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B&s 5 Hp Intake Valve Not Seating


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#1 ol' stonebreaker ONLINE  

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Posted March 18, 2014 - 10:27 PM

  This makes twice in the last few months I've seen this on these flat head engines. Apparently Briggs put soft valve seats in them. I think I posted a thread about the first on an MTD snowblower. Now the same engine on my MTD chipper has done the same thing. About 30 psi compression, removed head and can turn the intake w/ my thumb w/ it at TDC. I remove the valve, measure the length w/ digital caliper and grind the stem end 'til I've removed about 6-8 thousandths. Then put it back in the guide and check lash. The valve seats in both have a groove worn in it so that's why I think the seat is too soft. Opinions? 

                                                       Mike


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#2 jdslednut ONLINE  

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Posted March 18, 2014 - 10:59 PM

If you are checking the lash and spinning the intake valve at TDC after the exhaust stroke, there is probably cam lift for the intake for the beginning of the intake stroke.  I believe B&S recommends checking lash at 1/4" past below TDC just after the compression stroke to ensure the maximum lash value.  I haven't run into any soft seats but I've seen plenty of students at school adjust their lash/grind their stems with the piston in the wrong position.  If the engine has a compression release, 30 psi might be about all you would get with a compression test.  A leakdown test is recommended to check for possible leaks due to compression issues.  I hope this helps a bit.


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#3 trowel OFFLINE  

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Posted March 19, 2014 - 07:17 AM

If you are talking about the post 1978 and up flatties then yes, they are a little softer, as jdsldnut stated depending on the engine there may be a comp. release on the exhaust valve.

Bring the piston to almost BDC after comp. stroke and try spinning the valves.



#4 ol' stonebreaker ONLINE  

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Posted March 19, 2014 - 10:06 AM

Update: This apparently has the comp release. After further checking I found the intake valve only stayed slightly open while on the comp stroke. I turned the engine backward w/ my cordless drill and comp is 90psi. So I was trying to jump the gun!! I found this backward trick in the JD manual for the Kohler in the 314 I had.
Mike
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#5 Bruce Dorsi OFFLINE  

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Posted March 19, 2014 - 10:55 AM

There is a foolproof method of checking/setting valve clearances, especially to avoid any doubts about compression relief.

 

Check/set intake valve clearance with the exhaust valve fully raised

 

Check/set exhaust valve clearance with the intake valve fully raised.


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#6 DougT ONLINE  

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Posted March 19, 2014 - 01:34 PM

There is a foolproof method of checking/setting valve clearances, especially to avoid any doubts about compression relief.

 

Check/set intake valve clearance with the exhaust valve fully raised

 

Check/set exhaust valve clearance with the intake valve fully raised.

That pretty much eliminates all doubt. I thought Briggs used the intake for compression relief instead of the exhaust but didn't know if it was all engines or not.






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