The dreaded stripped threads, Husky 572

cory

Tree House enthusiast
Joined
Aug 23, 2008
Messages
26,482
Location
CT
Aite, one of the 4 screws affixing the starter assembly to the saw is stripped. Rather, the hole seems to be stripped, the screw's threads seem to be good. Presumably a case of a loose screw that got worse over time and vibration destroyed the threads. I've never done a heli-coil. Can you guys clue me in to what is involved or better yet lmk how I can remedy the sitch with something as good or better than a heli-coil. Asking for a friend :|: :lol:
 
How /I/ would "fix" it is jam some copper & maybe some loctite in the hole, then replace the screw. If it doesn't work, it won't affect a proper fix using inserts.
 
  • Thread Starter Thread Starter
  • #4
Lxs- I did something similar, jamming in some plastic from a fairly heavy duty dog food bag, put in the screw and tightened, it seemed to work for now. We'll see how it does. I certainly didn't torque it hard but we'll see.

Alt- yes the other 3 are holding strong and secure. Lord only knows how long it was running with only 3 good ones but it was too annoying once I noticed the loose 4th one to leave it as is.
 
Glad you've got it going without messing with it, drilling and tapping is never fun. I've surprisingly never done a helicoil on an engine repair, they're used to keep the same size bolt as the original and I've never had that constraint yet, a slightly larger bolt has always been acceptable for what i was working on. A helicoil will need a much bigger hole too, so I've always just gone up to the next size up bolt so it's less metal removed from the block. But the process is the same as doing it without, you just add the helicoil, i would use a threadlocker on it since you don't want it out ever again (on the outside of the helicoil obviously). You drill and tap it to a oversize thread, and then screw in the helicoil, and then if it's too tall you grind it down. If you've never drilled and tapped something before it might be a good idea to practice on a scrap chunk of something a couple times before doing it on an engine, it's not difficult but it does take a certain amount of feel to not mess it up.

You'll need the size of tap that you're going to use, and the appropriate drill bit (not the size of the bolt but smaller so there's metal for the threads, so you gotta look up exactly which size you need). When you drill it try to follow the hole exactly, and when you tap it you must be perfectly in line with it too or the tap will break off in the hole, turning this miserable job into an even bigger miserable job. Use a heavy thick oil, go a bit in, and then back it out a bit, which breaks off the chips, and if it's a deep one or a blind hole (yours would be both) pull out the tap frequently and blow the chips out with a blowgun, they'll pack in there and break the tap. A really good trick for most taps is to drill it in a drill press, and then use a center pin in the center hole to align the tap, which ensures it's straight with the hole. It'll be aluminum that you're working with, so at least it'll drill and tap easy, and you may need to follow up with a bottoming tap because it's a blind hole.

One final thing i wanna add is that if you ever take a bolt or a nut off something, it should get something on the threads, either locktite or neversieze, almost always neversieze. The bolts are either steel or stainless steel, and the block is aluminum, so there's going to be corrosion. Without neversieze the 2 dissimilar metals will fill the small voids of the threads with corrosion, which will then freeze the bolt in place, rust expands so corrosion will push everything tight, and stainless is known for galling like crazy (where the surface actually welds together with the friction). With neversieze filling the void and lubricating the threads the bolt should come out easily in the future, so much so that bolts that have been sitting outside and have all but rusted away will still come undone, you may have to cut the extra threads past the nut off but 95% or more will be able to come apart without even heating it. Bolt comes out, it gets cleaned and brushed, coated, then tightened to the correct torque (it's ok to estimate, but you don't need to kill stuff to make it stay put), and hopefully you won't have to do this drill and tap thing too frequently.
 
Can you JB weld a nut on the back side of the hole? You can get brass threaded inserts from mcmaster-carr often found pressed into nylon, like what the carb screws go into on a 201t handle. You can drill the hole out, clean and dry it well, and JB weld a brass insert in there. I've used one to fix the top cover hole on a 395.
 
One of a few times I’m qualified to give advice on this forum, haha.

I prefer time or keen serts over heli coils. They are usually a standard thread/tap on the outside and they are a solid piece of metal vs. a coil.

My older huskies are 5mm x .8 pitch IIRC.

If we can verify that @huskihl ? I could send you a little kit of what you’d need @cory

Putting some steel wool in the hole works surprisingly well. I’ve found it in some saws and it works so well I haven’t gotten around to fixing them properly.

