Stihl 261c blowing out spark plugs

[Nutball]

I have two 261's (a 2018 and 2023) that have stripped the spark plug out of the cylinder. Is this common? Will the Stihler fix it for free under some kind of extended warranty recall?

What's the best way to fix, what is your preferred helicoil?

 

[Stump Shot]

I have two 261's (a 2018 and 2023) that have stripped the spark plug out of the cylinder. Is this common? Will the Stihler fix it for free under some kind of extended warranty recall?

What's the best way to fix, what is your preferred helicoil?

Would surprise me if they did.

I use the Helicoil brand spark plug thread repair kit, with the edition of a bit of Hi-temp thread locker. The trick is to get the proper length coil in place so the ends are well within the new threads, this is what keeps them from backing out. What's nice about this version is it can be done on the saw with some grease applied to the cutting/threading tool to capture the chips.
The absolute best repair is to take it off and get @srcarr52 to weld and rethread it for you. He does excellent work and I highly recommend.
I've seen plenty of saws come in with timesert repairs done that come off when the spark plug is removed.

 

[Nutball]

Great info, thanks.

This is my first time working on a 261. What's up with the plastic part blocking the spark plug, and the rubber in the hole that keeps a wrench from reaching the plug? Am I missing something, or did Stihl go full retard on that? A 291 at least has a big enough hole for the wrench.

 

[singinwoodwackr]

Plug holes only strip from over tightening or from plug not being tight enough and rattling around till the threads are chewed up.
There is no warranty that would ever cover that unless it was a factory screwup that the final inspection missed…unlikely.
A common mistake when replacing a plug is not torquing it correctly so the crush washers, well, crush . Eventually the plug will loosen up from vibration, and…

 

[Nutball]

That's what I'm thinking, I just didn't know if 261's had some defect causing it. I just fixed another saw that was victim to botched basic maintenance.

 

[EFSM]

Would surprise me if they did.

I use the Helicoil brand spark plug thread repair kit, with the edition of a bit of Hi-temp thread locker. The trick is to get the proper length coil in place so the ends are well within the new threads, this is what keeps them from backing out. What's nice about this version is it can be done on the saw with some grease applied to the cutting/threading tool to capture the chips.
The absolute best repair is to take it off and get @srcarr52 to weld and rethread it for you. He does excellent work and I highly recommend.
I've seen plenty of saws come in with timesert repairs done that come off when the spark plug is removed.

I second this. However, no matter what repair kit style you go with, make sure the plug isn’t leaking compression once you’re done. If the hole was really damaged or the insert isn’t totally in line with the old threads, the plugs tend to leak a bit. Sometimes I flip around the crush washer on the plug to give it a larger sealing circumference.

 

[heimannm]

This is the Helicoil kit with solid inserts. The swaging tool locks them in place when done properly. Available at most auto parts stores.



Timesert also makes spark plug inserts of different types. including washer seat and taper seat designs. They require a special tap, seat cutter, and insert tool in addition to the inserts themselves.





Mark

 

[Nutball]

Would surprise me if they did.

I use the Helicoil brand spark plug thread repair kit, with the edition of a bit of Hi-temp thread locker. The trick is to get the proper length coil in place so the ends are well within the new threads, this is what keeps them from backing out. What's nice about this version is it can be done on the saw with some grease applied to the cutting/threading tool to capture the chips.
The absolute best repair is to take it off and get @srcarr52 to weld and rethread it for you. He does excellent work and I highly recommend.
I've seen plenty of saws come in with timesert repairs done that come off when the spark plug is removed.

Looks like Helicoil brand makes every size except M14 X 1.25 from what I can find. Lots of other brands

 

[Coupe]

Make sure you get the tap square to the hole and not on an angle bring the cylinder
bit over half and put the Helicoil in. Put plenty of grease on to catch any swarf
and as said above use the sparkplug kit. Apply some good thread locking paste and you
should be right. Don't even bother getting at Stihl cause I can guarantee they
will not help you as you will get you have over tighten
it or cross threaded it.

 

[Mad Professor]

Plug holes only strip from over tightening or from plug not being tight enough and rattling around till the threads are chewed up.
There is no warranty that would ever cover that unless it was a factory screwup that the final inspection missed…unlikely.
A common mistake when replacing a plug is not torquing it correctly so the crush washers, well, crush . Eventually the plug will loosen up from vibration, and…

I can think of two other causes.

I've seen lots of cross threaded plugs in aluminum heads strip the threads.

Also seen plugs left in for years with no anti-seize and the threads come out with the plug.

 

[av8or3]

I love helicoils. I’ve done several saw spark plug holes and quite a few aircraft repairs involving their use. Every single threaded hole on an aircraft engine block has a helicoil in it. For strength, durability and ease of use over and over. Here’s one I did for practice in a worn out S-D 143 cylinder.

 

[heimannm]

The Helicoil Sav-A-Thread kit is M14x1.25

Mark

 

[Al Smith]

I had to look it up and evidently it's a low emissions engine .That I once worked on an early 441 that also blew out plugs .If I recall the owner took it to a shop that used a time-sert style insert .I suspect but can't prove it that the partial fresh air portion of the transfer cycle was responsible for it to happen .As for the low emission designs I'm not really impressed and seldom work on any .Fact of the matter the next time somebody wants me to work on one I will nicely tell them to go some place else .Old school forever and too old and grumpy to change.

 

[hacskaroly]

rubber in the hole that keeps a wrench from reaching the plug?

It think this is just a way to isolate the cylinder side from the carb side. The rubber is tough, but will give way to the scrench if you push in hard enough.

 

[Junk Meister]

I'm not really impressed and seldom work on any .Fact of the matter the next time somebody wants me to work on one I will nicely tell them to go some place else .Old school forever and too old and grumpy to change.

DITTO and DOUBLE DITTO. Next week I will be asking advice for this same thing but for myself who knows.

 

[srcarr52]

Try an insert first, when that fails I can weld it.

 

[Junk Meister]

I can think of two other causes.

I've seen lots of cross threaded plugs in aluminum heads strip the threads.

Also seen plugs left in for years with no anti-seize and the threads come out with the plug.

I "THINK" I read on a Browning taper hup NOT to use Never/no/anti Seize when installing ... This would be Steel on Steel , The rest is foggy but I "THINK" the reasoning was the ease of over-tightening was possible and stripping threads or sheering bolts . Clean surfaces were in there some where.

 

[TheDarkLordChinChin]

Happened to my 2018 ms261c in November.
Decompression valve came out of my 2018 ms462c in march 2024
The spark plug in my 1998 020t was coming loose a while back but I noticed before it stripped the threads.

Mine and my work partners 2 new 2025 ms500is both had loose spark plugs from the dealership, they could both be tightened 1/4 turn.
Any new combi system head I've seen needed the plug tightening at least 1/2 turn.

Never seen a loose spark plug or decompression valve on a husqvarna. Seems to be a stihl problem. And im more of a stihl guy.

 

[Al Smith]

There has to be a reason why this is happening .Figuring thermal expansion unless I've missed something I would not think the higher section of the cylinder would be any different than a standard non low emission design .Based on my falf-fast theory the top of the cylinder would have to expand for the plug hole to get loose .If I recall the standard traped compresion ratio on most Stihls is 9.5 to 1 .Would think even with low emission it wouldn't be any higher .

 

[MtnHaul]

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?