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Old 05-31-2015, 09:55 AM   #21
cmbrucew
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Default Re: Stripped flywheel bolt

Ross F1
For peace of mind, remove the crank and have it drilled and tapped 45 around.
This would also give you fresh ring gear teeth for the starter
Bruce
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Old 05-31-2015, 10:01 AM   #22
Ross F-1
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Default Re: Stripped flywheel bolt

If I were going to pull it all apart, I'd just replace the crank. I have three others on the shelf. I don't think I'd want to add any more holes to the flange, and the dowels would be problematic.

Not sure how that would change the teeth? I use a mini-starter anyway.
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Old 05-31-2015, 01:10 PM   #23
CT AV8
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Default Re: Stripped flywheel bolt

Or just replace the flywheel. Easier than messing with the crank.
Has anyone here welded up a flywheel hole and retapped it?
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Old 05-31-2015, 01:17 PM   #24
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Default Re: Stripped flywheel bolt

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Originally Posted by CT AV8 View Post
Or just replace the flywheel. Easier than messing with the crank.
Has anyone here welded up a flywheel hole and retapped it?
Threaded hole in CRANKSHAFT flange........not flywheel! DD
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Old 05-31-2015, 01:29 PM   #25
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Default Re: Stripped flywheel bolt

I just did some calculations and if you can get some proper good quality bolts, it does sound like 12x1.25mm would be a good fix. If I were doing it this way I would do at least 2 bolts and might even do all 4. Don't drill out any holes in the crank as they are already above the minor diameter for 12x 1.25. You will have to drill the flywheel to 12mm.

Holding the tap square to the block might be a little tricky. Maybe drill the flywheel first then thap through. If doing it in vehicle it may be hard to ensure good alignment and removal of chips. They will just fall to the bottom of the bellhousing though, so no big deal.

You might be able to rig some sort of v block or something to hold the drill square.

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Old 05-31-2015, 02:16 PM   #26
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Default Re: Stripped flywheel bolt

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Mart, I am planning to make a drill guide to keep the bit square, and will go thru the flywheel. The tap drill for a 12mm x 1.25 is a 27/64, which is .422". The pitch diameter on the 7/16"-20 is .405", so I'm only removing about 8 thou all around.

This is an 8BA, so chips will just fall to the floor. I have the offending hole on the bottom.
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Old 05-31-2015, 04:48 PM   #27
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Default Re: Stripped flywheel bolt

Hi Ross, fix it with the correct heli-coil thread. It's actually quite simple if you make a simple drill & tap guide. We've made dozens of these "guides" over the years. We have most "slotted" but you can do it by the center-to-center method on the bolt locations.

Thanks, Gary in N.Y.

P.S. Here's a couple shots of a few with one showing the tooling mounted. The same tool is used first as the drill guide then moved and used as the tap guide. The tools have all been tapped with the respective heli-coils taps.
Attached Images
File Type: jpg Heli-Coil Drill and Tap Guide B.JPG (77.7 KB, 173 views)
File Type: jpg Heli-Coil Drill and Tap Guide C.JPG (66.7 KB, 48 views)
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Old 05-31-2015, 05:54 PM   #28
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Default Re: Stripped flywheel bolt

That there chingadero is geniusly simple! It don't get no slicker'n that. DD

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Old 06-01-2015, 04:37 PM   #29
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Default Re: Stripped flywheel bolt

Got 'er done! Actually doing it once I had all the pieces in hand, fixture made, etc. took a lot less time than all the hand-wringing! Par for the course...

Gary's excellent drilling fixture inspired me to make one out of square tubing. Worked like a champ. The 27/64" tap drill leaves a little bit of the old thread, but since the 12mmx1.25 is almost exactly 20 TPI, it actually helps keep the tap going in the right way. There is almost no room behind the flange, so I rigged a piece of heavy sheet metal with a magnet to keep from drilling into the oil pan. The tap just barely made it thru to the full-size threaded part.

Thanks for all the help, glad to have this behind me!
Attached Images
File Type: jpg Drilling Fixture-1.jpg (35.4 KB, 52 views)
File Type: jpg Finished hole.jpg (52.7 KB, 46 views)
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Old 06-01-2015, 06:03 PM   #30
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Default Re: Stripped flywheel bolt

Looks good, I will need to store that in the memory banks. Good use of a metric bolt size.
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Old 06-02-2015, 08:00 AM   #31
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Default Re: Stripped flywheel bolt

Ya just GOTTA love this forum.....The wealth of information and willingness to help each other is unmatched.....anywhere.....I have no plans to drill a crank flange.... but.... the methods described will certainly come in handy in one of my upcoming disasters...I'm sure....
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Old 06-02-2015, 08:16 AM   #32
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Default Re: Stripped flywheel bolt

Ross, did you take a brave pill and do all 4? Just the one? Or two?

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Old 06-02-2015, 09:45 AM   #33
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Default Re: Stripped flywheel bolt

Just the one, Mart. I'll post a pic of how I will compensate for the heavier 12mm bolt, not that I think it's really an issue. Amazing how close the 12mm is to a 7/16".
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