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Old 07-07-2012, 03:37 AM
68/70Vette 68/70Vette is offline
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Default Installing a Heli-Coil ??

My 42 year old "612" cast aluminum bell housing needs heli-coils. To many transmissions in and outs has taken the toll.

The transmissions bolt up with 7/16 inch 14 thread bolts. My bell housing has one really wiped out mounting hole and the others are distressed. Is this something I can do myself? I'd be glad to pay a machine shop, but I don't know where to go. I live in the South Bay area of Torrance and the nearest "racing shop" I deal with is Team C in Downey. They recommended a machine shop there, but's its about 30 miles away. A local auto repairer said they'd do it, but that was Friday afternoon. I'm thinking it's just not a real priority with them. I took the bell housing into them for the helicons.

Anyhow, for now...can bolt holes in aluminum castings be efficiently machined out for helicoils by simple do it yourself labor? I have some aluminum cylinder heads and I'd like to heli coil them also for the exhaust manifold holes in preparation for future header installation.

Thanks!!!
...............................

BTW. Why did I wipe out the bell housing threads? It was because in mounting previous transmissions, I could not get them to mount up snuggly to the bell housing. So once I got the transmission past the clutch spline openings, I used the four transmission mounting bolts to pull the 100 pound transmissions up into place. The aluminum threads just gave out under the stress. I understand that when you're trying to snub up a tranny, it's a good idea to have someone rock the crank back and forth or the transmission shaft back and forth while you push the input shaft in past the clutch disk. Unfortunately, working by my self, I don't have anyone to do this "rocking" for me.
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Old 07-07-2012, 04:28 AM
Corvettes White Corvettes White is offline
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I did some Helicoils in a few locations on my car in aluminum castings. Just followed the instructions and took my time. Used a hand drill but a press would be better. I bought the Helicoil brand not the Harbor Freight brand. If you do not want to do them, there is a guy in Santa Ana “Jerry’s Tap” and all he does is fix screw-ups. George
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Old 07-07-2012, 10:55 AM
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You might as well have someone do it. It will probably cost less than the helicoil inserts and special tap. I would be a good idea to do it on a drill press also.
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Old 07-07-2012, 01:25 PM
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The correct size drill and special tap comes in the kit, roughly $25 with like 6 inserts .... Funny that metric helicoils are twice as expensive
I've used these inserts at home and while a drill press is not required it would make life easier.
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Old 07-07-2012, 02:37 PM
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How much material is around the holes?

I'm not a big fan of Heli-coils if it's going to be disassembled repeatedly.

Here's one of the better solutions in my opinion. Another variation is Keen-serts with pins to drive in and lock the inserts in place.

I like the flange on these Tine-serts...

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Old 07-07-2012, 05:40 PM
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I was just going to mention time serts. They are the only thing I use now, given up on heli coils. These are much much easier to work with and give a much better result
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Old 07-08-2012, 01:05 AM
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Quote:
Originally Posted by Twin_Turbo View Post
I was just going to mention time serts. They are the only thing I use now, given up on heli coils. These are much much easier to work with and give a much better result
That's what GM uses for all the head bolt failures in their Northstar engines.
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Old 07-08-2012, 08:06 AM
Garys 68 Garys 68 is offline
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You might want to double check, I'm pretty sure the bell housing to trans bolts on a 621 are 1/2". If you tighten a 7/16" bolt in, that will wipe out your threads.
And you can put a helicoil in yourself, very easy in aluminum.

Last edited by Garys 68; 07-08-2012 at 08:25 AM..
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Old 07-09-2012, 11:47 PM
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any old time automotive machine shop should be able to do the job.
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Old 07-11-2012, 02:58 AM
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Quote:
Originally Posted by redvetracr View Post
any old time automotive machine shop should be able to do the job.
Finding one of those is getting really near impossible. At least one that really knows what's going on. One I used for years was taken over by the kids of the guy that started the shop. If you want something really screwed up, that's the place to take it.
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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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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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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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Old 07-18-2012, 09:59 PM
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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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Old 08-28-2013, 05:23 PM
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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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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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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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