OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S 12hp Valve Timing

I have a B&S 12hp motor Model No 283707 0111-01 91090411.
Air and fuel mixture is being pushed out of the carby on the compression stroke.

I have reseated the valve and adjusted the valve clearance and checked for valve free movement.

At the start of the compression stroke the inlet valve hasn't closed completely.
As the piston goes up on the compression stroke the valve closes completely at about a third of the way up to top dead center.

Ive noticed the inlet valve tappet seems to rotate during the upward motion of the piston on the compression stroke
till the valve is closed at about a third of the way up to top dead center.

The valve clearance was set at about .007in

Does anybody have any suggestions on this ?

Does the valve stem have a lash cap between the valve stem and the tapper follower? Perhaps it has shifted not allowing the valve to close fully

There are no lash caps between the valve stem and the tapper follower
I was thinking may be the Tappet head that contacts the cam may be bent

Thanks for your reply

Karl.

It is normal for the tappet to rotate when it is being lifted, though there is nothing wrong if it doesn't. You might check whether it rotates all the way around over a few turns, or rotates part way and then slips back to its original position. The latter would indicate a bent tappet.

It is also normal for some air and fuel to be pushed back through the inlet port and carburetor during the early part of the compression stroke, when the inlet valve is still intentionally open. It should not be a lot of gas, but it is always quite noticeable. Normally the air cleaner traps it so it does not cause a fire hazard.

Does your engine start easily and run properly?

Thanks for the info Grumpy,

I will check the rotation more throughly in the next few days.
Good to know some blow back is normal.

I haven't got to the stage of firing it up again yet.

Will post the results when it happens.