Through mechanical use and wear, small gas engines require valve adjustment from time to time.If your engine is not starting or running poorly, it could be the valves are not fully opening and closing.
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To keep your engine running it"s best, valve clearance should be checked and adjusted as part of periodic maintenance.The procedure for adjusting valves on Briggs OHV motors is basically the same for all models.
NOTE: Lawn mowers, lawn tractors, and pressure washers all operate at a low RPM level.Unless your engine is powering a race kart, there is no need to adjust valves if they"re only out of spec by .001" or .002".
This article describes how to adjust valves on two different Briggs & Stratton motors.The first is a Craftsman pressure washer with a 7-hp motor, the second is a John Deere lawn tractor with a 19.5 hp motor.
Why Valve Clearance Is Important
If a valve has too much clearance, it doesn"t fully open.This robs the engine of power.
If a valve doesn"t have enough clearance, it doesn"t fully close. This allows some compression to escape through one or both valves.Aside from losing power, the affected valve(s) may become overheated.
Valve Clearance Specs
Valve lash, or the space between the valve and rocker arm, differ slightly from engine to engine, so check the specs on yours.Valve clearance specs can be found in an owners manual or shop manual. You can also find the specs online, but will need to know the engine model number.
NOTE: Always check and adjust valves when engine is cold.
Set Up Your Workspace
Rather than kneel and bend down while working, I prefer to bring the work up to a more comfortable height.The less contorting you have to do, the easier the service will go.
Briggs-powered Craftsman pressure washer (7 horsepower)
3/8" socket (1/4" drive ratchet preferred)Spark plug socket (3/8" drive ratchet preferred)Feeler Gauge3/16" Allen key5/8" Open end wrenchLong screwdriver (optional)
NOTE: You do not have to drain the engine oil before taking the valve cover off.
Remove Valve Cover
Here"s another advantage to propping up the work to a better working angle.The valve cover comes off with four 3/8" headed bolts.The first time I took a Briggs OHV valve cover off, I only saw the two side bolts, and after removing those two, proceeded to try prying off the still-bolted-on cover!
Looking inside the valve cover gives you a good indication as to whether the engine oil was changed regularly.On this motor, I was pleased to see how clean the rocker arms, valve springs and valves were.
Remove Spark Plug
Removing the spark plug reduces engine compression, making it much easier to pull the start rope to move the piston and valves into position.With the valve cover off and the spark plug removed, you can pull the start rope and watch the valves open and close.
How To Check Valve Clearance
There are two popular methods for checking valve clearances.The recommended procedure from most service manuals is method #1, where a screwdriver is used to gauge the piston"s range of motion.
Insert a narrow screwdriver into the spark plug hole and touch the piston. Pull the start rope and move the piston/valves. The screwdriver goes up and down accordingly. When the screwdriver sticks out the most, the piston is at the top of it"s travel. This is known as top dead center, or TDC.
Move past TDC until the piston has moved down 1/4".You will now have slack on both intake (upper) and exhaust (lower) rocker arms.
Check the valve clearances one at a time by placing a feeler gauge between the each valve and rocker arm.Adjust as needed (see "How To Adjust Valve Clearance" below).
For this method, you don"t need to find piston TDC, but it will take an additional step.You will start with the intake side first, followed by the exhaust side.
NOTE: Some motors will have the intake rocker arm on the top.Some motors will have the exhaust rocker arm on the top.You can usually follow the path of the intake manifold (or the muffler pipe) to determine which is which.
Intake On Top, Exhaust On Bottom
Pull the start rope slowly.When the bottom rocker pushes the exhaust valve in, the top (intake) valve will have slack.You can now check the intake valve clearance and adjust if needed.
After the intake side is done, pull the start rope slowly, and watch for the top rocker to push the intake valve in.The exhaust valve will now have slack.Check clearance and adjust if needed.
How To Adjust Valve Clearance
Loosen the lock nut on top of the rocker arm by turning it counterclockwise. Make a mental note as to how tight it was.This will help when re-tightening.
Set your feeler gauge to the recommended setting for your engine.Remember that intake and exhaust settings may be different.
Insert the feeler gauge between the rocker arm and the valve and check the clearance.
If the gap is too wide, take an Allen key to turn the center adjusting screw clockwise in the rocker arm.You will only have to turn it a very small amount.When the gap is correct, the feeler gauge should fit snug, but still able to move in and out without binding.
Once the adjustment is completed, hold the Allen key in place and tighten the rocker nut with an open-end wrench.
Remember when you loosened the lock nut, how tight it was?The proper torque value is about 45 inch-pounds.Hold the rocker nut with a wrench and tighten the rocker ball set-screw. Be careful not to over-tighten it.
Using the same procedures, check and adjust the exhaust valve.
NOTE: On some Briggs engines, the nut and set-screw are positioned above the push rod ends.
The valve clearance specs on my Craftsman pressure washer were:
Intake Valve .004" to .006"
Exhaust Valve .004" to .008"
When done, double-check the settings before re-installing the rocker cover and spark plug.
Rocker Cover Gasket
Inspect the old rocker cover gasket.If it"s not ripped or torn, re-use it.If it"s damaged in any way, you can either replace it with a new one (easier) or use RTV gasket maker (messier).Be careful not to over-tighten the bolts (a common mistake).
Shop:Briggs & Stratton 691890 Rocker Cover Gasket
After the engine is back together, start it up and let it run for 10 minutes or so.This will burn off any residual grease and oil. Then check the rocker cover bolts and re-tighten as needed.
Adjust Valves On Briggs Intek OHV
Adjusting valves on my Briggs-powered lawn tractor was similar to the pressure washer.A minor difference was that the top valve was exhaust, not intake like the 7-hp motor.
Remove the bolts holding on the rocker cover.Remember that valve clearances are checked and adjusted while the engine is cold.
Since there"s no start rope to pull on this lawn tractor, here"s an alternate way to move the valves.With the spark plug removed, grab the top of the flywheel screen and you can turn the motor over by hand.
Exhaust On Top, Intake On Bottom
When the bottom rocker pushes the intake valve in, the top (exhaust) valve will have slack.You can now check exhaust valve clearance with a feeler gauge.
If not within spec, loosen/adjust rocker nut to obtain the desired clearance, then re-tighten.Hold rocker nut and tighten the rocker ball set-screw to the proper torque value (about 45 inch-pounds).
After the exhaust side is done, turn the motor slowly, and watch for the top rocker to push the exhaust valve in.The intake valve will now have slack.Using a feeler gauge, check valve lash.
If not within spec, loosen/adjust rocker nut to obtain the desired clearance.Hold rocker nut and tighten the rocker ball set-screw to the proper torque value (about 45 inch-pounds).
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The valve clearance specs on my John Deere LA110 lawn tractor were:
Intake Valve .003" to .005"
Exhaust Valve .005" to .007"
After I was done with the valve adjustment, I double-checked my settings, then re-installed the rocker cover with a new gasket (Briggs # 272475s).
Shop:Briggs & Stratton Rocker Cover Gasket
I also installed a new spark plug (Champion RC12YC) with .030 gap.