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Discussion Starter · #1 ·
Hi, I'm preparing to mate the C6 back up to the 390 and put them back into the car, and I discover this play, due to an enlarged portion in the outermost bellhousing starter bolt hole. It seems like my choices are, in preferred order based on time and expense...


1) Do nothing, the bolt still holds, even with the play, and the other two bolts will hold the starter just fine.
2) Coat a longer test bolt in anti-seize, thread it through the hole, and use a two part resin substance to fill in the missing metal. Choices I have on hand include JB Weld, Bondo and All-Metal. After it hardens, I just back out the test bolt, and use the real one.
3) Heli-coil repair.
4) Drill and tap to a larger size.

My old flexplate had a problem, and I wonder if this bolt play had anything to do with it?

Side question. In the bag labelled bellhousing bolts I found these four. I appear to be missing two lock washers, and two additional short bolts and lock washers, is this right for the install on a 68 GT390/C6 setup? These don't seem to be anything special, so I'm hoping I can just buy two more grade 8's and the washers at the hardware store. Thanks.

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Non of the above. Just use a bolt and nut on it. The housing and block plate along with the other bolts will keep the starter aligned. and Yes it probably is what caused the flexplate issue. Lock washers on all 6 bellhousing bolts. Looks like someone played with it and didn't put them back in.
 

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I'd Helicoil it, but that's just me.

Actually I Helicoil any and all questionable threaded holes in any aluminum castings.

Putting a long bolt thru with a nut on the back side is an emergency/temporary/side of the road/amateur/backyard/hack fix.

If you have the time and tools, and it's all apart where it's easy to work on....

.... fix it right or don't do it at all.
 

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Discussion Starter · #5 ·
I'd Helicoil it, but that's just me.

Actually I Helicoil any and all questionable threaded holes in any aluminum castings.

Putting a long bolt thru with a nut on the back side is an emergency/temporary/side of the road/amateur/backyard/hack fix.

If you have the time and tools, and it's all apart where it's easy to work on....

.... fix it right or don't do it at all.
And the winner is...Heli-coil...and Muggy Weld Super Alloy 1. Upon closer inspection, I found two more holes which were suspect, so I took Gallaxiex's advice and picked up a 5/16th-18 heli-coil kit which Oreilly had in stock. For the two holes on the non-starter side of the bellhousing, Heli-coil worked like a charm. If you have doubts that heli-coil is just snake-oil, it worked just as advertised for me. However, the starter bolt was a problem, the hole was already stripped out larger than the tap which comes with the heli-coil. I think some PO tried to run a 3/8ths 1/3 of the way down the hole, then stripped that out as well.

Then I found this video, and remembered I had some Muggy Weld Super Alloy 1 leftover from another project. Super Alloy 5 is stronger, but this should get the job done. I brazed the hole up, made a pattern from the blockplate, and then drilled and tapped back to 5/16th. In the video, his brazing exceeds the strength of the original metal. All I need is probably 10 to 15 ft pounds?

Delboy's Garage, "Aluminium Thread Repair" ? - YouTube

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Discussion Starter · #10 · (Edited)
But.... The starter bolts are usually 3/8 UNC
These three holes were definitely 5/16th, but it looks like the problem with the outermost hole was that someone tried to force a 3/8th about 1/3 of the way in, stripped it backing it out, and then "got by" with the bottom threads in the hole. The bolts I removed were 5/16-18 x 1-1/8th.

The id tag on the transmission revealed that it wasn't original to the 1968 car, but from a 70 or 71. On other forums I've seen the same discussion, and apparently in some applications 3/8ths starter bolts were used.
 

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Discussion Starter · #12 ·
Hi, No issues with the starter becoming "trapped" behind the exhaust when using studs? I will be using the original stock GT390 manifolds/exhaust pipes.
Update, I put the engine/trans back in the car today, and with the stock exhaust manifolds, it doesn't look like there would be any problems using studs to mount the starter.
 
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