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Briggs and Stratton valve clearance #5441854 05/29/20 02:38 PM
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supton Offline OP
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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.


2011 Toyota Camry, base, 2.5L/6MT, 206k
2010 Toyota Tundra DC, 4.6L/6AT, 160k
2003 CRV, 2.4L/4AT, 161k
1999 Toyota Camry LE, 2.2L/4AT, 225k
Re: Briggs and Stratton valve clearance [Re: supton] #5441859 05/29/20 02:44 PM
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Brian123 Offline
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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.

Re: Briggs and Stratton valve clearance [Re: Brian123] #5441864 05/29/20 02:49 PM
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ragtoplvr Offline
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This

Re: Briggs and Stratton valve clearance [Re: supton] #5441869 05/29/20 02:58 PM
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supton Offline OP
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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.

Last edited by supton; 05/29/20 03:27 PM.

2011 Toyota Camry, base, 2.5L/6MT, 206k
2010 Toyota Tundra DC, 4.6L/6AT, 160k
2003 CRV, 2.4L/4AT, 161k
1999 Toyota Camry LE, 2.2L/4AT, 225k
Re: Briggs and Stratton valve clearance [Re: supton] #5441946 05/29/20 04:32 PM
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mk378 Offline
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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.

Last edited by mk378; 05/29/20 04:35 PM.
Re: Briggs and Stratton valve clearance [Re: supton] #5441955 05/29/20 04:37 PM
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jhellwig Offline
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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.


Sparks fly from my fingers.

1995 Chevy K2500 Suburban lt 5.7
2014 Toyota Sienna
1983 Chevy K5 350
Re: Briggs and Stratton valve clearance [Re: supton] #5442018 05/29/20 06:06 PM
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Slick17601 Offline
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On a flathead go .008" on the intake and .010" on the exhaust.


2018 RAM Bighorn 5.7
2008 Toyota Sienna 3.5
Re: Briggs and Stratton valve clearance [Re: supton] #5443243 05/31/20 02:37 PM
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supton Offline OP
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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. shrug Will order a plug and air filter and see what happens in the future.


2011 Toyota Camry, base, 2.5L/6MT, 206k
2010 Toyota Tundra DC, 4.6L/6AT, 160k
2003 CRV, 2.4L/4AT, 161k
1999 Toyota Camry LE, 2.2L/4AT, 225k
Re: Briggs and Stratton valve clearance [Re: supton] #5444110 06/01/20 05:11 PM
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jeepman3071 Offline
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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.


1998 Jeep Wrangler Sahara 4.0L/5MT (157k) - PHM 10w30, Wix 51085
2009 BMW 328i N51 (63k) - Liqui Moly 5w40, MANN HU816X
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