What valve clearance is and why it matters on your SP702

Valve clearance is the small gap between the valve stem and the rocker arm on your Briggs & Stratton SP702 engine. This gap must be set to an exact measurement — too tight and the valve won't close fully, causing compression loss and hard starting; too loose and the valve opens late and closes early, reducing power and efficiency. The SP702 is a single-cylinder, overhead-valve engine commonly found in pressure washers and portable generators, and checking this clearance is part of regular maintenance.

The clearance exists because metal expands when hot. If you set the gap with the engine warm, it will close too much as the engine cools, and the valve will never fully seat. That's why the measurement must be taken with the engine cold — at room temperature — and why the specification is so precise.

Key Takeaways

  • The SP702 intake valve clearance should be 0.003 to 0.005 inches, and the exhaust valve clearance should be 0.005 to 0.007 inches, measured with the engine cold.
  • You must position the piston at top dead center on the compression stroke before measuring either valve, or the reading will be wrong.
  • A feeler gauge — a thin metal blade of a known thickness — is the correct tool for this measurement, not a ruler or eyeballing.
  • If clearance is out of spec, you adjust it by loosening the rocker arm nut and turning the adjusting screw until the gauge slides through with light resistance.
  • Valve clearance should be checked every 100 to 200 hours of engine run time, or whenever the engine is hard to start or running rough.

Finding top dead center on the compression stroke

Before you measure anything, the piston must be at the top of its stroke on the compression side of the cycle. If the piston is on the exhaust stroke, both valves will be partially open and your measurement will be meaningless.

To find top dead center, remove the spark plug and look through the hole with a flashlight. Slowly turn the crankshaft by hand (using the recoil starter handle or a wrench on the crankshaft bolt, depending on your model) until you see the piston rise to the very top of the cylinder. At that point, both valves should be closed. You can verify this by gently trying to move the rocker arms — they should have no play. If they move, turn the crankshaft another full rotation and try again.

Mark this position somehow — a piece of tape on the crankshaft or a mark on the engine block — so you can return to it if you accidentally turn the engine while working.

Measuring intake valve clearance

With the piston at top dead center on compression, locate the intake valve rocker arm. On the SP702, this is the rocker arm closer to the carburetor side of the engine. You will see an adjusting screw with a locknut on top of the rocker arm.

Select a feeler gauge blade that matches the intake specification: 0.003 to 0.005 inches. Start with 0.003 inches. Slide the blade between the valve stem and the rocker arm. The blade should slide through with light resistance — not so tight that you have to force it, and not so loose that it falls through. If the blade is too tight, the clearance is too small. If it's too loose, the clearance is too large.

If the clearance is wrong, loosen the locknut on the adjusting screw with a wrench. Turn the adjusting screw counterclockwise to increase clearance (make the gap larger) or clockwise to decrease it (make the gap smaller). Make small turns — a quarter turn makes a noticeable difference. After each adjustment, test with the feeler gauge again. Once the 0.003-inch blade slides through with light resistance, try the 0.005-inch blade. It should be snug but not forced. When both blades feel right, hold the adjusting screw steady and tighten the locknut.

Measuring exhaust valve clearance

The exhaust valve rocker arm is on the opposite side of the engine from the intake, usually toward the muffler. The process is identical to the intake, except the specification is larger: 0.005 to 0.007 inches.

Slide the 0.005-inch feeler gauge first. If it's too tight, loosen the locknut and turn the adjusting screw counterclockwise to increase the gap. If it's too loose, turn the screw clockwise to decrease it. Once 0.005 inches slides through with light resistance, test with the 0.007-inch blade. It should be snug but not forced. Tighten the locknut when you're satisfied.

The exhaust valve clearance is larger than the intake because the exhaust valve runs hotter and expands more. Using the wrong specification for either valve will cause starting problems or rough running.

Tools you need and where to get them

A feeler gauge set is essential and inexpensive — most hardware stores and online retailers carry them for $8 to $15. Look for a set that includes both 0.003, 0.005, and 0.007-inch blades. A set with many blades is fine; you'll only use three of them for this job.

You'll also need two wrenches: one to hold the adjusting screw and one to loosen and tighten the locknut. The sizes vary by model, but 7/16-inch and 1/2-inch are common. A socket wrench set works well. A spark plug socket and ratchet are useful for removing the spark plug at the start, though you can do this by hand if the plug isn't too tight.

A small flashlight or headlamp helps you see into the spark plug hole when finding top dead center. A piece of tape or a marker is helpful for marking your reference point on the crankshaft.

When to check valve clearance and what to do if it's out of spec

Check valve clearance every 100 to 200 hours of engine run time. If you use the engine regularly, that's roughly once a season. You should also check it if the engine is hard to start, runs rough at idle, or loses power under load — these are all signs that valve clearance may have drifted out of spec.

If you find that clearance is consistently too tight or too loose, and it drifts again after you adjust it, the rocker arm or valve stem may be worn. Wear on these parts is normal over time, but it means the adjustment won't hold. At that point, the rocker arm or valve may need replacement. This is beyond routine maintenance and requires more disassembly than most owners want to do, so it's a good time to contact a small-engine repair shop.

If clearance is correct and the engine still won't start or runs rough, the problem is elsewhere — possibly the spark plug, fuel system, or compression. Valve clearance is only one part of engine tuning.

Frequently Asked Questions

Can I measure valve clearance with the engine warm?

No. Metal expands when hot, so a warm engine will show clearance that is too small. The specification assumes a cold engine at room temperature. Always let the engine cool completely before measuring, or your adjustment will be wrong and the engine will run poorly.

What happens if I set the clearance too tight?

A valve that is too tight will not close fully, causing compression loss. The engine will be hard to start, run rough, and lose power. You may also hear a ticking noise from the valve train because the rocker arm is pushing on the valve stem constantly.

What happens if I set the clearance too loose?

A valve that is too loose will open late and close early, reducing the time it's actually open. The engine will lose power, run rough, and may overheat because the exhaust valve isn't opening fully to let heat escape. You may also hear a loud clacking noise from the rocker arm.

Do I have to remove the valve cover to adjust clearance?

Yes. The valve cover is the metal or plastic cap on top of the engine that protects the rocker arms. It's held on by bolts or screws and usually has a gasket underneath. Remove it, do your adjustment, and reinstall it with a new gasket if the old one is cracked or compressed.

Can I use a different feeler gauge size if I don't have the exact one?

No. The specification is precise because it accounts for thermal expansion. Using 0.004 inches instead of 0.003 to 0.005 inches may seem close, but it will cause the same problems as being out of spec. Buy the correct set — it's inexpensive and will last for years.