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Old 05-30-2015, 02:24 PM   #1
Ross F-1
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Default Stripped flywheel bolt

Doing some clutch/trans work, had the flywheel off. Putting it back on one of the bolts went soft at 45 ft-lbs. It was sketchy last time, guess this was the last straw. (it's not the bolt threads). I used a different bolt and can get 30 ft-lbs but I'm kind of reluctant to count on it, even with Loctite 271. With the pegs locating the FW, and the spigot on the crank, I could probably let it go, but I'm thinking a helicoil is the right way, and will never be easier.

Anyone had to do it before? Anything to watch out for? It looks like the next size up (just drilling and re-tapping, no helicoil) would be a metric 12mm, likely less material removal than using a helicoil.

BTW, is the sheet metal locking plate supposed to be bent up against the bolt heads? I have yet to find one that was.

Opinions, please!
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Old 05-30-2015, 04:13 PM   #2
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Default Re: Stripped flywheel bolt

Ross
Would a longer bolt, or a stud reach good threads?
Bruce
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Old 05-30-2015, 04:14 PM   #3
Ross F-1
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Default Re: Stripped flywheel bolt

No, unfortunately.
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Old 05-30-2015, 04:17 PM   #4
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Default Re: Stripped flywheel bolt

Ross,
I'd go with the 12mm if it was mine.
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Old 05-30-2015, 04:36 PM   #5
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Default Re: Stripped flywheel bolt

I would probably use a Heli-Coil if it were mine. I've never seen the thin plate under the bolts bent to lock the bolt heads either. I'm not sure the purpose for it , unless the mild steel would give more "grip" to the bolt heads to help keep them torqued than the cast iron flywheel would
Mark.
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Old 05-30-2015, 05:29 PM   #6
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Default Re: Stripped flywheel bolt

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Quote:
Originally Posted by Charlie ny View Post
Ross,
I'd go with the 12mm if it was mine.
Charlie ny
Quote:
Originally Posted by 49fordv8f4 View Post
I would probably use a Heli-Coil if it were mine. ..
I like the 12mm because I'd be using the parent metal directly, with little removed for new threads. But I hate to have one unique bolt. I need to check whether a 12mm will fit thru the flywheel hole without drilling it out too, in which case the flywheel would have to go a specific way.

I don't suppose anyone thinks I can get away with it as-is???
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Old 05-30-2015, 05:46 PM   #7
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Default Re: Stripped flywheel bolt

You KNOW you don't want to leave it like it is. And if it makes you feel better, you could always do a second 12 mm bolt 180 degrees out from this one. DD
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Old 05-30-2015, 06:00 PM   #8
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Default Re: Stripped flywheel bolt

I checked, 12mm doesn't fit thru flywheel without drilling it out.
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Old 05-30-2015, 06:01 PM   #9
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Default Re: Stripped flywheel bolt

I'd probably go the other way and helicoil it. The flywheel bolts are drilled for safety wire, there is no reason to bend the plate up. The bolts are a fine pitch. Unless you went for a fine pitch metric you might not get the loading you need. The flywheel bolts are a highly critical item, they need to be right. A helicoiled thread is no weaker than the original thread in the parent metal.

Ideally you wouldn't want to have to use either remedy, but my gut feeling is that a helicoiled repair and keeping the bolts and flywheel stock would be the preferred method.

Too thick a bolt head can cause problems with the clutch plate too.

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Old 05-30-2015, 06:33 PM   #10
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Default Re: Stripped flywheel bolt

Quote:
Originally Posted by 49fordv8f4 View Post
I would probably use a Heli-Coil if it were mine. I've never seen the thin plate under the bolts bent to lock the bolt heads either. I'm not sure the purpose for it , unless the mild steel would give more "grip" to the bolt heads to help keep them torqued than the cast iron flywheel would
Mark.
The thin plate is called a flywheel dowel retainer, keeps the dowels
from working there way out.

Bob
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Old 05-30-2015, 06:58 PM   #11
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Default Re: Stripped flywheel bolt

Quote:
Originally Posted by Bob C View Post
The thin plate is called a flywheel dowel retainer, keeps the dowels
from working there way out.

Bob
Well, that makes sense!

The thing with the Helicoil solution is that there is precious little metal between the OD of the crank flange and the OD of the stock bolt hole. Helicoil OD would be real close to the edge.

Out hunting for parts, believe it or not my local True Value has both 12mm x 1.5 (standard fine) and 12mm x 1.25 (extra fine) taps. But so far I haven't located 12mm x 1.5 or x 1.25 grade 10.9 bolts. I have a helicoil kit in hand. I'll see what I can dig up tomorrow.

I did try a bolt about 1/4" longer, which barely clears the back of the block. Got it to 45 ft-lbs before it felt squeamish. The threads are just shot.

Mart, none of the bolts I have are drilled for safety wire (all from 8BA's)
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Old 05-30-2015, 10:45 PM   #12
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Default Re: Stripped flywheel bolt

auto parts store for your bolts.
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Old 05-30-2015, 11:33 PM   #13
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Default Re: Stripped flywheel bolt

Helicoil it Ross, be a reliable repair.
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Old 05-30-2015, 11:42 PM   #14
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Default Re: Stripped flywheel bolt

Ross, you might look into these.
I have not compared them to heli-coil but have heard they are superior.
Maybe more suited to your situation.
http://www.timesert.com
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Old 05-31-2015, 01:27 AM   #15
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Default Re: Stripped flywheel bolt

My 49 has had a helicoil in it for several years and I don't know how many miles with no problems. I think I used the OD size bolt but don't remember for sure.
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Old 05-31-2015, 06:55 AM   #16
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Default Re: Stripped flywheel bolt

I would rethink using "hardware store" bolts for retaining a flywheel. Use bolts designed for the application; either originals or aftermarket like ARP.
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Old 05-31-2015, 07:15 AM   #17
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Default Re: Stripped flywheel bolt

Most of the 8BA engines don't have safety wire flywheel bolts. Walt
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Old 05-31-2015, 07:26 AM   #18
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Default Re: Stripped flywheel bolt

I would not use a heli coil in light of the OD of the coil,why not get a 12mm fine thread bolt,drill or ream out the hole it the flywheel.
I would feel a lot better if it were mine doing it this way.
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Old 05-31-2015, 08:57 AM   #19
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Default Re: Stripped flywheel bolt

I like CA Victoria's solution.
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Old 05-31-2015, 09:36 AM   #20
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Default Re: Stripped flywheel bolt

I looked into the Time Serts, but they require even more material removal than a helicoil. The engine is in the truck, I would not feel comfortable doing the countersink they require in place.

I wasn't planning to use a hardware store bolt, although the True Value has a hardened 10.9 line, but only in 12mm coarse. I'll get one at NAPA or a fastener store. I'll believe I'll be going back with a 12mm x 1.25, which has almost exactly the same pitch as a 20 thrds/inch.

Thanks for all the help!
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Old 05-31-2015, 09:55 AM   #21
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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
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Old 05-31-2015, 10:01 AM   #22
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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
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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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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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