Can a stripped thread repair be repaired?

[NewToStihl]

Well...

Cylinder is about $65 (aftermarket)

Vs repairing... I'd charge the customer probably an hr (R&R the cylinder and repair the threads) plus parts so there's $90... so maybe $100ish and it's still a patch together cylinder.
To replace the jug, probably around $100 total.

All true, but personally I don't use aftermarket parts. Also, I can tap the new threads myself, so there wouldn't be a dealer charge on that. Not a patched together cylinder, just re-tapped with a larger plug. I'm definitely growing on the idea . . . as long as I can figure out which plug to use.

 

[hotshot]

I just acquired a saw with a cylinder that had had the spark plugs repaired with a Sav-A-Thread at some point in it's life and now that has been stripped out (previous owner must love to wrench that plug in!). I assume that means the cylinder is shot, but I would love to be proven wrong! I've never ceased to be amazed with some of the tricks & tips you guys have tucked away.

So, is there any way to make a quality repair in this scenario? I believe I've heard of welding a stripped hole shut and re-tapping it. It's an MS460 though, nothing rare or hard to replace, so I don't think it would be worth the cost and/or trouble of making that happen. Anything else?

Thanks!

The spark plug thread repair kits all vary in their insert major diameters & taps supplied, none are "standardized"...WTF is that China?.

I measured five different insert & "helicoil" type kits before I did this little 60cc Poulan 361 fix (see below thread). I do remember that
McMaster-Carr sold the largest major diameter inserts for a standard 14mm plug, and that would surely fix your stripped out
Sav-A-Thread issue. Measure what you've got left for a hole, they require a large 11/16" hole & a 3/4"-16 TPI tap for a 76% fit. Look up part
number 90248A092 or A095. They were way bigger than I needed to seal this cylinder up.

http://www.arboristsite.com/community/threads/poulan-thread.98495/page-1649#post-4885471

 

[NewToStihl]

The spark plug thread repair kits all vary in their insert major diameters & taps supplied, none are "standardized"...WTF is that China?.

I measured five different insert & "helicoil" type kits before I did this little 60cc Poulan 361 fix (see below thread). I do remember that
McMaster-Carr sold the largest major diameter inserts for a standard 14mm plug, and that would surely fix your stripped out
Sav-A-Thread issue. Measure what you've got left for a hole, they require a large 11/16" hole & a 3/4"-16 TPI tap. Look up part
number 90248A092 or A095.

http://www.arboristsite.com/community/threads/poulan-thread.98495/page-1649#post-4885471

That's a great suggestion - thanks!

 

[shawn022]

If you decide to retap to a larger plug, take a look at the "shorty" plugs. They're used sometimes when you have clearance issues running headers.
As far as a heat range, I have no idea.

 

[NewToStihl]

The spark plug thread repair kits all vary in their insert major diameters & taps supplied, none are "standardized"...WTF is that China?.

I measured five different insert & "helicoil" type kits before I did this little 60cc Poulan 361 fix (see below thread). I do remember that
McMaster-Carr sold the largest major diameter inserts for a standard 14mm plug, and that would surely fix your stripped out
Sav-A-Thread issue. Measure what you've got left for a hole, they require a large 11/16" hole & a 3/4"-16 TPI tap for a 76% fit. Look up part
number 90248A092 or A095. They were way bigger than I needed to seal this cylinder up.

http://www.arboristsite.com/community/threads/poulan-thread.98495/page-1649#post-4885471

Looks like the McMaster-Carr insert might work! I measured the hole and got just under 0.66", so I should be able to clean it out with an 11/16" bit and then tap it with a 3/4". Thanks again for the tip.

 

[hotshot]

Note that there are two different insert thicknesses. I've never used those, but they are so large that the plug crush gasket
may land right on top of the thread seam...so you can't mechanically lock them in.

