How to Pump Up Hydraulic Lifters on a Mower Engine (+ How Long)

Hear a ticking or tapping noise when you start your zero-turn or lawn tractor? On many mower engines, that sound comes from the hydraulic lifters, small parts in the valve train that need oil pressure to work quietly.

In most cases, the noise goes away on its own once the lifters fill with oil. In others, it points to an oil problem or a worn part. This guide explains what hydraulic lifters do in a mower engine, how to pump them up, how long it takes, what causes lifter noise and how to prevent it.

What Are Hydraulic Lifters in a Mower Engine?

Hydraulic lifters (also called hydraulic tappets) sit between the camshaft and the pushrods in an engine's valve train. Inside each lifter is a small plunger that fills with engine oil. That oil cushion automatically keeps zero clearance between the parts, so the valves open and close quietly without manual adjustment.

When a mower sits unused, some oil can drain out of the lifters. At the next startup, they may tick briefly until oil pressure refills them.

Hydraulic vs. Solid Lifters in Small Engines

Solid (mechanical) lifters have no oil cushion. They need a small gap, called valve lash, that must be checked and adjusted periodically. Hydraulic lifters adjust themselves, run quieter and need less maintenance, but they depend on clean oil at the right level and pressure.

Does My Mower Engine Have Hydraulic Lifters?

Not all mower engines use them. Some twin-cylinder engines found on zero-turns and lawn tractors, such as Kohler Command twin-cylinder engines, use hydraulic lifters, while many other small engines use solid lifters with adjustable valve lash.

The easiest way to know is to check your engine's owner's manual or service manual. If the maintenance schedule includes periodic valve lash adjustment, your engine most likely has solid lifters.

Hydraulic Lifters vs. Your Mower's Hydraulic Drive System

They share the word "hydraulic," but they are completely separate systems:

If your mower runs quietly but drives poorly, the problem is likely in the drive system, not the lifters. See our guide to Hydro-Gear ZT-3400 problems and maintenance, learn how to check a hydraulic pump, or browse our hydraulic pumps and hydraulic motors.

Signs of Hydraulic Lifter Problems in a Mower Engine

Ticking or Tapping Noise at Startup

A light ticking for a few seconds after starting, especially after the mower has been sitting, is usually normal. It means oil drained from the lifters and they are refilling.

Ticking That Doesn't Go Away

If the noise continues after the engine is fully warmed up, or comes back every time you mow, something is keeping the lifters from filling properly. Check the oil level and condition first.

Rough Running or Loss of Power

A lifter that can't hold oil may keep a valve from opening or closing fully. That can cause rough idle, misfires or reduced power, often together with a louder ticking sound.

How to Pump Up Hydraulic Lifters (Step-by-Step)

In most cases, you don't need to do anything special: running the engine with clean oil at the correct level pumps up the lifters automatically. The steps below cover the two situations where you need to help them along: a ticking engine that won't quiet down, and installing new lifters.

Before You Start: Safety and Tools

• Work on a cool engine, on level ground, with the parking brake set.
• Remove the key and disconnect the spark plug wires before working inside the engine.
• Have fresh engine oil of the grade your engine manufacturer specifies, a new oil filter if your engine uses one, and the engine's service manual.

Pumping Up Lifters on a Ticking Engine

How to Prime New Lifters Before Installation

1. If your engine or lifter manufacturer recommends it, soak the new lifters in clean engine oil of the correct grade before installation.
2. If the service manual allows it, gently compress the lifter plunger several times while it's submerged to push out air.

Installing Lifters on a Small Engine

1. Install the lifters following the engine service manual. If you're reusing lifters, return each one to the same position it came from.
2. Many small engines with hydraulic lifters have no valve adjustment, so don't apply automotive preload settings. Follow only the procedure for your engine model.
3. Reassemble the engine, start it and let it idle so oil pressure can finish filling the lifters.

How Long Does It Take for Hydraulic Lifters to Pump Up?

