heli-coil for starter bolt hole repair - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-10-2008, 09:56 AM
GMR GMR is offline
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heli-coil for starter bolt hole repair

The outermost starter bolt hole on my sbc 350 (1970) seems to have been drilled out and tapped (at least partially) to 7/16. Can a heli-coil be used to restore it to 3/8?

I've read instructions for a 3/8 heli-coil kit and it says to use a 25/64 drill bit. That's smaller than 7/16. So it seems the 7/16 hole is too big for the 3/8 insert to seat properly.

If I can't reduce the threads back to 3/8 somehow, I guess I'll have to heli-coil the hole to 7/16 and drill out the starter from 3/8 to 7/16.

I've heard about a starter brace. I have a GMPP mini starter. How would I attach a starter brace?
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Old 07-10-2008, 11:22 AM
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Quote:
Originally Posted by GMR
The outermost starter bolt hole on my sbc 350 (1970) seems to have been drilled out and tapped (at least partially) to 7/16. Can a heli-coil be used to restore it to 3/8?
Probably not unless the 7/16 tapped hole is not too deep. Then you may be able to install a heli-coil deeper and use a longer bolt.


Quote:
Originally Posted by GMR
If I can't reduce the threads back to 3/8 somehow, I guess I'll have to heli-coil the hole to 7/16 and drill out the starter from 3/8 to 7/16.
You might consider using a "thread insert". They will work in situations where a heli-coil can not be used. I prefer heli-coils when they can be fitted.
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Old 07-11-2008, 07:23 AM
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Thankyou for your suggestion Frisco.
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Old 07-11-2008, 08:59 AM
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There are many brands of thread inserts, one brand name is KeenSert. You can buy them at McMaster Carr (www.mcmaster.com) among other places. They are thicker wall than helicoils. The other big advantage of a thread insert like this is that they typically have locking tabs that are tapped into place after the insert is installed. This prevents the insert backing out problem that is common with helicoils.
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Old 07-11-2008, 07:18 PM
GMR GMR is offline
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Joe, thanks. I did find some info on keenserts and also timeserts after Frisco mentioned thread inserts. As a matter of fact, I believe I saw a post from you mentioning keensert in reply to someone else's question, while I was researching thread inserts.
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