Stripped bolt hole in aluminum crankcase cover plate?

C

cmayo

Active Member
One of the threaded bolt holes that attach the throttle bracket to the crankcase cover is stripped on my Kohler Courage 20. The parts list calls for a thread forming M6 (Kohler 25086403S) and my calipers say the hole is 6.11mm wide. Is there a relatively easy way to get a new bolt threaded into that hole?


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I would think going to a M7-1.00 is the best choice and you may need to widen the slot in the bracket a hair. I don't think a fine thread 1/4 will work.
 
Hmmm there is not enough metal to tap to 3/8-16 [9.5mm] for a thread insert and the OP probably don't have the Helicoil tools as it requires a STI tap which is around 7mm and the insertion tool. Helicoil tools are not that cheap.

By using the M7-1.00 screw it is just a matter of resizing for the M7-1.00 tap. I have done this multiple times on the M6 rocker cover screws where I have to cut out the broken screws. This is the low cost method.
 
Yeah... I'm not really tracking that. I have a Harbor Freight tap & die set but have never used it (or any tap & die, actually). Could I just screw in a standard/tread-forming/thread-cutting bolt? If so, which type do I need?
 
cmayo said:
One of the threaded bolt holes that attach the throttle bracket to the crankcase cover is stripped on my Kohler Courage 20. The parts list calls for a thread forming M6 (Kohler 25086403S) and my calipers say the hole is 6.11mm wide. Is there a relatively easy way to get a new bolt threaded into that hole?


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Buy an M6 heli-coil kit that has the special drill bit, installer tool and the thread inserts with it in one kit. Trying to use a self-tap bolt will end up cracking the aluminum. The tread inserts are stainless and much stronger than the original threads. Don't toy around try to rig it.
 
If the OP already have a HFT Metric tap and die set all he needs is 15/64 drill bit and the M7-1.00 tap;preferably a bottom tap since he would doing a blind hole. All he needs is to practice on some scrap metal first to learn how either tap works. Now for a lubricate on the standard tap or the M6 STI tap use rubbing alcohol when doing aluminum.
 
Auto Doc's said:
Buy an M6 heli-coil kit that has the special drill bit, installer tool and the thread inserts with it in one kit. Trying to use a self-tap bolt will end up cracking the aluminum. The tread inserts are stainless and much stronger than the original threads. Don't toy around try to rig it.
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This sounds like the least-risky DIY way to go, so that's what I'll do. Thanks much!
 
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Thanks for your help, all. I need some practice with my tap and die set before I'd feel good about trying it on my engine, the single-size heli-coil kits aren't too expensive and I think I can manage that repair!
 
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