New MS 661-c broken spark plug.

[pinkfireman]

Hello all, I hope this finds you well.

So I have a new MS 661-C with maybe 12 to 13 hours on it. The other day it just stopped running and would not start again. Today I found the spark plug was loose, so I tightened it up and nothing. After further investigation I pulled the plug and found this. I have never in my life seen a plug do this, have you?

I pulled the muffler and tried my best to find the piece with no luck. I blew out the cylinder and reassemble everything and a new plug and it fired right up.

 

[Maintenance Chief]

I've seen it in a car motor.

 

[thinair]

I had this happen with an NGK in a snowmobile once. I contacted them and they said the plug was overtightened but sent me a case of new plugs...

 

[Nutball]

I've seen cracks around the weld at the base of the missing part. It could be a bad weld that causes it.

 

[Creaky limb tree care]

Bosch plug, yes, I have had to rebuild a couple of saws where this has happened!

 

[pinkfireman]

Bosch plug, yes, I have had to rebuild a couple of saws where this has happened!

I guess that's why, I have never used Bosch. Thanks for the reply.

 

[huskyboy]

Those newer bosch plugs are junk.

 

[Bjorn]

Hello. Japanese quality. https://www.densoproducts.com/denso-6027-w22mp-u-nickel-u-groove-spark-plug

 

[Creaky limb tree care]

I think they are now made in China

 

[dirter]

Chinese version of quality control is make a bunch of them cause when it brakes they’re gonna need another one.

 

[drf256]

Personally wouldn’t run that saw. I’d pull the jug and flush the case out until I found that ground strap. Unless you were lucky enough to find it in your muffler, it went somewhere.

 

[av8or3]

^^^^^^^^^^^^^^^^^^^^^
What he said. I have seen that happen in a saw. If you run it you will ruin it. You’ll find that electrode stuck in either the piston or the combustion chamber. If you’re lucky I suppose you’d get by with minor or no damage. I wasn’t so lucky. It ruined the piston in my machine. I found the electrode stuck in the piston, with corresponding damage to the cyl head. I didn’t even know what it was ‘till I picked up the spark plug (NKG) to reinstall it in the cylinder and spotted the missing electrode. Up to then I thought a small cotter pin had found it’s way into the machine. What a surprise!

 

[huskyboy]

Hello. Japanese quality. https://www.densoproducts.com/denso-6027-w22mp-u-nickel-u-groove-spark-plug

That isn’t a resistor plug. You can risk damaging the ignition coil on newer saws if you run that plug on them. I’d try and source the resistor version of that plug if you can. I choose to use the ngk bpmr7a or champion rcj7y. Those have worked well for me.

 

[sawmikaze]

Happened to me once.

 

[Bjorn]

That isn’t a resistor plug. View attachment 312625 You can risk damaging the ignition coil on newer saws if you run that plug on them. I’d try and source the resistor version of that plug if you can. I choose to use the ngk bpmr7a or champion rcj7y. Those have worked well for me.

You have totalt right. I use Denso sparkplug in all My saws that are old. But I have One new 362 cm and that i use NGK bpmr7a, same as you. All saws that have elektric carburator or fuel injektion needs the resistor sparkplug.

 

[Motorka]

NGK bpmr7a Denso W22MPR-U

 

[Redfin]

Personally wouldn’t run that saw. I’d pull the jug and flush the case out until I found that ground strap. Unless you were lucky enough to find it in your muffler, it went somewhere.

Indeed, if you have a screen in your muffler, that lil piece is inside that saw just waiting to bite your ass.

 

[pinkfireman]

Personally wouldn’t run that saw. I’d pull the jug and flush the case out until I found that ground strap. Unless you were lucky enough to find it in your muffler, it went somewhere.

I'm too late on that one. I took the front off of the muffler and got the piston on a down stroke so I could see in the cylinder. Left the plug out and shined a light inside and never saw it, blew it out with compressed air though the plug hole. Ran it Thursday for about 2 hours and it runs fine so far, if it's still in there I don't where.

 

[pinkfireman]

Indeed, if you have a screen in your muffler, that lil piece is inside that saw just waiting to bite your ass.

While I'm sure it's true with my luck, please don't help it along. lol

So for the sake of learning what is the tolerance of the chamber when the piston is at the top of the stroke? Wouldn't there be enough space for that little thing until it got moved out to the muffler?

Seems the piston wouldn't be hitting the head to me.

 

[Redfin]

There is room in the chamber but not around the edge of the cylinder. The flat around the circumference of the chamber has way less clearance than that electrode strap.