valve angle

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  #1  
Old 07-01-05, 08:52 PM
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valve angle

Hello fellas!!!!!! I am attempting to fix my grampa's pushmower but I need some technical advice. I am 99.99% sure that the valve and the valve seat need to be ground and lapped together. The only problem is that I have no idea what the valve and valve seat angles should be. The engine is about 20 or 25 years old. It is a 3.5 hp briggs. It is amazig how expensive those valve grinders are, the entire set-up from snap-on is about $10,000. Plus snap-on is about the only company still making them. How do you guys afford these things? Also, is there an "interferance angle" (that 1/2 degree to 1 degree wider angle that some engines require) that has to be ground into the seat after the correct angle has been ground? The local lawn repair shop said that they would charge about $60 to do this repair, so I would like to do as much as possible myself. One last question, when encountering valve sealling trouble, do ya'll just lap them in or change the seat? I have done this once before on a briggs and turned an engine that wouldn't start into an engine that would start on the second pull after sitting for 6 months, so I will attemp to grind them as best as I can. Thanks for the advice!!!!!!
P.S. What are the intake and exhaust valve clearances? Thanks!!!!!
 
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  #2  
Old 07-01-05, 10:59 PM
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Hi mower17!

Where ya' been?

I don't do valve grinding, but the angle will be 45 degrees on that engine. The seat width should be around 1 to 1 1/2 millimeter. Lap them after grinding to get them to seal well. After grinding and lapping the valve, the edge of the valve between the ground area and the face should be no less than 1/64". If it's less, replace it.
 
  #3  
Old 07-04-05, 12:40 AM
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Thanks for the advice. I have been around, just haven't been surfing the forum in a while.

P.S. Any idea what the valve cleanances are on this engine?
 
  #4  
Old 07-05-05, 11:25 PM
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The intake valve is .005 to .007" and the exhaust is .009 to .011"

If valve grinding is necessary, which is seldom (when it is, it's usually not worth doing due to cost unless it's an ohv where just the head can be sent in), I send it to a machine shop to be repaired. Lapping the valves is usually all I ever need to do around my shop.
 
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