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No spark - Gordon

#1

gordo2023

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??


#2

B

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


#3

StarTech

StarTech

Bertrrr said:
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
Click to expand...
BS...They do fail under compression.

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


#4

R

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.


#5

gordo2023

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!!,


#6

gordo2023

gordo2023

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


#7

H

hlw49

gordo2023 said:
Forgot, I replaced the head gasket and have good compression.
Click to expand...


#8

H

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.


#9

Tiger Small Engine

Tiger Small Engine

hlw49 said:
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.
Click to expand...
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.


#10

StarTech

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.


#11

gordo2023

gordo2023

hlw49 said:
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.
Click to expand...


#12

gordo2023

gordo2023

I do not follow your thinking! Are you referring to the plug gap or the spark arc?


#13

H

hlw49

gordo2023 said:
I do not follow your thinking! Are you referring to the plug gap or the spark arc?
Click to expand...
you have to have a tester that has a gap of at least 1/4 inch gap for the spark to jump


#14

gordo2023

gordo2023

After so many attempts I, using advice from others, decided to check the valves again and found I did not have the exhaust push rod in place! The engine started when fixed but knocked loudly and finally died. Do not know where to go from here!


#15

Tiger Small Engine

Tiger Small Engine

gordo2023 said:
After so many attempts I, using advice from others, decided to check the valves again and found I did not have the exhaust push rod in place! The engine started when fixed but knocked loudly and finally died. Do not know where to go from here!
Click to expand...
The push rod sits in a tiny indentation on the tappet, down the cylinder head valve valley. When you think you have push rod in correct place, rotate the engine to make sure intake and exhaust valve are moving. Then you have to set the valves to correct clearance. If you do not know how to set valves, take it to shop, don’t guess.


#16

gordo2023

gordo2023

gordo2023 said:
After so many attempts I, using advice from others, decided to check the valves again and found I did not have the exhaust push rod in place! The engine started when fixed but knocked loudly and finally died. Do not know where to go from here!
Click to expand...

Tiger Small Engine said:
The push rod sits in a tiny indentation on the tappet, down the cylinder head valve valley. When you think you have push rod in correct place, rotate the engine to make sure intake and exhaust valve are moving. Then you have to set the valves to correct clearance. If you do not know how to set valves, take it to shop, don’t guess.
Click to expand...


#17

gordo2023

gordo2023

Tiger Small Engine said:
The push rod sits in a tiny indentation on the tappet, down the cylinder head valve valley. When you think you have push rod in correct place, rotate the engine to make sure intake and exhaust valve are moving. Then you have to set the valves to correct clearance. If you do not know how to set valves, take it to shop, don’t guess.
Click to expand...
Why the loud knocking and then dying after a start-up?


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