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Hi,
My Stihl BG55 stopped running yesterday. It was making a bit of noise, kind of like a small rattle that wasn't normal, and was periodically losing power before it abruptly stopped. Initially, the flywheel wouldn't move when it shut off, so I took the cover off, removed the spark plug, and freed the flywheel up. I started it back up twice and it ran for about a minute and it started to lose power before it stalled. Those two times it wasn't an abrupt shut off like it did initially, more of a slow stall. It didn't lock up the flywheel again, but after two tries it will not start. I checked the spark arrestor and it was clean. I checked the air filter and it was clean. The spark plug looked great. I've had this unit about 5-7 yrs and never had an issue until yesterday. Any ideas would be appreciated.

Take the muffler off and have a peek at the piston & cylinder walls
ME thinks it will not be a pretty sight

Okay first when you remove the spark plug is it coated with grey looking stuff? If so you might have ran it too lean which cause PNC damage. Also you can pull the muffler and look at piston for damage from overheating.

Most PNC is from straight gassing but running too lean on oil or fuel mixture can also cause the same damage.

Time to look for a new one! good luck and be well...also winter is far from over ..at least here!

bertsmobile1 said:

Take the muffler off and have a peek at the piston & cylinder walls
ME thinks it will not be a pretty sight

Click to expand...

Thanks, I'll have a look.

StarTech said:

Okay first when you remove the spark plug is it coated with grey looking stuff? If so you might have ran it too lean which cause PNC damage. Also you can pull the muffler and look at piston for damage from overheating.

Most PNC is from straight gassing but running too lean on oil or fuel mixture can also cause the same damage.

Click to expand...

The spark plug looked perfect, I'll pull it again and have another look. What is PNC? I've always used the manufacturers specs for fuel and oil mixture. Thanks!

da324 said:

The spark plug looked perfect, I'll pull it again and have another look. What is PNC? I've always used the manufacturers specs for fuel and oil mixture. Thanks!

Click to expand...

da324 said:

The spark plug looked perfect, I'll pull it again and have another look. What is PNC? I've always used the manufacturers specs for fuel and oil mixture. Thanks!

Click to expand...

I've attached a few pictures. The piston has some slight scoring at the top, but none on the bottom. Is it possible I sheared a flywheel key? I'm curious because there was a small rattling sound before it stopped running.

The photos did not come through