If not, I would also notch the insert's outer top edge with a Dremel cutoff wheel to create two thin "locking slots" (180° apart), then
stake that sucker in after using red Loctite. You could even use 4 slots @ 90° like the Sav-A-Thred insert if you wanted to, and never
have a problem.

 

[blsnelling]

How does this locking slot work?

 

[hotshot]

Instead of mechanically staking the insert into the head, stake the head into the insert in four slotted places
that you create on the insert rim edge, or just the opposite of this crappy photo I took.

I wish I had your talent for photography, but I don't.

Those huge MMC inserts are not ribbed at the top, and could screw themselves deeper or be unscrewed
while you're servicing the plug. What's shown is a different type "Sav-A -Thred" & it's designed to flare out
at the top, with a tool they supply, but I still made slots & staked it too. Every bit helps in this soft alumimum.

However, what I was trying to explain is if the MMC insert diameter is so large that the stake spots
interfere with the spark plugs crush gasket, I wouldn't do it at all. It could create gas leaks in those
four spots as the OP's saw also uses a flat plug & not a tapered type plug.

 

[Giles]

I just acquired a saw with a cylinder that had had the spark plugs repaired with a Sav-A-Thread at some point in it's life and now that has been stripped out (previous owner must love to wrench that plug in!). I assume that means the cylinder is shot, but I would love to be proven wrong! I've never ceased to be amazed with some of the tricks & tips you guys have tucked away.

So, is there any way to make a quality repair in this scenario? I believe I've heard of welding a stripped hole shut and re-tapping it. It's an MS460 though, nothing rare or hard to replace, so I don't think it would be worth the cost and/or trouble of making that happen. Anything else?

Thanks!

I posted this earlier, but dought it will help you----
"Although this is probably not an option, I think some here will find this interesting.
Over the years, I have repaired many stripped spark plug threads. Although I haven't done this repair in quite some time, I will attempt to remember just how I did this ===I made a special cutter (pilot counter bore) and after drilling damaged threads to the proper tap size, I inserted this cutter and counter bored .020 deep. I made up several aluminum inserts with a .020 flange. These inserts had an outside thread that was tapered .002 ?? larger on the top end and it was installed with a spark plug screwed into the insert, after tapping, and tightened down. I did this entire repair, without removing the head from the machine that I was doing the work with.
It didn't require thread sealer because the tapered thread and sealing flange did the sealing. Never had one fail and have many hours on a Husqvarna I did years ago.
This type repair would not be feasible to only do one or two, but at the time I was running a small engine shop and did a lot of motorcycles and quite a few chainsaws.
I did repair for several other businesses."

 

[pioneerguy600]

I posted this earlier, but dought it will help you----
"Although this is probably not an option, I think some here will find this interesting.
Over the years, I have repaired many stripped spark plug threads. Although I haven't done this repair in quite some time, I will attempt to remember just how I did this ===I made a special cutter (pilot counter bore) and after drilling damaged threads to the proper tap size, I inserted this cutter and counter bored .020 deep. I made up several aluminum inserts with a .020 flange. These inserts had an outside thread that was tapered .002 ?? larger on the top end and it was installed with a spark plug screwed into the insert, after tapping, and tightened down. I did this entire repair, without removing the head from the machine that I was doing the work with.
It didn't require thread sealer because the tapered thread and sealing flange did the sealing. Never had one fail and have many hours on a Husqvarna I did years ago.
This type repair would not be feasible to only do one or two, but at the time I was running a small engine shop and did a lot of motorcycles and quite a few chainsaws.
I did repair for several other businesses."

Nice setup, tapered threads make a nice tight fit.

 

[zogger]

I've always wondered about this stuff. Glue that insert back in there. http://www.newpig.com/pig/US/high-t...0651&ddkey=http:US/ap/PPCHDEP25/PPCHD25GC250O

Man, I wonder if you could patch gouges and scores in cylinders with that stuff? Ya, it wouldn't be plated, but sanded down once cured, it shouldn't wear much more than the surrounding plated areas.