In most mower engines, hydraulic lifters pump up within a few seconds to a few minutes after startup. The time depends on:

• How long the mower has been sitting.
• Oil level, condition and viscosity.
• Outside temperature, since cold oil flows more slowly.
• Whether the lifters are new and were primed before installation.

New lifters, or an engine that has sat all winter, may take longer than usual the first time.

What If the Ticking Doesn't Stop?

If the ticking continues after the engine is fully warmed up (roughly 20 to 30 minutes of running), one or more lifters may be clogged with sludge or worn out. Change the oil and filter, run the engine again, and if the noise persists, have the engine inspected by a qualified small engine technician.

Common Causes of Hydraulic Lifter Problems in Mower Engines

Old or Dirty Engine Oil

Mowers work in dusty conditions, and old oil carries dirt and sludge that can clog the tiny oil passages inside the lifters. This is the most common cause of persistent lifter noise.

Low Oil Level or Pressure

If the oil level is low, the oil pump can't supply enough pressure to keep the lifters full. Mowing on steep slopes with low oil makes this worse.

Wrong Oil Viscosity

Oil that's too thick flows slowly on cold starts; oil that's too thin may not hold pressure when hot. Always use the grade your engine manufacturer specifies for your temperature range.

Overheating from Clogged Cooling Fins

Most mower engines are air-cooled. Grass and debris packed around the cooling fins raise engine temperature, which thins the oil and lowers pressure at the lifters.

Normal Wear

After many hours, the internal parts of a lifter can wear and stop holding oil. In that case, no oil change will fix the noise, and the lifter needs to be replaced.

How to Prevent Lifter Noise: Mower Engine Maintenance

Most lifter problems are oil problems, so good engine maintenance prevents nearly all of them:

• Check the engine oil level before every mowing session.
• Change the oil and filter at the intervals in your engine manual, and more often in dusty or hot conditions.
• Use the oil grade your engine manufacturer recommends.
• Keep the cooling fins, screen and shrouds clean of grass and debris.
• Before storing the mower for the season, change the oil so old, contaminated oil doesn't sit in the engine.

A well-maintained engine and drive system go hand in hand. While you're servicing the engine, it's a good time to check your transmission fluid and filters too. Shop genuine Hydro-Gear transaxle oil filters, such as the 52114 spin-on filter, or browse all filters.

When to Replace Hydraulic Lifters

Consider replacing the lifters if:

• The ticking continues after an oil and filter change and a full warm-up.
• The noise gets louder over time or comes with rough running and power loss.
• An inspection shows a lifter that collapses, sticks or has visible wear on its face.

Lifter replacement requires opening the engine, so follow the engine service manual or have a qualified small engine technician do the work. Always use parts specified for your engine model.

Hydraulic Lifter FAQs

Is It Safe to Mow with a Ticking Lifter?

A brief tick at startup is normal and harmless. A constant tick means something is wrong; check the oil level right away. If the ticking turns into a louder knock or the engine runs rough, stop mowing and have it inspected to avoid more serious damage.

Will an Oil Change Fix Lifter Tick?

Often, yes. If the noise is caused by old, dirty or low oil, fresh oil of the correct grade and a new filter can quiet the lifters after a few run cycles. If the lifter is worn, an oil change won't fix it.

Do Hydraulic Lifters Need Adjustment on Mower Engines?

Usually not. Hydraulic lifters are designed to adjust themselves, and many small engines with hydraulic lifters have no valve adjustment at all. Check your engine's service manual to be sure.

Key Takeaways

• Hydraulic lifters keep valve clearance at zero automatically, using engine oil pressure.
• Not every mower engine has them; check your engine manual.
• A short tick at startup is normal. Most lifters pump up within seconds to a few minutes.
• Persistent ticking usually points to low, old or wrong-grade oil. Start with an oil and filter change.
• If the noise continues after a full warm-up and fresh oil, the lifter may be worn and need replacement.
• Lifter noise comes from the engine; drive problems come from the hydraulic transmission. Diagnose the right system first.

Need parts for your mower's hydrostatic drive? Browse genuine Hydro-Gear parts at Hydro Pumps Parts or contact our team for help finding the right part.