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Camshaft Install and Ignition Timing - Curios about how it all works !!

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paulbaker1954:
Just on my final stage of engine rebuild and about to put back Cam but I have some confusion/questions around how all this works. This is really about satisfying my curiosity more than anythinig else............

So you line up the 1.4 timing mark so pistons 1 and 4 are at TDC and then line up the marks on the cam - I get all that but this got me thinking -- cos as an engineer I like to understand how all this works so here's my confusion.

Lets say Pots 1 and 4 fire at TDC , crank then  rotates 180 on the bang stroke, then rotates another 180 on the exhaust stroke and 1 and 4 then get to TDC again at the end of the exhaust stroke. Now surely the 1 an4 points will open again and fire the plug again. I would have thought the crank needed to rotate 360 before firing 1 and 4 again.

Clearly I am missing something obvious here or dooes it fire again at the top of the exhaust stroke.

Looking forward to demystifying this !!!

I am a bit mystified  >:( >:( >:(

SteveD CB500K0:
You are absolutely correct. The system fires twice in every cycle - it's called a wasted spark.

It saves having four points/coils (or a distributor!)

Steve

Bryanj:
As steve sez, cheaper to fit two double ended coils than four single ones and can you imagine the clutter with four sets of points in there!

paulbaker1954:
Thanks guys all now makes sense, at least my logic was correct  :) :)

Johnwebley:
and if you fit a Boyer ignition you get all 4 plugs sparking every 180 degrees of the crank


 but it works !!!

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