Helicoil problem - Team Camaro Tech
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post #1 of 6 (permalink) Old May 14th, 01, 02:46 AM Thread Starter
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Join Date: Nov 2000
Location: Pass Christian, MS
Posts: 294

Have a good friend who is assembling a 302 for his 69 rs Z/28. Heres the problem, when he went to install the head, one of the bolts wouldn't go down all the way, so he backed it out and the helicoil that was installed came out with the bolt. I go over and take a look and determined that when the helicoil was installed they didn't square it with the deck so that know it is about 3-4 degrees off each way and the bolt pinches on the head. What are his options in getting this bolt installed and torqured. BTW, this blocked was sent to a local builder and bored and prepped, also they installed an additional helicore on another hole, and a new one in the hole in question, should this have been checked before returning it to the owner for assembly?

69 rallye green X77 Z/28,1967 SS 396 Conv. 1974 c-10 454 swb
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post #2 of 6 (permalink) Old May 14th, 01, 06:03 AM
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Join Date: Sep 2000
Location: Va Beach VA
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Usually, when a shop replaces threads, the "machinist" will use a hand drill to drill the installation hole rather than use a magnetic base drill thereby making for a crooked hole.

Now, the fix for this hole is to replace/repair with a threaded insert. Redreilling and retapping for a Helicoil will put too much slop at the bottom of the thread.

I have the insert and installation tool for said insert but, it's 7/16-20 thread vs. 7/16-14. You can order the inserts from McMaster-Carr, 732-329-3200, they take credit cards.P/N 91731A015, Catalog #104, page 2671, $52.57 for Stainless steel inserts. Just be sure to use a sealant on the external threads.

When redrilling for insert, use/rent borrow a magnetic base drill and use a head gasket for location of hole. Getting the hole straight and centered is most important.

As far as checking hole, this is your job as owner,before pick-up/payment. You might try for warranty work from machine shop.

Good luck, Everett 68/350/PG/11.90/115mph
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post #3 of 6 (permalink) Old May 14th, 01, 02:30 PM
Join Date: Aug 1998
Location: Waldorf Md. USA
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pm, (wish you guys would include your real names)
There is a thread insert available that is 5/8 coarse thread od and 7/16 coarse id. I have used tham a couple of times when the holes were too far gone for even a helicoil. Your machine shop should be able to get them I know that Pioneer for one makes them.
Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md
1971 Chevelle "Heavy Chevy" original owner
1973 Z-28 ..one family car...Brother bought it new in 73
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post #4 of 6 (permalink) Old May 21st, 01, 03:05 AM Thread Starter
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Join Date: Nov 2000
Location: Pass Christian, MS
Posts: 294

Just an update, after several different options, we came up with this, installed a head stud in the bad thread hole, after a new helicoil of course, and then tweeked it a little until the head would slide on and torqued everything down. The thing that really ticked me about this problem was the guy who did the work on the block, boring and such, responded that "If the helicoil is installed wrong, it cannot be fixed" this after he worked the block and installed a new coil in the bad hole! Thanks for all the replies guys, and now lets get this mighty mouse fired up! Will keep you posted
One more thing, the ARP bolts call for 85 ft lbs. of torque, seems a little high and we don't won't to do the headbolt thing again, would you follow ARP's directions or torque them according to the GM specs, and at that torque is there any chance of stripping out another hole?
69 rallye green X77 Z/28,1967 SS 396 Conv. 1974 c-10 454 swb

[This message has been edited by pipeman (edited 05-21-2001).]
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post #5 of 6 (permalink) Old May 22nd, 01, 02:08 AM
Join Date: May 2001
Location: NewarOHk
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I wouldn't torque them to 85#. That's a good way to destort the cylinder walls causing bad ring seal.
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post #6 of 6 (permalink) Old May 23rd, 01, 04:52 PM
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Join Date: Dec 2000
Location: Kentwood, MI
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Torque them to exactly what ARP recommends with the lubricant they recommend!

By torquing a bolt you are trying to achieve an exact stretch in the bolt. (In fact, I've seen rod bolts torqued and stretch checked with a micrometer to see if a used fastener is still good). ARP bolts are different material than factory and require a different torque to make them stretch the right amount.

BTW if I recall ARP sbc head bolts get torqued to 65# with iron heads and 60# with aluminum heads when using the ARP thread lube. If you use 80 weight oil, I think the spec they recommend goes up to 85#. It should be on the instructions and they usually include some lube.

Good luck!
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