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  #11  
Old 07-11-2012, 08:52 PM
mold99 mold99 is offline
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don't use a helicoil, they are not very tolerent of old bolts or any kind of misuse. solid inserts are the only way to go, i have been a toolmaker/machinist/owner for 45 years, and have done both. a helicoil can fail or start to rip out much easier than a solid type insert. especially with a used boogered bolt.
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  #12  
Old 07-17-2012, 10:14 PM
68/70Vette 68/70Vette is offline
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Followed Corvettes White's recommendation and took the bellhousing to Jerry's Tap and Die in Santa Anna. The bellhousing needs all four tranny to bellhousing holes repaired. He's going to charge $35 per insert (Timeinsert). In my original post, I referred to it as a 612 bellhousing, actually it's a "621" bellhousing, or to be more precise, it's a 3899621 bellhousing. I noticed Paragon sells them new for $275. I would guess it's a repro. My believe is that the original GM bellhousings were machined very accurately, and I'd wonder if a repro part was machined to the same accuracy. If I were sure the Paragon part was as accurate, I'd bought one. Hopefully having the inserts won't create a noticeable inaccuracy as regards the centerline of the inserts relative to the centerline of the original threaded hole. The man who owns "Jerry's" said he would start by removing the original damaged threads with a reamer. He said he would red locktite the inserts just to make sure they wouldn't unscrew. He said he would use locktite after I told him that the four tranny/bellhousing bolts were under a lot of stress when the loose 100 pound transmission was hanging cantilevered on the bolts as the bolts were being tightened to pull the tranny up snug to the bellhousing.

The current owner is "Tom," Jerry passed away.

Last edited by 68/70Vette; 07-17-2012 at 10:29 PM..
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  #13  
Old 07-18-2012, 12:18 PM
Garys 68 Garys 68 is offline
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The trans is centered in the bell by the bearing retainer, bolts just hold it together. You are correct on the 621 repops, mine was 0.020 off.
I would suggest you get the corrrect bolt size, 1/2"not 7/16". The bell housing is pretty thick there and a coarse thread bolt is difficult to crossthread. However threading a 7/16" bolt into a 1/2" hole is a very effective way to strip the threads in alunimin or steel.

Last edited by Garys 68; 07-18-2012 at 12:25 PM..
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  #14  
Old 07-18-2012, 09:59 PM
68/70Vette 68/70Vette is offline
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Quote:
Originally Posted by Garys 68 View Post
The trans is centered in the bell by the bearing retainer, bolts just hold it together. You are correct on the 621 repops, mine was 0.020 off.
I would suggest you get the corrrect bolt size, 1/2"not 7/16". The bell housing is pretty thick there and a coarse thread bolt is difficult to crossthread. However threading a 7/16" bolt into a 1/2" hole is a very effective way to strip the threads in alunimin or steel.
Thanks for the info, especially about the repop being 0,020 off. About the 7/16. Right before I wrote the original post, I had been mounting the diff to the diff crossmember. It uses 7/16X14 by 1 1/2 bolts, so I had 7/16 on my mind. When I took the bellhousing to the shop, I told them to match the existing thread/bolt size. There was good thread definition on two of the holes.
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  #15  
Old 08-28-2013, 05:23 PM
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7t9l82 7t9l82 is offline
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the big issue most people have had with helicoils is they didn't know they came in different lengths. they drill out and then go back with half as many threads. but i agree the timeserts are nice
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  #16  
Old 02-15-2014, 03:43 AM
Ralphy Ralphy is offline
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Also working as a machinist for many years, I agree with mold99. I've seen a lot of issues with helicoils from repeated use. If you use a machine shop make sure they locate the holes in true position. Not just eye the existing hole and go, down and dirty. Won't take more than a few extra minutes if he's worthy.

Ralphy
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  #17  
Old 03-02-2014, 03:22 AM
68/70Vette 68/70Vette is offline
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As a machinist, You'd find Jerry's Tap and Die in Santa Ana interesting. They specialize in broken bolts and stripped threads...that's their only business.!!!

For a broken off bolt, that won't come out with the drill, reverse tap procedure, applications of torch heat and the same, etc. ,,,,they remove errant bolt sections by electro static discharge etching. The broken off part of the bolt is simply just eroded by electric discharge etching. For equipment that can't be brought to their shop, they can transport their equipment to the job site. wu
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