Stihl 261c blowing out spark plugs

[EFSM]

I have no idea why, but most of the stripped plugs I’ve seen were Stihl’s. I don’t think it has anything to do with strato scavenging though.

 

[TheDarkLordChinChin]

I dunno, some people just find a way to break things while other folk manage to use the exact same item/tool/whatever and have zero problems. Nothing but Stihl OPE in my shed and I can't say I ever had a loose spark plug. I may have more than a few screws loose, but no spark plugs. I wonder if some people are afraid of over-tightening the plugs and are leaving them loose and prone to further loosening from vibrations?

Id say youre right.
However half of the loose plugs/decompression valves I've seen have been on machines that were fresh from the dealership and had never been used or tampered with.
So no one other than a stihl professional had touched the machine.

I can't remember if I ever took the plug out of my 261.
I probably did but I know full well I would have tightened it down fully again.

 

[Al Smith]

In my case with the 441 it was relatively new .The owner ,an owner of a tree service thought it blew a hole in the piston ,bought another new saw and gave the 441 to me.I did not get to it for a week or two and discovered the blown out spark plug and gave it back to him .Over a period of several weeks it blew out several more times even using a new plug .After the time-sert repair it stayed put and might still be in service as far as I know .I usually get his ragged out saws but not that one -yet .

 

[Al Smith]

In my case with the 441 it was relatively new .The owner ,an owner of a tree service thought it blew a hole in the piston ,bought another new saw and gave the 441 to me.I did not get to it for a week or two and discovered the blown out spark plug and gave it back to him .Over a period of several weeks it blew out several more times even using a new plug .After the time-sert repair it stayed put and might still be in service as far as I know .I usually get his ragged out saws but not that one -yet .

On the above a story about another model ,this time an 038 mag that spent twenty hard years in a tree service .Over that twenty years I had rebuilt it twice .Finaly it grenaded a piston so badly it fouled one of the main bearigs and it was given to me and I did it a third time .It became a shelf queen because I have a modified 038 mag .It stayed retired for few years until it was loaned back to temporary serve until he bought several new saws to replace stolen ones .I've got it back again .Say what you want but that's one tough old saw that refuses to die .

 

[av8or3]

I’ve uncovered a few loose plugs but none were mine. I will say that it’s easy to leave one loose, especially if you get re-assigned mid project and the like. I have left plug leads loose. And was very surprised to discover them on a QC inspection. I was glad nobody else found them. It’s not the end of the world when someone else does, just embarrassing. But it’s easy to do.

 

[huskihl]

I believe it’s from loose plugs that don’t completely crush the washer. Vibration allows it to loosen up. Only decomp I’ve seen stripped was a brand new 572 where the threads actually came out with the valve

 

[Al Smith]

This whole thing could be a design problem related to aluminum alloy to thread engagement .For example in aluminum it takes approx 4 times the thread depth related to the fastener IE spark plug ,cylinder head bolt etc to maintain max. holding strength .Ford used extremely long thread holes and long threaded spark plugs .Roush racing took it one step further and installed steel time-serts on every racing engine they built .Matter of fact Ford right in the factory used serts as a repair . I can testify to that because I spent 29 years in that engine plant .