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Valve Tappet


tweeter6216

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When I check the valve tappet on my twin 16 horse briggs, is the clearance checked with a feeler gauge between the back of the valve stem and the tappet (not sure what the name of that piece that pushes on the valve)? In the manual it says to check clearance and i'm unsure how to check it.
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You got the right spot. Just follow what the book tells you so you know your crank is in the right position when you check for clearance.
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Could someone explain to me the reason for the gap? Why cant the valve touch the tappet while seating properly and work?
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quote:
Originally posted by tweeter6216
Could someone explain to me the reason for the gap? Why cant the valve touch the tappet while seating properly and work?
When parts get hot, they expand. You need that gap to allow for expansion. And you will always need some sort gap to insure that the valve is fully seated.
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Bob is right but there is more also. When you look at a cam shaft for a single cylinder you will see 2 lobes on it, as the cam turns, a lobe will move to alinement with the tappet and start lifting the valve. Well, On some engines there is more that one lift area on a single lobe. While the piston is heading up on the compression stroke, one valve will open a tiny amount for a fraction of a second. This is Briggs way of making a compression release. It you have to much space between the tappet and valve stem, this compression release can't work and the engine will be hard to start. Another reason for having space is that valves wear on the seat. As wear occurs, The "stem" gets longer ! and before you know it, your low on compression because the valve face makes only very light contact with the seat. This can and will cause the valve face and seat to burn if allowed to go on. In an overhead valved engine and even in a flathead thats had the head shaved you can run into trouble with the valve hitting things from opening to far.. The piston in the case of an OHV engine and the head in a flathead. So to answer your question, Tappet clearance is very important. Hope this helps you understand why.
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  • 2 weeks later...
I checked and made sure that the tappet clearance for all 4 valves were correct. They are all within the specs in the repair manual. The engine has a loud tap now when I got it started. I do not understand. Was the tap created by the clearance or something else?
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It is hard to tell without hearing the sound my self. It is either a valve tappet, wrist pin on one of the pistons or a loose piston rod. Scarey isn't it. Wish I could tell you more.
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Make sure when you check the clearance with the feeler guage, that the cam lobe is totally off (at the bottom/ no lift) or you will wind up with way too much clearance and the valve will tap loudly
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I rechecked the clearances and got rid of the tapping noise. I have another problem. When I move the thottle, the engine delays before picking up throttle. Any suggestions?
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The tappet clearance is to specs and the motor runs sometimes. It seems that it will not start when the temp. is around freezing. The engine cranks and every couple revolutions you can hear it almost kick over. Spark plug on the left cylinder is always damp while the right is dry. Both plugs have bright spark. When it does start, I can start it within a couple of hours after running. The battery is always charged and/or is at maximum potential (using charger). I use 5W-30 oil in the 16Hp for the winter. I just cannot figure out why it does not start in the cold temperatures.
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Hi, Be sure the clutch is pushed in. This takes the load off the engine so it doesn't have to pull a stiff belt and the tranny. Were the tappets in spec when you checked them? Did you have to grind the valves to correct them? You also have a leaky valve. On the early twins the intake manifold was made in 2 pieces and screwed and glued together, sometimes the runner glue cracks and they leak air. Will the plug for the weak cylinder jump a 3/8" spark? Also if the tepperature is around 35 to 40 degrees and the humidity is up, could be carb icing, the temp drop as the air goes through the venturi can cause the miosture to condense and collect as frost on the main nozzle in the carb. My 2 cents worth and its free, value accordingly, Al Eden
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