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 Briggs 12HP Compression Leak?

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Murray modder
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PostSubject: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeWed Aug 14, 2013 11:20 pm

So, I JUST picked up this engine from the scrap yard to go on the Trail Mower I built (profile picture) After it had threw both intake rods. Now, First it had NO compression, so I opened up the head and fixed the valves (intake valve stuck open, and all I had to do was push it down with my hand and after a few pushed it kinda fixed itself?) SO I got that fixed. Now it has some compression, but now I've noticed a compression leak, yes leak, around the cylinder head. When it turns over to the compression stage, I can hear the air coming out of the cylinder seal. Now, This is an 12 HP I/C engine, and as far as Sears, and Partstree goes, they don't carry the Cylinder Head if that's the problem. Could this be my issue?

Tags say 289707 0254-01 9304074D
(Sorry for my downside of posts, haven't been able to do anything interesting lately.)
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k2500life
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeWed Aug 14, 2013 11:45 pm

Is the head gasket good and is there any scratches or scaring on the surface
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeWed Aug 14, 2013 11:59 pm

@k2500life wrote:
Is the head gasket good and is there any scratches or scaring on the surface
It's not all busted up or anything. Its solid and everything and I didnt see any huge gashes. Its leaking in a small spot...and you can REALLY hear it. Im spinning the engine by hand and I can hear a wheez standing upright.
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Marines2621
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeThu Aug 15, 2013 12:54 am

If it was me id put gasket sealent on it and Go!
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Doc Sprocket
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeThu Aug 15, 2013 7:03 am

Well- a few thoughts here- One, keep an eye on that valve. If it stuck before, why did it stick? Bent? Dirty? Maybe look into that. two- When rolling an engine over by hand, compression leaks can often be heard, even past the valves. Any chance you're listening to the air rushing past an unseated valve, as opposed to a cylinder head leak? Three- The compression relief mechanism- to make starting easier, these engines have a compression relief mechanism on the camshaft that prevents full compression at speeds lower than idle, by preventing complete valve closure. This makes cranking easier. You may be getting a false impression of poor compression because of this. This mechanism is defeated when the engine is spinning faster than cranking speed (running). Lastly- If you are 100% sure it's the head gasket- get yerself a new one. Inspect surfaces for tiny damage, install new gasket, and be sure to torque cylinder head bolts in the correct pattern to specified torque. Do not forget to doublecheck valve lash. It's very possible for it to get out of spec, especially with a new gasket.

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Briggs 12HP Compression Leak? Facebo12
Put down the wrench, and come out with your hands up!-Doc "Tranny Crusher" Sprocket, ATLTF Forum Admin, Thinkerer and Tinkerer, and all-around good dood. Wink

Gen. Mayhem- https://www.atltf.com/t2597-general-mayhem-race-tractor
MULE- https://www.atltf.com/t2153-lawn-boy-utltv
MULEII- https://www.atltf.com/t3328-1970-john-deere-112-the-beginnings-of-mule-ii
MULEIII https://www.atltf.com/t4263-mule3-brainstorming-ideas-etc#58287
Wrench, Wheel, Wreck, Repeat...
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Murray modder
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeThu Aug 15, 2013 11:20 am

@Doc Sprocket wrote:
Well- a few thoughts here- One, keep an eye on that valve. If it stuck before, why did it stick? Bent? Dirty? Maybe look into that. two- When rolling an engine over by hand, compression leaks can often be heard, even past the valves. Any chance you're listening to the air rushing past an unseated valve, as opposed to a cylinder head leak? Three- The compression relief mechanism- to make starting easier, these engines have a compression relief mechanism on the camshaft that prevents full compression at speeds lower than idle, by preventing complete valve closure. This makes cranking easier. You may be getting a false impression of poor compression because of this. This mechanism is defeated when the engine is spinning faster than cranking speed (running). Lastly- If you are 100% sure it's the head gasket- get yerself a new one. Inspect surfaces for tiny damage, install new gasket, and be sure to torque cylinder head bolts in the correct pattern to specified torque. Do not forget to doublecheck valve lash. It's very possible for it to get out of spec, especially with a new gasket.
A few things came up in chat, I think it was K2500life(?) that mentioned it could be warped. He said to lay it on a flat surface and try to put a piece of paper under it. I tried this and one the far top right corner the Paper got under. Now, this is the opposite side of where I thought the original leak was. (Left side) How would I check the last on a flathead?
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Doc Sprocket
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeThu Aug 15, 2013 12:30 pm

Sure- warpage could be a problem, too.

Lash is checked on a flatty the same way it is checked on an OHV. Adjustment is a different process. Check my posts, I know I have written about it here before- I'll check back, rebuilding a carb right now.

_______________________________________________
***Get YOUR official "Doc Locked, And Ready To Rock!" Stickers by clicking here!***
***Official Sprocket's Garage vinyl graphics and tees for sale HERE!***
Briggs 12HP Compression Leak? Facebo12
Put down the wrench, and come out with your hands up!-Doc "Tranny Crusher" Sprocket, ATLTF Forum Admin, Thinkerer and Tinkerer, and all-around good dood. Wink

Gen. Mayhem- https://www.atltf.com/t2597-general-mayhem-race-tractor
MULE- https://www.atltf.com/t2153-lawn-boy-utltv
MULEII- https://www.atltf.com/t3328-1970-john-deere-112-the-beginnings-of-mule-ii
MULEIII https://www.atltf.com/t4263-mule3-brainstorming-ideas-etc#58287
Wrench, Wheel, Wreck, Repeat...
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Murray modder
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeThu Aug 15, 2013 3:59 pm

@Doc Sprocket wrote:
Sure- warpage could be a problem, too.

Lash is checked on a flatty the same way it is checked on an OHV. Adjustment is a different process. Check my posts, I know I have written about it here before- I'll check back, rebuilding a carb right now.
I've check the lash on an OHV under the valve cover...So The ones on a Flathead are internal, right?
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Doc Sprocket
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PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitimeThu Aug 15, 2013 4:55 pm

You'll find an access cover on the side of the block, where the valves are.

_______________________________________________
***Get YOUR official "Doc Locked, And Ready To Rock!" Stickers by clicking here!***
***Official Sprocket's Garage vinyl graphics and tees for sale HERE!***
Briggs 12HP Compression Leak? Facebo12
Put down the wrench, and come out with your hands up!-Doc "Tranny Crusher" Sprocket, ATLTF Forum Admin, Thinkerer and Tinkerer, and all-around good dood. Wink

Gen. Mayhem- https://www.atltf.com/t2597-general-mayhem-race-tractor
MULE- https://www.atltf.com/t2153-lawn-boy-utltv
MULEII- https://www.atltf.com/t3328-1970-john-deere-112-the-beginnings-of-mule-ii
MULEIII https://www.atltf.com/t4263-mule3-brainstorming-ideas-etc#58287
Wrench, Wheel, Wreck, Repeat...
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Briggs 12HP Compression Leak? Empty
PostSubject: Re: Briggs 12HP Compression Leak?   Briggs 12HP Compression Leak? Icon_minitime

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