# briggs 15.5 riding lawn mower exhaust valve question.



## pmeseck (Aug 20, 2008)

Hello everyone,
I have a 15.5 briggs on a craftsman lawn mower. I have a question about the exhaust valve stroke. I took the ohv cap off and was resetting the gap on the valves because of carbon buildup and loss of power. I gapped them according to briggs settings. .005 intake and .008 exhaust w/ piston 1/4 inch down from tdc. this worked OK but I noticed that the exhaust valve only moves about 1/4 the distance that the intake moves. What I mean by that is that the exhaust valve pushes in about .25 inches and the intake pushes in about .75 inches when you rotate the engine by hand. I was expecting them both to be the same. So I took off the rocker arms and compaired the push rods. both showed no defects. I put them back in and decided this was design. I still have a carbon issue and I burn a lot of gas. one tank lasts about 1 hour. I'm thinking that the exhaust valve is not opening enough so the engine is loosing power and burning more gas to suppliment. however, i've replaced all gaskets in the head and reset the gap. so what's my next step. The engine doesn't burn oil so I don't think it's the valve seats and I should have seen carbon in the ohv exhaust valve when I was there. 

at an idle the engine runs great. it I move it to the mow position it sounds like it's fludding out. about halve way to mow it starts sounding like it flods. I can hold the govenor open at mow with no change like it's still flooding out.

need a dirrection to go please advise what I should do next.

thank you
Paul


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## 30yearTech (Sep 14, 2006)

pmeseck said:


> I noticed that the exhaust valve only moves about 1/4 the distance that the intake moves. What I mean by that is that the exhaust valve pushes in about .25 inches and the intake pushes in about .75 inches when you rotate the engine by hand.


You may have a problem with the camshaft in your engine, its possible the lobe that operates the exhaust valve is worn down and not operating the valve as it should. I have run across this problem before. Unfortunately this requires removing the engine in order to get to the camshaft.

Best Of Luck... :thumbsup:


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## pyro_maniac69 (Aug 12, 2007)

30yearTech said:


> You may have a problem with the camshaft in your engine, its possible the lobe that operates the exhaust valve is worn down and not operating the valve as it should. I have run across this problem before. Unfortunately this requires removing the engine in order to get to the camshaft.
> 
> Best Of Luck... :thumbsup:


exactly was I was going to suggest, probably one of the engines with a plastic lobed camshaft

them cheapo's


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## pmeseck (Aug 20, 2008)

*options.*

so how much is it for a new cam? should I just look for a new mower?
pm


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## 30yearTech (Sep 14, 2006)

pmeseck said:


> so how much is it for a new cam? should I just look for a new mower?
> pm


Post the model type and code number off your engine and someone can give you an idea, but I would think the part is less then $50.00


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## pyro_maniac69 (Aug 12, 2007)

I think its around the $30 range, it isn't to bad to replace, as long as you don't mind taking the engine off and taking it apart


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## pmeseck (Aug 20, 2008)

*sears 15.5 lawn tractor model no 917.270612*

briggs motor model 28u707 type 1174-E1
the part # if i'm understanding what needs to be replaced is..496884

thank you for your help

Paul.


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## pyro_maniac69 (Aug 12, 2007)

the part number that I came up with for that model number is a 790400, and according to jacks small engine, is 38.90


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