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Dutch

Briggs 18hp Vertical shaft Flat twin

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Dutch
Need some advise from a Briggs guru. Have a 1980 B&S 18hp Flat Twin. Model 421707 Type 0134-01 Code 80120812 Basically the same engine as used in a Simplicity 6118 - #1690598. Never heard it run, or worked on one before. 1) The points plunger only moves about .001”. I assume some type of eccentric causes the plunger to move in and out. Am I correct? If so, is the eccentric part of the camshaft or crankshaft? Do those eccentrics wear? Are they replaceable? 2) Do you usually remove the carb or manifold to replace the points (it’s tight in there)? 3) When testing spark, are you supposed to ground the other plug or something (seems I remember reading something like that somewhere)? I know I could / should install a Magnetron, but I’d like not to spend $50 only to find out the engine is junk. TIA

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PatRarick
Dutch, The eccentric is on the camshaft. It is not replaceable as such. The entire camshaft would have to be replaced. I have never seen one wear to the point of having such little movement. Perhaps a bent plunger, not allowing it to retract completely? In the event the eccentric is worn that bad, I would be concerned with the wear on the rest of the engine. I have never removed the manifold to change points, but it is very tight. Yes, when you check for spark on these engines, you should ground the opposite plug. I usually remove the opposite plug and clamp it to a convenient spot on the engine with a vise-grip. Pat

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Dutch
Thanks Pat. So it's a typical lobe on the cam? I'll remove the plunger and stick a wire in there to try and measure the movement. Thought I read the opposite plug wire was supposed to be grounded. Why remove and clamp the plug? Just so the engine spins faster, or won't start accidentally?

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HubbardRA
Dutch, on any two cylinder that has a single coil, each end of the high tension coil is hooked to a different plug. On a single coil one side is grounded to chassis. You have to ground one plug because if either side goes open, the entire output side of the coil is open. Since they are both in the same circuit, one plug can affect the other. Rod H.

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Dutch
Rod, For some reason I’m not grasping the concept (getting old?). Why can’t spark be checked just like on an auto (pull only one plug wire off and hold it near a ground)? BTW – I broke out of the mental box I was in. Think I’ll install a $12 universal electronic trigger (like Roy just posted), and forget about the points & plunger. That way, if the engine is junk, I can use the trigger on another engine.

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HubbardRA
Dutch, An ignition coil is a step-up transformer. In other words, two coils of wire packaged side by side internal to the unit. The relationship between the number of windings in each of the two coils determines whether the voltage will be increased or decreased. An ignition coil increases the voltage. Now picture the two coils. The input coil is connected to positive battery voltage with ground connected through the points. The secondary coil of a single ignition has the negative side connected to the metal case for chassis grounding and the positive side firing through the plug to ground. On a double fire coil, the positive is connected the same, but the negative is not case grounded but connected to the other plug. In other words the firing pulse current flow must jump two gaps, one on the positive side of the coil and one on the negative side. Both plugs must fire in this set-up to complete the circuit of the output coil. If one plug is not firing and you short that lead to ground it will make the other plug fire. I would draw you a diagram, but I'm not sure how to insert an image into this forum. Tell me how, and I'll send you a picture. Rod H.

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HubbardRA
Dutch, See if you can read this picture. It may explain the coils. [url="pop_download.asp?mode=Edit&dir=HubbardRA&file=198"][/url] Rod H.

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Dutch
Rod, Thanks, I "think" I understand now. Spark can be checked just like a car PROVIDED both plugs are firing. However, IF one plug's gap is too wide, or fouled, and spark at the other plug is checked, there will be no spark because the coil circuit is not complete. Right? Anyway, just got back from my local Briggs dealer. He advised me against buying one of those $12 electronic triggers. Instead, he sold me a genuine used $50 Magnetron for $5. Put it on..... two cranks it fired up. Doesn't sound bad either. Now I have to fix the leaking carb. Thanks guys................

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Dutch
Roy, I always stay f...a...r away from cesspools. I always smell like roses anyway. Just goes to show, nice things happen to nice people..........

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PatRarick
Dutch, I see your other questions have been answered. As to why I remove and clamp the plug, it is to prevent the engine from starting, and it is a convenient way to ground the plug wire. Pat

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