaper. If you require an abrasive, use the scouring face of a household sponge.
I use a deep socket to drive the seal in this guide, you may not have one. Instead use a suitable size piece of timber and hammer or better use a rubber hammer to drive the seal. The seal must be driven home square, gently tapping uniformly all the way around the seal will seat it correctly.
clean & lube
clean & lube
Use your reference marks or picture you took earlier to note where the seal seats. Over egging the seal will damage it.
That's it, you did it, Nice work!
Now refit the engine and not forgetting to refill the oil.
Why is my lawn mower leaking oil? The most common cause of lawn mower oil leaks is an over filled crankcase. Draining off the excess oil will often fix the leak.