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Stripped Spark Plug

MustangMike

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How would this cause the sparkplug hole to strip out?

I was referring to the piston Dan, the spark plug stripped cause they have very heavy hands, I almost could not get the rest of the saw apart! Everything is over tightened, and border line stripping. The recoil bolts were so tight I was surprised they were not stripped, but I think a lower muffler bolt is.
 

paragonbuilder

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I was referring to the piston Dan, the spark plug stripped cause they have very heavy hands, I almost could not get the rest of the saw apart! Everything is over tightened, and border line stripping. The recoil bolts were so tight I was surprised they were not stripped, but I think a lower muffler bolt is.

Ahh, gotcha!
[emoji106]
 

Al Smith

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On the subject it seems Stihl might have had a bunch get loose with perhaps an over sized bore before it was tapped .My buddy who is tree trimmer had both a 460 and a 441 blow the plug .
As a general rule in engine production a plug hole is drilled with a three drill progressive size rotation then reamed then tapped .Perhaps they had a slightly over sized reamer .Things happen .
 

PogoInTheWoods

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Uh....that's not me. Any debris in a 2 cycle and you have a problem. Unless you have a bores cope to prove you got everything out I wouldn't do that. Even then...I dunno.

I wasn't exactly recommending tapping the threads with the cylinder on the saw. Just saying it was possible (and occasionally more practical) if enough care were exercised. I've done it without issue.

Not sure how many folks/shops would actually tear a MS290 (or any clamshell for that matter) all the way down and pull the short block apart just to install a plug thread insert.
 
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Al Smith

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I'm not sure if they still repair plug holes at work ,usually just scrap the head .Back in the days of the cast iron engines they did .Damned plugs in those aluminum heads have about an inch of threads .
 

Al Smith

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I could make an insert if I had to but I suppose most people couldn't unless they had the machining knowledge and the tools to do it .My bud who had the two Stihls had both done at a shop and I don't think they charged him too much .Maybe 40-50 bucks .Then again something like an 029 who would even sink that much in one ,a 460 is a horse of a different color .
 

LondonNeil

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As you know Mike, stripped plug ports are in my mind too, so I've been reading up on inserts. The time serts from wurth are the daddy because they have a neat tool that slides over the tap/ream while that's in place and cuts a recess for the lip on the insert, the other big plus it's the insert last 3 threads aren't cut full depth. As the insert is fitted the inserting tool cold forges these last 3 turns and deforms the outside of the insert, sealing it and securing it permanently in place. Nice design. However its of little use to me. As far as I can see the 038 cylinder has 4 or 4.5 threads through it, so about 6-7mm thick. The shortest timesert is 9.5mm. if correctly installed the last 3 threads would go right through and inside the cylinder where they would be unable to expand against anything to seal and secure the insert. Ie, it won't work. The 460 cylinder may be thicker though. For thin cylinders though, a solid insert installed with loctite red lock and seal is your best solution I think.

As for on or off saw.... Remove muffler, set piston to opening exhaust but not transfer ports, stuff an oil soaked rag in on top of the piston. USE COPIOUS AMOUNTS OF GREASE AS YOU REAM/TAP TO CUT THE NEW THREADS TO CATCH THE CHIPS ON THE REAM. remove oil rag, blow out, inspect and clean more if you see a problem but you're probably good to go. This is how is done on 4 strokes like cars and bikes without removing the head ( rag goes in through plug port)
 

pro94lt

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Ever tried a spark plug thread chaser? I've fixed some pretty bad ones on aluminum Chevrolet heads. These threads were cross threaded.
 

RI Chevy

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I think it was caused by excessive dirt in the intake and carbon buildup.

Mike, looks like some bad filtration or no filtration at all.
What a mess. If guys would only use the saws like they were their own.
 

PogoInTheWoods

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As for on or off saw.... Remove muffler, set piston to opening exhaust but not transfer ports, stuff an oil soaked rag in on top of the piston. USE COPIOUS AMOUNTS OF GREASE AS YOU REAM/TAP TO CUT THE NEW THREADS TO CATCH THE CHIPS ON THE REAM. remove oil rag, blow out, inspect and clean more if you see a problem but you're probably good to go. This is how is done on 4 strokes like cars and bikes without removing the head ( rag goes in through plug port)

Bingo.
 

Al Smith

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That's known as a forming tap .It displaces the metal not cut it .
A forming type tap is what you use to swedge the "Time serts ".Those style by the way are what Roush racing use on every aluminum block engine they rework in every threaded hole .They build a good engine so there must be something to it .
 

twinstaged

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88C35F66-0CE0-41A8-BBF1-D1CFDC75CBF2.jpeg
I have a timesert kit now after seeing how the save a thread kits are made... they both work though. I would have to order shorter sleeves with my timesert kit. A bit overkill, but it does make her nice and straight. Work is back manageable heading into winter if anyone needs a hand.
 

earlthegoat2

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Ive used the Savathread and have removed the cylinder and have not removed the cylinder. Maybe 30 or so times on both 2 and 4 strokes. I grease the reamer and tap if I don't remove the cyl. That is what is in the Timesert instructions.....which I have also used on Ford modulars.....without removing the head. Also, grease a paper towel and feed it in through the exhaust port to catch any chips. It is important to use some kind of thread locking sealant. Even more important than swaging the serrations since those have proven to not work in the inserts that were not properly thread locked. I like to use the high heat and high strength Loctite. IME, it is very difficult to defeat that stuff even with high heat from a MAPP torch.

Best practice is to remove the head.....and use an actual Timesert brand thread insert kit......

On one 460 I had, I did not remove the head and used the greased reamer and tap method as well as stuffing a greased towel in. Then Mathew hit and I proceeded to put about 100 abusive hours on it cutting up several hundred (you read that right) 30"+ downed trees. Not saying it is the best way to not remove the head but I hardly think it is absolutely necessary as long as some precautions are taken.
 
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