Likewise, plastic trimmer string works well in plastic.
 
I know a guy who can weld the magnesium hole shut and drill a new one.

That's awesome, I've never messed with magnesium, very cool, very dangerous. That's exactly how i like doing them in materials that i can weld, that or braze welding them shut too, works great with cast iron. The al carb for my welder was cracked from the fuel fitting being over tightened, so i welded that up and chased the threads. In my factory days i did that with steel as a full time job working salvage, they would break taps off in parts and we would have to fix them. They were often helical taps, so we would have to get them out by any means necessary, weld up the area and blend it with a grinder or prep for machining, and then drill and tap it to size and on location. Frustrating nightmare, and then you had to fix weld defects on other parts. Needless to say i got the weld a nut on it trick down pat for the easier ones (anneal the top of the tap before you weld it), and have screamed no at them if they broke off deep below the surface, your nightmare just beginning. :lol:

That's a brilliant idea with a plug or better yet sleeve glued in, I'm stealing that one. I think loctite makes a glue now for what traditionally would be a pressed or interference fit (also an option sometimes, so you would drill to whatever size rod you have that would fill it and then glue in a plug. Put the cover on and mark the hole, then drill and tap it. I'm definitely gonna use that in the future, thx man.
 
Steel wool sounds great. When I was a teen my old man showed me using a toothpick (back when every diner had a toothpick dispenser by the door). I have a box of old saw screws from both Husqvarna and Stihl (and some old Echo stuff as well). I usually just dig around and find something slightly larger or coarser pitch that will bite in the hole.
 
That's awesome, I've never messed with magnesium, very cool, very dangerous. That's exactly how i like doing them in materials that i can weld, that or braze welding them shut too, works great with cast iron. The al carb for my welder was cracked from the fuel fitting being over tightened, so i welded that up and chased the threads. In my factory days i did that with steel as a full time job working salvage, they would break taps off in parts and we would have to fix them. They were often helical taps, so we would have to get them out by any means necessary, weld up the area and blend it with a grinder or prep for machining, and then drill and tap it to size and on location. Frustrating nightmare, and then you had to fix weld defects on other parts. Needless to say i got the weld a nut on it trick down pat for the easier ones (anneal the top of the tap before you weld it), and have screamed no at them if they broke off deep below the surface, your nightmare just beginning. :lol:

That's a brilliant idea with a plug or better yet sleeve glued in, I'm stealing that one. I think loctite makes a glue now for what traditionally would be a pressed or interference fit (also an option sometimes, so you would drill to whatever size rod you have that would fill it and then glue in a plug. Put the cover on and mark the hole, then drill and tap it. I'm definitely gonna use that in the future, thx man.
20240611_162659.jpg
 
  • Thread Starter Thread Starter
  • #16
Ooo, another good idea re a readily available material to tweak the hole
 
Saws are mostly magnesium now. I don't know, but magnesium might be easier to fix with a self tapping screw. Manufacturers commonly use them: slightly triangular screws with either machine threads or coarse threads like what's used in plastic. I don't like it because it makes a mess of metal shavings and fragile threads.
 
For my deere mower that was how they have you attach a replacement bearing for the blades :lol: They have their place, but i still like to drill a small pilot hole because an actual drill bit cuts better and gives better results. They're often used for sheet metal so they work great for that, but if you aren't careful you can strip them out of you slam them home. They work, but a tapped hole is going to be a much better and secure option, and will have a lot higher threads per inch, which will apply more force and hold better than the very coarse self tapper threads. Engines aren't solid metal all the way through and carefully drilling and tapping a hole sounds like a safer bet to me, but with careful sizing would likely work splendidly. They're also great for block and concrete when using the string trimmer line or wire in the hole you drilled to mount smaller stuff, never thought of trying it with metal, gonna have to try that now
 
  • Thread Starter Thread Starter
  • #19
So the saw sat for a week, I was afraid to try it and see if the fix worked. :lol: :wall::|:.

I have a big job tomorrow where it will be used so I decided to examine the repair. I took off the starter and the material I'd placed in the hole didn't appear to be in there, I wonder if the screw pushed it outta the hole.

So I used Alt's idea of can-aluminum. I put it in, screwed it in and it felt tighter than last time. Fingers crossed!🤞
 
Back
Top