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Valve Specs for Briggs 31P777

#1

N

nograsstomow

Can somebody please give me the valve specs, lift and duration, for a Briggs and Stratton 18.5 hp Intec engine. I suspect the the cam shaft is my problem as the exhaust valve just barely opens. This engine is giving me nightmares! I've done and replaced everything I can think of that causes it to backfire thru carb when throttled up. I give thanks in advance for any replies!


#2

GetTechnicalWithJd

GetTechnicalWithJd

I do not have the specs you are looking for but have had several 31 series engines with similar symptoms.

Your Inlet and Exhaust valves should have the same lift and duration as the cam lobes are identical. This is easily diagnosed by removing the tappet cover and turning the engine over slowly by hand. I have had many 31 series engine where the exhaust valve cam lobe wears almost round due to a factory defect in the hardening process.

So I would recommend buying a new camshaft part number 793880. If the engine is still under warranty contact your nearest B&S dealer.


#3

EngineMan

EngineMan

Intake .003in-.005in/.07-.12mm
Exhaust .005in-.007in/.12-.18mm


#4

N

nograsstomow

Thanks for the replies. Time to get oily!


#5

N

nograsstomow

It's the cam shaft alright. Lobe is nearly all gone.

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#6

GetTechnicalWithJd

GetTechnicalWithJd

nograsstomow said:
It's the cam shaft alright. Lobe is nearly all gone.


That's what I suspected. Is the engine still under warranty?
Click to expand...


#7

N

nograsstomow

A month later, here's an update. I've had the mower for quite a while so I doubt it was under warranty. I spent about $80 on the cam(new tappets came with cam) and the gasket for the lower half. I did all the work myself. It's installed and hasn't ran this good since the day I purchased it! Thanks again for the replies I received.


#8

EngineMan

EngineMan

Well done and all the best..:thumbsup:


#9

GetTechnicalWithJd

GetTechnicalWithJd

nograsstomow said:
A month later, here's an update. I've had the mower for quite a while so I doubt it was under warranty. I spent about $80 on the cam(new tappets came with cam) and the gasket for the lower half. I did all the work myself. It's installed and hasn't ran this good since the day I purchased it! Thanks again for the replies I received.
Click to expand...

Excellent news. Well done!


#10

D

DeanT

EngineMan said:
Intake .003in-.005in/.07-.12mm
Exhaust .005in-.007in/.12-.18mm
Click to expand...


these are the factory valve to rocker arm clearance measurements.


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