Quick answer
On most vertical-shaft Briggs & Stratton mower engines, the camshaft sits behind the sump (oil pan) cover on the underside of the engine. You drain the oil, remove the blade and adapter, unbolt the sump, lift out the old cam, then fit the new one with its timing mark lined up with the mark on the crankshaft gear. Fit a new sump gasket, torque the bolts to spec, refill the oil and check the valve clearance. Getting the timing marks wrong is the main way this job fails.
Camshaft replacement is a common repair on Briggs engines with worn cam lobes, a cracked cam gear, or a failed compression release (which makes the engine very hard to pull over). It’s a moderate DIY job, about 1–2 hours with basic hand tools. The one thing you must get right is the cam timing.
Signs the camshaft needs replacing
- Very hard to pull the starter rope, or the rope kicks back, often a failed compression release on the cam.
- Low compression with good valves and rings, from worn cam lobes.
- Knocking from the bottom of the engine, or broken teeth on the cam gear (often after a blade strike).
- Metal flakes in the drained oil.
Tools and parts
- Correct replacement camshaft for your engine model/type/code
- New sump (oil pan) gasket. Briggs sumps use a gasket, not just sealant.
- Socket set, torque wrench, blade-removal tools
- Feeler gauge set for setting valve clearance
- Fresh engine oil and a drain pan
How to replace the camshaft
Step 1: Prepare the engine
Disconnect the spark plug wire and remove the plug. Drain the oil and the fuel (or run the tank dry). On a push mower, remove the engine from the deck, or tip it with the air filter and carburetor facing up. Remove the blade and blade adapter.
Step 2: Clean the crankshaft
Clean rust, burrs and dirt from the exposed crankshaft so the sump cover slides off without damaging its oil seal. Fine emery cloth works well.
Step 3: Remove the sump cover
Remove the sump bolts and tap the cover gently with a soft mallet to break the gasket seal. Never pry between the mating faces. Lift the cover off the crankshaft. Note any thrust washers and the governor and oil slinger parts, and keep them in order.
Step 4: Note the timing marks
Before removing anything else, find the timing marks. There’s usually a mark or dot on the cam gear and a matching mark on the crankshaft gear (on some engines it’s on the crank counterweight). Photograph them.
Step 5: Remove the old camshaft
Rotate the crankshaft so the timing marks line up, which takes pressure off the valve lifters. Then lift the camshaft straight out, keeping the tappets (lifters) in place and noting which is intake and which is exhaust.
Step 6: Install the new camshaft
Lubricate the cam lobes and journals with fresh engine oil. With the tappets in position, slide the new cam in so its timing mark lines up exactly with the crankshaft gear mark. Check the alignment twice. One tooth off means the engine won’t run properly, or at all.
Step 7: Refit the sump cover
Fit a new gasket and any thrust washers, then slide the cover over the crankshaft, rotating it slightly to engage the governor and oil pump gears if fitted. Don’t force it. Tighten the bolts gradually in a cross pattern to the torque in the manual.
Step 8: Check valve clearance and reassemble
Set the valve clearance to spec with a feeler gauge. Many Briggs engines are in the few-thousandths-of-an-inch range, with intake and exhaust specs that often differ, so use your manual’s numbers. Refit the blade adapter and blade, torque the blade bolt, refill the oil, refit the spark plug and test-run.
Frequently asked questions
What happens if the cam timing is off?
The valves open at the wrong time. The engine may not start, may backfire, or may run with very low power. Remove the sump and realign the marks.
Is it worth replacing a camshaft on a push mower?
On a quality engine in good condition, yes, because the part is inexpensive. On an older engine with other wear, or if the crankshaft is bent, a replacement engine may make more sense.
Can I reuse the sump gasket?
No. Always fit a new one. A reused gasket is the most common cause of oil leaks after this job.
Related: Valve adjustment symptoms · Replacement lawn mower engines
Method: This is the general camshaft replacement procedure for common vertical-shaft Briggs & Stratton single-cylinder engines. Exact parts, torque values, valve clearances and timing details depend on your engine’s model/type/code, so use the Briggs & Stratton repair manual or an authorized dealer.
Update log: November 2026: rewrote the guide. We added symptoms, a parts list, a detailed timing-mark procedure, the sump gasket and valve clearance steps, and an FAQ.