Thread repair in plastic

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  #1  
Old 08-05-09, 05:35 AM
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Thread repair in plastic

Oh boy...I foolishly stripped the threads to mount the carb, out of my husky chainsaw. They pulled right out and they are on my bench right now. Apparently you don't need to torque them very much. I tried to fill the holes with JB weld, but it was the steel stuff. I didn't think it would matter, so I let it cure over night, drilled a small hole in the center, then put the screw back in. It didn't work at all. My first idea was to go to the next size screw and let it tap its own threads in the plastic...but the next size screw won't fit through the actual carb. If i have no other options, I will drill the holes through the carbs bigger. I only have experience with metal, not plastic. Does anyone have any ideas on repairing these threads in plastic?
 
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Old 08-05-09, 06:06 AM
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a heli-coil insert should work -

basically a heli-coil looks like a spring but is an insert that recreates the original threads on the ID and has a whole new thread dia on the outside diameter

used for repairing or recreating threads in metal, but should work well in plastic, if you use the kind that have "stakes" that once the heli-coil is threaded in, you then tap the stakes in to keep the heli-coil from unscrewing

see link McMaster-Carr

scroll to bottom and you'll see "key-locking threaded inserts" and in case the link doesn't take you to the very page, it's page 3230 on McMaster-Carr

if you don't have an account with them you can call the order in with a credit card - mcmaster-carr is to mfgrs, machine shops, etc what sears & roebucks used to be to the commercial market in the 1950 & 60s
 
  #3  
Old 08-05-09, 06:26 AM
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What is the model number of your Husqvarna chainsaw.
 
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Old 08-05-09, 06:35 AM
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its a 55 rancher. I am pretty familiar with helicoils, but was unsudre if they'd work in plastic.
 
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Old 08-05-09, 07:18 AM
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Replacing the part may be less expensive than purchasing helicoil tools if you do not have them.

Parts list:
http://www.mymowerparts.com/pdf/Husq...s/I0401083.pdf

Is this the part the hole is stripped in?
eBay.com.sg: New Husqvarna Bulkhead Assembly Kit Part No. 503764801 (item 170282823476 end time Jul 04, 2009 05:55:34 SGT)
 
  #6  
Old 08-05-09, 08:19 AM
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Originally Posted by strider380 View Post
its a 55 rancher. I am pretty familiar with helicoils, but was unsudre if they'd work in plastic.
if the original set up was a steel threading screwing into a plastic part, no reason why it shouldn't - would actually be a little stronger as the load would be spread over a larger area (ie larger outside diameter) but Airman suggestion might be better - i'm not familiar with your chainsaw - was just offering a generic solution

but in case, you shouldn't really need any tools with the helicoil except for the correct tap for the OD threading on the helicoil
 
  #7  
Old 08-05-09, 01:00 PM
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Geeze you guys are great. Thank you for all the options you have provided. I was told that my JB weld method would have worked, provided I had used something designed for plastic and not steel Haha, regardless I might try a plastic resin, but the new part for 6.99 on ebay is looking more tempting. Thanks Airman.
 
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