No spark - Gordon

[gordo2023]

At wits end with this machine. New here so please bare or bear with me. Briggs & Stratton 17.5 hp engine no start no spark!
Long story short I had adjusted the valves and apparently did not tighten down the lock screw enough and damaged the intake push rod, broke in half. I replaced the push rod and adjusted the valves, setting them at 5, intake, and exhaust 7 thousandths. I get spark to the plug when grounded to the block but nothing when put in the engine. I have used a light to test the coil as well as a multimeter and it tests ok, in fact new. None of the safety wiring has been touched - brake, seat and kill switch.
What can it be??

 

[Bertrrr]

If it fires when touching off to ground , it's firing while installed.
you may have a fuel problem or your key is sheared at the flywheel throwing off your timing

 

[StarTech]

If it fires when touching off to ground , it's firing while installed.
you may have a fuel problem or your key is sheared at the flywheel throwing off your timing

BS...They do fail under compression.

Used a known good for testing. You could have one that fails under compression load.

 

[Rivets]

I’ve seen units which have weak spark when the air gap is too large. Should be set at .008-.010”. Plus, as Star states try replacing the coil with a known good one. There is no way to test today’s coils without an expensive piece of equipment. I don’t know of any repair shop which even has one.

 

[gordo2023]

The coil is new, spark plug gap is .30. As I stated, I have a spark with the plug out and grounded but cannot get even a pop with plug in engine. Stater fluid into carb, even sprayed into the combustion chamber and replace the spark plug and nothing!!,

 

[gordo2023]

Forgot, I replaced the head gasket and have good compression.

 

[hlw49]

Forgot, I replaced the head gasket and have good compression.

 

[hlw49]

Just because it fires out side the cylinder @ .030 does not mean it will fire under compression. To similate compression the gap outside the cylinder has to be at least 1/4 inch.

 

[Tiger Small Engine]

Just because it fires out side the cylinder @ .030 does not mean it will fire under compression. To similate compression the gap outside the cylinder has to be at least 1/4 inch.

Sometimes new parts fail right out of the box (3 times for me this year). Bite the bullet and buy another coil, maybe from a different vendor, install and hopefully it will fire.

 

[StarTech]

Come on get it through to your head spark plugs due fail under compression load. I had just proved that to a customer here last month. Nice blue spark out of the engine just means the coil are usually good. The customer brought in his mower that would not start. I did my normal tests and said I needed to go to the parts room to get spark plug and the customer said but the plug is firing. Well when I installed a new known good plug it fired right up.

Plugs can do some strange things too. I had one to cause engine knocking even though it was the correct plug. And one to cause a 2 cycle engine to diesel; it had run away rpms at full throttle. Even had plugs to short out. Plug insulator do crack inside the metal shells. I have personally take plugs apart looking for failure causes.

This why I suggest using a known good plug from a running engine for test purposes.

And as said you can not test these coils that internal triggers with a multi meter. It requires a very expensive tester that nearly no shop has on hand. They are plug and play mag packs that either works or don't work.