Briggs and Stratton valve clearance

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So I have a Snapper bagger mower with a 6hp B&S 120000 series engine. Starts good--unless if it is hot. Then it just doesn't want to. Flooding, vapor lock, sticking valve--not sure. I just checked and it has nearly 0.015" valve clearance for both valves. Manual says 4 to 6mils intake, 4 to 8 on exhaust: but I don't think that is my problem. That said, any reason to adjust? If valve seats erode over time, then this should just close up eventually, no?

I'm guessing it just needs a carb rebuild but I was hoping for a tight valve and a fast fix there.
 
Originally Posted by supton
So I have a Snapper bagger mower with a 6hp B&S 120000 series engine. Starts good--unless if it is hot. Then it just doesn't want to. Flooding, vapor lock, sticking valve--not sure. I just checked and it has nearly 0.015" valve clearance for both valves. Manual says 4 to 6mils intake, 4 to 8 on exhaust: but I don't think that is my problem. That said, any reason to adjust? If valve seats erode over time, then this should just close up eventually, no?

I'm guessing it just needs a carb rebuild but I was hoping for a tight valve and a fast fix there.


Try taking the cover off and make sure there is no debris obstructing airflow, I blow my small mower out a few times a year, if the coil gets to hot it might not restart.
 
I'll pull the cover and see what I find. It has been getting heavy usage in dusty areas lately.

Edit: too hot in the garage to work. I tried to pull it, but no go--it appears the gas tank is on top of the engine cover, but one of the bolt heads is stripped and won't mate with any socket I have. Might be a while before I get to this.
 
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The valves tend to get looser due to wear of the pushrods, rocker arms, etc easily exceeds any recession into the seats.

But like the others said if you aren't in the habit to clean it out at least once a season you'll have the cooling passages full of grass and mouse nests and that leads to overheating.

Keep in mind most of the hardware on a Briggs will be inch dimensioned. Most of it.
 
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Since you have the valve cover off go ahead and adjust them into spec. Overhead valves don't get better and the seats don't recess like the flatheads did.

First thing to try is a new plug. That has bit me in the but before thinking it was a carb issue.
 
It's OHV.

Funny, gave no problems today, not over a few hours of usage. Granted it'd get a minute off out of maybe 2, as the field is pretty overgrown still, so maybe it never got hot enough. Made the mistake of filling the gas tank fully once (plastic seam is bad) and half-filled twice, so, two full tanks of gas and no problems.
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Will order a plug and air filter and see what happens in the future.
 
Not saying it isn't possible, but I rarely find valve clearance to be an issue for hot no-starts. Usually if the clearance is bad they just won't start at all, and you can tell because it will be very easy to pull over (very low compression).

I'm betting it is either a coil issue, or carburetor related. When it won't restart hot, check the spark. It should have a nice blue spark, or if using a tester the light should be just as bright as on a cold engine. I have replaced a few coils on these B&S OHV engines from similar symptoms.
 
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